Burr-Brown ADS8402 16-bit, 1.25 msps, unipolar differential input, micro power sampling analog-to-digital converter with parallel interface and reference Datasheet

ADS8402
SLAS154B – DECEMBER 2002 – REVISED MAY 2003
16-BIT, 1.25 MSPS, UNIPOLAR DIFFERENTIAL INPUT, MICRO POWER SAMPLING
ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
FEATURES
APPLICATIONS
D DWDM
D Instrumentation
D High-Speed, High-Resolution, Zero Latency
D 1.25-MHz Sample Rate
D 16-Bit NMC Ensured Over Temperature
Data Acquisition Systems
D Zero Latency
D Onboard Reference
D Transducer Interface
D Medical Instruments
D Communication
D Onboard Reference Buffer
DESCRIPTION
D High-Speed Parallel Interface
The ADS8402 is a 16-bit, 1.25 MHz A/D converter with an
internal 4.096-V reference. The device includes a 16-bit
capacitor-based SAR A/D converter with inherent sample
and hold. The ADS8402 offers a full 16-bit interface and an
8-bit option where data is read using two 8-bit read cycles.
D Unipolar Differential Input Range: Vref to –Vref
D Power Dissipation: 155 mW at 1.25 MHz Typ
D Wide Digital Supply
D 8-/16-Bit Bus Transfer
The ADS8402 has a unipolar differential input. It is
available in a 48-lead TQFP package and is characterized
over the industrial –40°C to 85°C temperature range.
D 48-Pin TQFP Package
SAR
+IN
–IN
+
_
Output
Latches
and
3-State
Drivers
CDAC
BYTE
16-/8-Bit
Parallel DATA
Output Bus
Comparator
RESET
REFIN
REFOUT
4.096-V
Internal
Reference
Clock
Conversion
and
Control Logic
CONVST
BUSY
CS
RD
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date. Products
conform to specifications per the terms of Texas Instruments standard warranty.
Production processing does not necessarily include testing of all parameters.
Copyright  2002–2003, Texas Instruments Incorporated
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during
storage or handling to prevent electrostatic damage to the MOS gates.
ORDERING INFORMATION
MODEL
MAXIMUM
INTEGRAL
LINEARITY
(LSB)
ADS8402I
ADS8402IB
MAXIMUM
DIFFERENTIAL
LINEARITY
(LSB)
±6
±3 5
±3.5
–2~+3
2 3
–1~+2
1 2
NO
MISSING
CODES
RESOLUTION (BIT)
PACKAGE
TYPE
15
48 Pin
TQFP
16
48 Pin
TQFP
PACKAGE
DESIGNATOR
TEMPERATURE
RANGE
PFB
–40 C to
–40°C
85°C
PFB
–40 C to
–40°C
85°C
ORDERING
INFORMATION
TRANSPORT
MEDIA
QUANTITY
ADS8402IPFBT
Tape and
reel 250
ADS8402IPFBR
Tape and
reel 1000
ADS8402IBPFBT
Tape and
reel 250
ADS8402IBPFBR
Tape and
reel 1000
NOTE: For the most current specifications and package information, refer to our website at www.ti.com.
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range unless otherwise noted(1)
UNIT
+IN to AGND
Voltage
Voltage range
+VA + 0.1 V
–IN to AGND
+VA + 0.1 V
+VA to AGND
–0.3 V to 7 V
+VBD to BDGND
–0.3 V to 7 V
+VA to +VBD
–0.3 V to 2.5 V
Digital input voltage to BDGND
–0.3 V to +VBD + 0.3 V
Digital output voltage to BDGND
–0.3 V to +VBD + 0.3 V
Operating free-air temperature range, TA
–40°C to 85°C
Storage temperature range, Tstg
–65°C to 150°C
Junction temperature (TJ max)
Power dissipation
TQFP package
θJA thermal impedance
Vapor phase (60 sec)
Lead temperature,
temperature soldering
Infrared (15 sec)
150°C
(TJMax – TA)/θJA
86°C/W
215°C
220°C
(1) Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
2
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
SPECIFICATIONS
TA = –40°C to 85°C, +VA = 5 V, +VBD = 3 V or 5 V, Vref = 4.096 V, fSAMPLE = 1.25 MHz (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Analog Input
Full-scale input voltage (see Note 1)
+IN – –IN
