TI1 ADS8910BRGET Ads891xb 18-bit, high-speed sar adcs with integrated reference buffer, integrated ldo, and multispiâ ¢ digital interface Datasheet

Product
Folder
Sample &
Buy
Support &
Community
Tools &
Software
Technical
Documents
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
ADS891xB 18-Bit, High-Speed SAR ADCs With Integrated Reference Buffer,
Integrated LDO, and multiSPI™ Digital Interface
1 Features
3 Description
•
•
The ADS8910B, ADS8912B, and ADS8914B
(ADS891xB) belong to a family of pin-to-pin
compatible, high-speed, high-precision successive
approximation register (SAR) based analog-to-digital
convertors (ADCs) with an integrated reference buffer
and integrated low-dropout regulator (LDO). These
devices support unipolar, fully differential, analog
input signals with ±0.5-LSB INL and 102.5-dB SNR
specifications under typical operating conditions.
1
•
•
•
•
•
•
•
•
Resolution: 18-bit
High Sample Rate With No Latency Output:
– ADS8910B : 1 MSPS
– ADS8912B : 500 kSPS
– ADS8914B : 250 kSPS
Integrated LDO Enables Single-Supply Operation
Burst-Mode Operation With Precise First Sample
Excellent AC and DC Performance:
– SNR: 102.5 dB, THD: –125 dB
– INL: ±0.5 LSB (Typ), ±1.5 LSB (Max)
– DNL: ±0.5 LSB (Max), 18-Bit NMC
Wide Input Range:
– Unipolar Differential Input Range: ±VREF
– VREF Input Range: 2.5 V to 5 V
Single-Supply, Low-Power Operation
(Includes Internal Reference Buffer and LDO)
– ADS8910B : 21 mW at 1 MSPS
– ADS8912B : 16 mW at 500 kSPS
– ADS8914B : 14 mW at 250 kSPS
multiSPI™ Digital Interface
Extended Temperature Range: –40°C to +125°C
Small Footprint: 4-mm × 4-mm VQFN
The integrated LDO enables single-supply operation
with low power consumption. The integrated
reference buffer supports burst-mode data acquisition
with 18-bit precision for the first sample. External
reference voltages in the range 2.5 V to 5 V are
supported, offering a wide selection of input ranges
without additional input scaling.
The integrated multiSPI digital interface is backwardcompatible to the traditional SPI protocol.
Additionally, configurable features simplify board
layout, timing, and firmware, and support high
throughput at lower clock speeds. The multiSPI digital
interface allows for easy interface with a variety of
microcontrollers, digital signal processors (DSPs),
and field-programmable gate arrays (FPGAs).
The ADS891xB family is offered in a space-saving,
4-mm × 4-mm, VQFN package, and is specified over
the extended temperature range of –40°C to +125°C.
2 Applications
•
•
•
Device Information
Test and Measurement
Medical Imaging
High-Precision, High-Speed Data Acquisition
PART NUMBER
ADS891xB
PACKAGE
VQFN (24)
BODY SIZE (NOM)
4.00 mm × 4.00 mm
(1) For all available packages, see the package option addendum
at the end of the datasheet.
Multiple-ADC Design
AVDD
REF5050
VOUT
VIN
GND
ADS89xxB
AVDD
ADS89xxB
AVDD
BUF
LDO
OPA2625
ADC
BUF
LDO
OPA2625
ADC
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.
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Table of Contents
1
2
3
4
5
6
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
7
1
1
1
2
3
5
Absolute Maximum Ratings ..................................... 5
ESD Ratings.............................................................. 5
Recommended Operating Conditions....................... 5
Thermal Information .................................................. 5
Electrical Characteristics........................................... 6
Timing Requirements ................................................ 8
Switching Characteristics .......................................... 9
Typical Characteristics ............................................ 13
Detailed Description ............................................ 17
7.1
7.2
7.3
7.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
17
17
18
23
7.5 Programming........................................................... 25
7.6 Register Maps ......................................................... 49
8
Application and Implementation ........................ 55
8.1 Application Information............................................ 55
8.2 Typical Application .................................................. 58
9 Power-Supply Recommendations...................... 60
10 Layout................................................................... 61
10.1 Layout Guidelines ................................................. 61
10.2 Layout Example .................................................... 62
11 Device and Documentation Support ................. 63
11.1
11.2
11.3
11.4
11.5
11.6
11.7
Documentation Support ........................................
Related Links ........................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
63
63
63
63
63
63
63
12 Mechanical, Packaging, and Orderable
Information ........................................................... 64
4 Revision History
Changes from Original (June 2016) to Revision A
•
2
Page
Changed from product preview to production data ............................................................................................................... 1
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
5 Pin Configuration and Functions
CS
SCLK
SDI
RVS
SDO-0
SDO-1
24
23
22
21
20
19
RGE Package
24-Pin VQFN
Top View
CONVST
1
18
SDO-2
RST
2
17
SDO-3
REFIN
3
16
DVDD
REFM
4
15
GND
REFBUFOUT
5
14
DECAP
NC
6
13
DECAP
Thermal
7
8
9
10
11
12
REFBUFOUT
REFM
AINP
AINM
GND
RVDD
Pad
Not to scale
Pin Functions
PIN
NAME
NO.
FUNCTION
AINM
10
Analog input
Negative analog input
AINP
9
Analog input
Positive analog input
CS
24
Digital input
Chip-select input pin; active low
The device takes control of the data bus when CS is low.
The SDO-x pins go to Hi-Z when CS is high.
CONVST
1
Digital input
Conversion start input pin.
A CONVST rising edge brings the device from ACQ state to CNV state.
13, 14
Power supply
Place decoupling capacitor here for internal power supply. Short pin 13 and 14 together.
16
Power supply
Interface power supply pin
11, 15
Power supply
Ground
6
No connection
Float these pins; no external connection.
DECAP
DVDD
GND
NC
REFBUFOUT
5, 7
DESCRIPTION
Analog input/output Reference buffer output, ADC reference input. Short pin 5 and 7 together.
REFIN
3
Analog input
Reference voltage input
REFM
4, 8
Analog input
Reference ground potential
RST
2
Digital input
Asynchronous reset input pin.
A low pulse on the RST pin resets the device. All register bits return to the default state.
RVDD
12
Power supply
Analog power supply pin.
RVS
21
Digital output
Multifunction output pin.
With CS held high, RVS reflects the status of the internal ADCST signal.
With CS low, the status of RVS depends on the output protocol selection.
SCLK
23
Digital input
Clock input pin for the serial interface.
All system-synchronous data transfer protocols are timed with respect to the SCLK signal.
SDI
22
Digital input
Serial data input pin.
This pin is used to feed data or commands into the device.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
3
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Pin Functions (continued)
PIN
NAME
NO.
FUNCTION
SDO-0
20
Digital output
Serial communication pin: data output 0
SDO-1
19
Digital output
Serial communication pin: data output 1
SDO-2
18
Digital output
Serial communication pin: data output 2
SDO-3
17
Digital output
Serial communication pin: data output 3
Supply
Exposed thermal pad; connect to GND.
Thermal pad
4
Submit Documentation Feedback
DESCRIPTION
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
6 Specifications
6.1
Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
RVDD to GND
–0.3
7
V
DVDD to GND
–0.3
7
V
REFIN to REFM
–0.3
RVDD + 0.3
V
REFM to GND
–0.1
0.1
V
Analog Input (AINP, AINM) to GND
–0.3
VREF + 0.3
V
Digital input (RST, CONVST, CS, SCLK, SDI) to GND
–0.3
DVDD + 0.3
V
Digital output (READY, SDO-0, SDO-1, SDO-2, SDO-3) to GND
–0.3
DVDD + 0.3
V
Analog Input (AINP, AINM) to RVDD and GND
–130
130
mA
Operating free-air temperature, TA
–40
125
°C
Storage temperature, Tstg
-65
150
°C
(1)
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.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
±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.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
RVDD
MIN
NOM
MAX
3
5
5.5
Operating
1.65
3
5.5
Specified throughput
2.35
3
3.6
Analog supply voltage (RVDD to AGND)
DVDD
Digital supply voltage (DVDD to AGND)
VREF
Reference input voltage on REFIN
2.5
CREFBUF
External ceramic decoupling capacitor
10
RESR
External series resistor
TA
Specified free-air operating temperature
RVDD – 0.3
22
UNIT
V
V
V
µF
0
1
1.3
Ω
–40
25
125
°C
6.4 Thermal Information
ADS891xB
THERMAL METRIC (1)
RGE (VQFN)
UNITS
24 PINS
RθJA
Junction-to-ambient thermal resistance
31.9
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
29.9
°C/W
RθJB
Junction-to-board thermal resistance
8.9
°C/W
ψJT
Junction-to-top characterization parameter
0.3
°C/W
ψJB
Junction-to-board characterization parameter
8.9
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
2.0
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
5
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
6.5 Electrical Characteristics
At RVDD = 5.5 V, DVDD = 2.35 V to 3.6 V, VREF = 5 V, and maximum throughput (unless otherwise noted).
Minimum and maximum values at TA = –40°C to +125°C; typical values at TA = 25°C.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
–VREF
VREF
V
0
VREF
V
(VREF / 2) + 0.1
V
ANALOG INPUT
FSR
Full-scale input range
(AINP – AINM)
VIN
Absolute input voltage
(AINP and AINM to REFM)
VCM
Common-mode voltage
(AINP + AINM) / 2
CIN
Input capacitance
(VREF / 2) – 0.1
Sample mode
VREF / 2
60
pF
Hold mode
4
pF
VREF = 5 V
0.1
VOLTAGE REFERENCE INPUT (REFIN)
IREF
Reference input current
CREF
Internal capacitance
1
10
µA
pF
REFERENCE BUFFER OUTPUT (REFBUFOUT)
V(RO)
Reference buffer offset voltage
(VREFBUFOUT – VREF)
CREFBUF
External ceramic decoupling
capacitor
RESR
External series resistor
ISHRT
Short-circuit current
With EN_MARG = 0b (1)
–250
10
0
250
22
1
µV
µF
1.3
Ω
30
mA
Margining range
With EN_MARG = 1b (1)
±4.5
mV
Margining resolution
With EN_MARG = 1b (1)
280
µV
18
Bits
DC ACCURACY (2) (CREFBUF = 22 µF, RESR = 1 Ω)
Resolution
NMC
No missing codes
INL
Integral nonlinearity
DNL
Differential nonlinearity
E(IO)
Input offset error
dVOS/dT
Input offset thermal drift
18
TA = 25°C
(4)
TA = –40°C to +125°C (4)
±0.5
1.5
LSB (3)
-0.5
±0.2
0.5
LSB (3)
-3
±0.5
3
-20
±3
20
10
(1) (5)
GE
Gain error
EN_MARG = 0b
dGE/dT
Gain error thermal drift
EN_MARG = 0b (1) (5)
TNS
Transition noise
CMRR
Bits
-1.5
First output code deviation for
burst-mode data acquisition
See Reference Buffer
Module
Common-mode rejection ratio
dc to 20 kHz
-0.02
±0.005
LSB (3)
μV/°C
0.02
%FSR
2.5
ppm/°C
0.72
LSB (3)
–3
3
TNS
80
dB
AC ACCURACY (2) (6) (CREFBUF = 22 µF, RESR = 1 Ω)
SINAD
Signal-to-noise + distortion
fIN = 2 kHz
100
102.48
dB
SNR
Signal-to-noise ratio
fIN = 2 kHz
101
102.5
dB
THD
Total harmonic distortion
fIN = 2 kHz
–125
dB
SFDR
Spurious-free dynamic range
125
dB
(1)
(2)
(3)
(4)
(5)
(6)
6
See the REF_MRG Register.
While operating with internal reference buffer and LDO.
LSB = least-significant bit. 1 LSB at 18-bit resolution is approximately 3.8 ppm.
For selected VREF, see the OFST_CAL Register.
Includes internal reference buffer errors and drifts.
For VIN = –0.1 dBFS.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Electrical Characteristics (continued)
At RVDD = 5.5 V, DVDD = 2.35 V to 3.6 V, VREF = 5 V, and maximum throughput (unless otherwise noted).
