TI1 ADS8578SIPM 14-bit, high-speed, 8-channel, simultaneous-sampling adc with bipolar inputs on a single supply Datasheet

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ADS8578S
SBAS825 – APRIL 2017
ADS8578S 14-Bit, High-Speed, 8-Channel, Simultaneous-Sampling ADC with
Bipolar Inputs on a Single Supply
1 Features
3 Description
•
•
•
•
•
•
•
•
The ADS8578S device is an 8-channel, integrated
data acquisition (DAQ) system based on a 14-bit
successive approximation (SAR) analog-to-digital
converter
(ADC).
All
input
channels
are
simultaneously sampled to achieve a maximum
throughput of 200 kSPS per channel. The device
features a complete analog front-end for each
channel, including a programmable gain amplifier
(PGA) with high input impedance of 1 MΩ, input
clamp, low-pass filter, and an ADC input driver. The
device also features a low-drift, precision reference
with a buffer to drive the ADC. A flexible digital
interface supporting serial, parallel, and parallel byte
communication enables the device to be used with a
variety of host controllers.
1
•
•
•
•
•
14-Bit ADC With Integrated Analog Front-End
Simultaneous Sampling: 8 Channels
Pin-Programmable Bipolar Inputs: ±10 V and ±5 V
High Input Impedance: 1 MΩ
5-V Analog Supply: 2.3-V to 5-V Digital Supply
Overvoltage Input Clamp With 7-kV ESD
Low-Drift, On-Chip Reference (2.5 V) and Buffer
Excellent Performance:
– 200-kSPS Max Throughput per Channels
– DNL: ±0.2 LSB; INL: ±0.2 LSB
– SNR: 85.8 dB; THD: −109 dB
Overtemperature Performance:
– Max Offset Drift: 3 ppm/°C
– Gain Drift: 6 ppm/°C
On-Chip Digital Filter for Oversampling
Flexible Parallel, Byte, and Serial Interface
Temperature Range: –40°C to +125°C
Package: 64-Pin LQFP
The ADS8578S can be configured to accept ±10-V or
±5-V true bipolar inputs using a single 5-V supply.
The high input impedance allows direct connection
with sensors and transformers, thus eliminating the
need for external driver circuits. The high
performance and accuracy, along with zero-latency
conversions offered by this device, also make the
ADS8578S a great choice for many industrial
automation and control applications.
2 Applications
•
•
•
•
•
Device Information(1)
Monitoring and Control for Power Grids
Protection Relays
Multiphase Motor Controls
Industrial Automation and Controls
Multichannel Data Acquisition Systems
PART NUMBER
PACKAGE
ADS8578S
LQFP (64)
BODY SIZE (NOM)
10.00 mm × 10.00 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
DVDD
AVDD
BUSY
ADS8578S
FRSTDATA
STBY
1 M:
AIN_1P
AIN_1GND
Clamp
PGA
Clamp
3rd-Order
LPF
ADC
Driver
CONVSTA, CONVSTB
14-Bit
SAR
ADC
RESET
RANGE
1 M:
CS
RD/SCLK
1 M:
AIN_2P
AIN_2GND
Clamp
PGA
Clamp
3rd-Order
LPF
ADC
Driver
14-Bit
SAR
ADC
1 M:
SAR
Logic
and
Digital Control
SER/PAR
Interface
PAR/SER
DB[15:0]
DOUTA
DOUTB
OS0
Digital Filter
AIN_7GND
OS1
OS2
1 M:
AIN_7P
Clamp
PGA
Clamp
3rd-Order
LPF
ADC
Driver
14-Bit
SAR
ADC
REFCAPA
1 M:
REFCAPB
1 M:
AIN_8P
AIN_8GND
Clamp
PGA
Clamp
3rd-Order
LPF
ADC
Driver
14-Bit
SAR
ADC
2.5 VREF
REFIN/REFOUT
1 M:
REFSEL
AGND
REFGND
Copyright © 2017, Texas Instruments Incorporated
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
ADS8578S
SBAS825 – APRIL 2017
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Family Comparison Table ........................
Pin Configuration and Functions .........................
Specifications.........................................................
7.17 Switching Characteristics: Parallel Data Read
Operation, CS and RD Separate .............................
7.18 Switching Characteristics: Serial Data Read
Operation .................................................................
7.19 Switching Characteristics: Byte Mode Data Read
Operation .................................................................
7.20 Typical Characteristics ..........................................
1
1
1
2
3
3
5
8
Absolute Maximum Ratings ...................................... 5
ESD Ratings.............................................................. 6
Recommended Operating Conditions....................... 6
Thermal Information .................................................. 6
Electrical Characteristics........................................... 7
Timing Requirements: CONVST Control ................ 10
Timing Requirements: Data Read Operation.......... 10
Timing Requirements: Parallel Data Read Operation,
CS and RD Tied Together ....................................... 10
7.9 Timing Requirements: Parallel Data Read Operation,
CS and RD Separate ............................................... 11
7.10 Timing Requirements: Serial Data Read
Operation ................................................................. 11
7.11 Timing Requirements: Byte Mode Data Read
Operation ................................................................. 11
7.12 Timing Requirements: Oversampling Mode.......... 11
7.13 Timing Requirements: Exit Standby Mode............ 11
7.14 Timing Requirements: Exit Shutdown Mode......... 12
7.15 Switching Characteristics: CONVST Control ........ 12
7.16 Switching Characteristics: Parallel Data Read
Operation, CS and RD Tied Together ..................... 13
9
14
14
18
Detailed Description ............................................ 25
8.1
8.2
8.3
8.4
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
13
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
25
25
26
34
Application and Implementation ........................ 47
9.1 Application Information............................................ 47
9.2 Typical Application ................................................. 47
10 Power Supply Recommendations ..................... 50
11 Layout................................................................... 51
11.1 Layout Guidelines ................................................. 51
11.2 Layout Example .................................................... 51
12 Device and Documentation Support ................. 53
12.1
12.2
12.3
12.4
12.5
12.6
Documentation Support ........................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
53
53
53
53
53
53
13 Mechanical, Packaging, and Orderable
Information ........................................................... 53
4 Revision History
2
DATE
REVISION
NOTES
April 2017
*
Initial release.
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5 Device Family Comparison Table
PRODUCT
RESOLUTION (Bits)
CHANNELS
SAMPLE RATE (kSPS)
ADS8578S
14
8, single-ended
200
ADS8588S
16
8, single-ended
200
ADS8586S
16
6, single-ended
250
ADS8584S
16
4, single-ended
330
6 Pin Configuration and Functions
AIN_8GND
AIN_8P
AIN_7GND
AIN_7P
AIN_6GND
AIN_6P
AIN_5GND
AIN_5P
AIN_4GND
AIN_4P
AIN_3GND
AIN_3P
AIN_2GND
AIN_2P
AIN_1GND
AIN_1P
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
PM Package
64-Pin LQFP
Top View
OS2
5
44
REFCAPA
PAR/SER/BYTE SEL
6
43
REFGND
STBY
7
42
REFIN/REFOUT
RANGE
8
41
AGND
CONVSTA
9
40
AGND
CONVSTB
10
39
REGCAP2
RESET
11
38
AVDD
RD/SCLK
12
37
AVDD
CS
13
36
REGCAP1
BUSY
14
35
AGND
FRSTDATA
15
34
REFSEL
DB0
16
33
DB15/BYTE SEL
DB14/HBEN
DB13
DB12
DB11
DB10
DB9
AGND
DB8/DOUTB
DB7/DOUTA
DVDD
DB6
DB5
DB4
DB3
DB2
DB1
32
REFCAPB
31
45
30
4
29
OS1
28
REFGND
27
46
26
3
25
OS0
24
AGND
23
47
22
2
21
AGND
20
AVDD
19
48
18
1
17
AVDD
Not to scale
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Pin Functions
NO.
TYPE (1)
2, 26, 35, 40,
41, 47
P
Analog ground pins
AIN_1GND
50
AI
Analog input channel 1: negative input
AIN_1P
49
AI
Analog input channel 1: positive input
AIN_2GND
52
AI
Analog input channel 2: negative input
AIN_2P
51
AI
Analog input channel 2: positive input
AIN_3GND
54
AI
Analog input channel 3: negative input
AIN_3P
53
AI
Analog input channel 3: positive input
AIN_4GND
56
AI
Analog input channel 4: negative input
AIN_4P
55
AI
Analog input channel 4: positive input
AIN_5GND
58
AI
Analog input channel 5: negative input
AIN_5P
57
AI
Analog input channel 5: positive input
AIN_6GND
60
AI
Analog input channel 6: negative input
AIN_6P
59
AI
Analog input channel 6: positive input
AIN_7GND
62
AI
Analog input channel 7: negative input
AIN_7P
61
AI
Analog input channel 7: positive input
AIN_8GND
64
AI
Analog input channel 8: negative input
AIN_8P
63
AI
Analog input channel 8: positive input
AVDD
1, 37, 38, 48
P
Analog supply pins. Decouple these pins to the closest AGND pins
(see the Power Supply Recommendations section).
BUSY
14
DO
Active high digital output indicating an ongoing conversion
(see the BUSY (Output) section)
CONVSTA
9
DI
Active high logic input to control start of conversion for first half count of device input channels
(see the CONVSTA, CONVSTB (Input) section)
CONVSTB
10
DI
Active high logic input to control start of conversion for second half count of device input channels
(see the CONVSTA, CONVSTB (Input) section)
CS
13
DI
Active low logic input chip-select signal (see the CS (Input) section)
DB0
16
DO
DB0 is driven low in parallel interface mode; in parallel byte interface mode, DB0 is ADC data
output bit 6 and is driven low (see the DB[6:0] section)
DB1
17
DO
Driven low in parallel interface mode; in parallel byte interface mode, DB1 is ADC data output bit 7
and is driven low (see the DB[6:0] section)
DB2
18
DO
ADC data output bit 0 in parallel interface mode; in parallel byte interface mode, DB2 is ADC data
output bits 8 and 0 and is driven low (see the DB[6:0] section)
DB3
19
DO
ADC data output bit 1 in parallel interface mode; in parallel byte interface mode, DB3 is ADC data
output bits 9 and 1 and is driven low (see the DB[6:0] section)
DB4
20
DO
ADC data output bit 2 in parallel interface mode; in parallel byte interface mode, DB4 is ADC data
output bits 10 and 2 and is driven low (see the DB[6:0] section)
DB5
21
DO
ADC data output bit 3 in parallel interface mode; in parallel byte interface mode, DB5 is ADC data
output bits 11 and 3 and is driven low (see the DB[6:0] section)
DB6
22
DO
ADC data output bit 4 in parallel interface mode; in parallel byte interface mode, DB6 is ADC data
output bits 12 and 4 and is driven low (see the DB[6:0] section)
DB7/DOUTA
24
DO
Multifunction logic output pin (see the DB7/DOUTA section):
this pin is ADC data output bit 5 in parallel interface mode, ADC data output bits 13 and 5 in
parallel byte interface mode, and is a data output pin in serial interface mode.
DB8/DOUTB
25
DO
Multifunction logic output pin (see the DB8/DOUTB section):
this pin is ADC data output bit 6 in parallel interface mode and is a data output pin in serial
interface mode.
DB9
27
DO
ADC data output bit 7 in parallel interface mode (see the DB[13:9] section)
DB10
28
DO
ADC data output bit 8 in parallel interface mode (see the DB[13:9] section)
DB11
29
DO
ADC data output bit 9 in parallel interface mode (see the DB[13:9] section)
DB12
30
DO
ADC data output bit 10 in parallel interface mode (see the DB[13:9] section)
DB13
31
DO
ADC data output bit 11 in parallel interface mode (see the DB[13:9] section)
DB14/HBEN
32
DIO
Multifunction logic input or output pin (see the DB14/HBEN section):
this pin is ADC data output bit 12 in parallel interface mode, and is a control input pin for byte
selection (high or low) in parallel byte interface mode.
NAME
AGND
(1)
4
DESCRIPTION
AI = analog input; AO = analog output; AIO = analog input/output; DI = digital input; DO = digital output; DIO = digital input/output; P =
power supply; and NC = no connect.
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Pin Functions (continued)
NAME
NO.
TYPE
(1)
DESCRIPTION
Multifunction logic input or output pin (see the DB15/BYTE SEL section):
this pin is ADC data output bit 13 (MSB) in parallel interface mode, and is an active high control
input pin to enable parallel byte interface mode.
DB15/BYTE SEL
33
DIO
DVDD
23
P
FRSTDATA
15
DO
Active high digital output indicating data read back from channel 1 of the device (see the
FRSTDATA (Output) section)
OS0
3
DI
Oversampling mode control pin (see the Oversampling Mode of Operation section)
OS1
4
DI
Oversampling mode control pin (see the Oversampling Mode of Operation section)
OS2
5
DI
Oversampling mode control pin (see the Oversampling Mode of Operation section)
PAR/SER/BYTE SEL
6
DI
Logic input pin to select between parallel, serial, or parallel byte interface mode (see the Data
Read Operation section)
RANGE
8
DI
Multifunction logic input pin (see the RANGE (Input) section):
when the STBY pin is high, this pin selects the input range of the device (±10 V or ±5 V); when the
STBY pin is low, this pin selects between the standby and shutdown modes.
RD/SCLK
12
DI
Multifunction logic input pin (see the RD/SCLK (Input) section):
this pin is an active-low ready input pin in parallel and parallel byte interface, and is a clock input
pin in serial interface mode.
REFCAPA
44
AO
Reference amplifier output pin. This pin must be shorted to REFCAPB and decoupled to AGND
using a low equivalent series resistance (ESR), 10-µF ceramic capacitor.
REFCAPB
45
AO
Reference amplifier output pin. This pin must be shorted to REFCAPA and decoupled to AGND
using a low ESR, 10-µF ceramic capacitor.
REFGND
43, 46
P
Reference GND pin. This pin must be shorted to the analog GND plane and decoupled with
REFIN/REFOUT on pin 42 using a 10-µF capacitor.
REFIN/REFOUT
42
AIO
This pin acts as an internal reference output when REFSEL is high;
this pin functions as input pin for the external reference when REFSEL is low; decouple with
REFGND on pin 43 using a 10-µF capacitor.
REFSEL
34
DI
Active high logic input to enable the internal reference (see the REFSEL (Input) section)
REGCAP1
36
AO
Output pin 1 for the internal voltage regulator; decouple separately to AGND using a 1-µF
capacitor
REGCAP2
39
AO
Output pin 2 for the internal voltage regulator; decouple separately to AGND using a 1-µF
capacitor
RESET
11
DI
Active high logic input to reset the device digital logic (see the RESET (Input) section)
STBY
7
DI
Active low logic input to enter the device into one of the two power-down modes: standby or
shutdown (see the Power-Down Modes section)
Digital supply pin; decouple with AGND on pin 26
7 Specifications
7.1 Absolute Maximum Ratings
at TA = 25°C (unless otherwise noted) (1)
MIN
MAX
UNIT
AVDD to AGND
–0.3
7.0
V
DVDD to AGND
–0.3
7.0
V
Analog input voltage to AGND (2)
–15
15
V
Digital input to AGND
–0.3
DVDD + 0.3
V
REFIN to AGND
–0.3
AVDD + 0.3
V
Input current to any pin except supplies (2)
–10
10
mA
–40
125
Operating
Temperature
Junction, TJ
150
Storage, Tstg
(1)
(2)
–65
°C
150
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Transient currents of up to 100 mA do not cause SCR latch-up.