Minimum and maximum values at TA = –40°C to +125°C; typical values at TA = 25°C.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SAMPLING DYNAMICS
Aperture delay
4
ns
tj-rms
Aperture jitter
2
ps RMS
f3-DB(small)
Small-signal bandwidth
23
MHz
LDO OUTPUT (DECAP)
VLDO
LDO output voltage
(DECAP pins)
CLDO
External ceramic capacitor on
DECAP pins
tPU_LDO
LDO power-up time
ISHRT-LDO
Short-circuit current
2.85
V
1
CLDO = 1 µF, RVDD > VLDO
µF
1
ms
100
mA
DIGITAL INPUTS
VIH
High-level input voltage
VIL
Low-level input voltage
1.65 V < DVDD < 2.3 V
0.8 DVDD
DVDD + 0.3
2.3 V < DVDD < 3.6 V
0.7 DVDD
DVDD + 0.3
1.65 V < DVDD < 2.3 V
–0.3
0.2 DVDD
2.3 V < DVDD < 3.6 V
–0.3
0.3 DVDD
Input current
±0.01
V
V
0.1
μA
0.8 DVDD
DVDD
V
0
0.2 DVDD
V
DIGITAL OUTPUTS
VOH
High-level output voltage
IOH = 500-µA source
VOL
Low-level output voltage
IOH = 500-µA sink
POWER SUPPLY
IRVDD
Analog supply current
ADS8910B at RVDD = 5 V,
1-MSPS
4.2
5.8
mA
ADS8912B at RVDD = 5 V,
500-KSPS
3.2
4
mA
ADS8914B at RVDD = 5 V,
250-KSPS
2.8
3.6
mA
Static, no conversion
970
μA
900
μA
120
μA
40
μA
1
μA
Static, PD_ADC = 1b
(7)
Static, PD_REFBUF = 1b (7)
Static, PD_ADC = 1b and
PD_REFBUF = 1b (7)
IDVDD
PRVDD
(7)
DVDD = 3 V, CLOAD = 10 pF,
no conversion
Digital supply current
Power dissipation
ADS8910B at RVDD = 5 V,
1-MSPS
21
29
ADS8912B at RVDD = 5 V,
500-KSPS
16
20
ADS8914B at RVDD = 5 V,
250-KSPS
14
18
mW
See the PD_CNTL Register.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
7
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
6.6 Timing Requirements
MIN
TYP
MAX
UNIT
TIMING
DIAGRAM
CONVERSION CYCLE
fcycle
Sampling frequency
tcycle
ADC cycle-time period
ADS8910B
1000
ADS8912B
500
ADS8914B
250
ADS8910B
1
ADS8912B
2
ADS8914B
4
twh_CONVST Pulse duration: CONVST high
twl_CONVST
Pulse duration: CONVST low
tacq
Acquisition time
tqt_acq
td_cnvcap
kHz
µs
30
ns
30
ns
300
ns
Quiet acquisition time
30
ns
Quiet aperture time
20
ns
100
ns
Figure 1
Figure 41,
see Data
Transfer
Protocols
ASYNCHRONOUS RESET, AND LOW POWER MODES
twl_RST
Pulse duration: RST low
Figure 2
SPI-COMPATIBLE SERIAL INTERFACE
fCLK
Serial clock frequency
tCLK
Serial clock time period
14.3
70
MHz
tph_CK
SCLK high time
0.45
0.55
tCLK
tpl_CK
SCLK low time
0.45
0.55
tCLK
tsu_CSCK
Setup time: CS falling to the first SCLK capture edge
12
ns
tsu_CKDI
Setup time: SDI data valid to the SCLK capture edge
1.5
ns
tht_CKDI
Hold time: SCLK capture edge to (previous) data valid on SDI
1
ns
tht_CKCS
Delay time: last SCLK falling to CS rising
7
ns
ns
Figure 3
Figure 3
SOURCE-SYNCHRONOUS SERIAL INTERFACE (External Clock)
fCLK
Serial clock frequency
tCLK
Serial clock time period
8
SDR (DATA_RATE = 0b)
70
DDR (DATA_RATE = 1b)
35
SDR (DATA_RATE = 0b)
14.3
DDR (DATA_RATE = 1b)
28.6
Submit Documentation Feedback
MHz
ns
Figure 4,
see Data
Transfer
Protocols
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
6.7 Switching Characteristics
At RVDD = 5.5 V, DVDD = 2.35 V to 3.6 V, VREF = 5 V, and maximum throughput (unless otherwise noted).
Minimum and maximum values at TA = –40°C to +125°C; typical values at TA = 25°C.
PARAMETER
MIN
TYP
MAX
UNIT
TIMING
DIAGRAM
ns
Figure 1
ms
Figure 2
CONVERSION CYCLE
tconv
Conversion time
ADS8910B
580
640
ADS8912B
1100
1200
ADS8914B
2400
2500
ASYNCHRONOUS RESET, AND LOW POWER MODES
td_rst
Delay time: RST rising to RVS rising
tPU_ADC
Power-up time for converter module
tPU_REFBUF Power-up time for internal reference buffer, CREFBUF = 22 µF
tPU_Device
Power-up time for
device
CLDO = 1 µF, CREFBUF = 22 µF
3
1
ms
10
ms
10
ms
See
PD_CNTL
Register
SPI-COMPATIBLE SERIAL INTERFACE
tden_CSDO
Delay time: CS falling to data enable
9
ns
tdz_CSDO
Delay time: CS rising to SDO going to Hi-Z
10
ns
td_CKDO
Delay time: SCLK launch edge to (next) data valid on SDO
13
ns
td_CSRDY_f
Delay time: CS falling to RVS falling
12
ns
Figure 4
td_CSRDY_r
Delay time:
CS rising to RVS rising
ns
Figure 4
After NOP operation
30
After WR or RD operation
120
Figure 3
SOURCE-SYNCHRONOUS SERIAL INTERFACE (External Clock)
td_CKSTR_r
Delay time: SCLK launch edge to RVS rising
13
ns
td_CKSTR_f
Delay time: SCLK launch edge to RVS falling
13
ns
toff_STRDO_f Time offset: RVS falling to (next) data valid on SDO
-2
2
ns
toff_STRDO_r Time offset: RVS rising to (next) data valid on SDO
-2
2
ns
15
50
ns
Figure 4
SOURCE-SYNCHRONOUS SERIAL INTERFACE (Internal Clock)
td_CSSTR
Delay time: CS falling to RVS rising
tSTR
Strobe output time
period
INTCLK option
15
INTCLK / 2 option
30
INTCLK / 4 option
60
ns
tph_STR
Strobe output high time
0.45
0.55
tSTR
tpl_STR
Strobe output low time
0.45
0.55
tSTR
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Figure 5
Submit Documentation Feedback
9
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Sample
S
Sample
S+1
twh_CONVST
twl_CONVST
CONVST
tcycle
tconv_max
tconv
tacq
tconv_min
ADCST (Internal)
CNV (C)
ACQ (C + 1)
CS
RVS
Figure 1. Conversion Cycle Timing
trst
twl_RST
RST
td_rst
CONVST
CS
SCLK
RVS
SDO-x
Figure 2. Asynchronous Reset Timing
10
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
tCLK
tph_CK
CS
tpl_CK
(1)
SCLK
tsu_CKDI
tsu_CSCK
tht_CKCS
tht_CKDI
SCLK(1)
SDI
tden_CSDO
tdz_CSDO
td_CKDO
SDO-x
(1)
SDO-x
The SCLK polarity, launch edge, and capture edge depend on the SPI protocol selected.
Figure 3. SPI-Compatible Serial Interface Timing
tCLK
tph_CK
CS
tpl_CK
SCLK
td_CKSTR_f
tsu_CSCK
tht_CKCS
SCLK
td_CKSTR_r
RVS
tden_CSDO
tdz_CSDO
toff_STRDO_f
toff_STRDO_r
SDO-x
(DDR)
SDO-x
td_CSRDY_f
td_CSRDY_r
toff_STRDO_r
SDO-x
(SDR)
RVS
Figure 4. Source-Synchronous Serial Interface Timing (External Clock)
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
11
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
tSTR
RVS
CS
tph_STR
tden_CSDO
tdz_CSDO
toff_STRDO_r
tpl_STR
toff_STRDO_f
SDO-x
(DDR)
SDO-x
td_CSRDY_f
td_CSRDY_r
toff_STRDO_r
SDO-x
(SDR)
RVS
td_CSSTR
Figure 5. Source-Synchronous Serial Interface Timing (Internal Clock)
12
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
6.8 Typical Characteristics
at TA = 25°C, RVDD = 5.5 V, DVDD = 3 V, VREF = 5 V, and maximum-rated throughput (unless otherwise noted)
1
Integral Nonlinearity (LSB)
0.25
0
-0.25
-0.5
-131072
0
-0.5
-1
-131072
131071
ADC Output Code
0.5
131071
ADC Output Code
D001
Typical DNL = ±0.4 LSB
Figure 6. Typical DNL
Figure 7. Typical INL
500
400
400
1
8
6
0.
4
0.
2
0.
0.
0
.2
.4
-0
-1
0.
0
0
05
0.
1
0.
15
0.
2
0.
25
0.
3
0
-0
.1
-0
.0
5
100
-0
.2
-0
.1
5
100
.6
200
.8
200
300
-0
300
-0
Frequency
500
-0
.3
-0
.2
5
Frequency
D002
Typical INL = ±0.5 LSB
-0
Differential Nonlinearity(LSB)
0.5
D008
D007
1000 devices
1000 devices
Figure 8. Typical DNL Distribution
Figure 9. Typical INL Distribution
0.5
1.5
Maximum
Minimum
1
Integral Nonlinearity (LSB)
Differential Nonlinearity (LSB)
Minimum
Maximum
0.25
0
-0.25
0.5
0
-0.5
-1
-0.5
-40
-7
26
59
Free-Air Temperature (qC)
92
Figure 10. DNL vs Temperature
125
D003
-1.5
-40
-7
26
59
Free-Air Temperature (qC)
92
125
D004
Figure 11. INL vs Temperature
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
13
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Typical Characteristics (continued)
at TA = 25°C, RVDD = 5.5 V, DVDD = 3 V, VREF = 5 V, and maximum-rated throughput (unless otherwise noted)
0.5
1.5
Maximum
Minimum
1
Integral Nonlinearity (LSB)
Differential Nonlinearity (LSB)
Maximum
Minimum
0.25
0
-0.25
0.5
0
-0.5
-1
-0.5
2.5
3
3.5
4
Reference Voltage (V)
4.5
-1.5
2.5
5
3
D005
Figure 12. DNL vs Reference Voltage
3.5
4
Reference Voltage (V)
4.5
5
D006
Figure 13. INL vs Reference Voltage
3000
1250
2700
2400
1000
Frequency
Frequency
2100
750
500
1800
1500
1200
900
600
250
300
5
00
3
0.
00
1
0.
5
0
00
0
0.
00
1
D019
4000 devices
0.
-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3
-0
.0
03
-0
.0
01
5
-3
-0
.0
01
-0
.0
00
5
0
0
D022
4000 devices
Figure 14. Typical Offset Distribution
Figure 15. Typical Gain Error Distribution
1
10
0.75
6
Offset (mV)
Offset (LSB)
0.5
2
-2
0.25
0
-0.25
-0.5
-6
-0.75
-10
-40
-7
26
59
Free-Air Temperature (qC)
92
REF_SEL[2:0] = 000b
Figure 16. Offset vs Temperature
14
Submit Documentation Feedback
125
-1
2.5
3
3.5
4
Reference Voltage (V)
D020
4.5
5
D021
With appropriate REF_SEL[2:0], see OFST_CAL
Figure 17. Offset vs Reference Voltage
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Typical Characteristics (continued)
at TA = 25°C, RVDD = 5.5 V, DVDD = 3 V, VREF = 5 V, and maximum-rated throughput (unless otherwise noted)
0.01
0.02
Gain (%FS) ADC only
Gain (%FS) ADC + REFBUF
Gain (%FS) ADC only
Gain (%FS) ADC + REFBUF
0.01
Gain Error (%FS)
Gain Error (%FS)
0.005
0
-0.005
0
-0.01
-0.01
-40
-7
26
59
Free-Air Temperature (0C)
92
-0.02
2.5
125
3
3.5
4
Reference Voltage (V)
D023
EN_MARG = 0b
4.5
5
D024
EN_MARG = 0b
Figure 18. Gain Error vs Temperature
Figure 19. Gain Error vs Reference Voltage
1200
0
1000
-50
Power (dB)
Frequency
800
600
-100
-150
400
-200
200
0
0
19
66
11
100
D009
Standard Deviation = 0.65 LSB
fIN = 2 kHz
200
300
fIN, Input Frequency (kHz)
SNR = 102.8 dB
Figure 20. DC Input Histogram
400
D011
THD = –125 dB
Figure 21. Typical FFT
105
-116
17
132
THD
SFDR
16.75
103
16.5
102
16.25
-7
26
59
Free-Air Temperature (qC)
92
16
125
D013
THD (dBFS)
104
ENOB (Bits)
SNR, SINAD (dBFS)
SNR
SINAD
ENOB
101
-40
500
-118
128
-120
124
-122
120
-124
-40
-7
26
59
Free-Air Temperature (qC)
fIN = 2 kHz
92
SFDR (dBFS)
19
66
10
19
66
09
08
19
66
07
19
66
19
66
06
-250
116
125
D014
fIN = 2 kHz
Figure 22. Noise Performance vs Temperature
Figure 23. Distortion Performance vs Temperature
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
15
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Typical Characteristics (continued)
at TA = 25°C, RVDD = 5.5 V, DVDD = 3 V, VREF = 5 V, and maximum-rated throughput (unless otherwise noted)
105
99
16
97
15.5
15
3
3.5
4
Reference Voltage (V)
4.5
5
-121.5
126
-122
125
-122.5
124
-123
2.5
SFDR (dBFS)
16.5
ENOB (Bits)
17
101
95
2.5
127
THD
SFDR
THD (dBFS)
103
SNR, SINAD (dBFS)
-121
17.5
SNR
SINAD
ENOB
123
3
3.5
4
Reference Voltage (V)
D015
fIN = 2 kHz
4.5
5
D016
fIN = 2 kHz
Figure 24. Noise Performance vs Reference Voltage
Figure 25. Distortion Performance vs Reference Voltage
4
3.6
3.55
3.75
IRVDD (mA)
IRVDD (mA)
3.5
3.45
3.4
3.35
3.5
3.25
3.3
3.25
3
3.5
4
4.5
RVDD
5
5.5
D026
3
-40
-7
26
59
Free-Air Temperature (qC)
92
125
D028
RVDD = 5 V
Figure 26. Analog Supply Current vs Supply Voltage
16
Submit Documentation Feedback
Figure 27. Analog Supply Current vs Temperature
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7 Detailed Description
7.1 Overview
The ADS891xB is a family of high-speed, successive approximation register (SAR), analog-to-digital converters
(ADC) based on a charge redistribution architecture. These compact devices integrate a reference buffer and
LDO, and feature high performance at a high throughput rate with low power consumption.
This device family supports unipolar, fully differential, analog input signals. The integrated reference buffer
supports the burst mode of data acquisition for external reference voltages in the range 2.5 V to 5 V, and offers a
wide selection of input ranges without additional input scaling.
When a conversion is initiated, the differential input between the AINP and AINM pins is sampled on the internal
capacitor array. The device uses an internal clock to perform conversions. During the conversion process, both
analog inputs are disconnected from the internal circuit. At the end of conversion process, the device reconnects
the sampling capacitors to the AINP and AINM pins and enters an acquisition phase.
The integrated LDO allows the device to operate on a single supply, RVDD. The device consumes only 21 mW,
16 mW, or 14 mW of power when operating at the rated maximum throughput of 1 MSPS, 500 kSPS, or 250
kSPS, respectively, with the internal reference buffer and LDO enabled.