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7.2 ESD Ratings
VALUE
V(ESD)
Electrostatic discharge
Human-body model (HBM), per
ANSI/ESDA/JEDEC JS-001 (1)
Charged-device model (CDM), per JEDEC
specification JESD22-C101 (2)
(1)
(2)
All pins except analog inputs
±2000
Analog input pins only
±7000
All pins
±500
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
NOM
MAX
UNIT
AVDD
Analog supply voltage
4.75
5
5.25
V
DVDD
Digital supply voltage
2.3
3.3
AVDD
V
7.4 Thermal Information
ADS8578S
THERMAL METRIC
(1)
PM (LQFP)
UNIT
64 PINS
RθJA
Junction-to-ambient thermal resistance
46.0
°C/W
RθJC(top)
RθJB
Junction-to-case (top) thermal resistance
7.8
°C/W
Junction-to-board thermal resistance
20.1
°C/W
ψJT
Junction-to-top characterization parameter
0.3
°C/W
ψJB
Junction-to-board characterization parameter
19.6
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
N/A
°C/W
(1)
6
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
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7.5 Electrical Characteristics
minimum and maximum specifications are at TA = –40°C to +125°C, AVDD = 4.75 V to 5.25 V; typical specifications are at TA
= 25°C; AVDD = 5 V, DVDD = 3 V, VREF = 2.5 V (internal), and fSAMPLE = 200 kSPS (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
TEST
LEVEL (1)
ANALOG INPUTS
Full-scale input span (2)
(AIN_nP to AIN_nGND)
RANGE pin = 1
–10
10
RANGE pin = 0
–5
5
AIN_nP
Operating input range,
positive input
RANGE pin = 1
–10
10
RANGE pin = 0
–5
5
AIN_nGND
Operating input range,
negative input
All input ranges
–0.3
RIN
Input impedance
At TA = 25°C
Input impedance drift
All input ranges
Input leakage current
With voltage at AIN_nP = VIN,
all input ranges
IIkg(in)
0
0.3
0.85
1
1.15
–25
±7
25
(VIN – 2) / RIN
V
V
A
A
A
A
V
B
MΩ
B
ppm/°C
B
µA
A
SYSTEM PERFORMANCE
Resolution
14
Bits
A
NMC
No missing codes
14
Bits
A
DNL
Differential nonlinearity
All input ranges
–0.5
±0.2
0.5
LSB (3)
A
INL
Integral nonlinearity (4)
All input ranges
–0.45
±0.2
0.45
LSB
A
TA = –40°C to
+85°C
–16
±1
16
TA = –40°C to
+125°C
–16
±1
24
EG
Gain error (5)
All input
ranges,
external
reference
All input ranges,
internal reference
Gain error matching
(channel-to-channel)
Gain error temperature drift
EO
Offset error
Input range = ±5 V,
external and internal reference
2.5
15
±6
14
15
–14
B
±10
B
–1.8
±0.15
1.8
Input range = ±5 V
–1.8
±0.15
1.8
0.3
2.4
±0.3
3
All input ranges
A
ppm/°C
Input range = ±10 V
Offset error temperature drift
A
LSB
All input ranges,
internal reference
All input ranges
A
A
2
Offset error matching
(channel-to-channel)
LSB
±0.3
Input range = ±10 V,
external and internal reference
All input ranges,
external reference
A
–3
mV
B
B
mV
B
ppm/°C
B
µs
A
kSPS
A
SAMPLING DYNAMICS
tACQ
Acquisition time
fS
Maximum throughput rate per channel
without latency
(1)
(2)
(3)
(4)
(5)
1
All eight channels included
200
Test Levels: (A) Tested at final test. Overtemperature limits are set by characterization and simulation. (B) Limits set by characterization
and simulation, across temperature range. (C) Typical value only for information, provided by design simulation.
Ideal input span, does not include gain or offset error.
LSB = least significant bit.
This parameter is the endpoint INL, not best-fit INL.
Gain error is calculated after adjusting for offset error, which implies that positive full scale error = negative full scale error = gain error ÷
2.
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Electrical Characteristics (continued)
minimum and maximum specifications are at TA = –40°C to +125°C, AVDD = 4.75 V to 5.25 V; typical specifications are at TA
= 25°C; AVDD = 5 V, DVDD = 3 V, VREF = 2.5 V (internal), and fSAMPLE = 200 kSPS (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
TEST
LEVEL (1)
DYNAMIC CHARACTERISTICS
Signal-to-noise ratio,
no oversampling
(VIN – 0.5 dBFS at 1 kHz)
Input range = ±10 V
84.5
85.7
SNR
Input range = ±5 V
84.2
85.6
Signal-to-noise ratio,
oversampling = 4x
(VIN – 0.5 dBFS at 130 Hz)
Input range = ±10 V
85.5
85.8
SNROSR
Input range = ±5 V
85.2
85.6
A
dB
A
A
dB
A
(6)
THD
Total harmonic distortion
(VIN – 0.5 dBFS at 1 kHz)
Signal-to-noise + distortion ratio,
no oversampling
(VIN – 0.5 dBFS at 1 kHz)
Input range = ±10 V
SINAD
Input range = ±5 V
84.3
85.3
Input range = ±10 V
85.4
85.5
SINADOSR
Signal-to-noise + distortion ratio,
oversampling = 4x
(VIN – 0.5 dBFS at 130 Hz)
SFDR
Spurious-free dynamic range
(VIN – 0.5 dBFS at 1 kHz)
All input ranges
Input range = ±5 V
–109
84.5
85.2
All input ranges
Crosstalk isolation (7)
BW(–3
–3 dB
dB)
Small-signal
bandwidth
BW(–0.1 dB)
tGROUP
–0.1 dB
Group delay
–95
dB
85.4
B
A
dB
A
A
dB
85.4
A
–111
dB
B
–95
dB
A
At TA = 25°C,
input range = ±10 V
24
At TA = 25°C,
input range = ±5 V
16
At TA = 25°C,
input range = ±10 V
14
At TA = 25°C,
input range = ±5 V
9.5
Input range = ±10 V
13
Input range = ±5 V
19
B
kHz
B
B
kHz
B
µs
C
C
INTERNAL REFERENCE OUTPUT (REFSEL = 1)
Voltage on the REFIN/REFOUT pin
(configured as output)
VREF (8)
C(REFIN_
REFOUT)
V(REFCAP)
At TA = 25°C
2.4975
2.5025
V
A
Internal reference temperature drift
7.5
ppm/°C
B
Decoupling capacitor on
REFIN/REFOUT (9)
10
µF
B
Reference voltage to the ADC
(on the REFCAPA, REFCAPB pin)
At TA = 25°C
3.996
Reference buffer output impedance
C(REFCAP)
2.5
4.0
4.004
V
A
0.5
1
Ω
C
Reference buffer output temperature
drift
5
ppm/°C
B
Decoupling capacitor on REFCAPA,
REFCAPB
10
μF
B
25
ms
B
V
B
Turn-on time
C(REFCAP) = 10 µF,
C(REFIN_REFOUT) = 10 µF
EXTERNAL REFERENCE INPUT (REFSEL = 0)
VREFIO_EXT
(6)
(7)
(8)
(9)
8
External reference voltage on REFIO
(configured as input)
2.475
2.5
2.525
Reference input impedance
100
MΩ
C
Reference input capacitance
10
pF
C
Calculated on the first nine harmonics of the input frequency.
Isolation crosstalk is measured by applying a full-scale sinusoidal signal up to 160 kHz to a channel, not selected in the multiplexing
sequence, and measuring the effect on the output of any selected channel.
Does not include the variation in voltage resulting from solder shift effects.
Recommended to use an X7R-grade, 0603-size ceramic capacitor for optimum performance (see the Layout Guidelines section).
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Electrical Characteristics (continued)
minimum and maximum specifications are at TA = –40°C to +125°C, AVDD = 4.75 V to 5.25 V; typical specifications are at TA
= 25°C; AVDD = 5 V, DVDD = 3 V, VREF = 2.5 V (internal), and fSAMPLE = 200 kSPS (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
TEST
LEVEL (1)
POWER-SUPPLY REQUIREMENTS
AVDD
Analog power-supply voltage
Analog supply
DVDD
Digital power-supply voltage
Digital supply range
IAVDD_DYN
IAVDD_STC
IAVDD_STDBY
Analog supply current
(operational)
Analog supply current
(static)
AVDD supply
STANDBY current
4.75
5
5.25
V
A
2.3
3.3
AVDD
V
A
For ADS8578S, AVDD = 5 V,
fS = 200 kSPS,
internal reference
17.7
24.0
For ADS8578S, AVDD = 5 V,
fS = 200 kSPS,
external reference
17.1
24.0
A
For ADS8578S, AVDD = 5 V,
internal reference,
device not converting
12.4
17.0
A
For ADS8578S, AVDD = 5 V,
external reference,
device not converting
12.0
17.0
At AVDD = 5 V, device in STDBY
mode, internal reference
4.2
5.5
At AVDD = 5 V, device in STDBY
mode, external reference
3.8
5.5
0.2
6
µA
A
A
mA
mA
A
A
mA
A
IAVDD_PWR_ DN
AVDD supply
power-down current
At AVDD = 5 V, device in
PWR_DN, internal or external
reference,
TA = –40°C to +85°C
IDVDD_DYN
Digital supply current
For ADS8578S,
DVDD = 3.3 V,
fS = 200 kSPS
0.15
0.3
mA
A
IDVDD_STDBY
DVDD supply STANDBY current
At AVDD = 5 V, device in STDBY
mode
0.05
1.5
µA
A
IDVDD_PWR-DN
DVDD supply power-down current
At AVDD = 5 V, device in
PWR_DN mode
0.05
1.5
µA
A
DIGITAL INPUTS (CMOS)
VIH
Digital high input voltage logic level
DVDD > 2.3 V
0.7 × DVDD
DVDD + 0.3
V
A
VIL
Digital low input voltage logic level
DVDD > 2.3 V
–0.3
0.3 × DVDD
V
A
Input leakage current
100
nA
A
Input pin capacitance
5
pF
A
DIGITAL OUTPUTS (CMOS)
VOH
Digital high output voltage logic level
IO = 100-μA source
VOL
Digital low output voltage logic level
IO = 100-μA sink
Floating state leakage current
Only for SDO
0.8 × DVDD
DVDD
V
A
0
0.2 × DVDD
V
A
1
µA
A
5
pF
A
°C
A
Internal pin capacitance
TEMPERATURE RANGE
TA
Operating free-air temperature
–40
125
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7.6 Timing Requirements: CONVST Control
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), BUSY load = 20 pF, VIL and VIH at datasheet limits, and fSAMPLE = 200 kSPS
(unless otherwise noted) (see Figure 1)
MIN
tACQ
Acquisition time:
BUSY falling edge to rising edge of trailing CONVSTA or CONVSTB
tPH_CN
tPL_CN
NOM
MAX
UNIT
1
µs
CONVSTA, CONVSTB pulse high time
25
ns
CONVSTA, CONVSTB pulse low time
25
ns
tSU_BSYCS
Setup time: BUSY falling to CS falling
0
ns
tSU_RSTCN
Setup time: RESET falling to first rising edge of CONVSTA or CONVSTB
25
ns
tPH_RST
RESET pulse high time
50
tD_CNAB
Delay between rising edges of CONVSTA and CONVSTB
ns
500
µs
7.7 Timing Requirements: Data Read Operation
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), BUSY load = 20 pF, VIL and VIH at datasheet limits, and fSAMPLE = 200 kSPS
(unless otherwise noted) (see Figure 2)
MIN
NOM
MAX
UNIT
tDZ_CNCS
Delay between CONVSTA, CONVSTB rising edge to CS falling edge, start of
data read operation during conversion
10
ns
tDZ_CSBSY
Delay between CS rising edge to BUSY falling edge, end of data read
operation during conversion
40
ns
tSU_BSYCS
Setup time: BUSY falling edge to CS falling edge, start of data read operation
after conversion
0
ns
tD_CSCN
Delay between CS rising edge to CONVSTA, CONVSTB rising edge, end of
data read operation after conversion
10
ns
7.8 Timing Requirements: Parallel Data Read Operation, CS and RD Tied Together
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DB[15:0] and FRSTDATA = 20 pF, VIL and VIH at datasheet limits,
and fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 3)
MIN
NOM
MAX
UNIT
tPH_CS,
tPH_RD
CS and RD high time
15
ns
tPL_CS,
tPL_RD
CS and RD low time
15
ns
2.5
ns
tHT_RDDB,
Hold time: RD and CS rising edge to DB[15:0] invalid
tHT_CSDB
10
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7.9 Timing Requirements: Parallel Data Read Operation, CS and RD Separate
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DB[15:0] and FRSTDATA = 20 pF, VIL and VIH at datasheet limits,
and fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 4)
MIN
NOM
MAX
UNIT
tSU_CSRD
Set-up time: CS falling edge to RD falling edge
0
ns
tHT_RDCS
Hold time: RD rising edge to CS rising edge
0
ns
tPL_RD
RD low time
15
ns
tPH_RD
RD high time
15
ns
tHT_CSDB
Hold time: CS rising edge to DB[15:0] becoming invalid
6
ns
tHT_RDDB
Hold time: RD rising edge to DB[15:0] becoming invalid
2.5
ns
7.10 Timing Requirements: Serial Data Read Operation
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DOUTA, DOUTB, and FRSTDATA = 20 pF, VIL and VIH at datasheet
limits, and fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 5)
MIN
NOM
MAX
UNIT
0.45
0.55
tSCLK
0.45
0.55
tSCLK
tSCLK
SCLK time period
50
tPH_SCLK
SCLK high time
ns
tPL_SCLK
SCLK low time
tHT_CKDO
Hold time: SCLK rising edge to DOUTA, DOUTB invalid
7
ns
tSU_CSCK
Setup time: CS falling to first SCLK edge
8
ns
tHT_CKCS
Hold time: last SCLK active edge to CS high
10
ns
7.11 Timing Requirements: Byte Mode Data Read Operation
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DB[7:0] and FRSTDATA = 20 pF, VIL and VIH at datasheet limits, and
fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 6)
MIN
NOM
MAX
UNIT
tSU_CSRD
Setup time: CS falling edge to RD falling edge
0
ns
tHT_RDCS
Hold time: RD rising edge to CS rising edge
0
ns
tPL_RD
RD low time
15
ns
tPH_RD
RD high time
15
ns
tHT_CSDB
Hold time: CS rising edge to DB[15:0] becoming invalid
6
ns
tHT_RDDB
Hold time: RD rising edge to DB[15:0] becoming invalid
2.5
ns
7.12 Timing Requirements: Oversampling Mode
MIN
NOM
MAX
UNIT
tHT_OS
Hold time: BUSY falling to OSx
20
ns
tSU_OS
Setup time: BUSY falling to OSx
20
ns
7.13 Timing Requirements: Exit Standby Mode
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C, AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), VIL and VIH at datasheet limits, and fSAMPLE = 200 kSPS (unless otherwise
noted) (see Figure 8)
MIN
tD_STBYCN
(1)
Delay between STBY rising edge to CONVSTA or CONVSTB rising edge (1)
NOM
MAX
UNIT
100
µs
First conversion data must be discarded or RESET must be issued if the maximum timing is exceeded.