The integrated multiSPI digital interface is backward-compatible with the traditional SPI protocol. Configurable
features simplify board layout, timing, and firmware, and support high throughput at lower clock speeds, thus
allowing an easy interface with a variety of microcontrollers, DSPs, and FPGAs.
The ADS891xB enables Test & Measurement, Medical, and Industrial applications to achieve fast, low noise, low
distortion, low power data acquisition in small form factors.
7.2 Functional Block Diagram
REFIN
REFBUFOUT
BUF
REFM
RVDD
LDO
DVDD
DECAP
multiSPITM
Digital
Interface
AINP
SAR ADC
AINM
To
Digital
Host
GND
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
17
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.3 Feature Description
From a functional perspective, the device comprises four modules: the low-dropout regulator (LDO), the
reference buffer (BUF), the converter (SAR ADC), and the interface (multiSPI digital interface), as shown in the
Functional Block Diagram section.
The LDO module is powered by the RVDD supply, and generates the bias voltage for internal circuit blocks of the
device. The reference buffer module buffers the external reference voltage source from the dynamic, capacitive
switching load present of the reference pins during the conversion process. The converter module samples and
converts the analog input into an equivalent digital output code. The interface module facilitates communication
and data transfer between the device and the host controller.
7.3.1 LDO Module
To enable single-supply operation, the device features an internal low-dropout regulator (LDO). The LDO is
powered by the RVDD supply, and the output is available on the two DECAP pins. This LDO output powers the
critical analog blocks within the device, and must not be used for any other external purposes.
Short the two DECAP pins together, and decouple with the GND pin by placing a 1-μF, X7R-grade, ceramic
capacitor with a 10-V rating, as shown in Figure 28. There is no upper limit on the value of the decoupling
capacitor; however, a larger decoupling capacitor results in higher power-up time for the device. See the Layout
section for layout recommendations.
RVDD
DECAP
LDO
DECAP
CLDO
1 F
GND
Figure 28. Internal LDO Connections
7.3.2 Reference Buffer Module
During the conversion process (in CNV state), binary-weighted capacitors are switched onto the reference pins.
The switching frequency is proportional to the conversion clock frequency, but the dynamic charge requirements
are a function of the absolute values of the input voltage and the reference voltage. Reference capacitors
decouple the dynamic reference loads, and a low-impedance reference driver is required to keep the voltage
regulated to within 1 LSB. The device features an internal reference buffer to meet this requirement.
Figure 29 shows the block diagram of the internal reference buffer.
ADS89xxB
RVDD
±
BUF
REFIN
REFBUFOUT
+
REFBUFOUT
Margin
REFM
GND
REFM
Figure 29. Internal Reference Buffer Block Diagram
18
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Feature Description (continued)
The input range for the device is set by the external voltage applied at the REFIN pin (VREF). The REFIN pin has
electrostatic discharge (ESD) protection diodes to RVDD and GND pins. For minimum input offset error (see E(IO)
specified in the Electrical Characteristics), set the REF_SEL[2:0] bits to the value closest to VREF (see the
OFST_CAL register).
The internal reference buffer has a typical gain of 1 V/V with minimal offset error (see V(RO) specified in the
Electrical Characteristics), and the output of the buffer is available between the REFBUFOUT pins and the REFM
pins. Set the REF_OFST[4:0] bits to add or subtract an intentional offset voltage (see the REF_MRG register).
Figure 30 shows the external connections required for the internal reference buffer.
+VA
RVDD
External
Reference
Source
IREF
ADS89xxB
VREF
REFBUFOUT
BUF
REFIN
+
RREF_FLT
REFBUFOUT
Margin
CREF_FLT
GND
REFM
RESR
CREFBUF
REFM
Figure 30. External Connections for the Internal Reference Buffer
Select RREF_FLT and CREF_FLT to limit the broadband noise contribution from the external reference source. The
device takes very little current, IREF, from the REFIN pin (typically, 0.1 µA). However, this current flows through
RREF_FLT and may result in additional gain error.
Short the two REFBUFOUT pins externally. Short the two REFM pins to GND externally. As shown in Figure 30,
place a combination of RESR and CREFBUF (see the Electrical Characteristics) between the REFBUFOUT pins and
the REFM pins as close to the device as possible. See the Layout section for layout recommendations.
The device takes very little static current from the reference pins in the RST and ACQ states. Therefore, when a
conversion is initiated after a long idle time (device in ACQ state), there is a sudden change in the average
current taken from the reference pins for the first sample. The internal reference buffer of the ADS8910B is
designed to address this step change in current, and the conversion result for the first sample is as per the
datasheet specifications. Use specified values of RESR and CREFBUF for optimum performance.
7.3.3 Converter Module
As shown in Figure 31, the converter module samples the analog input signal (provided between the AINP and
AINM pins), compares this signal with the reference voltage (between the pair of REFBUFOUT and REFM pins),
and generates an equivalent digital output code.
The converter module receives RST and CONVST inputs from the interface module, and outputs the ADCST
signal and the conversion result back to the interface module.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
19
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Feature Description (continued)
REFP
DVDD
AVDD
RST
OSC
CONVST
CS
RST
AINP
AINM
SCLK
CONVST
Sampleand-Hold
Circuit
ADCST
SDI
Interface
Module
ADC
SDO-0
SDO-1
Conversion
Result
SDO-2
SDO-3
AGND
RVS
Converter Module
REFM
DGND
GND
Figure 31. Converter Module
7.3.3.1 Sample-and-Hold Circuit
These devices support unipolar, fully differential, analog input signals. Figure 32 shows a small-signal equivalent
circuit of the sample-and-hold circuit. Each sampling switch is represented by a resistance (RS1 and RS2, typically
50 Ω) in series with an ideal switch (SW1 and SW2). The sampling capacitors, CS1 and CS2, are typically 60 pF.
RS1
SW1
AINP
4 pF
CS1
REFBUFOUT
4 pF
CS2
GND
RS2
GND
SW2
AINM
Device in Hold Mode
Figure 32. Input Sampling Stage Equivalent Circuit
During the acquisition process (ACQ state), both positive and negative inputs are individually sampled on CS1
and CS2, respectively. During the conversion process (CNV state), the device converts for the voltage difference
between the two sampled values: VAINP – VAINM.
Each analog input pin has electrostatic discharge (ESD) protection diodes to REFBUFOUT and GND. Keep the
analog inputs within the specified range to avoid turning the diodes on.
Equation 1 and Equation 2 show the full-scale input range (FSR) and common-mode voltage (VCM), respectively,
supported at the analog inputs for any external reference voltage provided on the REFIN pin (VREF).
FSR r VREF
(1)
VCM
20
§ VREF ·
¨ 2 ¸ r 0.1 V
©
¹
Submit Documentation Feedback
(2)
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Feature Description (continued)
7.3.3.2 Internal Oscillator
The device family features an internal oscillator (OSC) that provides the conversion clock; see Figure 31.
Conversion duration varies, but is bounded by the minimum and maximum value of tconv, as specified in the
Switching Characteristics table.
The interface module uses this internal clock (OSC), an external clock (provided by the host controller on the
SCLK pin), or a combination of both the internal and external clocks, to execute the data transfer operations
between the device and host controller; see the Interface Module section for more details.
7.3.3.3 ADC Transfer Function
The device family supports unipolar, fully differential analog inputs. The device output is in two's compliment
format. Figure 33 and Table 1 show the ideal transfer characteristics for the device.
The least significant bit (LSB) for the ADC is given by Equation 3:
1 LSB
FSR
18
2
2u
VREF
218
(3)
ADC Code (Hex)
1FFFF
00000
3FFFF
20001
20000
VIN
±VREF + 1 LSB
±1 LSB
0
VREF ± 1 LSB
Differential Analog Input
(AINP AINM)
Figure 33. Differential Transfer Characteristics
Table 1. Transfer Characteristics
DIFFERENTIAL ANALOG INPUT VOLTAGE
(AINP – AINM)
OUTPUT CODE
(HEX)
< –VREF
20000
–VREF + 1 LSB
20001
–1 LSB
3FFFF
0
00000
1 LSB
00001
> VREF – 1 LSB
1FFFF
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
21
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.3.4 Interface Module
The interface module facilitates the communication and data transfer between the device and the host controller.
As shown in Figure 34, the module consists of shift registers (both input and output), configuration registers, and
a protocol unit.
Shift Registers
RST
Output Data Register (ODR)
D21
D20
D1
CONVST
D0
CS
22 Bits
SCLK
Converter Module
B21
B20
B1
Protocol
22 Bits
B0
Input Data Register (IDR)
SDI
SDO-0
SDO-1
SDO-2
Command Processor
SCLK
Counter
Configuration Registers
SDO-3
RVS
Interface Module
Figure 34. Interface Module
The Pin Configuration and Functions section provides descriptions of the interface pins. The Data Transfer
Frame section details the functions of shift registers, the SCLK counter, and the command processor. The Data
Transfer Protocols section details supported protocols. The Register Maps section explains the configuration
registers and bit settings.
22
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.4 Device Functional Modes
As shown in Figure 35, this device family supports three functional states: RST, ACQ, and CNV. The device
state is determined by the status of the CONVST and RST control signals provided by the host controller.
Power Up
ACQ
RST Rising Edge
CONVST Rising Edge
RST Falling Edge
End of Conversion
CNV
RST
RST Falling Edge
Figure 35. Device Functional States
7.4.1 RST State
The RST pin is an asynchronous digital input for the device. To enter RST state, the host controller pulls the RST
pin low and keeps it low for the twl_RST duration (as specified in the Timing Requirements table).
In RST state, all configuration registers (see the Register Maps section) are reset to their default values, the RVS
pin remains low, and the SDO-x pins are Hi-Z.
To exit RST state, the host controller pulls the RST pin high, with CONVST and SCLK held low and CS held
high, as shown in Figure 36. After a delay of td_rst, the device enters ACQ state and the RVS pin goes high.
trst
twl_RST
RST
td_rst
CONVST
CS
SCLK
RVS
SDO-x
Figure 36. Asynchronous Reset
To operate the device in either ACQ or CNV state, RST must be held high. With RST held high, transitions on
the CONVST pin determine the functional state of the device.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
23
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Device Functional Modes (continued)
Figure 37 shows a typical conversion process. The internal ADCST signal goes low during conversion and goes
high at the end of conversion. With CS held high, RVS reflects the status of ADCST.
Sample
S
Sample
S+1
twh_CONVST
twl_CONVST
CONVST
tcycle
tconv_max
tconv
tacq
tconv_min
ADCST (Internal)
CNV (C)
ACQ (C + 1)
CS
RVS
Figure 37. Typical Conversion Process
7.4.2 ACQ State
In ACQ state, the device acquires the analog input signal. The device enters ACQ state at power-up, when
coming out of power down (See the PD Control section), after any asynchronous reset, and at the end of every
conversion.
An RST falling edge takes the device from ACQ state to RST state. A CONVST rising edge takes the device
from ACQ state to CNV state.
7.4.3 CNV State
The device moves from ACQ state to CNV state on a rising edge of the CONVST pin. The conversion process
uses an internal clock. The device ignores any further transitions on the CONVST signal until the ongoing
conversion is complete (that is, during the time interval of tconv).
At the end of conversion, the device enters ACQ state. The cycle time for the device is given by Equation 4:
t cycle-min
tconv
t acq-min
(4)
NOTE
The conversion time, tconv, varies within the specified limits of tconv_min and tconv_max (as
specified in the Switching Characteristics table). After initiating a conversion, the host
controller must monitor for a low-to-high transition on the RVS pin or wait for the tconv_max
duration to elapse before initiating a new operation (data transfer or conversion). If RVS is
not monitored, substitute tconv in Equation 4 with tconv_max.
24
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.5 Programming
This device family features nine configuration registers (as described in the Register Maps section). To access
the internal configuration registers, these devices support the commands listed in Table 2.
Table 2. Supported Commands
B[21:17]
B[16:8]
B[7:0]
COMMAND
ACRONYM
COMMAND DESCRIPTION
00000
000000000
00000000
NOP
10000
<9-bit address>
<8-bit unmasked bits>
CLR_BITS
No operation
10001
<9-bit address>
00000000
RD_REG
Read contents from the <9-bit address>
10010
<9-bit address>
<8-bit data>
WR_REG
Write <8-bit data> to the <9-bit address>
10011
<9-bit address>
<8-bit unmasked bits>
SET_BITS
Set <8-bit unmasked bits> from <9-bit address>
11111
111111111
11111111
NOP
Remaining
combinations
xxxxxxxxx
xxxxxxxx
Reserved
Clear <8-bit unmasked bits> from <9-bit address>
No operation
These commands are reserved and treated by the
device as no operation
These devices support two types of data transfer operations: data write (the host controller configures the
device), and data read (the host controller reads data from the device).
Any data write to the device is always synchronous to the external clock provided on the SCLK pin. The
WR_REG command writes the 8-bit data into the 9-bit address specified in the command string. The CLR_BITS
command clears the specified bits (identified by 1) at the 9-bit address (without affecting the other bits), and the
SET_BITS command sets the specified bits (identified by 1) at the 9-bit address (without affecting the other bits).
The data read from the device can be synchronized to the same external clock or to an internal clock of the
device by programming the configuration registers (see the Data Transfer Protocols section for details).
7.5.1 Output Data Word
In any data transfer frame, the contents of an internal, 22-bit, output data word are shifted out on the SDO pins.
The D[21:4] bits of the 22-bit output data word for any frame F + 1, are determined by:
• Value of the DATA_VAL bit applicable to frame F + 1 (see the DATA_CNTL register)
• The command issued in frame F
If a valid RD_REG command is executed in frame F, then the D[21:14] bits in frame F + 1 reflect the contents of
the selected register, and the D[13:0] bits are zeros.
If the DATA_VAL bit for frame F + 1 is set to 1, then the D[21:4] bits in frame F + 1 are replaced by the
DATA_PATN[17:0] bits.
For all other combinations, the D[21:4] bits for frame F + 1 are the latest conversion result.
Figure 38 shows the output data word. Figure 39 shows further details of the parity computation unit illustrated in
Figure 38.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
25
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Output Data
Word D[21:0]
A valid RG_READ command is received in
the previous frame?