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7.14 Timing Requirements: Exit Shutdown Mode
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), VIL and VIH at datasheet limits, and fSAMPLE = 200 kSPS (unless otherwise
noted) (see Figure 9)
MIN
Internal reference mode
50
External reference mode (1)
13
NOM
MAX
UNIT
tD_SDRST
Delay between STBY rising edge to RESET rising edge
tPH_RST
RESET high time
50
ns
tD_RSTCN
Delay between RESET falling edge to CONVSTA or CONVSTB rising edge
25
µs
(1)
ms
Excludes wake-up time for external reference device.
7.15 Switching Characteristics: CONVST Control
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), BUSY load = 20 pF, VIL and VIH at datasheet limits, and fSAMPLE = 200 kSPS
(unless otherwise noted) (see Figure 1)
PARAMETER
tCYC
ADC cycle time period
TEST CONDITIONS
MIN
No oversampling, parallel read, serial
read with both DOUTA and DOUTB
during conversion
5
No oversampling, serial read after
conversion with both DOUTA and
DOUTB,
7
No oversampling, serial read after
conversion with only DOUTA or
DOUTB,
9.7
No oversampling, 8 channels
3.7
No oversampling, 6 channels
Conversion time: BUSY high time
tD_CNBSY
12
MAX
µs
3.8
3.9
2
Oversampling by 2
8.4
8.8
Oversampling by 4
17.5
18.5
Oversampling by 8
36
38
Oversampling by 16
73
77
Oversampling by 32
148
155
Oversampling by 64
298
311
Delay between trailing rising edges of
CONVSTA or CONVSTB and BUSY
rising
15
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UNIT
3
No oversampling, 4 channels
tCONV
TYP
µs
ns
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7.16 Switching Characteristics: Parallel Data Read Operation, CS and RD Tied Together
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DB[15:0] and FRSTDATA = 20 pF, VIL and VIH at datasheet limits,
and fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 3)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
tD_CSDB
Delay time: CS falling edge to DB[15:0]
becoming valid
(out of tri-state)
12
ns
tD_RDDB
Delay time: RD falling edge to new
data on DB[15:0]
17
ns
tD_CSFD,
tD_RDFD
Delay time: CS and RD falling edge to
FRSTDATA going high or low out of tristate
10
ns
tDHZ_CSDB,
tDHZ_RDDB
Delay time: CS and RD rising edge to
DB[15:0] tri-state
12
ns
tDHZ_CSFD,
tDHZ_RDFD
Delay time: CS and RD rising edge to
FRSTDATA tri-state
10
ns
7.17 Switching Characteristics: Parallel Data Read Operation, CS and RD Separate
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DB[15:0] and FRSTDATA = 20 pF, VIL and VIH at datasheet limits,
and fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 4)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
tD_CSDB
Delay time: CS falling edge to DB[15:0]
becoming valid
(out of tri-state)
12
ns
tD_RDDB
Delay time: RD falling edge to new data
on DB[15:0]
17
ns
tDHZ_CSDB
Delay time: CS rising edge to DB[15:0]
becoming tri-state
12
ns
tD_CSFD
Delay time: CS falling edge to
FRSTDATA going low out of tri-state
15
ns
tDHZ_CSFD
Delay time: CS rising edge to
FRSTDATA going to tri-state
10
ns
tD_RDFD
Delay time: RD falling edge to
FRSTDATA going high or low
15
ns
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7.18 Switching Characteristics: Serial Data Read Operation
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DOUTA, DOUTB, and FRSTDATA = 20 pF, VIL and VIH at datasheet
limits, and fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 5)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
tD_CSDO
Delay time: CS falling edge to DOUTA,
DOUTB enable
(out of tri-state)
12
ns
tD_CKDO
Delay time: SCLK rising edge to valid
data on DOUTA, DOUTB
15
ns
tDZ_CSDO
Delay time: CS rising edge to DOUTA,
DOUTB going to tri-state
12
ns
tD_CSFD
Delay time: CS falling edge to
FRSTDATA from tri-state to high or low
10
ns
tDZ_CKFD
Delay time: 14th SCLK falling edge to
FRSTDATA falling edge
15
ns
tDHZ_CSFD
Delay time: CS rising edge to
FRSTDATA going to tri-state
10
ns
7.19 Switching Characteristics: Byte Mode Data Read Operation
minimum and maximum specifications are at TA = –40°C to +125°C, typical specifications are at TA = 25°C; AVDD = 5 V,
2.3 V ≤ DVDD ≤ 5.25 V, VREF = 2.5 V (internal), load on DB[7:0] and FRSTDATA = 20 pF, VIL and VIH at datasheet limits, and
fSAMPLE = 200 kSPS (unless otherwise noted) (see Figure 6)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
tD_CSDB
Delay time: CS falling edge to DB[7:0]
becoming valid
(out of tri-state)
12
ns
tD_RDDB
Delay time: RD falling edge to new data
on DB[7:0]
17
ns
tDHZ_CSDB
Delay time: CS rising edge to DB[7:0]
becoming tri-state
12
ns
tD_CSFD
Delay time: CS falling edge to
FRSTDATA going low out of tri-state
10
ns
tD_RDFD
Delay time: RD falling edge to
FRSTDATA going low or high state
15
ns
tDHZ_CSFD
Delay time: CS rising edge to
FRSTDATA going to tri-state
10
ns
14
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tCYC
CONVSTA
tD_CNAB
tACQ
tPL_CN
CONVSTB
tPH_CN
tD_CNBSY
BUSY
tCONV
tSU_BSYCS
CS
tSU_RSTCN
RESET
tPH_RST
Figure 1. CONVST Control Timing Diagram
CONVSTA
CONVSTB
tD_CSCN
tSU_BSYCS
BUSY
tDZ_CNCS
tDZ_CSBSY
CS
Read During Conversion
Read After Conversion
tSU_RSTCN
RESET
tPH_RST
Figure 2. Data Read Operation Timing Diagram
tPH_CS
tPH_RD
tPL_CS
tPL_RD
tHT_CSDB
tHT_RDDB
CS , RD
tD_CSDB
tD_RDDB
DB[15:0]
AIN_1
Data
AIN_2
Data
AIN_3
Data
AIN_4
Data
AIN_5
Data
AIN_6
Data
AIN_7
Data
tD_CSFD
tD_RDFD
AIN_8
Data
tDHZ_CSDB
tDHZ_RDDB
tDHZ_CSFD
tDHZ_RDFD
FRSTDATA
Figure 3. Parallel Data Read Operation, CS and RD Tied Together
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CS
tPH_RD
tHT_RDCS
tSU_CSRD
tPL_RD
RD
tD_CSDB
DB[15:0]
Invalid
AIN_1
Data
AIN_2
Data
tD_CSFD
tHT_CSDB
tDHZ_CSDB
tD_RDDB
tHT_RDDB
AIN_3
Data
AIN_4
Data
AIN_5
Data
AIN_6
Data
AIN_7
Data
AIN_8
Data
tD_RDFD
tDHZ_CSFD
FRSTDATA
Figure 4. Parallel Data Read Operation, CS and RD Separate
tSU_CSCK
tSCLK
CS
tPH_SCLK
tHT_CKCS
tPL_SCLK
SCLK
tD_CSDO
DOUTA
DOUTB
DB13
DB12
tDZ_CSDO
tD_CKDO
tHT_CKDO
DB11
DB1
DB0
tDZ_CKFD
tD_CSFD
tDHZ_CSFD
FRSTDATA
Figure 5. Serial Data Read Operation Timing Diagram
CS
tPH_RD
tHT_RDCS
tSU_CSRD
tPL_RD
RD
tD_CSDB
DB[7:0]
Invalid
tD_CSFD
High Byte
AIN_1
Low Byte
AIN_1
tHT_CSDB
tDHZ_CSDB
tD_RDDB
tHT_RDDB
High Byte
AIN_2
Low Byte
AIN_2
High Byte
AIN_8
tD_RDFD
Low Byte
AIN_8
tDHZ_CSFD
FRSTDATA
Figure 6. Byte Mode Data Read Operation Timing Diagram
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CONVSTA
CONVSTB
OSR latched for
Conversion (N+1)
Conversion
N
BUSY
tSU_OS
Conversion
N+1
tHT_OS
OSR x
Figure 7. Oversampling Mode Timing Diagram
STBY
RANGE
tD_STBYCN
CONVSTA
CONVSTB
Figure 8. Exit Standby Mode Timing Diagram
STBY
RANGE
tD_SDRST
RESET
tPH_RST
CONVSTA
CONVSTB
tD_RSTCN
Figure 9. Exit Shutdown Mode Timing Diagram
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7.20 Typical Characteristics
at TA = 25°C, AVDD = 5 V, DVDD = 3 V, internal reference VREF = 2.5 V, and fS = 200 kSPS per channel (unless otherwise
noted)
9
25 C
-40 C
125 C
9
25 C
-40 C
125 C
6
Analog Input Current (uA)
Analog Input Current (uA)
15
3
-3
-9
3
0
-3
-6
-15
-10
-9
-6
-2
2
Input Voltage (V)
6
-5
10
-3
-1
1
Input Voltage (V)
D002
Figure 10. Analog Input Current vs Input Voltage Over
Temperature (±10 V)
3
5
D003
Figure 11. Analog Input Current vs Input Voltage Over
Temperature (±5 V)
70000
1.05
± 10 V
±5V
56000
Number of Hits
Input Impedance (M:)
1.03
1.01
0.99
28000
14000
0.97
0.95
-40
42000
0
-7
26
59
Free-Air Temperature (qC)
92
-1
125
0
Output Codes
D004
D009
Mean = –0.012, sigma = 0.11, number of hits = 65536, VIN = 0 V
Figure 12. Input Impedance vs Temperature
Figure 13. DC Histogram of Codes (±10 V)
70000
Differential Nonlinearity (LSB)
0.5
Number of Hits
56000
42000
28000
14000
0
-1
0.3
0.1
-0.1
-0.3
-0.5
-8192
0
Output Codes
D010
-4096
0
Codes (LSB)
4096
8191
D015
Mean = –0.001, sigma = 0.04, number of hits = 65536, VIN = 0 V
Figure 14. DC Histogram of Codes (±5 V)
18
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Figure 15. DNL for All Codes
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Typical Characteristics (continued)
at TA = 25°C, AVDD = 5 V, DVDD = 3 V, internal reference VREF = 2.5 V, and fS = 200 kSPS per channel (unless otherwise
noted)
0.45
0.3
Maximum
Minimum
0.3
0.2
Integral Nonlinearity (LSB)
Differential Nonlinearity (LSB)
0.25
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
0.15
0
-0.15
-0.3
-0.2
-0.25
-40
-7
26
59
Free-Air Temperature (qC)
92
-0.45
-8192
125
0.45
0.45
0.3
0.3
0.15
0
-0.15
-0.3
8191
D013
Maximum
Minimum
0
-0.15
-0.3
-4096
0
Codes (LSB)
4096
-0.45
-40
8191
-7
D014
26
59
Free-Air Temperature (qC)
92
125
D015
Figure 19. INL vs Temperature (±10 V)
1.8
0.45
Maximum
Minimum
0.3
± 10 V
±5V
1.08
Offset Error (mV)
Integral Nonlinearity (LSB)
4096
0.15
Figure 18. INL vs All Codes (±5 V)
0.15
0
-0.15
0.36
-0.36
-1.08
-0.3
-0.45
-40
0
Codes (LSB)
Figure 17. INL vs All Codes (±10 V)
Integral Nonlinearity (LSB)
Integral Nonlinearity (LSB)
Figure 16. DNL vs Temperature
-0.45
-8192
-4096
D012
-7
26
59
Free-Air Temperature (qC)
92
125
-1.8
-40
D016
Figure 20. INL vs Temperature (±5 V)
-7
26
59
Free-Air Temperature (qC)
92
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D017
Figure 21. Offset Error vs Temperature
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Typical Characteristics (continued)
130
120
110
100
90
80
70
60
50
40
30
20
10
0
1.8
0.355
0.76
1.165 1.57 1.975
Offset Drift (ppm/qC)
2.38
Channel 7
Channel 8
0.36
-0.36
-1.8
-40
2.785 3
-7
D018
Figure 22. Offset Drift Histogram Distribution (±10 V)
130
120
110
100
90
80
70
60
50
40
30
20
10
0
26
59
Free-Air Temperature (qC)
92
125
D019
Figure 23. Offset Error Across Channels vs Temperature
(±10 V)
1.8
Channel 1
Channel 2
Channel 3
1.08
Offset Error (mV)
Number of Hits
Channel 4
Channel 5
Channel 6
-1.08
0
Channel 4
Channel 5
Channel 6
Channel 7
Channel 8
0.36
-0.36
-1.08
0
0.22 0.49 0.76 1.03 1.3 1.57 1.84 2.11 2.38 2.65
Offset Drift (ppm/qC)
-1.8
-40
3
D020
Figure 24. Offset Drift Histogram Distribution (±5 V)
-7
26
59
Free-Air Temperature (qC)
92
125
D021
Figure 25. Offset Error Across Channels vs Temperature
(±5 V)
80
16
± 10 V
±5V
70
9.6
60
Number of Hits
Gain Error (LSB)
Channel 1
Channel 2
Channel 3
1.08
Offset Error (mV)
Number of Hits
at TA = 25°C, AVDD = 5 V, DVDD = 3 V, internal reference VREF = 2.5 V, and fS = 200 kSPS per channel (unless otherwise
noted)
3.2
-3.2
50
40
30
20
-9.6
10
-16
-40
0
-7
26
59
Free-Air Temperature (qC)
92
125
0
D022
D023
External reference
External reference
Figure 26. Gain Error vs Temperature
20
1.76 4.21 5.595 6.98 8.365 9.75 11.13512.52 14
Gain Drift (ppm/qC)
Figure 27. Gain Error Drift Histogram Distribution (±10 V)
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Typical Characteristics (continued)
at TA = 25°C, AVDD = 5 V, DVDD = 3 V, internal reference VREF = 2.5 V, and fS = 200 kSPS per channel (unless otherwise
noted)
80
30
Channel 1
Channel 2
Channel 3
Channel 7
Channel 8
70
60
Number of Hits
Gain Error (LSB)
20
Channel 4
Channel 5
Channel 6
10
0
50
40
30
20
-10
10
0
-20
-40
-7
26
59
Free-Air Temperature (qC)
92
0
125
1.76 4.21 5.595 6.98 8.365 9.75 11.13512.52 14
Gain Drift (ppm/qC)
D024
Figure 29. Gain Error Drift Histogram Distribution (±5 V)
Figure 28. Gain Error Across Channels vs Temperature
(±10 V)
25
30
Channel 6
Channel 7
Channel 8
±5V
± 10 V
20
Gain Error (%FS)
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
20
Gain Error (LSB)
D025
External reference
External reference
10
0
-10
15
10
5
0
-5
-20
-40
-7
26
59
Free-Air Temperature (qC)
92
0
125
50
D026
100
150
Source Resistance (k:)
200
D027
External reference
Figure 31. Gain Error as a Function of External Source
Resistance
0
0
-20
-20
-40
-40
-60
-60
Amplitude (dB)
Amplitude (dB)
Figure 30. Gain Error Across Channels vs Temperature
(±5 V)
-80
-100
-120
-80
-100
-120
-140
-140
-160
-160
-180
-180
-200
-200
0
10
20
30
40
50
60
Frequency (kHz)
70
80
90
100
0
10
D028
Number of points = 32k, SNR = 85.41 dB,
SINAD = 85.38 dB, THD = –110.57 dB, SFDR = 114.17 dB
20
30
40
50
60
Frequency (kHz)
70
80
90
100
D029
Number of points = 32k, SNR = 85.26 dB,
SINAD = 85.23 dB, THD = –110.25 dB, SFDR = 114.08 dB
Figure 32. Typical FFT Plot (±10 V)
Figure 33. Typical FFT Plot (±5 V)
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Typical Characteristics (continued)
0
0
-50
-50
Amplitude (dB)
Amplitude (dB)
at TA = 25°C, AVDD = 5 V, DVDD = 3 V, internal reference VREF = 2.5 V, and fS = 200 kSPS per channel (unless otherwise
noted)
-100
-100
-150
-150
-200
-200
0
5
10
15
Frequency (kHz)
20
0
25
5
D030
10
15
Frequency (kHz)
20
25
D031
Number of points = 32k, SNR = 85.42 dB,
SINAD = 85.39 dB, THD = –110.6 dB, SFDR = 115.27 dB
Number of points = 32k, SNR = 85.66 dB,
SINAD = 85.62 dB, THD = –110.63 dB, SFDR = 114.65 dB
Figure 35. Typical FFT Plot for OSR 4x (±5 V)
Figure 34. Typical FFT Plot for OSR 4x (±10 V)
86
87
Signal-to-Noise Ratio (dB)
Signal-to-Noise Ratio (dB)
± 10 V
±5V
85.5
85
84.5
86
85
84
± 10 V
±5V
84
10
100
1k
Input Frequency (Hz)
10k
83
-40
100k
-7
26
59
Free-Air Temperature (qC)
D032
OSR = 0
D033