D21
D20
Register Data
<8-bit REGDATA>_<10-bit 0's>
Yes
D[21:4]
18-bit Conversion Result
18-bit DATA_PATN[17:0]
0
No
1
D5
DATA_VAL
D4
D3
Parity Computation Unit
D2
0b
D1
0b
D0
Figure 38. Output Data Word (D[21:0])
26
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Output Data Word D[21:0]
Parity Computation Unit
D21
D20
XOR
D19
D18
XOR
D17
D16
XOR
D15
D14
XOR
D13
D12
XOR
D11
D10
XOR
D9
D8
XOR
D7
D6
D5
D4
FLPAR
D3
FTPAR
D2
)
D1
0
D0
0
XOR
11
16 MSBs
10
)
MUX
12 MSBs
01
8 MSBs
00
4 MSBs
PAR_EN
FPAR_LOC[1:0]
Figure 39. Parity Bits Computation
With the PAR_EN bit set to 0, the D[3] and D[2] bits of the output data word are set to 0 (default configuration).
When the PAR_EN bit is set to 1, the device calculates the parity bits (FLPAR and FTPAR) and appends them
as bits D[3] and D[2].
• FLPAR is the even parity calculated on bits D[21:4].
• FTPAR is the even parity calculated on the bits defined by FPAR_LOC[1:0].
See the DATA_CNTL register for more details on the FPAR_LOC[1:0] bit settings. Bits D[1:0] are set to 00b.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
27
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.5.2 Data Transfer Frame
A data transfer frame between the device and the host controller is bounded between a CS falling edge and the
subsequent CS rising edge. The host controller can initiate a data transfer frame (as shown in Figure 40) at any
time irrespective of the status of the CONVST signal; however, the data read during such a data transfer frame is
a function of relative timing between the CONVST and CS signals.
Frame F
CONVST
CS
RVS
As per output protocol selection.
td_CSRDY_r
SCLK
N SCLKs
SDI
Valid Command
SDO-x
ODR Data
SCLK Counter
SCLK Counter
0
N
Output Data Word
Input Data Register (IDR)
D21
D0
B21
B0
D21
D0
D21
D0
Output Data Register (ODR)
Command Processor
Figure 40. Data Transfer Frame
For this discussion, assume that the CONVST signal remains low.
A typical data transfer frame F follows this order:
1. The host controller pulls CS low to initiate a data transfer frame. On the CS falling edge:
– RVS goes low, indicating the beginning of the data transfer frame.
– The SCLK counter is reset to 0.
– The device takes control of the data bus. As shown in Figure 40, the 22-bit contents of the output data
word (see Figure 38) are loaded in to the 22-bit output data register (ODR; see Figure 34).
– The 22-bit input data register (IDR; see Figure 34) is reset to 000000h, corresponding to a NOP
command.
28
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
2. During the frame, the host controller provides clocks on the SCLK pin. Inside the device:
– For each SCLK capture edge, the SCLK counter is incremented and the data bit received on the SDI pin
is shifted in to the IDR.
– For each launch edge of the output clock (SCLK in this case), ODR data are shifted out on the selected
SDO-x pins.
– The status of the RVS pin depends on the output protocol selection (see the Protocols for Reading From
the Device section).
3. The host controller pulls CS high to end the data transfer frame. On the CS rising edge:
– The SDO-x pins go to Hi-Z.
– RVS goes high (after a delay of td_RVS).
– As illustrated in Figure 40, the 22-bit contents of the IDR are transferred to the command processor (see
Figure 34) for decoding and further action.
After pulling CS high, the host controller monitors for a low-to-high transition on the RVS pin, or waits for the
td_RVS time (see the Switching Characteristics table) to elapse before initiating a new operation (data transfer or
conversion). The delay, td_RVS, for any data transfer frame F varies based on the data transfer operation
executed in frame F.
At the end of data transfer frame F:
• If the SCLK counter is < 22, then the IDR captured less than 22 bits from the SDI. In this case, the device
treats frame F as a short command frame. At the end of a short command frame, the IDR is not updated and
the device treats the frame as a no operation (NOP) command.
• If the SCLK counter = 22, then the IDR captured exactly 22 bits from SDI. In this case, the device treats the
frame F as a optimal command frame. At the end of an optimal command frame, the command processor
decodes the 22-bit contents of the IDR as a valid command word.
• If the SCLK counter > 22, then the IDR captured more than 22 bits from the SDI; however, only the last 22
bits are retained. In this case, the device treats frame F as a long command frame. At the end of a long
command frame, the command processor treats the 22-bit contents of the IDR as a valid command word.
There is no restriction on the maximum number of clocks that can be provided within any data transfer frame
F. However, as explained above, make sure that the last 22 bits shifted into the device before the CS rising
edge constitute the desired command.
In a short command frame, the write operation to the device is invalidated; however, the output data bits
transferred during the short command frame are still valid output data. Therefore, the host controller can use
such shorter data transfer frames to read only the required number of MSB bits from the 22-bit output data word.
As shown in Figure 38, an optimal read frame for the ADS891xB devices must read only the 18 MSB bits of the
output data word. The length of an optimal read frame depends on the output protocol selection; see the
Protocols for Reading From the Device section for more details.
NOTE
The previous example shows data-read and data-write operations synchronous to the
external clock provided on the SCLK pin.
However, the device also supports data read operation synchronous to the internal clock;
see the Protocols for Reading From the Device section for more details. In this case, while
the ODR contents are shifted on the SDO (or SDOs) on the launch edge of the internal
clock, the device continues to capture the SDI data into the IDR (and increment the SCLK
counter) on SCLK capture edges.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
29
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.5.3 Interleaving Conversion Cycles and Data Transfer Frames
The host controller operates the device at the desired throughput by interleaving the conversion cycles and the
data transfer frames.
The cycle time of the device, tcycle, is the time difference between two consecutive CONVST rising edges
provided by the host controller. The response time of the device, tresp, is the time difference between the host
controller initiating conversion C, and the host controller receiving the complete result for conversion C.
Figure 41 shows three conversion cycles: C, C + 1, and C + 2. Conversion C is initiated by a CONVST rising
edge at time t = 0, and the conversion result becomes available for data transfer at tconv. However, this result is
loaded into the ODR only on the subsequent CS falling edge. This CS falling edge must be provided before the
completion of conversion C + 1 (that is, before tcycle + tconv).
To achieve the rated performance specifications, the host controller must make sure that no digital signals toggle
during the quiet acquisition time (tqt_acq) and quiet aperture time (td_cnvcap). Any noise during td_cnvcap may
negatively affect the result of the ongoing conversion, whereas any noise during tqt_acq may negatively affect the
result of the subsequent conversion.
Sample
S
Sample
S+1
Sample
S+2
tcycle
tconv
td_cnvcap
tacq
tqt_acq
CONVST
ADCST
(Internal)
Zone 1
Zone 2
Conversion
C
Conversion
C+1
Conversion
C+2
t=0
Figure 41. Data Transfer Zones
This architecture allows for two distinct time zones (zone 1 and zone 2) to transfer data for each conversion.
Zone 1 and zone 2 for conversion C are defined in Table 3.
Table 3. Data Transfer Zones Timing
ZONE
STARTING TIME
ENDING TIME
t conv
tcycle t qt_acq
Zone 1 for conversion C
Zone 2 for conversion C
tcycle
tcycle tcycle t qt_acq
t d_cnvcap
The response time includes the conversion time and the data transfer time, and thus is a function of the selected
data transfer zone.
30
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Figure 42 and Figure 43 illustrate interleaving of three conversion cycles (C, C + 1, and C + 2) with three data
transfer frames (F, F + 1, and F + 2) in zone 1 and in zone 2, respectively.
Sample
S
Sample
S+1
Sample
S+2
tcycle
tconv
td_cnvcap
tacq
tqt_acq
CONVST
ADCST
(Internal)
Zone 1
C
Zone 1
C+1
Zone 1
C+2
Conversion
C+1
Conversion
C
Conversion
C+2
Frame
F
Frame
F+1
Frame
F+2
CS
tread-Z1
tresp-Z1
SDO
C
C+1
C+2
SCLK
t=0
Figure 42. Zone 1 Data Transfer
Sample
S
Sample
S+1
Sample
S+2
tcycle
tconv
td_cnvcap
tacq
tqt_acq
CONVST
ADCST
(Internal)
Zone 2
C
Zone 2
C+1
Conversion
C
Conversion
C+1
Frame
F
Zone 2
C+2
Conversion
C+2
Frame
F+1
Frame
F+2
CS
tread-Z2
tresp-Z2
SDO
C±1
C
C+1
SCLK
t=0
Figure 43. Zone 2 Data Transfer
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
31
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
To achieve cycle time tcycle, the read time in zone 1 is given by Equation 5:
tread-Z1 d tcycle tconv t qt_acq
(5)
For an optimal data transfer frame, Equation 5 results in an SCLK frequency given by Equation 6:
18
fSCLK t
tread-Z1
(6)
Then, the zone 1 data transfer achieves a response time defined by Equation 7:
tresp-Z1-min tconv tread-Z1
(7)
At lower SCLK speeds, tread-Z1 increases, resulting in slower response times and higher cycle times.
To achieve the same cycle time, tcycle, the read time in zone 2 is given by Equation 8:
tread-Z2 d tcycle t d_cnvcap t qt_acq
(8)
For an optimal data transfer frame, Equation 8 results in an SCLK frequency given by Equation 9:
18
fSCLK t
tread_Z2
(9)
Then, the zone 2 data transfer achieves a response time defined by Equation 10:
tresp-Z2-min tcycle t d_cnvcap tread-Z2
(10)
Any increase in tread-Z2 increases response time and may increase cycle time.
For a given cycle time, the zone 1 data transfer clearly achieves faster response time, but also requires a higher
SCLK speed (as evident from Equation 5, Equation 6, and Equation 7); whereas, the zone 2 data transfer clearly
requires a lower SCLK speed but has a slower response time (as evident from Equation 8, Equation 9, and
Equation 10).
NOTE
In zone 2, the data transfer is active when the device is converting the next analog
sample. This digital activity can interfere with the ongoing conversion, and may cause
some degradation in SNR performance.
Additionally, a data transfer frame can begin in zone 1, and then extend into zone 2;
however, the host controller must make sure that no digital transitions occur during the
tqt_acq and td_cnvcap time intervals.
NOTE
For data transfer operations in zone 2 using the ADC-Clock-Master protocol
(SDO_MODE[1:0] = 11b), the device supports only the external-clock-echo option
(SSYNC_CLK_SEL[1:0] = 00b); see Table 9.
32
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.5.4 Data Transfer Protocols
This device family features a multiSPI digital interface that allows the host controller to operate at slower SCLK
speeds and still achieve the required throughput and response time. The multiSPI digital interface module offers
two options to reduce the SCLK speed required for data transfer:
• Increase the width of the output data bus.
• Enable double data rate (DDR) transfer.
These two options can be combined to achieve further reduction in SCLK speed.
Figure 44 shows the delays in the communication channel between the host controller and the device in a typical
serial communication.
Digital Isolator
(Optional)
Device
Host Controller
tpcb_CK
SCLK
SCLK
td_ckdo
tsu_h
td_ISO
SDO-x
td_ISO
SDI
tpcb_SDO
Figure 44. Delays in Serial Communication
For example, if tpcb_CK and tpcb_SDO are the delays introduced by the printed circuit board (PCB) traces for the
serial clock and SDO signals, td_CKDO is the clock-to-data delay of the device, td_ISO is the propagation delay
introduced by the digital isolator, and tsu_h is the setup time specification of the host controller, then the total
delay in the path is given by Equation 11:
t d_total_serial tpcb_CK t d_iso t d_ckdo t d_iso tpcb_SDO t su_h
(11)
In a standard SPI protocol, the host controller and the device launch and capture data bits on alternate SCLK
edges. Therefore, the td_total_serial delay must be kept to less than half of the SCLK duration. Equation 12 shows
the fastest clock allowed by the SPI protocol:
1
fclk-SPI d
2 u t d_total-serial
(12)
Larger values of the td_total_serial delay restricts the maximum SCLK speed for the SPI protocol, resulting in higher
read and response times, and can possibly limit the throughput.
Figure 45 shows a delay (td_delcap) introduced in the capture path (inside the host controller).
Digital Isolator
(Optional)
Device
Host Controller
tpcb_CK
SCLK
SCLK
td_ckdo
td_ISO
SDO-x
td_ISO
td_delcap
tsu_h
SDI
tpcb_SDO
Figure 45. Delayed Capture
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
33
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
The total delay in the path modifies to Equation 13:
t d_total_serial tpcb_CK t d_iso t d_ckdo t d_iso tpcb_SDO t su_h t d _ delcap
(13)
This reduction in total delay allows the SPI protocol to operate at higher clock speeds.
The multiSPI digital interface module offers two additional options to remove the restriction on the SCLK speed:
• Early data launch (EDL) mode of operation
In EDL mode, the device launches the output data on SDO-x pin (or pins) half a clock earlier compared to the
standard SPI protocol. Therefore, Equation 12 modifies to Equation 14:
1
fclk-SPI d
t d_total-serial
(14)
•
The reduction in total delay allows the serial interface to operate at higher clock speeds.
ADC-Clock-Master (source-synchronous) mode of operation
As illustrated in Figure 46, in ADC-Clock-Master mode, the device provides a synchronous output clock (on
the RVS pin) along with the output data (on the SDO-x pins).
Digital Isolator
(Optional)
Device
Host Controller
tpcb_CK
SCLK
SCLK
td_ckdo
SDO-x
td_ISO
td_ckstr
td_ISO
SDI
tsu_h
toff_strdo
tpcb_SDO
RVS
td_ISO
tpcb_RVS
Figure 46. Delays in ADC-Clock-Master (Source-Synchronous) Mode
For negligible values of toff_STRDO, the total delay in the path for a source-synchronous data transfer, is given
by Equation 15:
t d_total_srcsync tpcb_RVS tpcb_SDO t su_h
(15)
As shown by the difference between Equation 11 and Equation 15, using ADC-Clock-Master mode
completely eliminates the effect of isolator delays (td_ISO) and clock-to-data delays (td_CKDO); typically, the
largest contributors in the overall delay computation.
Furthermore, the actual values of tpcb_RVS and tpcb_SDO do not matter. In most cases, the td_total_srcsync delay
can be kept at a minimum by routing the RVS and SDO lines together on the PCB. Therefore, the ADCClock-Master mode allows the data transfer between the host controller and the device to operate at much
higher SCLK speeds.
34
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.5.4.1 Protocols for Configuring the Device
As shown in Table 4, the host controller can use any of the four legacy, SPI-compatible protocols (SPI-00-S, SPI01-S, SPI-10-S, or SPI-11-S) to write data to the device.
Table 4. SPI Protocols for Configuring the Device
SCLK PHASE
(Capture Edge)
SDI_CNTL
SDO_CNTL
NO. OF SCLK
(Optimal Command
Frame)
TIMING
DIAGRAM
Low
Rising
00h
00h
22
Figure 47
Low
Falling
01h
00h
22
Figure 48
SPI-10-S
High
Falling
02h
00h
22
Figure 49
SPI-11-S
High
Rising
03h
00h
22
Figure 50
PROTOCOL
SCLK POLARITY
(At CS Falling Edge)
SPI-00-S
SPI-01-S
At power-up or after coming out of any asynchronous reset, the device supports the SPI-00-S protocol for dataread and data-write operations.
To select a different SPI-compatible protocol, program the SDI_MODE[1:0] bits in the SDI_CNTL register. This
first write operation must adhere to the SPI-00-S protocol. Any subsequent data transfer frames must adhere to
the newly selected protocol.
Figure 47 to Figure 50 detail the four protocols using an optimal command frame; see the Timing Requirements
and Switching Characteristics tables for associated timing parameters.
NOTE
As explained in the Data Transfer Frame section, a valid write operation to the device
requires a minimum of 22 SCLKs to be provided within a data transfer frame.
Any data write operation to the device must continue to follow the SPI-compatible protocol
selected in the SDI_CNTL register, irrespective of the protocol selected for the data-read
operation.
CS
CS
SCLK
SCLK
SDI
B21
B20
B19
B1
B0
SDI
B21
B20
B1
B0
RVS
RVS
Figure 47. SPI-00-S Protocol, Optimal Command
Frame
Figure 48. SPI-01-S Protocol, Optimal Command
Frame
CS
CS
SCLK
SCLK
SDI
B21
B20
B19
B1
B0
RVS
SDI
B21
B20
B2
B1
B0
RVS
Figure 49. SPI-10-S Protocol, Optimal Command
Frame
Figure 50. SPI-11-S Protocol, Optimal Command
Frame
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
35
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.5.4.2 Protocols for Reading From the Device
The protocols for the data-read operation can be broadly classified into three categories:
1. Legacy, SPI-compatible (SPI-xy-S) protocol
2. SPI-compatible protocols with bus width options (SPI-xy-D and SPI-xy-Q)
3. Source-synchronous (SRC) protocols
7.5.4.2.1 Legacy, SPI-Compatible (SYS-xy-S) Protocols
As shown in Table 5, the host controller can use any of the four legacy, SPI-compatible protocols (SPI-00-S, SPI01-S, SPI-10-S, or SPI-11-S) to read data from the device.
Table 5. SPI Protocols for Reading From the Device
PROTOCOL
SCLK
POLARITY
(At CS Falling
Edge)
SCLK PHASE
(Capture Edge)
SPI-00-S
Low
Rising
MSB BIT
LAUNCH EDGE
SDI_CNTL
SDO_CNTL
NO. OF SCLK
(Optimal Read
Frame)
TIMING
DIAGRAM
CS falling
00h
00h
18
Figure 51
st
SPI-01-S
Low
Falling
1 SCLK rising
01h
00h
18
Figure 52
SPI-10-S
High
Falling
CS falling
02h
00h
18
Figure 53
SPI-11-S
High
Rising
1st SCLK falling
03h
00h
18
Figure 54
At power-up or after coming out of any asynchronous reset, the device supports the SPI-00-S protocol for dataread and data-write operations. To select a different SPI-compatible protocol for both the data transfer
operations:
1. Program the SDI_MODE[1:0] bits in the SDI_CNTL register. This first write operation must adhere to the SPI00-S protocol. Any subsequent data transfer frames must adhere to the newly selected protocol.
2. Set the SDO_MODE[1:0] bits = 00b in the SDO_CNTL register.
Figure 51 to Figure 54 explain the details of the four protocols using an optimal command frame to read all 22
bits of the output data word. Table 5 shows the number of SCLK required in an optimal read frame for the
different output protocol selections.
CS
D21
CS
D20
D19
D1
D21
D0
SCLK
D21
SDO-0
D20
D21
D19
D1
D20
D21
D0
D1
D0
RVS
SDO-0
D21
D21
D20
0
D20
D21
D19
D0
D20
D1
D0
Figure 52. SPI-01-S Protocol, 22 SCLKs
D19
D1
D21
D0
D20
D19
D1
D0
SCLK
D20
D21
D19
D20
D1
D0
D1
D21
D0
RVS
SDO-0
0
D20
D21
D20
D2
D1
D2
D0
D1
D0
RVS
Figure 53. SPI-10-S Protocol, 22 SCLKs
36
D0
CS
SCLK
SDO-0
D1
RVS
Figure 51. SPI-00-S Protocol, 22 SCLKs
CS
D20
SCLK
Submit Documentation Feedback
Figure 54. SPI-11-S Protocol, 22 SCLKs
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
For SDI_MODE[1:0] = 00b or 10b, the device supports an Early Data Launch (EDL) option. Set SDO_MODE[1:0]
= 01b in the SDO_CNTL register to enable the feature (see Table 6). Setting SDO_MODE[1:0] = 01b has no
effect if SDI_MODE[1:0] = 01b or 11b.
Table 6. SPI Protocols with Early Data Launch
SCLK POLARITY
(At CS Falling
Edge)
PROTOCOL
SCLK PHASE
(Capture Edge)
MSB BIT LAUNCH
EDGE
SDI_CNTL
SDO_CNTL
NO. OF SCLK
(Optimal Read
Frame)
TIMING
DIAGRAM
SPI-00-S-EDL
Low
Rising
CS falling
00h
01h
18
Figure 51
SPI-10-S-EDL
High
Falling
CS falling
02h
01h
18
Figure 53
As shown in Figure 55, and Figure 56, the device launches the output data bit on the SDO-0 pin half clock earlier
compared to the standard SPI protocol.
CS
D21
CS
D20
D19
D0
D18
SDO-0
D21
0
SCLK
D21
D20
D19
D1
D0
SCLK
D21
D20
D19
D1
D0
D21
D20
D19
D1
D0
RVS
D20
SDO-0
D21
D19
D20
D19
D18
D0
D1
D0
RVS
Figure 55. SPI-00-S-EDL Protocol, 22 SCLKs
Figure 56. SPI-10-S-EDL Protocol, 22 SCLKs
When using these SPI-compatible protocols, the RVS output remains low throughout the data transfer frame; see
the Timing Requirements and Switching Characteristics tables for associated timing parameters.
With SDO_CNTL[7:0] = 00h or 01h, if the host controller uses a long data transfer frame, the device exhibits
daisy-chain operation (see the Multiple Devices: Daisy-Chain Topology section).
NOTE
Use SPI-compatible protocols to execute the RD_REG, WR_REG, CLR_BITS, and
SET_BITS commands specified in Table 2.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
37
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.5.4.2.2 SPI-Compatible Protocols with Bus Width Options
The device provides an option to increase the SDO bus width from one bit (default, single SDO) to two bits (dual
SDO) or four bits (quad SDO) when operating with any of the four legacy, SPI-compatible protocols.
Set the SDO_WIDTH[1:0] bits in the SDO_CNTL register to select the SDO bus width. The SCLK launch edge
depends on the SPI protocol selection (as shown in Table 7).
Table 7. SPI-Compatible Protocols with Bus Width Options
PROTOCOL
SCLK
POLARITY
(At CS Falling
Edge)
SPI-00-D
Low
SPI-01-D
Low
SPI-10-D
High
SPI-11-D
High
SPI-00-Q
MSB BIT
LAUNCH EDGE
SDI_CNTL
SDO_CNTL
#SCLK
(Optimal Read
Frame)
TIMING
DIAGRAM
Rising
CS falling
00h
08h
9
Figure 57
Falling
First SCLK rising
01h
08h
9
Figure 58
Falling
CS falling
02h
08h
9
Figure 59
Rising
First SCLK falling
03h
08h
9
Figure 60
Low
Rising
CS falling
00h
0Ch
5
Figure 61
SPI-01-Q
Low
Falling
First SCLK rising
01h
0Ch
5
Figure 62
SPI-10-Q
High
Falling
CS falling
02h
0Ch
5
Figure 63
SPI-11-Q
High
Rising
First SCLK falling
03h
0Ch
5
Figure 64
SCLK PHASE
(Capture Edge)
In dual-SDO mode (SDO_WIDTH[1:0] = 10b), two bits of data are launched on the two SDO pins (SDO-0 and
SDO-1) on every SCLK launch edge.
In quad-SDO mode (SDO_WIDTH[1:0] = 11b), four bits of data are launched on the four SDO pins (SDO-0,
SDO-1, SDO-2, and SDO-3) on every SCLK launch edge.
CS
CS
SCLK
SCLK
SDO-1
D21
D19
D3
D1
SDO-1
0
D21
D19
D3
D1
SDO-0
D20
D18
D2
D0
SDO-0
0
D20
D18
D2
D0
RVS
RVS
Figure 57. SPI-00-D Protocol
Figure 58. SPI-01-D Protocol
CS
CS
SCLK
SCLK
SDO-1
D21
D19
D3
D1
SDO-1
0
D21
D19
D5
D3
D1
SDO-0
D20
D18
D2
D0
SDO-0
0
D20
D18
D4
D2
D0
RVS
RVS
Figure 59. SPI-10-D Protocol
38
Submit Documentation Feedback
Figure 60. SPI-11-D Protocol
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
CS
CS
SCLK
SCLK
SDO-3
D21
D17
D1
SDO-3
0
D21
D17
D5
D1
SDO-2
D20
D16
D0
SDO-2
0
D20
D16
D4
D0
SDO-1
D19
D15
0
SDO-1
0
D19
D15
D3
0
SDO-0
D18
D14
0
SDO-0
0
D18
D14
D2
0
RVS
RVS
Figure 61. SPI-00-Q Protocol
Figure 62. SPI-01-Q Protocol
CS
CS
SCLK
SCLK
SDO-3
D21
D17
D1
SDO-3
0
D21
D17
D5
D1
SDO-2
D20
D16
D0
SDO-2
0
D20
D16
D4
D0
SDO-1
D19
D15
0
SDO-1
0
D19
D15
D3
0
SDO-0
D18
D14
0
SDO-0
0
D18
D14
D2
0
RVS
RVS
Figure 63. SPI-10-Q Protocol
Figure 64. SPI-11-Q Protocol
For SDI_MODE[1:0] = 00b or 10b, the device supports an early data launch (EDL) option. Set SDO_MODE[1:0]
= 01b in the SDO_CNTL register to enable the feature (see Table 8). Setting SDO_MODE[1:0] = 01b has no
effect if SDI_MODE[1:0] = 01b or 11b.
Table 8. SPI Protocols with Early Data Launch
PROTOCOL
SCLK
POLARITY
(At CS Falling
Edge)
SCLK PHASE
(Capture Edge)
MSB BIT
LAUNCH EDGE
SDI_CNTL
SDO_CNTL
NO. OF SCLK
(Optimal Read
Frame)
TIMING
DIAGRAM
SPI-00-DEDL
Low
Rising
CS falling
00h
09h
9
Figure 57
SPI-10-DEDL
High
Falling
CS falling
02h
09h
9
Figure 59
SPI-00-QEDL
Low
Rising
CS falling
00h
0Dh
5
Figure 61
SPI-10-QEDL
High
Falling
CS falling
02h
0Dh
5
Figure 63
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
39
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
As shown in Figure 55, and Figure 56, the device launches the output data bits on the SDO-x pins half clock
earlier compared to the standard SPI protocol.
CS
CS
SCLK
SCLK
SDO-1
D21
D19
D17
D3
D1
SDO-1
D21
D19
D17
D3
D1
SDO-0
D20
D18
D16
D2
D0
SDO-0
D20
D18
D16
D2
D0
RVS
RVS
Figure 65. SPI-00-D-EDL Protocol
Figure 66. SPI-10-D-EDL Protocol
CS
CS
SCLK
SCLK
SDO-3
D21
D17
D1
SDO-3
D21
D17
D1
SDO-2
D20
D16
D0
SDO-2
D20
D16
D0
SDO-1
D19
D15
0
SDO-1
D19
D15
0
SDO-0
D18
D14
0
SDO-0
D18
D14
0
RVS
RVS
Figure 67. SPI-00-Q-EDL Protocol
Figure 68. SPI-10-Q-EDL Protocol
When using any of the SPI-compatible protocols, the RVS output remains low throughout the data transfer frame;
see the Timing Requirements and Switching Characteristics tables for associated timing parameters.
Figure 57 to Figure 68 illustrate how the wider data bus allows the host controller to read all 22 bits of the output
data word using shorter data transfer frames. Table 7 and Table 8 show the number of SCLK required in an
optimal read frame for the different output protocol selections.
NOTE
With SDO_CNTL[7:0] ≠ 00h or 01h, a long data transfer frame does not result in daisychain operation. On SDO pin (or pins), the 22 bits of output data word are followed by
zeros.
40
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.5.4.2.3 Source-Synchronous (SRC) Protocols
As described in the Data Transfer Protocols section, the multiSPI digital interface supports an ADC-Clock-Master
or a source-synchronous mode of data transfer between the device and host controller. In this mode, the device
provides an output clock that is synchronous with the output data. Furthermore, the host controller can also
select the output clock source, data bus width, and data transfer rate.