Figure 37. SNR vs Temperature for Different Input Ranges
90
90
OSR-0
OSR-2
89
OSR-4
OSR-8
OSR-16
OSR-32
OSR-64
OSR-0
OSR-2
OSR-4
89
88
Signal-to-Noise Ratio (dB)
Signal-to-Noise Ratio (dB)
125
OSR = 0
Figure 36. SNR vs Input Frequency for Different Input
Ranges
87
86
85
84
83
82
81
88
OSR-8
OSR-16
OSR-32
OSR-64
87
86
85
84
83
82
81
80
10
100
1k
Input Frequency (Hz)
10k
100k
80
10
D034
Figure 38. SNR vs Input Frequency for Different OSR
(±10 V)
22
92
100
1k
Input Frequency (Hz)
10k
100k
D035
Figure 39. SNR vs Input Frequency for Different OSR
(±5 V)
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Typical Characteristics (continued)
at TA = 25°C, AVDD = 5 V, DVDD = 3 V, internal reference VREF = 2.5 V, and fS = 200 kSPS per channel (unless otherwise
noted)
86
± 10 V
±5V
Signal-to-Noise + Distortion Ratio (dB)
Signal-to-Noise + Distortion Ratio (dB)
88
87
86
85
84
83
10
100
1k
Input Frequency (Hz)
10k
85.5
85.25
85
84.75
84.5
84.25
84
-40
100k
± 10 V
±5V
85.75
-7
D036
OSR = 0
-100
Total Harmonic Distortion (dB)
Total Harmonic Distortion (dB)
-95
-100
-105
-110
-105
-110
-115
± 10 V
±5V
100
1k
Input Frequency (Hz)
10k
-120
-40
100k
D038
Figure 42. THD vs Input Frequency for Different Input
Ranges
-7
26
59
Free-Air Temperature (qC)
92
125
D039
Figure 43. THD vs Temperature for Different Input Ranges
-60
-60
0 k:
10 k:
20 k:
30 k:
40 k:
50 k:
61 k:
68.1 k:
82.5 k:
90.9 k:
100 k:
-70
-80
-90
-100
Total Harmonic Distortion (dB)
Total Harmonic Distortion (dB)
D037
± 10 V
±5V
-90
-110
-120
1k
125
Figure 41. SINAD vs Temperature for Different Input Ranges
-80
-115
10
92
OSR = 0
Figure 40. SINAD vs Input Frequency for Different Input
Ranges
-85
26
59
Free-AirTemperature (qC)
10k
Input Frequency (Hz)
100k
-80
-90
-100
-110
-120
1k
D040
Figure 44. THD vs Input Frequency for Different Source
Impedances (±10 V)
0 k:
10 k:
20 k:
30 k:
40 k:
50 k:
61 k:
68.1 k:
82.5 k:
90.9 k:
100 k:
-70
10k
Input Frequency (Hz)
100k
D041
Figure 45. THD vs Input Frequency for Different Source
Impedances (±5 V)
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Typical Characteristics (continued)
at TA = 25°C, AVDD = 5 V, DVDD = 3 V, internal reference VREF = 2.5 V, and fS = 200 kSPS per channel (unless otherwise
noted)
-90
-100
-100
Isolation Cross Talk (dB)
Isolation Cross Talk (dB)
-90
-110
-120
-130
-110
-120
-130
-140
±5 V
±10 V
-140
100m
±5V
± 10 V
1
10
Frequency (kHz)
-150
100m
100
100
D043
14.5
± 10 V
±5V
19
± 10 V
±5V
14
Analog Supply Current (mA)
Analog Supply Current (mA)
19.5
18.5
18
17.5
17
13.5
13
12.5
12
11.5
16.5
-40
-7
26
59
Free-Air Temperature (qC)
92
11
-40
125
-7
D053
Figure 48. Analog Supply Current (Operational) vs
Temperature
4.5
6
4.48
5
4.46
4.44
4.42
4.4
4.38
26
59
Free-Air Temperature (qC)
92
125
D055
Figure 49. Analog Supply Current (Static) vs Temperature
(Sampling)
Analog Supply Current (PA)
Analog Supply Current (mA)
10
Frequency (kHz)
Figure 47. Isolation Crosstalk vs Noise Frequency
(Saturated Inputs)
Figure 46. Isolation Crosstalk vs Noise Frequency
(Inputs Within Range)
4
3
2
1
0
4.36
4.34
-40
-7
26
59
Free-Air Temperature (qC)
92
125
-1
-40
D056
Figure 50. Analog Supply Current vs Temperature
(Standby)
24
1
D042
-7
26
59
Free-Air Temperature (qC)
92
125
D001
Figure 51. Analog Supply Current vs Temperature
(Shutdown)
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8 Detailed Description
8.1 Overview
The ADS8578S is 14-bit data acquisition (DAQ) system with 8-channel analog inputs. Each analog input channel
consists of an input clamp protection circuit, a programmable gain amplifier (PGA), a third-order, low-pass filter,
and a track-and-hold circuit that facilitates simultaneous sampling of the signals on all input channels. The
sampled signal is digitized using a 14-bit analog-to-digital converter (ADC), based on the successive
approximation register (SAR) architecture. This overall system can achieve a maximum throughput of 200 kSPS
per channel. The device features a 2.5-V internal reference with a fast-settling buffer, a programmable digital
averaging filter to improve noise performance, and high-speed serial and parallel interfaces for communication
with a wide variety of digital hosts.
The device operates from a single 5-V analog supply and can accommodate true bipolar input signals of ±10 V
and ±5 V. The input clamp protection circuitry can tolerate voltages up to ±15 V. The device offers a constant
1-MΩ resistive input impedance irrespective of the sampling frequency or the selected input range. The
integration of multiple, simultaneously sampling precision ADC inputs and analog front-end circuits with high
input impedance operating from a single 5-V supply offers a simplified end solution without requiring external
high-voltage bipolar supplies and complicated driver circuits.
8.2 Functional Block Diagram
AVDD
DVDD
BUSY
AIN_1P
AIN_1GND
1M
Clamp
rd
PGA
Clamp
3 -Order
LPF
ADC
Driver
14-Bit
SAR
ADC
FRSTDATA
STBY
1M
CONVSTA, CONVSTB
RESET
AIN_2P
AIN_2GND
RANGE
1M
Clamp
PGA
Clamp
3rd -Order
LPF
ADC
Driver
1M
AIN_3P
AIN_3GND
14-Bit
SAR
ADC
Clamp
PGA
Clamp
3rd -Order
LPF
ADC
Driver
14-Bit
SAR
ADC
ADC
Driver
14-Bit
SAR
ADC
1M
1M
AIN_4P
Clamp
Clamp
RD/SCLK
SAR
Logic and
Digital Control
1M
AIN_4GND
CS
PGA
3rd -Order
LPF
1M
SER / PAR
Interface
PAR/ SER
DB[15:0]
DOUTA
DOUTB
OS0
Digital Filter
OS1
OS2
1M
AIN_5P
Clamp
AIN_5GND
Clamp
PGA
3rd -Order
LPF
ADC
Driver
1M
14-Bit
SAR
ADC
REFCAPA
REFCAPB
AIN_6P
AIN_6GND
1M
Clamp
PGA
Clamp
3rd -Order
LPF
ADC
Driver
14-Bit
SAR
ADC
1M
REFIN/REFOUT
2.5-V VREF
REFSEL
AIN_7P
AIN_7GND
1M
Clamp
PGA
3 -Order
LPF
ADC
Driver
PGA
3rd -Order
LPF
ADC
Driver
Clamp
rd
1M
AIN_8P
Clamp
AIN_8GND
Clamp
1M
14-Bit
SAR
ADC
14-Bit
SAR
ADC
1M
ADS8578S
AGND
REFGND
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8.3 Feature Description
8.3.1 Analog Inputs
The ADS8578S has 8 analog input channels, such that the positive inputs AIN_nP (n = 1 to 8) are the singleended analog inputs and the negative inputs AIN_nGND are tied to GND. Figure 52 shows the simplified circuit
schematic for each analog input channel, including the input clamp protection circuit, PGA, low-pass filter, highspeed ADC driver, and a precision 14-bit SAR ADC.
1 M:
AIN_nP
Clamp
PGA
AIN_nGND
Clamp
3rd-Order
LPF
ADC
Driver
14-bit
SAR
ADC
1 M:
Figure 52. Front-End Circuit Schematic for Each Analog Input Channel
The device can support two bipolar, single-ended input voltage ranges based on the logic level of the RANGE
input pin. As explained in the RANGE (Input) section, the input voltage range for all analog channels can be
configured to bipolar ±10 V or ±5 V. The device samples the voltage difference (AIN_nP – AIN_nGND) between
the selected analog input channel and the AIN_nGND pin. The device allows a ±0.3-V range on the AIN_nGND
pin for all analog input channels. Use this feature in modular systems where the sensor or signal conditioning
block is further away from the ADC on the board and when a difference in the ground potential of the sensor or
signal conditioner from the ADC ground is possible. In such cases, running separate wires from the AIN_nGND
pin of the device to the sensor or signal conditioning ground is recommended.
8.3.2 Analog Input Impedance
Each analog input channel in the device presents a constant resistive impedance of 1 MΩ. The input impedance
for each channel is independent of either the input signal frequency, the configured range of the ADC, or the
oversampling mode. The primary advantage of such high-impedance inputs is the ease of driving the ADC inputs
without requiring driving amplifiers with low output impedance. Bipolar, high-voltage power supplies are not
required in the system because this ADC does not require any high-voltage, front-end drivers. In most
applications, the signal sources or sensor outputs can be directly connected to the ADC input, thus significantly
simplifying the design of the signal chain.
In order to maintain the dc accuracy of the system, matching the external source impedance on the AIN_nP input
pin with an equivalent resistance on the AIN_nGND pin is recommended (see Figure 54). This matching helps to
cancel any additional offset error contributed by the external resistance.
8.3.3 Input Clamp Protection Circuit
As shown in Figure 52, the ADS8578S features an internal clamp protection circuit on each of the 8 analog input
channels. Use of external protection circuits is recommended as a secondary protection scheme to protect the
device. Using external protection devices helps with protection against surges, electrostatic discharge (ESD), and
electrical fast transient (EFT) conditions.
The input clamp protection circuit on the ADS8578S allows each analog input to swing up to a maximum voltage
of ±15 V. Beyond an input voltage of ±15 V, the input clamp circuit turns on, still operating off the single 5-V
supply. Figure 53 illustrates a typical current versus voltage characteristic curve for the input clamp. There is no
current flow in the clamp circuit for input voltages up to ±15 V. Beyond this voltage, the input clamp circuit turns
on.
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Feature Description (continued)
50
Input Clamp Current (mA)
40
30
20
10
0
-10
-20
-30
-40
-50
-20
-15
-10
-5
0
5
Input Voltage (V)
10
15
20
D007
Figure 53. I-V Curve for an Input Clamp Protection Circuit (AVDD = 5 V)
For input voltages above the clamp threshold, make sure that input current never exceeds the absolute
maximum rating (see the Absolute Maximum Ratings table) of ±10 mA to prevent any damage to the device. As
shown in Figure 54, a small series resistor placed in series with the analog inputs is an effective way to limit the
input current. In addition to limiting the input current, this resistor can also provide an antialiasing, low-pass filter
when coupled with a capacitor. In order to maintain the dc accuracy of the system, matching the external source
impedance on the AIN_nP input pin with an equivalent resistance on the AIN_nGND pin is recommended. This
matching helps to cancel any additional offset error contributed by the external resistance.
REXT
1M
AIN_nP
Clamp
Input
Signal
C
PGA
Clamp
REXT
AIN_nGND
1M
Figure 54. Matching Input Resistors on the Analog Inputs of Devices
The input overvoltage protection clamp on the ADS8578S is intended to control transient excursions on the input
pins. Leaving the device in a state such that the clamp circuit is activated for extended periods of time in normal
or power-down mode is not recommended because this fault condition can degrade device performance and
reliability.
8.3.4 Programmable Gain Amplifier (PGA)
The device offers a programmable gain amplifier (PGA) at each individual analog input channel that converts the
original single-ended input signal into a fully-differential signal to drive the internal 14-bit ADC. The PGA also
adjusts the common-mode level of the input signal before being fed into the ADC to ensure maximum usage of
the ADC input dynamic range. Depending on the range of the input signal, the PGA gain can be accordingly
adjusted by configuring the RANGE pin of the ADC (see the RANGE (Input) section).
The PGA uses a very highly matched network of resistors for multiple gain configurations. Matching between
these resistors and the amplifiers across all channels is accurately trimmed to keep the overall gain error low
across all channels and input ranges.
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Feature Description (continued)
8.3.5 Third-Order, Low-Pass Filter (LPF)
In order to mitigate the noise of the front-end amplifiers and gain resistors of the PGA, each analog input channel
of the ADS8578S features a third-order, Butterworth, antialiasing, low-pass filter (LPF) at the output of the PGA.
Figure 55 and Figure 56 show the magnitude and phase response of the analog antialiasing filter, respectively.
For maximum performance, the –3-dB cutoff frequency for the antialiasing filter is designed to be equal to 24 kHz
for a ±10-V range and 16 kHz for a ±5-V range.
30
0
25
Phase Delay (Ps)
-2
Magnitude (dB)
±5V
± 10 V
-4
-6
-8
20
15
10
5
±5V
± 10 V
0
-10
100
1k
10k
Input Frequency (Hz)
100k
1
10
100
1k
Input Frequency (Hz)
D046
Figure 55. Third-Order LPF Magnitude Response
10k
100k
D047
Figure 56. Third-Order LPF Phase Response
8.3.6 ADC Driver
In order to meet the performance of a 14-bit, SAR ADC at the maximum sampling rate (200 kSPS per channel),
the capacitors at the input of the ADC must be successfully charged and discharged during the acquisition time
window. The inputs of the ADC must settle to better than 14-bit accuracy before any sampled analog voltage
gets converted. This drive requirement at the inputs of the ADC necessitates the use of a high-bandwidth, lownoise, and stable amplifier buffer. The ADS8578S features an integrated input driver as part of the signal chain
for each analog input. This integrated input driver eliminates the need for any external amplifier, thus simplifying
the signal chain design for the user.