7.5.4.2.3.1 Output Clock Source Options with SRC Protocols
In all SRC protocols, the RVS pin provides the output clock. The device allows this output clock to be
synchronous to either the external clock provided on the SCLK pin or to the internal clock of the device.
Furthermore, this internal clock can be divided by a factor of two or four to lower the data rates.
As shown in Figure 69, set the SSYNC_CLK_SEL[1:0] bits in the SDO_CNTL register to select the output clock
source.
SCLK
OSC
00
INTCLK
01
Output Clock
10
INTCLK / 4
11
/2
/4
RVS
INTCLK / 2
SSYNC_CLK_SEL [1:0]
Figure 69. Output Clock Source Options With SRC Protocols
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
41
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.5.4.2.3.2 Bus Width Options With SRC Protocols
The device provides an option to increase the SDO bus width from one bit (default, single SDO) to two bits (dual
SDO) or to four bits (quad SDO) when operating with any of the SRC protocols. Set the SDO_WIDTH[1:0] bits in
the SDO_CNTL register to select the SDO bus width.
In dual-SDO mode (SDO_WIDTH[1:0] = 10b), two bits of data are launched on the two SDO pins (SDO-0 and
SDO-1) on every SCLK rising edge.
In quad-SDO mode (SDO_WIDTH[1:0] = 11b), four bits of data are launched on the four SDO pins (SDO-0,
SDO-1, SDO-2, and SDO-3) on every SCLK rising edge.
7.5.4.2.3.3 Output Data Rate Options With SRC Protocols
The device provides an option to transfer the data to the host controller at a single data rate (default, SDR) or at
a double data rate (DDR). Set the DATA_RATE bit in the SDO_CNTL register to select the data transfer rate.
In SDR mode (DATA_RATE = 0b), the RVS pin toggles from low to high, and the output data bits are launched
on the SDO pins on the output clock rising edge.
In DDR mode (DTA_RATE = 1b), the RVS pin toggles (from low-to-high or high-to-low), and the output data bits
are launched on the SDO pins on every output clock edge, starting with the first rising edge.
The device supports all 24 combinations of output clock source, bus width, and output data rate, as shown in
Table 9.
Table 9. SRC Protocol Combinations
SDO_CNTL
#OUTPUT CLOCK
(Optimal Read
Frame)
TIMING
DIAGRAM
SDR
03h
9
Figure 70
SDR
43h
9
SDR
83h
9
SDR
C3h
9
Dual
SDR
0Bh
9
Dual
SDR
4Bh
9
INTCLK / 2 (2)
Dual
SDR
8Bh
9
INTCLK / 4 (2)
Dual
SDR
CBh
9
SRC-EXT-QS
SCLK
Quad
SDR
0Fh
5
SRC-INT-QS
INTCLK (2)
Quad
SDR
4Fh
5
SRC-IB2-QS
INTCLK / 2 (2)
Quad
SDR
SRC-IB4-QS
INTCLK / 4 (2)
Quad
SDR
SRC-EXT-SD
SCLK
Single
DDR
SRC-INT-SD
INTCLK (2)
Single
DDR
SRC-IB2-SD
INTCLK / 2 (2)
Single
SRC-IB4-SD
INTCLK / 4 (2)
Single
SRC-EXT-DD
SCLK
SRC-INT-DD
INTCLK (2)
SRC-IB2-DD
SRC-IB4-DD
OUTPUT CLOCK
SOURCE
BUS WIDTH
OUTPUT DATA
RATE
SRC-EXT-SS
SCLK
Single
SRC-INT-SS
INTCLK (2)
Single
SRC-IB2-SS
INTCLK / 2 (2)
Single
SRC-IB4-SS
INTCLK / 4 (2)
Single
SRC-EXT-DS
SCLK
SRC-INT-DS
INTCLK (2)
SRC-IB2-DS
SRC-IB4-DS
PROTOCOL
SDI_CNTL
8Fh
5
CFh
5
13h
9
53h
9
DDR
93h
9
DDR
D3h
9
Dual
DDR
1Bh
5
Dual
DDR
5Bh
5
INTCLK / 2 (2)
Dual
DDR
9Bh
5
INTCLK / 4 (2)
Dual
DDR
DBh
5
SRC-EXT-QD
SCLK
Quad
DDR
1Fh
3
SRC-INT-QD
INTCLK (2)
Quad
DDR
5Fh
3
SRC-IB2-QD
INTCLK / 2 (2)
Quad
DDR
9Fh
3
SRC-IB4-QD
INTCLK / 4 (2)
Quad
DDR
DFh
3
(1)
(2)
42
00h, 01h,
02h, or 03h (1)
Figure 71
Figure 74
Figure 75
Figure 78
Figure 79
Figure 72
Figure 73
Figure 76
Figure 77
Figure 80
Figure 81
Any of the four values can be used; see the Protocols for Configuring the Device section for more information.
The device supports INTCLK, INTCLK / 2, and INTCLK / 4 options only for data transfer operations in zone 1. The EXTCLK option is
supported in zone 1 and zone 2; see Figure 41.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Figure 70 to Figure 81 show the details of various source synchronous protocols. Table 9 shows the number of
output clocks required in an optimal read frame for the different output protocol selections.
CS
CS
SCLK
SCLK
D21
SDO-0
D20
D21
D19
D20
D1
D0
D1
D2
D0
D21
D20
D1
D2
D0
RVS
RVS
Figure 70. SRC-EXT-SS: SRC, SCLK, Single SDO,
SDR
Figure 71. SRC-INT-SS: SRC, INTCLK, Single SDO,
SDR
CS
CS
D20
D2
D0
SCLK
SCLK
D21
SDO-0
SDO-0
D19
D21 D20
D1
D3
D2
D1
D0
SDO-0
D21 D20
D3
D2
D1
D0
RVS
RVS
Figure 72. SRC-EXT-SD: SRC, SCLK, Single SDO,
DDR
Figure 73. SRC-INT-SD: SRC, INTCLK, Single SDO,
DDR
CS
CS
SCLK
SCLK
SDO-1
D21
D19
D5
D3
D1
SDO-1
D21
D19
D5
D3
D1
SDO-0
D20
D18
D4
D2
D0
SDO-0
D20
D18
D4
D2
D0
RVS
RVS
Figure 74. SRC-EXT-DS: SRC, SCLK, Dual SDO,
SDR
Figure 75. SRC-INT-DS: SRC, INTCLK, Dual SDO,
SDR
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
43
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
CS
CS
SCLK
SCLK
SDO-1
D21 D19
D7
D5
D3
D1
SDO-1
D21 D19
D7
D5
D3
D1
SDO-0
D20 D18
D6
D4
D2
D0
SDO-0
D20 D18
D6
D4
D2
D0
RVS
RVS
Figure 76. SRC-EXT-DD: SRC, SCLK, Dual SDO,
DDR
Figure 77. SRC-INT-DD: SRC, INTCLK, Dual SDO,
DDR
CS
CS
SCLK
SCLK
SDO-3
D21
D17
D13
D9
D5
D1
SDO-3
D21
D17
D13
D9
D5
D1
SDO-2
D20
D16
D12
D8
D4
D0
SDO-2
D20
D16
D12
D8
D4
D0
SDO-1
D19
D15
D11
D7
D3
0
SDO-1
D19
D15
D11
D7
D3
0
SDO-0
D18
D14
D10
D6
D2
0
SDO-0
D18
D14
D10
D6
D2
0
RVS
RVS
Figure 78. SRC-EXT-QS: SRC, SCLK, Quad SDO,
SDR
Figure 79. SRC-INT-QS: SRC, INTCLK, Quad SDO,
SDR
CS
CS
SCLK
SCLK
SDO-3
D21
D17
D13
D9
D5
D1
SDO-3
D21
D17
D13
D9
D5
D1
SDO-2
D20
D16
D12
D8
D4
D0
SDO-2
D20
D16
D12
D8
D4
D0
SDO-1
D19
D15
D11
D7
D3
0
SDO-1
D19
D15
D11
D7
D3
0
SDO-0
D18
D14
D10
D6
D2
0
SDO-0
D18
D14
D10
D6
D2
0
RVS
RVS
Figure 80. SRC-EXT-QD: SRC, SCLK, Quad SDO,
DDR
44
Submit Documentation Feedback
Figure 81. SRC-INT-QD: SRC, INTCLK, Quad SDO,
DDR
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.5.5 Device Setup
The multiSPI digital interface and the device configuration registers offer multiple operation modes. This section
describes how to select the hardware connection topology to meet different system requirements.
7.5.5.1 Single Device: All multiSPI Options
Figure 82 shows the connections between a host controller and a single device in order to exercise all options
provided by the multiSPI digital interface.
DVDD
Isolation
(Optional)
RST
CONVST
CS
SCLK
SDI
Device
Host
Controller
SDO-0
SDO-1
SDO-2
SDO-3
RVS
Figure 82. MultiSPI Digital Interface, All Pins
7.5.5.2 Single Device: Minimum Pins for a Standard SPI Interface
Figure 83 shows the minimum-pin interface for applications using a standard SPI protocol.
DVDD
Isolation
(Optional)
RST
CONVST
(Optional)
(Optional)
CS
SCLK
SDI
Device
Host
Controller
SDO-0
SDO-1
SDO-2
SDO-3
RVS
(Optional)
Figure 83. SPI Interface, Minimum Pins
The CS, SCLK, SDI, and SDO-0 pins constitute a standard SPI port of the host controller. The CONVST pin is
tied to CS, and the RST pin is tied to DVDD. The SDO-1, SDO-2, and SDO-3 pins have no external connections.
The following features are also available:
• Control the CONVST pin independently to get additional timing flexibility.
• Control RST pin independently to add asynchronous reset functionality.
• Monitor the RVS pin for additional timing benefits.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
45
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.5.5.3 Multiple Devices: Daisy-Chain Topology
SDO
SDI
SDI
SCLK
CS
SCLK
Host Controller
Device 2
Device 1
RVS
SDO-0
SDI
SCLK
CS
CONVST
RVS
SDO-0
SDI
SCLK
CS
CONVST
RVS
SDO-0
CS
CONVST
Isolation
(Optional)
CONVST
A typical connection diagram showing multiple devices in a daisy-chain topology is shown in Figure 84.
Device N
Figure 84. Daisy-Chain Connections
The CONVST, CS, and SCLK inputs of all devices are connected together and controlled by a single CONVST,
CS, and SCLK pin of the host controller, respectively. The SDI input pin of the first device in the chain (Device 1)
is connected to the SDO pin of the host controller, the SDO-0 output pin of Device 1 is connected to the SDI
input pin of Device 2, and so on. The SDO-0 output pin of the last device in the chain (Device N) is connected to
the SDI pin of the host controller.
To operate multiple devices in a daisy-chain topology, the host controller sets the configuration registers in each
device with identical values and operates with any of the legacy, SPI-compatible protocols for data-read and
data-write operations (SDO_CNT[7:0] = 00h or 01h). With these configurations settings, the 22-bit ODR and 22bit IDR registers in each device collapse to form a single, 22-bit unified shift register (USR) per device, as shown
in Figure 85.
Host Controller
SDO
CONVST
CS
SCLK
SDI
22 Bits
SDI
DB
0
DB
1
22 Bits
DB
20
DB
21
SDO-0
SDI
DB
0
DB
1
22 Bits
DB
20
DB
21
SDO-0
SDI
DB
0
DB
1
DB
20
DB
21
Unified Shift Register (USR)
Unified Shift Register (USR)
Unified Shift Register (USR)
Device 1
Device 2
Device N
SDO-0
Figure 85. Unified Shift Register
46
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
All devices in the daisy-chain topology sample the respective device analog input signals on the CONVST rising
edge. The data transfer frame starts with a CS falling edge. On each SCLK launch edge, every device in the
chain shifts out the MSB of the respective USR on to the respective SDO-0 pin. On every SCLK capture edge,
each device in the chain shifts in data received on the respective SDI pin as the LSB bit of the respective USR.
Therefore, in a daisy-chain configuration, the host controller receives the data of Device N, followed by the data
of Device N – 1, and so on (MSB-first). On the CS rising edge, each device decodes the contents in the
respective USR, and takes appropriate action.
A typical timing diagram for three devices connected in daisy-chain topology using the SPI-00-S protocol is
shown in Figure 86.
CS
SCLK
1
2
21
22
23
24
43
44
45
46
65
66
Configuration Data Device 1
{SDO}HOST
{SDI}1
B65
B64
B45
B44
B43
B42
B23
B22
B21
B20
B1
B0
Configuration Data Device 2
{SDO-0}1
{SDI}2
{D21}1
{D20}1
{D1}1
{D0}1
B65
B64
B45
B44
B43
B42
B23
B22
Configuration Data Device 3
{SDO-0}2
{SDI}3
{D21}2
{D20}2
{D1}2
{D0}2
{D21}1
{SDO-0}3
{SDI}HOST
{D21}3
{D20}3
{D1}3
{D20}1
{D1}1
{D0}1
B65
Output Data ± Device 2
Output Data ± Device 3
{D0}3
{D21}2
{D20}2
{D1}2
B64
B45
B44
Output Data ± Device 1
{D0}2
{D21}1
{D20}1
{D1}1
{D0}1
Figure 86. Three-Device, Daisy-Chain Timing
In daisy-chain topology, the overall throughput of the system is proportionally reduced as more devices are
connected in the daisy-chain.
NOTE
For N devices connected in daisy-chain topology, an optimal data transfer frame must
contain 22 × N SCLK capture edges. For a longer data transfer frame (number of SCLK in
the frame > 22 × N), the host controller must appropriately align the configuration data for
each device before bringing CS high. A shorter data transfer frame (number of SCLK in
the frame < 22 × N) might result in an erroneous device configuration, and must be
avoided.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
47
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.5.5.4 Multiple Devices: Star Topology
A typical connection diagram showing multiple devices in a star topology is shown in Figure 87. The CONVST,
SDI, and SCLK inputs of all devices are connected together, and are controlled by a single CONVST, SDO, and
SCLK pin of the host controller, respectively. Similarly, the SDO output pin of all devices are tied together and
connected to the a single SDI input pin of the host controller. The CS input pin of each device is individually
controlled by separate CS control lines from the host controller.
Device 1
Device 2
RVS
SDO
SDI
SCLK
CS
CONVST
RVS
SDO
SDI
SCLK
CS
CONVST
RVS
SDO
SDI
SCLK
CS
CONVST
Isolation
(Optional)
Host Controller
Device N
Figure 87. Star-Topology Connection
The timing diagram for three devices connected in the star topology is shown in Figure 88. In order to avoid any
conflict related to multiple devices driving the SDO line at the same time, make sure that the host controller pulls
down the CS signal for only one device at any particular time.
SCLK
1
2
21
22
23
24
43
44
45
46
65
66
{CS}1
{CS}2
{CS}3
Configuration Data Device 1
{SDO}HOST
{SDI}1,2,3
{B21}1
{B20}1
{B1}1
Configuration Data Device 2
{B0}1
{B21}2
Output Data ± Device 1
{SDO-0}1,2,3
{SDI}HOST
{D21}1
{D20}1
{D1}1
{B20}2
{B1}2
Configuration Data Device 3
{B0}2
{B21}3
Output Data ± Device 2
{D0}1
{D21}2
{D20}2
{D1}2
{B20}3
{B1}3
{B0}3
Output Data ± Device 3
{D0}2
{D21}3
{D20}3
{D1}3
{D0}3
Figure 88. Three-Device, Star Connection Timing
48
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.6 Register Maps
7.6.1 Device Configuration and Register Maps
The device features nine configuration registers, mapped as described in Table 10.
Table 10. Configuration Registers Mapping
ADDRESS
REGISTER NAME
REGISTER DESCRIPTION
004h
PD_CNTL
Low-power modes control
008h
SDI_CNTL
SDI input protocol selection
00Ch
SDO_CNTL
SDO output protocol selection
010h
DATA_CNTL
Output data word configuration
014h
PATN_LSB
Eight least significant bits (LSB) of the output pattern
015h
PATN_MID
Eight middle bits of the output pattern
016h
PATN_MSB
Four most significant bits (MSB) of the output pattern
020h
OFST_CAL
Offset calibration
030h
REF_MRG
Reference margin
7.6.1.1 PD_CNTL Register (address = 04h) [reset = 00h]
This register controls the low-power modes offered by the device.
Figure 89. PD_CNTL Register
7
0
R-0b
6
0
R-0b
5
0
R-0b
4
0
R-0b
3
0
R-0b
2
PD_REFBUF
R/W-0b
1
PD_ADC
R/W-0b
0
0
R-0b
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 11. PD_CNTL Register Field Descriptions
Bit
Field
Type
Reset
Description
7-3
0
R
00000b
Reserved bits. Reads return 00000b.
2
PD_REFBUF
R/W
0b
This bit powers down the internal reference buffer.
0b = Internal reference buffer is powered up
1b = Internal reference buffer is powered down
1
PD_ADC
R/W
0b
This bit powers down the converter module.
0b = converter module is powered up
1b = converter module is powered down
0
0
R
0b
Reserved bits. Do not write. Reads return 0b.
To power-down the converter module, set the PD_ADC bit in the PD_CNTL register. The converter module
powers down on the rising edge of CS. To power-up the converter module, reset the PD_ADC bit in the
PD_CNTL register. The converter module starts to power-up on the rising edge of CS. Wait for tPU_ADC before
initiating any conversion or data transfer operation.
To power-down the internal reference buffer, set the PD_REFBUF bit in the PD_CNTL register. The internal
reference buffer powers down on the rising edge of CS. To power-up the internal reference buffer, reset the
PD_REFBUF bit in the PD_CNTL register. The internal reference buffer starts to power-up on the rising edge of
CS. Wait for tPU_REFBUF before initiating any conversion.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
49
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.6.1.2 SDI_CNTL Register (address = 008h) [reset = 00h]
This register selects the SPI protocol for writing data to the device.
Figure 90. SDI_CNTL Register
7
0
R-0b
6
0
R-0b
5
0
R-0b
4
0
R-0b
3
0
R-0b
2
0
R-0b
1
0
SDI_MODE[1:0]
R/W-00b
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 12. SDI_CNTL Register Field Descriptions
Bit
Field
Type
Reset
Description
7-2
0
R
000000b
Reserved bits. Do not write. Reads return 000000b.
1-0
SDI_MODE[1:0]
R/W
00b
These bits select the protocol for writing data into the device.
00b = Standard SPI with CPOL = 0 and CPHASE = 0
01b = Standard SPI with CPOL = 0 and CPHASE = 1
10b = Standard SPI with CPOL = 1 and CPHASE = 0
11b = Standard SPI with CPOL = 1 and CPHASE = 1
7.6.1.3 SDO_CNTL Register (address = 0Ch) [reset = 00h]
This register configures the protocol for reading data from the device.
Figure 91. SDO_CNTL Register
7
6
SSYNC_CLK_SEL[1:0]
R/W-00b
5
0
R-0b
4
DATA_RATE
R/W-0b
3
2
SDO_WIDTH[1:0]
R/W-00b
1
0
SDO_MODE[1:0]
R/W-00b
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 13. SDO_CNTL Register Field Descriptions
50
Bit
Field
Type
Reset
Description
7-6
SSYNC_CLK_SEL[1:0]
R/W
00b
These bits select the source and frequency of the clock for the ADCClock-Master mode, and are valid only if SDO_MODE[1:0] = 11b.
00b = External SCLK echo
01b = Internal clock (INTCLK)
10b = Internal clock / 2 (INTCLK / 2)
11b = Internal clock / 4 (INTCLK / 4)
5
0
R
0b
Reserved bit. Do not write. Reads return 0b.
4
DATA_RATE
R/W
0b
This bit is ignored if SDO_MODE[1:0] = 00b. When SDO_MODE[1:0] =
11b:
0b = SDOs are updated at single data rate (SDR) with respect to the
output clock
1b = SDOs are updated at double data rate (DDR) with respect to the
output clock
3-2
SDO_WIDTH[1:0]
R/W
00b
These bits set the width of the output bus.
0xb = Data are output only on SDO-0
10b = Data are output only on SDO-0 and SDO-1
11b = Data are output on SDO-0, SDO-1, SDO-2, and SDO-3
1-0
SDO_MODE[1:0]
R/W
00b
These bits select the protocol for reading data from the device.
00b = SDO follows the SPI protocol selected in the SDI_CNTL register
01b = SDO follows the SPI protocol selected in the SDI_CNTL register
but with Early Data Launch feature enabled. See Table 6.
10b = Invalid configuration, not supported by the device
11b = SDO follows the source-synchronous protocol
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.6.1.4 DATA_CNTL Register (address = 010h) [reset = 00h]
This register configures the contents of the 22-bit output data word (D[21:0]).
Figure 92. DATA_CNTL Register
7
0
R-0b
6
0
R-0b
5
0
R-0b
4
0
R-0b
3
2
1
PAR_EN
R/W-0b
FPAR_LOC[1:0]
R/W-00b
0
DATA_VAL
R/W-0b
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 14. DATA_CNTL Register Field Descriptions
Bit
Field
Type
Reset
Description
7-4
0
R
0000b
Reserved bits. Reads return 0000b.
3-2
FPAR_LOC[1:0]
R/W
00b
These bits control the data span for calculating the FTPAR bit (bit D[2] in
the output data word).
00b = D[2] reflects even parity calculated for 4 MSB
01b = D[2] reflects even parity calculated for 8 MSB
10b = D[2] reflects even parity calculated for 12 MSB
11b = D[2] reflects even parity calculated for 16 MSB
1
PAR_EN
R/W
0b
0b = Output data does not contain any parity information
D[3] = 0
D[2] = 0
1b = Parity information is appended to the LSB of the output data
D[3] = Even parity calculated on bits D[21:4]
D[2] = Even parity computed on selected number of MSB of D[21:4]
as per FPAR_LOC[1:0] setting
See Figure 39 for further details of parity computation.
0
DATA_VAL
R/W
0b
These bits control bits D[21:4] of the output data word.
0b = 18-bit conversion output
1b = 18-bit contents of the fixed-pattern registers
See PATN CNTL for more details.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
51
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.6.1.5 PATN_LSB Register (address = 014h) [reset = 00h]
This register controls the eight LSB of the output pattern when DATA_VAL = 1b; see Figure 96.
Figure 93. PATN_LSB Register
7
6
5
4
3
PATN_LSB_BITS
R/W-00000000b
2
1
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 15. PATN_LSB Register Field Descriptions
Bit
Field
Type
Reset
Description
7-0
PATN_LSB_BITS
R/W
00000000b
8 LSB of the output pattern
7.6.1.6 PATN_MID Register (address = 015h) [reset = 00h]
This register controls the middle eight bits of the output pattern when DATA_VAL = 1b; see Figure 96.
Figure 94. PATN_MID Register
7
6
5
4
3
PATN_MID_BITS
R/W-00000000b
2
1
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 16. PATN_MID Register Field Descriptions
Bit
Field
Type
Reset
Description
7-0
PATN_MID_BITS
R/W
00000000b
8 middle bits of the output pattern
7.6.1.7 PATN_MSB Register (address = 016h) [reset = 00h]
This register controls the four MSB of the output pattern when DATA_VAL = 1b; see Figure 96.
Figure 95. PATN_MSB Register
7
0
R-0b
6
0
R-0b
5
0
R-0b
4
0
R-0b
3
2
1
PATN_MSB_BITS
R/W-0000b
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 17. PATN_MSB Register Field Descriptions
Bit
Field
Type
Reset
Description
7-4
0
R
0000b
Reserved bits. Reads return 0000b.
3-0
PATN_MSB_BITS
R/W
0000b
4 MSB of the output pattern
18-bit pattern
DATA_PATN[17:0]
P17
P14
P13
P6
P5
P0
PATN_MSB[3:0]
PATN_MID[7:0]
PATN_LSB[7:2]
4-bits
8-bits
6-bits
Figure 96. DATA_PATN[17:0]
52
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
7.6.1.8 OFST_CAL Register (address = 020h) [reset = 00h]
This register selects the external reference range for optimal offset calibration.
Figure 97. OFST_CAL Register
7
0
R-0b
6
0
R-0b
5
0
R-0b
4
0
R-0b
3
0
R-0b
2
1
REF_SEL[2:0]
R/W-000b
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 18. OFST_CAL Register Field Descriptions
Bit
Field
Type
Reset
Description
7-3
0
R
00000b
Reserved bits. Reads return 00000b.
2-0
REF_SEL[2:0]
R/W
000b
These bits select the external reference range for optimal offset.
000b = Optimum offset calibration for VREF = 5.0 V
001b = Optimum offset calibration for VREF = 4.5 V
010b = Optimum offset calibration for VREF = 4.096 V
011b = Optimum offset calibration for VREF = 3.3 V
100b = Optimum offset calibration for VREF = 3.0 V
101b = Optimum offset calibration for VREF = 2.5 V
110b = Optimum offset calibration for VREF = 5.0 V
111b = Optimum offset calibration for VREF = 5.0 V
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
53
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
7.6.1.9 REF_MRG Register (address = 030h) [reset = 00h]
This register selects the margining to be added to or subtracted from the reference buffer output; see the
Reference Buffer Module section.
Figure 98. REF_MRG Register
7
0
R-0b
6
0
R-0b
5
EN_MARG
R/W-0b
4
3
2
REF_OFST[4:0]
R/W-00000b
1
0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 19. REF_MRG Register Field Descriptions
Bit
Field
Type
Reset
Description
7-6
0
R
00b
Reserved bits. Reads return 00b.
EN_MARG
R/W
0b
This bit enables margining feature.
0b = Margining is disabled
1b = Margining is enabled
REF_OFST[4:0]
R/W
00000b
These bits select the reference offset value as per Table 20.
5
4-0
Table 20. REF_OFST[4:0] settings
REF_OFST[4:0]
(1)
54
ΔVREFBUFOUT (typical (1))
00000b
0 mV
00001b
280 µV
00010b
580 µV
00011b
840 µV
00100b
1.12 mV
00101b
1.4 mV
00110b
1.68 mV
00111b
1.96 mV
01000b
2.24 mV
01001b
2.52 mV
01010b
2.8 mV
01011b
3.08 mV
01100b
3.36 mV
01101b
3.64 mV
01110b
3.92 mV
01111b
4.2 mV
10000b
–4.5 mV
10001b
–4.22 mV
10010b
–3.94 mV
10011b
–3.66 mV
10100b
–3.38 mV
10101b
–3.1 mV
10110b
–2.82 mV
10111b
–2.54 mV
11000b
–2.26 mV
11001b
–1.98 mV
11010b
–1.7 mV
11011b
–1.42 mV
11100b
–1.14 mV
11101b
–860 µV
11110b
–580 µV
11111b
–280 µV
The actual VREFBUFOUT value may vary by ±10% from Table 20
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
8 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.
8.1 Application Information
The two primary circuits required to maximize the performance of a high-precision, successive approximation
register (SAR), analog-to-digital converter (ADC) are the input driver and the reference driver circuits. This
section details some general principles for designing these circuits, followed by an application circuit designed
using the ADS891xB.
8.1.1 ADC Reference Driver
The external reference source must provide low-drift and very accurate voltage at the REFIN pin of the
ADS891xB. The output broadband noise of most references can be in the order of a few hundred μVRMS.
Therefore, to prevent any degradation in the noise performance of the ADC, appropriately filter the output of the
voltage reference by using a low-pass filter with a cutoff frequency of a few hundred hertz.
The internal reference buffer of the ADS891xB provides the dynamic load posed on the REFBUFOUT pin during
the conversion process. Decouple the REFBUFOUT pin with the REFM pin using the recommended CREFBUF and
RESR. See the Layout section for layout recommendations.
8.1.2 ADC Input Driver
The input driver circuit for a high-precision ADC mainly consists of two parts: a driving amplifier and a charge
kickback filter. The amplifier is used for signal conditioning of the input signal and the low output impedance of
the amplifier provides a buffer between the signal source and the switched capacitor inputs of the ADC. The
charge kickback filter helps attenuate the sampling charge injection from the switched-capacitor input stage of
the ADC, and band-limits the wideband noise contributed by the front-end circuit. Careful design of the front-end
circuit is critical to meet the linearity and noise performance of the ADS891xB.