8.3.7 Digital Filter and Noise
The ADS8578S features an optional digital averaging filter that can be used in slower throughput applications
requiring lower noise and higher dynamic range. Table 1 explains that the oversampling ratio of the digital filter is
determined by the configuration of the OS[2:0] pins. The overall throughput of the ADC decreases proportionally
with increase in the oversampling ratio.
Table 1. Oversampling Bit Decoding
OS[2:0]
OS
RATIO
SNR,
±10-V INPUT
(dB)
000
No OS
85.50
85.41
001
2
85.71
85.43
23
15.7
100
010
4
85.88
85.92
19.2
14.5
50
011
8
85.89
85.92
11.2
10.6
25
100
16
86.13
85.67
5.6
5.6
12.5
101
32
85.90
86.04
2.8
2.8
6.25
110
64
86.03
85.69
1.4
1.4
3.125
111
Invalid
—
—
—
—
—
28
SNR,
±5-V INPUT
(dB)
3-dB BANDWIDTH,
±10-V INPUT
(kHz)
3-dB BANDWIDTH,
±5-V INPUT
(kHz)
MAX THROUGHPUT
PER CHANNEL
(kSPS)
24
16
200
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In oversampling mode (see the Oversampling Mode of Operation section), the ADC takes the first sample for
each channel at the rising edge of the CONVSTA, CONVSTB signals. After converting the first sample, the
subsequent samples are taken by an internally generated sampling control signal. The samples are then
averaged to reduce the noise of the signal chain as well as to improve the SNR of the ADC. The final output is
also decimated to provide a 14-bit output for each channel. Table 1 lists the typical SNR performance for both
the ±10-V and ±5-V input ranges, including the –3-dB bandwidth and proportional maximum throughput per
channel. When the oversampling ratio increases, there is a proportional improvement in the SNR performance
and decrease in the bandwidth of the input filter.
8.3.8 Reference
The ADS8578S can operate with either an internal voltage reference or an external voltage reference using an
internal gain amplifier. The internal or external reference selection is determined by an external REFSEL pin, as
explained in the REFSEL (Input) section. The REFIN/REFOUT pin outputs the internal band-gap voltage (in
internal reference mode) or functions as an input to the external reference voltage (in external reference mode).
In both cases, the on-chip amplifier is always enabled. Use this internal amplifier to gain the reference voltage
and drive the actual reference input of the internal ADC core for maximizing performance. The REFCAPA (pin
45) and REFCAPB (pin 44) pins must be shorted together externally and a ceramic capacitor of 10 µF (minimum)
must be connected between this node and REFGND (pin 43) to ensure that the internal reference buffer is
operating as closed loop.
8.3.8.1 Internal Reference
The device has an internal 2.5-V (nominal value) band-gap reference. In order to select the internal reference,
the REFSEL pin must be tied high or connected to DVDD. When the internal reference is used, REFIN/REFOUT
(pin 42) becomes an output pin with the internal reference value. As shown in Figure 57, a 10-μF (minimum)
decoupling capacitor is recommended to be placed between the REFIN/REFOUT pin and REFGND (pin 43). The
capacitor must be placed as close to the REFIN/REFOUT pin as possible. The output impedance of the internal
band gap creates a low-pass filter with this capacitor to band-limit the noise of the band-gap output. The use of a
smaller capacitor increases the reference noise in the system, thus degrading SNR and SINAD performance. Do
not use the REFIN/REFOUT pin to drive external ac or dc loads because of the limited current output capability
of the pin. The REFIN/REFOUT pin can be used as a reference source if followed by a suitable op amp buffer.
AVDD
2.5-V VREF
DVDD
REFSEL
REFIN/REFOUT
REFCAPB
10 PF
REFCAPA
10 PF
REFGND
ADC
AGND
Figure 57. Device Connections for Using an Internal 2.5-V Reference
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Number of Hits
The device internal reference is factory trimmed to a maximum initial accuracy of ±2.5 mV. The histogram in
Figure 58 shows the distribution of the internal voltage reference output taken from more than 2100 production
devices.
700
650
600
550
500
450
400
350
300
250
200
150
100
50
0
-2.5
-2.2
-1.6
-1
-0.4 0.2
0.8
1.4
REFIO Initial Acuuracy (mV)
2
2.5
D048
Figure 58. Internal Reference Accuracy at Room Temperature Histogram
The initial accuracy specification for the internal reference can be degraded if the die is exposed to any
mechanical, thermal, or environmental stress (such as humidity). Heating the device when being soldered to a
printed circuit board (PCB) and any subsequent solder reflow is a primary cause for shifts in the VREF value. The
main cause of thermal hysteresis is a change in die stress and therefore is a function of the package, die-attach
material, and molding compound, as well as the layout of the device itself.
In order to illustrate this effect, 80 devices were soldered using lead-free solder paste with the suggested
manufacturer reflow profile, as explained in the AN-2029 Handling & Process Recommendations application
report. The internal voltage reference output is measured before and after the reflow process; Figure 59 shows
the typical shift in value. Although all tested units exhibit a positive shift in the output voltages, negative shifts are
also possible. The histogram in Figure 59 shows the typical shift for exposure to a single reflow profile. Exposure
to multiple reflows, which is common on PCBs with surface-mount components on both sides, causes additional
shifts in the output voltage. If the PCB is to be exposed to multiple reflows, solder the ADS8578S in the second
pass to minimize device exposure to thermal stress.
30
Number of Devices
25
20
15
10
5
0
-4
-3
-2
-1
Error in REFIO Voltage (mV)
0
1
C065
Figure 59. Solder Heat Shift Distribution Histogram
The internal reference is also temperature compensated to provide excellent temperature drift over an extended
industrial temperature range of –40°C to 125°C. Figure 60 illustrates the variation of the internal reference
voltage across temperature for different values of the AVDD supply voltage. The typical specified value of the
reference voltage drift over temperature is 7.5 ppm/°C.
30
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2.505
AVDD = 4.75 V
AVDD = 5 V
AVDD = 5.25 V
REFIO Voltage (V)
2.503
2.501
2.499
2.497
2.495
-40
-7
26
59
Free-Air Temperature (qC)
92
125
D049
Figure 60. Variation of Internal Reference Output (REFIN/REFOUT) vs Supply and Temperature
8.3.8.2 External Reference
For applications that require a reference voltage with lower temperature drift or a common reference voltage for
multiple devices, the ADS8578S offers a provision to use an external reference, using the internal buffer to drive
the ADC reference pin. In order to select the external reference mode, either tie the REFSEL pin low or connect
this pin to AGND. In this mode, an external 2.5-V reference must be applied at REFIN/REFOUT (pin 42), which
becomes a high-impedance input pin. Any low-drift, small-size external reference can be used in this mode
because the internal buffer is optimally designed to handle the dynamic loading on the ADC reference input. The
output of the external reference must be filtered to minimize the resulting effect of the reference noise on system
performance. Figure 61 shows a typical connection diagram for this mode.
AVDD
2.5-V VREF
REFSEL
AVDD
OUT
REFIN/REFOUT
REF5025
(Refer to Device
Datasheet for Detailed Pin
Configuration)
CREF
REFCAPB
REFCAPA
10 PF
REFGND
ADC
AGND
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Figure 61. Device Connections for Using an External 2.5-V Reference
For closed-loop operation of the internal reference buffer, the REFCAPA and REFCAPB pins must be externally
shorted together. The output of the internal reference buffer appears at the REFCAP pin. A minimum
capacitance of 10 μF must be placed between the REFCAPA, REFCAPB pins and REFGND (pin 43). Do not use
this internal reference buffer to drive external ac or dc loads because of the limited current output capability of
the buffer.
Figure 62 illustrates that the performance of the internal buffer output is very stable across the entire operating
temperature range of –40°C to +125°C. As Figure 63 illustrates, the typical specified value of the reference buffer
drift over temperature is 5 ppm/°C.
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8
4.01
7
6
4.005
Number of hits
REFCAP Voltage (V)
AVDD = 4.75 V
AVDD = 5 V
AVDD = 5.25 V
4
5
4
3
2
3.995
1
3.99
-40
0
-7
26
59
Free-Air Temperature (qC)
92
0
125
0.665
1.325
1.985
2.645
3.305
REFCAP Drift (ppm/qC)
D051
4
D052
Number of samples = 30
Figure 62. Variation of Reference Buffer Output
(REFCAPA, REFCAPB) Across Supply and Temperature
Figure 63. Reference Buffer Temperature Drift Histogram
8.3.8.3 Supplying One VREF to Multiple Devices
For applications that require multiple ADS8578S devices, using the same reference voltage source for all the
ADCs helps eliminate any potential errors in the system resulting from mismatch between multiple reference
sources.
Figure 64 shows the recommended connection diagram for an application that uses one device in internal
reference mode and provides the reference source for other devices. The device used as the source of the
voltage reference is bypassed by a 10-μF capacitor on the REFIN/REFOUT pin, whereas the other devices are
bypassed with a 100-nF capacitor.
DVDD
TI Device
TI Device
TI Device
REFSEL
REFSEL
REFIN/REFOUT
Configured as Output
DGND
REFIN/REFOUT
Configured as Input
REFIN/REFOUT
Configured as Input
10 PF
REFSEL
DGND
100 nF
100 nF
REFGND
REFGND
REFGND
Copyright © 2017, Texas Instruments Incorporated
Figure 64. Multiple Devices Connected With an Internal Reference From one Device
Figure 65 shows the recommended connection diagram for an application that uses an external voltage
reference (such as the REF5025) to provide the reference source for multiple devices.
TI Device
REFSEL
DGND
REFIN/REFOUT
AVDD
REF5025
OUT
(Refer to Device
Datasheet for Detailed
Pin Configuration)
TI Device
TI Device
REFSEL
DGND
REFIN/REFOUT
100 nF
REFGND
REFSEL
DGND
REFIN/REFOUT
100 nF
100 nF
REFGND
REFGND
CREF
Copyright © 2017, Texas Instruments Incorporated
Figure 65. Multiple Devices Connected Using an External Reference
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8.3.9 ADC Transfer Function
The ADS8578S is a multichannel device that supports two single-ended, bipolar input ranges of ±10 V and ±5 V
on all input channels. The device outputs 14 bits of conversion data in binary two's complement format for both
bipolar input ranges. The format for the output codes is the same across all analog channels.
Figure 66 shows the ideal transfer characteristic for each ADC channel for all input ranges. The full-scale range
(FSR) for each input signal is equal to the difference between the positive full-scale (PFS) input voltage and the
negative full-scale (NFS) input voltage. The LSB size is equal to FSR / 214 = FSR / 16384 because the resolution
of the ADC is 14 bits. Table 2 lists the LSB values corresponding to the different input ranges.
ADC Output Code
01 « « 1111
(1FFFh)
00 « « 0000
(0000h)
PFS ± 1.5LSB
10 « « 0000
(2000h)
NFS+0.5LSB
0V-0.5LSB
NFS
PFS
FSR = PFS - NFS
Analog Input (AIN_nP t AIN_nGND)
Figure 66. 14-Bit ADC Transfer Function (Two's Complement Binary Format)
Table 2. ADC LSB Values for Different Input Ranges
INPUT RANGE (V)
POSITIVE FULL-SCALE
(V)
NEGATIVE FULL-SCALE
FULL-SCALE RANGE (V)
(V)
±10
10
–10
20
1220.72
±5
5
–5
10
610.36
LSB (µV)
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8.4 Device Functional Modes
8.4.1 Device Interface: Pin Description
8.4.1.1 REFSEL (Input)
The REFSEL pin is a digital input pin that enables selection between the internal and external reference mode of
operation for the device. If the REFSEL pin is set to logic high, then the internal reference is enabled and
selected. If this pin is set to logic low, then the internal band-gap reference circuit is disabled and powered down.
In this mode, an external reference voltage must be provided to the REFIN/REFOUT pin. Under both conditions,
the internal reference buffer is always enabled.
The REFSEL pin is an asynchronous logic input. The device output on the REFIN/REFOUT pin starts changing
immediately with a change in state of the REFSEL input pin. During power-up, the device wakes up in internal or
external reference mode depending on the state of the REFSEL input pin.
8.4.1.2 RANGE (Input)
The RANGE pin is a digital input pin that allows the input range to be selected for all analog input channels. If
this pin is set to logic high, then the device is configured to operate in the ±10-V input range for all input
channels. If this pin is set to logic low, then all input channels operate in the ±5-V input range.
In applications where the input range remains the same for all input channels, the RANGE pin is recommended
to be hardwired to the appropriate signal. However, some applications can require an on-the-fly change in the
input range by the digital host. For such cases, the RANGE pin functions as an asynchronous input, meaning
that any change in the logic input results in an immediate change in the input range configuration of the device.
An additional 80 µs must typically be allowed in addition to the device acquisition time for the internal active
circuitry to settle to the required accuracy before initiating the next conversion.
The RANGE pin is also used to put the device in standby or shutdown mode depending on the state of the STBY
input pin, as explained in the Power-Down Modes section.
8.4.1.3 STBY (Input)
The STBY pin is a digital input pin used to put the device into one of the two power-down modes: standby or shut
down. Set the STBY pin to logic high for normal device operation. If this pin is set to logic low, the device enters
either standby mode or shutdown mode depending on the state of the RANGE input pin. Both of these modes
are low-power modes supported by the device. In shutdown mode, all internal circuitry is powered down, but in
standby mode the internal reference and regulators remain powered to enable a relatively quicker recovery to
normal operation.
The STBY pin functions as an asynchronous input, meaning that this pin can be pulled low at anytime during
device operation to put the device into one of the two power-down modes. However, if the STBY input is set high
to bring the device out of power-down mode, then wait for the specified recovery time, as specified in the Timing
Requirements: Exit Standby Mode table for proper operation. See the Power-Down Modes section for more
details on device operation in the two power-down modes.
8.4.1.4 PAR/SER/BYTE SEL (Input)
The PAR/SER/BYTE SEL pin is a digital input pin that selects between the parallel, serial, or parallel byte
interface for reading the data output from the device. If this pin is tied to logic low, then the device operates in the
parallel interface mode (see the Parallel Data Read section). If this pin is tied to logic high, then the serial or
parallel byte interface mode is selected depending on the state of the DB15/BYTE SEL pin. If the DB15/BYTE
SEL is tied low, then serial mode is selected (see the Serial Data Read section) and the parallel byte interface is
selected if this pin is tied high (see the Parallel Byte Data Read section).
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Device Functional Modes (continued)
8.4.1.5 CONVSTA, CONVSTB (Input)
Conversion start A (CONVSTA) and conversion start B (CONVSTB) are active-high, conversion control digital
input signals. CONVSTA can be used to simultaneously sample and initiate the conversion process for the first
half count of device input channels (channels 1-4 for the ADS8578S), whereas CONVSTB can be used to
simultaneously sample and initiate the conversion process for the latter half count of device input channels
(channels 5-8 for the ADS8578S). For simultaneous sampling of all input channels, both pins can be shorted
together and a single CONVST signal can be used to control the conversion on all input channels. However, in
the oversampling mode of operation (see the Oversampling Mode of Operation section), both the CONVSTA and
CONVSTB signals must be tied together.
On the rising edge of the CONVSTA, CONVSTB signals, the internal track-and-hold circuits for each analog input
channel are placed into hold mode and the sampled input signal is converted using an internal clock. The
CONVSTA, CONVSTB signals can be pulled low when the internal conversion is over, as indicated by the BUSY
signal (see the BUSY (Output) section). At this point, the front-end circuit for all analog input channels acquires
the respective input signals and the internal ADC is not converting. The output data can be read from the device
irrespective of the status of the CONVSTA, CONVSTB pins, as there is no degradation in device performance,
as explained in the Data Read Operation section.
8.4.1.6 RESET (Input)
The RESET pin is an active-high digital input. A dedicated reset pin allows the device to be reset at any time in
an asynchronous manner. All digital circuitry in the device is reset when the RESET pin is set to logic high and
this condition remains active until the pin returns low. The device must always be reset after power-up as well as
after recovery from shut-down mode when all the supplies and references have settled to the required accuracy.
If the RESET is issued during an ongoing conversion process, then the device aborts the conversion and output
data is invalid. If the reset signal is applied during a data read operation, then the output data registers are all
reset to zero.
In order to initiate the next conversion cycle after deactivating a reset condition, allow for a minimum time delay
between the falling edge of the RESET input and the rising edge of the CONVSTA, CONVSTB inputs (see the
Timing Requirements: CONVST Control table). Any violation in this timing requirement can result in corrupting
the results from the next conversion.
8.4.1.7 RD/SCLK (Input)
RD/SCLK is a dual-function pin. Table 3 explains the usage of this pin under different operating conditions of the
device.
Table 3. RD/SCLK Pin Functionality
DEVICE OPERATING CONDITION
FUNCTIONALITY OF THE RD/SCLK INPUT
Parallel interface
PAR/SER/BYTE SEL = 0
DB15/BYTE SEL = 0
Parallel byte interface
PAR/SER/BYTE SEL = 1
DB15/BYTE SEL = 1
Serial interface
PAR/SER/BYTE SEL = 1
DB15/BYTE SEL = 0
Functions as an active-low digital input pin to read the output data from the device.
In parallel or parallel byte interface mode, the output bus is enabled when both the
CS and RD inputs are tied to a logic low input (see the Data Read Operation
section).
Functions as an external clock input for the serial data interface. In serial mode, all
synchronous accesses to the device are timed with respect to the rising edge of
the SCLK signal (see the Serial Data Read section).
8.4.1.8 CS (Input)
The CS pin indicates an active-low, chip-select signal. A rising edge on the CS signal outputs all data lines in tristate mode. This function allows multiple devices to share the same output data lines. The falling edge of the CS
signal marks the beginning of the output data transfer frame in any interface mode of operation for the device. In
the parallel and parallel byte interface modes, both the CS and RD input pins must be driven low to enable the
digital output bus for reading the conversion data (DB[15:0] for parallel and DB[7:0] for parallel byte interface). In
serial mode, the falling edge of the CS signal takes the DOUTA, DOUTB serial data output lines out of tri-state
mode and outputs the MSB of the previous conversion result.
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8.4.1.9 OS[2:0]
The OS[2:0] pins are active-high digital input pins used to configure the oversampling ratio for the internal digital
filter on the device. OS2 is the MSB control bit and OS0 is the LSB control bit. Table 1 provides the decoding of
the OS[2:0] bits for different oversampling rates. As explained in Table 1, an increase in the OSR mode improves
the typical SNR performance for both input ranges and reduces the 3-dB input bandwidth as well as the
maximum-allowed throughput per channel.
8.4.1.10 BUSY (Output)
BUSY is an active-high digital output signal. This pin goes to logic high after the rising edges of both the
CONVSTA and CONVSTB signals, indicating that the front-end, track-and-hold circuits for all input channels are
in hold mode and that the ADC conversion has started. When the BUSY signal goes high, any activity on the
CONVSTA or CONVSTB inputs has no effect on the device. The BUSY output remains high until the conversion
process for all channels is completed and the conversion data are latched into the output data registers for read
out. If the conversion data is read for the previous conversion when BUSY is high, ensure that the data read
operation is complete before the falling edge of the BUSY output.
8.4.1.11 FRSTDATA (Output)
FRSTDATA is an active-high digital output signal that indicates if the conversion data output for the first analog
input channel of the ADC (AIN_1P and AIN_1GND) is being read out in either of the interface modes. The
FRSTDATA output pin comes out of tri-state when the CS input is pulled from a high to a low logic level. Table 4
indicates the functionality of the FRSTDATA output in different interface modes of the device.
Table 4. FRSTDATA Pin Functionality
DEVICE OPERATING CONDITION
Parallel mode
Parallel byte mode
Serial mode
FUNCTIONALITY OF THE FRSTDATA OUTPUT
PAR/SER/BYTE SEL = 0,
DB15/BYTE SEL = 0
The first falling edge of the RD signal corresponding to the output result of channel
1 sets the FRSTDATA output to a logic high level. This setting indicates that the
data output from channel 1 is being read on the parallel output bus (DB[15:0]). The
FRSTDATA output goes low at the next falling edge of the RD signal and remains
low until the conversion data output from all other channels is read.
PAR/SER/BYTE SEL = 1,
DB15/BYTE SEL = 1
The first falling edge of the RD signal corresponding to one byte of the output of
channel 1 sets the FRSTDATA output to a logic high level. This setting indicates
that one byte of the data output from channel 1 is being read on the parallel output
bus (DB[7:0]). The FRSTDATA output remains high at the next falling edge of the
RD signal to read the second byte of the channel 1 output. This pin goes low on
the third falling edge of the RD signal and remains low until the conversion data
output from all other channels is read.
PAR/SER/BYTE SEL = 1,
DB15/BYTE SEL = 0
The FRSTDATA output goes to a logic high state on the falling edge of the CS
signal when the MSB of the channel 1 conversion result is output on DOUTA at
this instant. The FRSTDATA pin goes low at the 14th falling edge of the SCLK
input, indicating that all 14 bits of the channel 1 output has been read. This pin
remains low until the conversion data output from all other channels is read.
8.4.1.12 DB15/BYTE SEL
DB15/BYTE SEL is a dual-function, digital input, output pin.
When the device operates in parallel interface mode (PAR/SER/BYTE SEL = 0), this pin functions as a digital
output. In this mode, this pin outputs the MSB of the conversion data when both the CS and RD signals are
pulled low.
When the device does not operate in parallel interface mode (PAR/SER/BYTE SEL = 1), this pin functions as a
digital control input pin to select between the serial and parallel byte interface modes. The device operates in the
serial interface mode when the DB15/BYTE SEL pin is tied low and the device operates in the parallel byte
interface mode when this pin is tied to a logic high input.
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8.4.1.13 DB14/HBEN
DB14/HBEN is a dual-function, digital input, output pin.
When the device operates in parallel interface mode (PAR/SER/BYTE SEL = 0), this pin functions as a digital
output. In this mode, this pin outputs the (MSB-1) bit or bit 13 of the conversion data when both the CS and RD
signals are pulled low.
When the device operates in parallel byte interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 1),
this pin functions as a digital control input pin that selects if the MSB byte or the LSB byte is output first. If the
DB14/HBEN pin is tied to logic high, then the MSB byte is output first followed by the LSB byte and vice-versa if
this pin is tied to logic low.
When the device operates in serial interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 0), this pin
must be tied to AGND or to a logic low input.
8.4.1.14 DB[13:9]
DB[13:9] are digital output pins. In parallel interface mode (PAR/SER/BYTE SEL = 0), these pins output bit 12 to
bit 7 of the conversion result for each analog channel when both the CS and RD signals are pulled low. When
the device is not in parallel interface mode (PAR/SER/BYTE SEL = 1), these pins must be tied to AGND or to a
logic low input.
8.4.1.15 DB8/DOUTB
DB8/DOUTB is a dual-function digital output pin.
In parallel interface mode (PAR/SER/BYTE SEL = 0), use this pin to output bit 6 of the conversion result for each
analog channel when both the CS and RD signals are pulled low.
When the device operates in parallel byte interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 1),
this pin remains in a tri-state mode.
In serial interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 0), this pin outputs the conversion
data for the second half count of device input channels (channels 5-8 for the ADS8578S).
8.4.1.16 DB7/DOUTA
DB7/DOUTA is a dual-function digital output pin.
In parallel interface mode (PAR/SER/BYTE SEL = 0), use this pin to output bit 5 of the conversion result for each
analog channel when both the CS and RD signals are pulled low.
When the device operates in parallel byte interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 1),
this pin outputs the MSB of the output byte of the conversion data.
In serial interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 0), use this pin to output conversion
data for the first half count of device input channels (channels 1-4 for the ADS8578S).
8.4.1.17 DB[6:0]
DB[6:0] are digital output pins.
In parallel interface mode (PAR/SER/BYTE SEL = 0), these pins output bit 4 to bit 0 (LSB) of the conversion
result for each analog channel when both the CS and RD signals are pulled low on pins DB[6:2]. Pins DB[1:0]
are pulled low.
When the device operates in parallel byte interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 1),
these pins along with the DB7 pin output the 14-bit ADC conversion result appended with two zero in MSB-first
fashion in two consecutive RD operations.
When the device operates in serial interface mode (PAR/SER/BYTE SEL = 1 and DB15/BYTE SEL = 0), these
pins must be tied to AGND or to a logic low input.
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8.4.2 Device Modes of Operation
The ADS8578S supports multiple modes of operation that can be programmed using the hardware pins. This
functionality allows the device to be easily configured without any complicated software programming. This
section provides details about the normal, power-down (standby and shutdown), and oversampling modes of
operation of the device.
8.4.2.1 Power-Down Modes
For applications that are sensitive to power consumption, the ADS8578S offers a built-in, power-down feature.
The device supports two power-down modes: standby mode and shutdown mode. As shown in Table 5, the
device can enter either power-down mode by pulling the STBY pin to a logic low level. Additionally, the selection
between these two power-down modes is done by the state of the RANGE pin.
Table 5. Power-Down Mode Selection
POWER-DOWN MODE
STBY
RANGE
Standby
0
1
Shutdown
0
0
8.4.2.1.1 Standby Mode
The device supports a low-power standby mode in which only part of the circuit is powered down. The analog
front-end, signal-conditioning circuit for each channel remains powered down in this mode, but the internal
reference and regulator are not powered down. In standby mode, the total power consumption of the device is
typically equal to 20 mW.
In order to enter standby mode, the STBY input pin must be set to logic low and the RANGE input pin must be
set to a logic high value. The device can be asynchronously put into this mode by configuring the STBY and
RANGE inputs at anytime during device operation.
The device exits standby mode when a logic high input is applied to the STBY pin. At this time, the internal
circuitry starts powering up and takes a minimum time of 100 µs to settle before the next conversion can be
initiated. See the Timing Requirements: Exit Standby Mode table and Figure 8 for timing details.
8.4.2.1.2 Shutdown Mode
The device supports a low-power shutdown mode in which the entire internal circuitry is powered down. In
shutdown mode, the total power consumption of the device is typically equal to 1 µW.
In order to enter shutdown mode, the STBY input pin must be set to logic low and the RANGE input pin must be
set to a logic low value. The device can be asynchronously put into this mode by configuring the STBY and
RANGE inputs at anytime during device operation.
The device exits shutdown mode when a logic high input is applied to the STBY pin. At this time, the internal
circuitry starts powering up and takes a minimum time of 13 ms to settle in external reference mode before the
next conversion can be initiated. After recovery from shutdown mode, a RESET signal must be applied before
the next conversion can be initiated. See the Timing Requirements: Exit Shutdown Mode table and Figure 9 for
timing details.
8.4.2.2 Conversion Control
The ADS8578S offers easy and precise control to simultaneously sample all analog input channels or pairs of
input channels. The sampling instant can be user-controlled through the digital pins, CONVSTA and CONVSTB.
Simultaneously capturing the input signal on all analog input channels is extremely useful in certain applications
that are sensitive to additional phase delay between input channels caused by sequential sampling. This section
describes the methodology to simultaneously sample all input channels or pairs of input channels for the device.
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8.4.2.2.1 Simultaneous Sampling on All Input Channels
The ADS8578S allows all the analog input channels to be simultaneously sampled. In order to do so (and as
shown in Figure 67), the CONVSTA and CONVSTB signals must be tied together and a single CONVST signal
must be used to control the sampling of all analog input channels of the device. Figure 67 also shows the
sequence of events described in this section.
CONVSTA
CONVSTB
BUSY
CS and RD
DB[15:0]
AIN_1
AIN_2
AIN_7
AIN_8
FRSTDATA
1
2
3
4
Figure 67. Simultaneous Sampling of All Input Channels in Parallel Interface Timing Diagram
There are four events that describe the internal operation of the device when all input channels are
simultaneously sampled and the data are read back. These events are:
• Event 1: Simultaneous sampling of all analog input channels is initiated with the rising edge of the CONVST
signal. The input signals on all channels are sampled at this same instant because both the CONVSTA and
CONVSTB inputs are tied together. The sampled signals are then converted by the ADC using a precise onchip oscillator clock. At the beginning of the conversion phase of the ADC, the BUSY output goes high and
remains high through a maximum-specified conversion time of tCONV (see the Timing Requirements: CONVST
Control table).
• Event 2: At this instant, the ADC has completed the conversion for all input channels and the BUSY output
goes to logic low. The falling edge of the BUSY signal indicates the end of conversion and that the internal
registers are updated with the conversion data. At this instant, the device is ready to output the correct
conversion results for all channels on the parallel output bus (DB[15:0]), serial output lines (DOUTA, DOUTB),
or parallel byte bus (DB[7:0]).
• Event 3: This example shows the data read operation in parallel interface mode with both CS and RD tied
together. After BUSY goes low, the first falling edges of CS and RD output the conversion result of channel 1
(AIN_1) on the parallel output bus. Similarly, the conversion results for the remaining channels are output on
the parallel bus on subsequent falling edges of the CS and RD signals in a sequential manner. If all channels
are not used in the conversion process, tie the unused channels to AGND or any known voltage within the
selected input range. The ADC always converts all analog input channels and the results for unused channels
are included in the output data stream, thus all unused channels must be tied. The FRSTDATA output goes
high on the first falling edges of the CS and RD signals, indicating that the parallel bus is carrying the output
result from channel 1. On the next falling edges of the CS and RD signals, FRSTDATA goes low and stays
low if the CS and RD inputs are low.
• Event 4: After the conversion results for all analog channels are output from the device, the data frame can
be terminated by pulling the CS and RD signals to logic high. The parallel bus and FRSTDATA output go to
tri-state until the entire sequence is repeated beginning from event 1.
Events 1 and 2 are common to all interface modes of operation (parallel, serial, or parallel byte).
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8.4.2.2.2 Simultaneous Sampling Two Sets of Input Channels
The ADS8578S allows two sets of analog input channels to be simultaneously sampled. In order to do so, the
CONVSTA and CONVSTB signals must be separate control inputs (as shown in Figure 68) and the device must
not operate in any oversampling mode. Electrical grid relay protection is an application that can benefit from
being able to sample the inputs in two groups. The delay of the signal through the voltage channels is often
different from the delay on the channels measuring current. The difference in delay created by the voltage and
current signal paths can be corrected by adjusting the sampling of the two groups of inputs (voltage and current)
to the device.
The timing diagram shown in Figure 68 shows the sequence of events described in this section.