8.1.2.1 Input Amplifier Selection
Selection criteria for the input amplifiers is highly dependent on the input signal type, as well as the performance
goals, of the data acquisition system. Some key amplifier specifications to consider when selecting an
appropriate amplifier to drive the inputs of the ADC are:
• Small-signal bandwidth. Select the small-signal bandwidth of the input amplifiers to be as high as possible
after meeting the power budget of the system. Higher bandwidth reduces the closed-loop output impedance
of the amplifier, thus allowing the amplifier to more easily drive the low cutoff-frequency RC filter (see the
Charge Kickback Filter section) at the inputs of the ADC. Higher bandwidth also minimizes the harmonic
distortion at higher input frequencies. In order to maintain the overall stability of the input driver circuit, select
the amplifier with a unity gain bandwidth (UGB) as described in Equation 16:
§
·
1
UGB t 4 u ¨
¸
© 2S u RFLT u CFLT ¹
(16)
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
55
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
Application Information (continued)
•
Noise. Noise contribution of the front-end amplifiers must be as low as possible to prevent any degradation in
SNR performance of the system. Generally, to make sure that the noise performance of the data acquisition
system is not limited by the front-end circuit, the total noise contribution from the front-end circuit must be
kept below 20% of the input-referred noise of the ADC. Noise from the input driver circuit is band-limited by
designing a low cutoff frequency RC filter, as explained in Equation 17.
§ V 1 _ AM P_ PP ·
¨
¸
NG u 2 u ¨ f
¸¸
6.6
¨
©
¹
2
en2 _ RM S u
S
uf
2
3 dB
d
1 VREF
u
u 10
5
2
§ SNR dB ·
¨
¸
20
©
¹
where:
•
•
•
•
•
V1 / f_AMP_PP is the peak-to-peak flicker noise in µV
en_RMS is the amplifier broadband noise density in nV/√Hz
f–3dB is the 3-dB bandwidth of the RC filter
NG is the noise gain of the front-end circuit that is equal to 1 in a buffer configuration
Distortion. Both the ADC and the input driver introduce distortion in a data acquisition block. To make sure
that the distortion performance of the data acquisition system is not limited by the front-end circuit, the
distortion of the input driver must be at least 10 dB less than the distortion of the ADC, as shown in
Equation 18.
THD AMP d THD ADC
•
56
(17)
10 dB
(18)
Settling Time. For dc signals with fast transients that are common in a multiplexed application, the input signal
must settle within an 18-bit accuracy at the device inputs during the acquisition time window. This condition is
critical to maintain the overall linearity performance of the ADC. Typically, amplifier data sheets specify the
output settling performance only up to 0.1% to 0.001%, which may not be sufficient for the desired 18-bit
accuracy. Therefore, always verify the settling behavior of the input driver by TINA-TI™ SPICE simulations
before selecting the amplifier.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
Application Information (continued)
8.1.2.2 Charge Kickback Filter
A RC filter at the input pins of the ADC filters the broadband noise from the front-end drive circuitry, and
attenuates the sampling charge injection from the switched-capacitor input stage of the ADC. A filter capacitor,
CFLT, is connected from each input pin of the ADC to the ground (as shown in Figure 99). This capacitor helps
reduce the sampling charge injection and provides a charge bucket to quickly charge the internal sample-andhold capacitors during the acquisition process. Generally, the value of this capacitor must be at least 20 times
the specified value of the ADC sampling capacitance. For the ADS891xB, the input sampling capacitance is
equal to 60 pF; therefore, keep CFLT greater than 1.2 nF. The capacitor must be a COG- or NPO-type because
these capacitor types have a high-Q, low-temperature coefficient, and stable electrical characteristics under
varying voltages, frequencies, and times.
RFLT
2.2
CFLT
10 nF
ADS89xxB
RFLT
2.2
CFLT
10 nF
Figure 99. Charge Kickback Filter Configuration
Driving capacitive loads can degrade the phase margin of the input amplifiers, thus making the amplifier
marginally unstable. To avoid amplifier stability issues, series isolation resistors (RFLT) are used at the output of
the amplifiers. A higher value of RFLT helps with amplifier stability, but adds distortion as a result of interactions
with the nonlinear input impedance of the ADC. Distortion increases with source impedance, input signal
frequency, and input signal amplitude. Therefore, the selection of RFLT requires balancing the stability and
distortion of the design. For the ADS891xB, limit the value of RFLT to a maximum of 2.5-Ω in order to avoid any
significant degradation in linearity performance. Keep the tolerance of the selected resistors less than 1% to keep
the inputs balanced.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
57
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
8.2 Typical Application
Design an application circuit optimized for using the ADS891xB to achieve:
• > 101-dB SNR, < –120-dB THD,
• < ±1-LSB linearity, and
• Maximum-specified throughput
ADS89xxB
5V
1k
VIN
1 F
REFIN
VOUT
REF5045
0.1
GND
10 F
REFBUFOUT
BUF
10 F
0.1
22 F
REFM
5V
RVDD
1 nF
1 F
1k
1 F
5V
DECAP
LDO
1k
2.2
10 nF
VCM
1.12 V
OPA2625
ADC
10 nF
2.2
GND
1k
1k
1 nF
Figure 100. Differential-Input Data Acquisition Circuit for Lowest Distortion and Noise Using the
ADS891xB
8.2.1 Design Requirements
For this design example, use the parameters listed in Table 21 as the input parameters.
Table 21. Design Parameters
58
DESIGN PARAMETER
EXAMPLE VALUE
Power supply
5V
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
8.2.2 Detailed Design Procedure
The application circuit is illustrated in Figure 100. For simplicity, power-supply decoupling capacitors are not
shown in these circuit diagrams; see the Power-Supply Recommendations section for suggested guidelines.
The reference voltage of 4.5 V in this design is generated by the high-precision, low-noise REF5045 circuit. The
output broadband noise of the reference is heavily filtered by a low-pass filter with a 3-dB cutoff frequency of 16
Hz.
The input signal is processed through the OPA2625 (a high-bandwidth, low-distortion, high-precision amplifier in
an inverting gain configuration) and a low-pass RC filter before being fed into the ADC. Generally, the distortion
from the input driver must be at least 10 dB less than the ADC distortion. The distortion resulting from variation in
the common-mode signal is eliminated by using the OPA2625 in an inverting gain configuration. The low-power
OPA2625 as an input driver provides exceptional ac performance because of its extremely low-distortion and
high-bandwidth specifications. To exercise the complete dynamic range of the device, the common-mode voltage
at the ADS891xB inputs is established at a value of 2.25 V (4.5 V / 2) by using the noninverting pins of the
OPA2625 amplifiers.
In addition, the components of the charge kickback filter keep the noise from the front-end circuit low without
adding distortion to the input signal. For a complete schematic, see the ADS8910BEVM-PDK user's guide
located in the ADS8910B SAR Analog to Digital Converter Evaluation Module web folder at www.ti.com.
The same circuit is used in reference design TIPD211, a step-by-step process to design a 18-Bit, 1-MSPS, 4-Ch
Small Form Factor Design for Test and Measurement Applications using four ADS8910B SAR ADCs, four
OPA2625 precision amplifiers and one REF5050 precision reference.
For step-by-step design procedure, circuit schematics, bill of materials, PCB files, simulation results, and test
results, refer to TI Precision Design TIPD211, 18-Bit, 1-MSPS, 4-Ch Small Form Factor Design for Test and
Measurement Applications (TIDUBW7).
8.2.3 Application Curves
0.5
0
0.3
-40
0.2
Power (dB)
Integral Nonlinearity (LSB)
0.4
0.1
0
-0.1
-80
-120
-0.2
-0.3
-160
-0.4
-0.5
-131072
-200
131071
ADC Output Code
18-bit NMC DNL, ±0.3-LSB INL
Figure 101. Typical Linearity
D009
0
100
200
300
fIN, Input Frequency ( kHz)
400
500
D011
101.2-dB SNR, –124-dB THD
Figure 102. Noise-Performance FFT Plot
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
59
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
9 Power-Supply Recommendations
The devices have two separate power supplies: RVDD and DVDD. The internal reference buffer and the internal
LDO operate on RVDD. The ADC core operates on the LDO output (available on the DECAP pins). DVDD is used
for the interface circuits. RVDD and DVDD can be independently set to any value within their permissible ranges.
The RVDD supply voltage value defines the permissible range for the external reference voltage VREF on REFIN
pin as:
2.5 V ≤ VREF ≤ (RVDD – 0.3) V
(19)
In other words, to use the external reference voltage of VREF, set RVDD so that:
3 V ≤ RVDD ≤ (VREF + 0.3) V
(20)
Place a 10-µF decoupling capacitor between the RVDD and GND pins, and between the DVDD and GND pins,
as shown in Figure 103. Use a minimum 1-µF decoupling capacitor between the DECAP pins and the GND pin.
ADS89xxB
RVDD
BUF
RVDD
DECAP
LDO
DVDD
10 F
1 F
ADC
DVDD
GND
10 µF
Figure 103. Power-Supply Decoupling
60
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
10 Layout
10.1 Layout Guidelines
This section provides some layout guidelines for achieving optimum performance with the ADS891xB device
family.
10.1.1 Signal Path
As illustrated in Figure 104, the analog input signals are routed in opposite directions to the digital connections.
The reference decoupling components are kept away from the switching digital signals. This arrangement
prevents noise generated by digital switching activity from coupling to sensitive analog signals.
10.1.2 Grounding and PCB Stack-Up
Low inductance grounding is critical for achieving optimum performance. Grounding inductance is kept below 1
nH with 15-mil grounding vias and a printed circuit board (PCB) layout design that has at least four layers. Place
all critical components of the signal chain on the top layer with a solid analog ground from subsequent inner
layers to minimize via length to ground.
For lowest inductance grounding, connect the GND pins of the ADS891xB (pin 11 and pin 15) directly to the
device thermal pad and place at least four 8-mil grounding vias on the device thermal pad.
10.1.3 Decoupling of Power Supplies
Place the decoupling capacitors on RVDD, the LDO output, and DVDD within 20 mil from the respective pins, and
use a 15-mil via to ground from each capacitor. Avoid placing vias between any supply pin and the respective
decoupling capacitor.
10.1.4 Reference Decoupling
Dynamic currents are also present at the REFBUFOUT and REFM pins during the conversion phase, and
excellent decoupling is required to achieve optimum performance. Place a 22-μF, X7R-grade, ceramic capacitor
with at least 10-V rating and an ESR of 1-Ω between the REFBUFOUT and the REFM pins, as illustrated in
Figure 104. Select 0603- or 0805-size capacitors to keep equivalent series inductance (ESL) low. Connect the
REFM pins to the decoupling capacitor before a ground via.
10.1.5 Differential Input Decoupling
Dynamic currents are also present at the differential analog inputs of the ADS891xB. Use C0G- or NPO-type
capacitors to decouple these inputs because with these type of capacitors, capacitance stays almost constant
over the full input voltage range. Lower-quality capacitors (such as X5R and X7R) have large capacitance
changes over the full input-voltage range that may cause degradation in the performance of the device.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
61
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
External
Reference
10.2 Layout Example
REFM
GND
External
Reference
Input
CREFBUF
Reference
Decoupling
RESR
GND
REFIN
REFBUFOUT
RST
1
GND
CS
7
GND
CONVST
GND
SCLK
SDI
AINP
RVS
AINM
GND
SDO-0
13
19
+
SDO-1
SDO-2
Differential
Analog Input
SDO-3
Digital Inputs
and Outputs
GND
GND
RVDD
Analog Input
DVDD
-
GND
GND
Power Supply
Figure 104. Recommended Layout
62
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
ADS8910B
ADS8912B
ADS8914B
www.ti.com
SBAS707A – JUNE 2016 – REVISED JULY 2016
11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
For related documentation see the following:
• ADS8910BEVM-PDK User's Guide (SBAU268)
• 18-Bit, 1-MSPS, 4-Ch Small Form Factor Design for Test and Measurement Applications Reference Design
(TIDUBW7)
• OPAx625 High-Bandwidth, High-Precision, Low THD+N, 16-Bit and 18-Bit Analog-to-Digital Converter (ADC)
Drivers Data Sheet (SBOS688)
• REF5050 Low-Noise, Very Low Drift, Precision Voltage Reference Data Sheet (SBOS410)
11.2 Related Links
The following table lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 22. Related Links
PARTS
PRODUCT FOLDER
SAMPLE & BUY
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
ADS8910B
Click here
Click here
Click here
Click here
Click here
ADS8912B
Click here
Click here
Click here
Click here
Click here
ADS8914B
Click here
Click here
Click here
Click here
Click here
11.3 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.
11.4 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.
11.5 Trademarks
multiSPI, TINA-TI, E2E are trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
11.6 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.
11.7 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
Submit Documentation Feedback
63
ADS8910B
ADS8912B
ADS8914B
SBAS707A – JUNE 2016 – REVISED JULY 2016
www.ti.com
12 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.
64
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: ADS8910B ADS8912B ADS8914B
PACKAGE OPTION ADDENDUM
www.ti.com
13-Jul-2016
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)
ADS8910BRGER
ACTIVE
VQFN
RGE
24
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 125
8910B
ADS8910BRGET
ACTIVE
VQFN
RGE
24
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 125
8910B
ADS8912BRGER
PREVIEW
VQFN
RGE
24
3000
TBD
Call TI
Call TI
-40 to 125
ADS8912BRGET
PREVIEW
VQFN
RGE
24
250
TBD
Call TI
Call TI
-40 to 125
ADS8914BRGER
PREVIEW
VQFN
RGE
24
3000
TBD
Call TI
Call TI
-40 to 125
ADS8914BRGET
PREVIEW
VQFN
RGE
24
250
TBD
Call TI
Call TI
-40 to 125
(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)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(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.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
13-Jul-2016
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 2
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation
www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom
www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2016, Texas Instruments Incorporated