CONVSTA
CONVSTB
BUSY
CS and RD
AIN_1
DB[15:0]
AIN_2
AIN_7
AIN_8
FRSTDATA
1a
1b
2
3
4
Figure 68. Simultaneous Sampling of All Input Channels in Parallel Interface Timing Diagram
There are four events that describe the internal operation of the device when pairs of input channels are
simultaneously sampled and the data are read back. These events are:
• Event 1(a): A rising edge on the CONVSTA signal initiates simultaneous sampling of the first set of analog
input channels (channels 1-4 for the ADS8578S). The sampling circuits on the first set of analog input
channels enter hold mode and the input signals on these channels are sampled at the same instant. The
ADC does not begin conversion until the input signals on the second set of channels are sampled.
• Event 1(b): A rising edge on the CONVSTB signal initiates simultaneous sampling of the second set of
analog input channels (channels 5-8 for the ADS8578S). The sampling circuits for the second set of analog
input channels enter hold mode and the input signals on these channels are sampled at the same instant.
When the rising edges of both the CONVSTA and CONVSTB signals have occurred, the ADC converts all
sampled signals using a precise, on-chip oscillator clock. At the beginning of the conversion phase of the
ADC, the BUSY output goes high and remains high through a maximum-specified conversion time of tCONV
(see the Timing Requirements: CONVST Control table).
• Event 2: Same as event 2 in the Simultaneous Sampling on All Input Channels section.
• Event 3: Same as event 3 in the Simultaneous Sampling on All Input Channels section.
• Event 4: Same as event 4 in the Simultaneous Sampling on All Input Channels section.
Events 1(a), 1(b), and 2 are common to all interface modes of operation (parallel, serial, or parallel byte).
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8.4.2.3 Data Read Operation
The ADS8578S updates the internal data registers with the 14-bit ADC conversion data followed by two zero to
generate a 16-bit word for all analog channels at the end of every conversion phase (when BUSY goes low). As
described in the Timing Requirements: Data Read Operation table, if the output data are read after BUSY goes
low, then the device outputs the conversion results for the current sample. However, if the output data are read
when BUSY is high, then the device outputs conversion results for the previous sample. Under both conditions
and as explained in Table 6, the device supports three interface options depending on the status of the
PAR/SER/BYTE SEL and DB15/BYTE SEL pins.
Table 6. Data Read Back Interface Mode Selection
SELECTED INTERFACE MODE
PAR/SER/BYTE SEL
DB15/BYTE SEL
Parallel interface
0
0
Parallel byte interface
1
1
Serial interface
1
0
8.4.2.3.1 Parallel Data Read
The ADS8578S supports a parallel interface mode for reading the device 16-bit (14-bit ADC data followed by two
trailing zeros) output data using the control inputs (CS and RD) the parallel output bus (DB[15:0]), and the BUSY
indicator. This interface mode is selected by applying a logic low input on the PAR/SER/BYTE SEL input pin.
Depending on the application requirements, the CS and RD control inputs can be tied together or used as
separate control inputs in the parallel interface mode.
For applications that use only one device in the system and does not share the parallel output bus with any other
devices, the CS and RD input signals can be tied together. Alternatively, the CS signal can be permanently tied
low and the RD signal can be used to clock the data out of the device. The timing diagram for this mode of
operation is described in the Timing Requirements: Parallel Data Read Operation, CS and RD Tied Together
table. In this mode, the parallel output bus, DB[15:0], is activated (comes out of tri-state) on the falling edge of
the CS/RD signal. At the first falling edge of the CS/RD signal, the output data of channel 1 becomes available
on the parallel bus to be read by the digital host. At this instant the FRSTDATA output also goes high, indicating
channel 1 data are ready to be read back. The output data for the remaining channels are clocked out on the
parallel bus on subsequent falling edges of the CS and RD signal in a sequential manner.
For applications that use multiple devices in the system, the CS and RD input signals must be driven separately.
The timing diagram for this mode of operation is described in the Timing Requirements: Parallel Data Read
Operation, CS and RD Separate table. A falling edge of the CS input can be used to activate the parallel bus for
a particular device in the system. The RD signal clocks the conversion data out of the device. At the first falling
edge of the RD signal, the output data of channel 1 become available on the parallel bus to be read by the digital
host. At this instant the FRSTDATA output also goes, high indicating channel 1 data are ready to be read back.
On subsequent falling edges of the RD signal, the output data for the remaining channels are clocked out on the
parallel bus in a sequential manner. At the second falling edge of the RD signal, the FRSTDATA output goes low
and remains low until going to tri-state at the next rising edge of the CS signal.
8.4.2.3.2 Parallel Byte Data Read
The ADS8578S supports a parallel byte interface mode for reading the device 16-bit (14-bit ADC data followed
by two trailing zeros) output data using the control inputs (CS and RD) the parallel output bus (DB[7:0]), and the
BUSY indicator. This interface mode is selected by applying a logic high input on the PAR/SER/BYTE SEL input
pin and a logic high input on the DB15/BYTE SEL input pin. The parallel byte interface mode is very similar to
the parallel interface mode, except that the output data for each channel is read in two data transfers of 8-bit byte
sizes.
The order of most significant byte (MSB byte) and least significant byte (LSB byte) is decided by the logic input
state of the DB14/HBEN pin. In parallel byte mode, the DB14/HBEN pin functions as a control input. When
DB14/HBEN pin is tied high, the MSB byte of the conversion results is output first followed by the LSB byte. This
order is reversed when DB14/HBEN is tied to logic low.
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The Timing Requirements: Byte Mode Data Read Operation table describes the data read back operation during
parallel byte mode when the DB14/HBEN pin is tied high. A falling edge of the CS input is used to activate the
parallel bus, DB[7:0] for the device. The RD signal is then used to clock the conversion data out of the device. In
this mode, two RD pulses are required to read the full data output for each analog channel. At the first falling
edge of the RD signal, the first byte of the channel 1 conversion result becomes available on DB[7:0]. This byte
is followed by the second byte of conversion data on the next falling edge of the RD signal. On subsequent
falling edges of the RD signal, the output data for the remaining channels are clocked out in chunks of 8-bit bytes
on DB[7:0] in a sequential manner. Thus, a total of 16 RD pulses are required to read the output from all input
channels of the ADS8578S.
In this mode, the FRSTDATA output goes high at the first falling of the RD signal. FRSTDATA remains high for
two RD pulses until both bytes of the channel 1 conversion result are output. At the third falling edge of the RD
signal, the FRSTDATA output goes low and remains low throughout the data read operation until going to tristate at the next rising edge of the CS signal.
8.4.2.3.3 Serial Data Read
The ADS8578S also supports a serial interface mode for reading the device output data. This interface mode is
selected by applying a logic high input on the PAR/SER/BYTE SEL input pin and a logic low input on the
DB15/BYTE SEL input pin. This interface mode uses a CS control input, a communication clock input (SCLK),
BUSY and FRSTDATA output indicators, and serial data output lines DOUTA and DOUTB.
Figure 5 illustrates the timing diagram for data read in serial mode for one channel of the ADC, framed by the CS
signal. When the CS input is high, the serial data output and FRSTDATA output lines are in tri-state and the
SCLK input is ignored. On the falling edge of the CS signal, the output lines become active and the MSB of the
conversion result comes out on DOUTA, DOUTB. The MSB can be read by the host processor on the next falling
edge of the SCLK signal. The remaining 15 bits of the conversion result are output on the subsequent rising
edges of the SCLK signal and can be read by the host processor on the corresponding falling edges. Thus, a
total of 14 SCLK cycles are required to clock out 14 bits of conversion result for each channel and the same
process can be repeated for the remaining channels in an ascending order. The CS input can be left at a logic
low level for the entire data retrieval process for all analog channels or used to frame the retrieval of the 14-bit
output data for each analog channel.
The ADS8578S can output the conversion on one or both of the serial data output lines, DOUTA and DOUTB.
The conversion results from the first set of channels (channels 1-4 for the ADS8578S) appear first on DOUTA,
followed by the second set of channels (channels 5-8 for the ADS8578S) if only DOUTA is used for reading data.
This order is reversed for DOUTB, in which the second set of channels appear first followed by the first set of
channels. The use of both data output lines reduces the time needed for data retrieval and a higher throughput
can therefore be achieved in this mode.
The FRSTDATA output is in tri-state when the CS signal is high. As illustrated in Figure 5, FRSTDATA goes high
on the first falling edge of the CS signal when the MSB of channel 1 is output on DOUTA. The FRSTDATA
output remains high for the next 14 SCLK cycles until all data bits of channel 1 are read from the device. The
FRSTDATA output returns to a logic low level at the 14th falling edge of the SCLK signal. If data are also read on
DOUTB in serial mode, then FRSTDATA remains high when the first channel of the second set of channels is
read from the device. The high state of FRSTDATA corresponds to channel 5 for the ADS8578S.
Based on the above description of the different pins in serial interface mode, conversion data can be read out of
the device in several different ways. Some example recommendations are provided below:
• The conversion data can be read out of the device using only one of the two serial output lines, DOUTA or
DOUTB. In this case, using DOUTA for output data read back is recommended because channel 1 data
appear first on DOUTA followed by the data for other channels in ascending order. To read the data for all
channels, provide a total of 14 × 8 = 112 SCLK cycles for the ADS8578S. This entire data frame can be
created within a single CS pulse or each group of 14 SCLK cycles can be individually framed by the CS
signal. The primary disadvantage of using just one data line for reading conversion data is that the throughput
is reduced if a data read operation is performed after conversion. Figure 69 illustrates this operation.
• Alternatively, only DOUTB can be used for reading the conversion data from all channels. In this case,
everything else remains the same and the output bit stream contains data for all channels in the following
order: channels 5, 6, 7, 8, 1, 2, 3, and 4 for the ADS8578S. Figure 69 illustrates this operation.
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CS
SCLK
DOUTA
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
Channel 6
Channel 7
Channel 8
DOUTB
Channel 5
Channel 6
Channel 7
Channel 8
Channel 1
Channel 2
Channel 3
Channel 4
FRSTDATA
Figure 69. Data Read Back in the Serial Interface Using Either DOUTA or DOUTB Timing Diagram
•
In order to minimize the time for the data read operation in serial mode, both DOUTA and DOUTB can be
used to read data out of the device. In this case, the conversion results from the first set of channels
(channels 1-4 for the ADS8578S) appear on DOUTA and the conversion results from the second set of
channels (channels 5-8 for the ADS8578S) appear first on DOUTB. To read the data for all channels, provide
a total of 14 × 4 = 56 SCLK cycles for the ADS8578S. This entire data frame can be created within a single
CS pulse or each group of 14 SCLK cycles can be individually framed by the CS signal. Figure 70 shows an
example timing diagram.
CS
SCLK
DOUTA
Channel 1
Channel 2
Channel 3
Channel 4
DOUTB
Channel 5
Channel 6
Channel 7
Channel 8
FRSTDATA
Figure 70. Data Read Back in the Serial Interface Using Both DOUTA and DOUTB Timing Diagram
8.4.2.3.4 Data Read During Conversion
The ADS8578S supports data read operation when the BUSY output is high and the internal ADC is converting.
The ADC outputs conversion results for previous samples if data read back is performed during an ongoing
conversion. Any of the three interface modes (parallel, parallel byte, or serial) in any combination of oversampling
modes can be used to read the device output during an ongoing conversion. The data read back during
conversion mode allows faster throughput to be achieved from the device. There is no degradation in
performance if data are read from the device during the conversion process, using any of the three interface
modes.
The Timing Requirements: Data Read Operation table describes the timing diagram for data read back during
conversion. The timing specification tDZ_CSBSY (the delay between the rising edge of the CS signal and the falling
edge of the BUSY signal) must be met because the output data registers are updated with the current conversion
results just before the falling edge of the BUSY signal and any read operation during this time can corrupt the
register update.
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8.4.2.4 Oversampling Mode of Operation
The ADS8578S supports the oversampling mode of operation using an on-chip averaging digital filter, as
explained in the Digital Filter and Noise section. The device can be configured in oversampling mode by the
OS[2:0] pins (see the OS[2:0] section). Figure 71 shows a typical timing diagram for the oversampling mode of
operation. The input on the OS pins is latched on the falling edge of the BUSY signal to configure the
oversampling rate for the next conversion.
tCONV
CONVSTA,
CONVSTB
18 µs
8.6 µs
3.8 µs
OS =
0
BUSY
OS =
2
OS =
4
CS, RD
DB[15:0]
AIN_1
AIN_2
AIN_7
AIN_8
Figure 71. OSR Mode Operation Timing Diagram
In the oversampling mode of operation, both the CONVST A and CONVST B signals must be tied together or
driven together. As shown in Figure 71, the BUSY signal duration varies with the OSR setting because the
conversion time increases with increases in OSR. The high time for the BUSY signal increases with the OSR
setting, as listed in the Timing Requirements: CONVST Control table.
For any particular OSR setting, the maximum achievable throughput per channel is specified in Table 1. If the
application is running at a lower throughput, then a higher OSR setting can be selected for further noise
reduction and SNR improvement. To maximize the throughput per channel, perform a data read when BUSY is
high and a conversion is ongoing in OSR mode. This process enables data read for the previous conversion (see
the Data Read During Conversion section). At the falling edge of the BUSY signal, the internal data registers are
updated with the new conversion data; thus the read operation must complete and CS must be pulled high for at
least tSU_CSBSY before BUSY goes low (see the Timing Requirements: Data Read Operation table).
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70000
70000
56000
56000
Number of Hits
Number of Hits
Oversampling the input signal reduces noise during the conversion process, thus reducing the histogram code
spread for a dc input signal to the ADC. Figure 72 to Figure 77 show the effect of oversampling on the output
code spread in a dc histogram plot.
42000
28000
14000
42000
28000
14000
0
0
-1
0
Output Codes
1
-1
D062
Mean = 0, sigma = 0.06
D063
Figure 73. DC Histogram for OSR4
70000
70000
56000
56000
Number of Hits
Number of Hits
1
Mean = 0, sigma = 0.05
Figure 72. DC Histogram for OSR2
42000
28000
42000
28000
14000
14000
0
0
-1
0
Output Codes
-1
1
D064
Mean = 0, sigma = 0.04
0
Output Codes
1
D065
Mean = 0, sigma = 0.02
Figure 74. DC Histogram for OSR8
Figure 75. DC Histogram for OSR16
70000
70000
56000
56000
Number of Hits
Number of Hits
0
Output Codes
42000
28000
14000
42000
28000
14000
0
0
-1
0
Output Codes
1
-1
D066
Mean = 0, sigma = 0.03
0
Output Codes
1
D067
Mean = 0, sigma = 0.02
Figure 76. DC Histogram for OSR32
Figure 77. DC Histogram for OSR64
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50
50
0
0
Magnitude Response (dB)
Magnitude Response (dB)
In OSR modes, the device adds a digital filter at the output of the ADC. The digital filter affects the frequency
response of the entire data acquisition system including the internal low-pass analog filter and the oversampling
digital filter. Figure 78 to Figure 83 show the frequency response curves for different OSR settings in the ±10-V
range.
-50
-100
-150
-200
-50
-100
-150
-200
-250
-250
1
10
100
1k
10k
Frequency (Hz)
100k
1M
10M
1
AVDD = 5 V, DVDD = 5 V, TA = 25°C, input range = ±10 V
50
50
0
0
Magnitude Response (dB)
Magnitude Response (dB)
1k
10k
Frequency (Hz)
100k
1M
10M
D069
Figure 79. Digital Filter Response for OSR = 4
-50
-100
-150
-200
-50
-100
-150
-200
-250
-250
1
10
100
1k
10k
Frequency (Hz)
100k
1M
10M
1
10
100
D070
AVDD = 5 V, DVDD = 5 V, TA = 25°C, input range = ±10 V
1k
10k
Frequency (Hz)
100k
1M
10M
D071
AVDD = 5 V, DVDD = 5 V, TA = 25°C, input range = ±10 V
Figure 80. Digital Filter Response for OSR = 8
Figure 81. Digital Filter Response for OSR = 16
50
50
0
0
Magnitude Response (dB)
Magnitude Response (dB)
100
AVDD = 5 V, DVDD = 5 V, TA = 25°C, input range = ±10 V
Figure 78. Digital Filter Response for OSR = 2
-50
-100
-150
-50
-100
-150
-200
-200
-250
-250
1
10
100
1k
10k
Frequency (Hz)
100k
1M
10M
1
10
D072
AVDD = 5 V, DVDD = 5 V, TA = 25°C, input range = ±10 V
Figure 82. Digital Filter Response for OSR = 32
46
10
D068
100
1k
10k
Frequency (Hz)
100k
1M
10M
D073
AVDD = 5 V, DVDD = 5 V, TA = 25°C, input range = ±10 V
Figure 83. Digital Filter Response for OSR = 64
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The ADS8578S enables high-precision measurement of up to eight analog signals simultaneously. The device is
a fully integrated data acquisition (DAQ) system based on a 14-bit successive approximation (SAR) analog-todigital converter (ADC). The device includes an integrated analog front-end for each input channel and an
integrated voltage reference with a precision reference buffer. As such, this device does not require any
additional active circuits for driving the reference analog input pins of the ADC.
9.2 Typical Application
PT Input
±10-V Amplitude
f = 50 Hz, 60 Hz
CT Input
¨
¨ = Measured Phase Difference
Between Signals
AVDD = 5 V(1)
1µF
AIN_1P
1 MW
ADS8578S
PGA
C1
AIN_1GND
DVDD
AVDD
rd
R1M
0.1µF
0.1µF
REGCAP1, REGCAP2(2)
R1P
DVDD = 3.3 V
3 -Order
LPF
ADC
Driver
14-Bit
SAR
ADC
REFCAPA
1 MW
10 µF
REFCAPB
REFGND
2.5-V
VREF
10 µF
R8P
AIN_8P
1 MW
PGA
C8
R8M
Typical 50-Hz, 60-Hz
Sine-Wave from PT, CT
REFIN/REFOUT
AIN_8GND
3rd-Order
LPF
ADC
Driver
REFGND
14-Bit
SAR
ADC
DVDD
1 MW
Balanced RC Filter
on Each Input
REFSEL
AGND
(1)
Decoupling the AVDD capacitor applies to each AVDD pin.
(2)
REGCAP1 and REGCAP2: each pin requires separate decoupling capacitors.
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Figure 84. 8-Channel DAQ for Power Automation Using the ADS8578S
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Typical Application (continued)
This application example involves the measurement of electrical variables in a power system. The accurate
measurement of electrical variables in a power grid is extremely critical because this measurement helps to
determine the operating status and running quality of the grid. Such accurate measurements also help to
diagnose potential problems with the power network so that these problems can be resolved quickly without
having any significant service impact. The key electrical parameters include amplitude, frequency, and phase
measurement of the voltage and current on the power lines. These parameters are important to enable metrology
in the power automation system to perform harmonic analysis, power factor calculation, power quality
assessment, and so forth.
9.2.1 Design Requirements
To
•
•
•
•
•
•
begin the design process, a few parameters must be decided upon. The designer must know the following:
Output range of the potential transformers (elements labeled PT in Figure 84)
Output range of the current transformers (elements labeled CT in Figure 84)
Input impedance required from the analog front-end for each channel
Fundamental frequency of the power system
Number of harmonics that must be acquired
Type of signal conditioning required from the analog front end for each channel
9.2.2 Detailed Design Procedure
For the ADS8578S, each channel incorporates an analog front-end composed of a programmable gain amplifier
(PGA), analog low-pass filter, and ADC input driver. The analog input for each channel presents a constant
resistive impedance of 1 MΩ independent of the ADC sampling frequency and range setting. The high input
impedance of the analog front-end circuit allows direct connection to potential transformers (PT) and current
transformers (CT). The ADC inputs can support up to ±10-V or ± 5-V bipolar inputs and the integrated signal
conditioning eliminates the need for external amplifiers or ADC driver circuits.
The PT and CT used in the system (see Figure 84) have a ±10-V output range. Although the PT and CT provide
isolation from the power system, a series resistor must be placed on the analog input channels. The series
resistor helps limit the input current to ±10 mA if the input voltages exceed ±15 V. For applications that require
protection against overvoltage or fast transient events beyond the specified absolute maximum ratings of the
device, an external protection clamp circuit using transient voltage suppressors (TVS) and ESD diodes is
recommended.
A low-pass filter is used on each analog input channel to eliminate high-frequency noise pickup and minimize
aliasing. Figure 85 shows an example of the recommended configuration for an input RC filter. A balanced RC
filter configuration matches the external source resistance on the positive path (AIN_nP) with an equal resistance
on the negative path (AIN_nGND). Matching the source impedance in the positive and negative path allows for
better common-mode noise rejection and helps maintain the dc accuracy of the system by canceling any
additional offset error contributed by the external series resistance.
10 V
0V
ADS8578S
ESD
-10 V
4.3 kŸ
1 M:
AIN_nP
5.6 nF
4.3 kŸ
PGA
COG
AIN_nGND
Signal from PT, CT
50 Hz, 60 Hz
Low-Pass Filter with
Matched Source
Resistance
3rd-Order
LPF
ADC
Driver
14-Bit
SAR
ADC
1 M:
ESD
Copyright © 2016, Texas Instruments Incorporated
Figure 85. Input RC Low-Pass Filter
48
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Typical Application (continued)
The primary goal of the data acquisition system illustrated in Figure 84 is to measure up to 20 harmonics in a 60Hz power network. Thus, as shown in Equation 1, the analog front-end must have sufficient bandwidth to detect
signals up to 1260 Hz.
fMIN
20 1 u 60 Hz 1260 Hz
(1)
Based on the bandwidth calculated in Equation 1, the ADS8578S is set to simultaneously sample all eight
channels at 20 kSPS, which is sufficient throughput to clearly resolve the highest harmonic component of the
input signal. The pass band of the low-pass filter configuration shown in Figure 85 is determined by the –3-dB
frequency, calculated according to Equation 2.
f
1
3 dB
1
2S u 4.3k: 4.3k: u 5.6nF
2S u R1 R2 u Cf
3.3 kHz
(2)
The value of CF is selected as 5.6 nF, a standard capacitance value available in 0603-size surface-mount
components. In combination with the resistor RF, this low-pass filter provides sufficient bandwidth to
accommodate the required 20 harmonics for the input signal of 60 Hz.
The ADS8578S can operate with either the internal voltage reference or an external reference. The Internal
Reference section describes the electrical connections and recommended bypass capacitors when using the
internal reference. Alternatively for applications that require a higher precision voltage reference, Figure 86
shows an example of an external reference circuit. The REF5025 provides a very low drift, and very accurate
external 2.5-V reference. The resistor RFILT and capacitor CFILT form a low-pass filter to reduce the broadband
noise and minimize the resulting effect of the reference noise on the system performance.
AVDD = 5 V
RFILT
VIN
VREF
REFIN/REFOUT
100
1 µF
REF5025
0.220
CFILT
10 µF
REFCAPA
GND
TRIM/NR
10 µF
ADS8588S
REFCAPB
10 µF
REFGND
AGND
REFSEL
Copyright © 2017, Texas Instruments Incorporated
Figure 86. External Reference Circuit for the ADS8578S
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Typical Application (continued)
9.2.3 Application Curve
Figure 87 shows the frequency spectrum of the data acquired by the ADS8578S for a sinusoidal, ±10-V input at
60 Hz.
The ac performance parameters measured by this design are:
• SNR = 84.97 dB; SINAD = 84.85 dB
• THD = –106.5 dB; SFDR = 109.8 dB
0
-20
Amplitude (dBc)
-40
-60
-80
-100
-120
-140
-160
-180
0
500
1000
Frequency (Hz)
1500
2000
D070
Figure 87. Frequency Spectrum for a Sinusoidal ±10-V Signal at 50 Hz
10 Power Supply Recommendations
The ADS8578S uses two separate power supplies: AVDD and DVDD. The AVDD supply provides power to the
ADC and internal circuits, and DVDD is used for the digital interface. AVDD and DVDD can be set independently
to voltages within the permissible range.
The AVDD supply can be set in the range of 4.75 V to 5.25 V. A low-noise, linear regulator is recommended to
generate the analog supply voltage. The device has four AVDD pins. Each AVDD pin must be decoupled with
respect to AGND using a 1-µF capacitor. Place the 1-µF capacitor as close to the supply pins as possible.
The DVDD supply is used to drive the digital I/O buffers and can be set in the range of 2.3 V to a maximum value
equal to the AVDD voltage. This range allows the device to interface with most state-of-the-art processors and
controllers. Place a 1-µF (minimum 100-nF) decoupling capacitor in close proximity to the DVDD supply to
provide the high-frequency digital switching current.
There are no specific requirements with regard to the power-supply sequencing of the device. However, issue a
reset after the supplies are powered up and are stable to ensure the device is properly configured.
Figure 88 shows a typical PSRR curve with the decoupling capacitors.
Power Supply Rejection Ratio (dB)
-70
±5V
± 10 V
-80
-90
-100
-110
-120
-130
-140
-150
1
10
Input Frequency (kHz)
100
D044
Figure 88. PSRR vs Frequency (With Decoupling Capacitor)
50
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11 Layout
11.1 Layout Guidelines
Figure 89 and Figure 90 illustrate a PCB layout example for the ADS8578S.
• Partition the PCB into analog and digital sections. Care must be taken to ensure that the analog signals are
kept away from the digital lines. This layout helps keep the analog input and reference input signals away
from the digital noise. In this layout example, the analog input and reference signals are routed on the left
side of the board and the digital connections are routed on the right side of the board.
• Using a single common ground plane is strongly recommended. For designs requiring a split analog and
digital ground planes, the analog and digital ground planes must be at the same potential joined together in
close proximity to the device.
• Power sources to the ADS8578S must be clean and well-bypassed. As a result of dynamic currents during
conversion, each AVDD must have a decoupling capacitor to keep the supply voltage stable. Use wide traces
or a dedicated analog supply plane to minimize trace inductance and reduce glitches. Using a 1-μF, X7Rgrade, 0603-size ceramic capacitor is recommended in close proximity to each analog (AVDD) supply pins.
Bypass capacitors for AVDD pins 1 and 48 are located on the top layer; see Figure 89. AVDD supply pins 37
and 38 are connected to bypass capacitors in the bottom layer using an isolated via (1); see Figure 90. A
separate via (2) is used to connect the bypass capacitor to the AVDD plane.
• For decoupling the digital (DVDD) supply pin, a 1-μF, X7R-grade, 0603-size ceramic capacitor is
recommended. The DVDD bypass capacitor is located in the bottom layer; see Figure 90.
• REFCAPA and REFCAPB must be shorted together and decoupled to REFGND using a 10-μF, X7R-grade,
0603-size ceramic capacitor placed in close proximity to the pins of the device. This capacitor is placed on
the top layer and directly connected to the pins of the device. Avoid placing vias between the REFCAPA,
REFCAPB pins and the decoupling capacitor.
• The REFIN/REFOUT pin also must be decoupled to REFGND with a 10-μF, X7R-grade, 0603-size ceramic
capacitor if the internal reference of the device is used. The capacitor must be placed on the top layer in
close to the device pin. Avoid placing vias between the REFIN/REFOUT pin and the decoupling capacitor.
• The REGCAP1 and REGCAP2 pins must be decoupled to GND using a separate 1-μF, X7R-grade, 0603-size
ceramic capacitor on each pin.
• All ground pins (AGND) must be connected to the ground plane using short, low-impedance paths and
independent vias to the ground plane. Connect REFGND to the common GND plane.
• For the optional channel input low-pass filters, ceramic surface-mount capacitors, COG (NPO) ceramic
capacitors provide the best capacitance precision. The type of dielectric used in COG (NPO) ceramic
capacitors provides the most stable electrical properties over voltage, frequency, and temperature changes.
11.2 Layout Example
Figure 89 and Figure 90 illustrate a recommended layout for the ADS8578S along with proper decoupling and
reference capacitor placement and connections.
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Layout Example (continued)
AVDD Plane
AIN_1P
AIN_1GND
AIN_2P
AIN_2GND
AIN_3P
AIN_3GND
AGND
AGND
AVDD (2)
AGND
1 PF
1 PF
REFSEL
10 PF
AGND
REFGND
REFCAP
REFCAP
REFGND
REFI/O
AGND
AGND
REGCAP2
AVDD
AVDD
REGCAP1
AGND
AVDD
1 PF
10 PF
DVDD Plane
GND
AGND
Isolated
Via (1)
AGND
AGND
DVDD (2)
AIN_4P
AIN_4GND
AIN_5P
AIN_5GND
AIN_6P
AIN_6GND
DVDD
DVDD
Digital
Inputs and
Outputs
Isolated
Via
AVDD
AGND
1 PF
AVDD
AGND
AGND
Figure 89. Top Layer Layout
GND
GND
AVDD
AVDD
AVDD Plane
DVDD Plane
AVDD (2)
Isolated
Via (1)
DVDD
AGND
AGND AGND
Isolated
Via
AGND
Figure 90. Bottom Layer Layout
52
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12 Device and Documentation Support
12.1 Documentation Support
12.1.1 Related Documentation
For related documentation see the following:
• OPAx320 Precision, 20MHz, 0.9pA, Low-Noise, RRIO, CMOS Operational Amplifier with Shutdown
• AN-2029 Handling & Process Recommendations
• REF50xx Low-Noise, Very Low Drift, Precision Voltage Reference
12.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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27-Apr-2017
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
ADS8578SIPM
PREVIEW
LQFP
PM
64
160
Green (RoHS
& no Sb/Br)
CU NIPDAU-DCC
Level-3-260C-168 HR
-40 to 125
ADS8578S
ADS8578SIPMR
PREVIEW
LQFP
PM
64
1000
Green (RoHS
& no Sb/Br)
CU NIPDAU-DCC
Level-3-260C-168 HR
-40 to 125
ADS8578S
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
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27-Apr-2017
Addendum-Page 2
MECHANICAL DATA
MTQF008A – JANUARY 1995 – REVISED DECEMBER 1996
PM (S-PQFP-G64)
PLASTIC QUAD FLATPACK
0,27
0,17
0,50
0,08 M
33
48
49
32
64
17
0,13 NOM
1
16
7,50 TYP
Gage Plane
10,20
SQ
9,80
12,20
SQ
11,80
0,25
0,05 MIN
0°– 7°
0,75
0,45
1,45
1,35
Seating Plane
0,08
1,60 MAX
4040152 / C 11/96
NOTES: A.
B.
C.
D.
All linear dimensions are in millimeters.
This drawing is subject to change without notice.
Falls within JEDEC MS-026
May also be thermally enhanced plastic with leads connected to the die pads.
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
1
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