Absolute input voltage
Common-mode input range
+IN
–Vref
–0.2
–IN
–0.2
ADS8402I
(Vref/2) – 0.2
Input capacitance
Input leakage current
Vref
Vref + 0.2
Vref + 0.2
Vref/2
25
(Vref/2) + 0.2
V
V
V
pF
0.5
nA
16
Bits
System Performance
Resolution
No missing codes
ADS8402I
15
ADS8402IB
16
–6
±2.5
6
–3.5
±2
3.5
ADS8402I
–2
±1
3
ADS8402IB
–1
±0.75
2
ADS8402I
Integral linearity (see Notes 2 and 3)
Differentiallinearity
Differential
linearity
ADS8402IB
ADS8402I
Offset error (see Note 4)
ADS8402IB
ADS8402I
Gain error (see Notes 4 and 5)
Common mode rejection ratio
Common-mode
ADS8402IB
LSB
LSB
–3
±1
3
mV
–1.5
±0.5
1.5
mV
–0.15
0.15
–0.098
0.098
At dc (±0.2 V around Vref/2)
80
+IN – –IN = 1 Vpp at 1 MHz
80
Noise
DC Power supply rejection ratio
Bits
At 7FFFh output code,
+VA = 4.75 V to 5.25 V,
Vref = 4.096 V, See Note 4
%FS
dB
60
µV RMS
1
LSB
Sampling Dynamics
Conversion time
Acquisition time
ns
1.25
MHz
150
ns
Throughput rate
Aperture delay
610
2
ns
Aperture jitter
25
ps
Step response
100
ns
100
ns
Overvoltage recovery
(1) Ideal input span, does not include gain or offset error.
(2) LSB means least significant bit
(3) This is endpoint INL, not best fit
(4) Measured relative to an ideal full-scale input (+IN – –IN) of 8.192 V
(5) This specification does not include the internal reference voltage error and drift.
3
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
SPECIFICATIONS (CONTINUED)
TA = –40°C to 85°C, +VA = +5 V, +VBD = 3 V or 5 V, Vref = 4.096 V, fSAMPLE = 1.25 MHz (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Dynamic Characteristics
Total harmonic distortion (THD) (see Note 1)
Signal-to-noise ratio (SNR)
Signal-to-noise + distortion (SINAD)
Spurious free dynamic range (SFDR)
VIN = 8 Vpp at 100 kHz
VIN = 8 Vpp at 100 kHz
–95
dB
90
dB
VIN = 8 Vpp at 100 kHz
VIN = 8 Vpp at 100 kHz
88
dB
95
dB
5
MHz
–3dB Small signal bandwidth
External Voltage Reference Input
Reference voltage at REFIN, Vref
2.5
Reference resistance (see Note 2)
4.096
4.2
500
V
kΩ
Internal Reference Output
Internal reference start-up time
From 95% (+VA), with 1 µF
storage capacity
4.065
4.096
120
ms
4.13
V
Vref range
Source Current
IOUT = 0
Line Regulation
+VA = 4.75 ~ 5.25 V
0.6
mV
Drift
IOUT = 0
36
PPM/C
Static load
10
µA
Digital Input/Output
CMO
S
Logic family
L i level
Logic
l
l
VIH
VIL
IIH = 5 µA
IIL = 5 µA
VOH
VOL
IOH = 2 TTL loads
IOL = 2 TTL loads
+VBD–1
+VBD + 0.3
–0.3
0.8
+VBD – 0.6
+VBD
0
0.4
V
2’s
Complement
Data format
Power Supply Requirements
P
Power
supply
l voltage
lt
+VBD (see Notes 3 and 4)
2.95
3.3
5.25
V
+VA (see Note 4)
4.75
5
5.25
V
31
34
+VA Supply current (see Note 5)
Power dissipation (see Note 5)
fs = 1.25 MHz
fs = 1.25 MHz
155
mA
mW
Temperature Range
Operating free-air
–40
85
(1) Calculated on the first nine harmonics of the input frequency
(2) Can vary ±20%
(3) The difference between +VA and +VBD should not be less than 2.3 V, i.e., if +VA is 5.25 V, +VBD should be minimum of 2.95 V.
(4) +VBD ≥ +VA – 2.3 V
(5) This includes only VA+ current. +VBD current is typically 1 mA with 5 pF load capacitance on output pins.
4
°C
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
TIMING CHARACTERISTICS
All specifications typical at –40°C to 85°C, +VA = +VBD = 5 V (see Notes 1, 2, and 3)
PARAMETER
tCONV
tACQ
Conversion time
tpd1
tpd2
CONVST low to conversion started (BUSY high)
tw1
tsu1
Pulse duration, CONVST low
tw2
Pulse duration, CONVST high
Acquisition time
MIN
TYP
MAX
UNIT
600
610
ns
150
Propagation delay time, End of conversion to BUSY low
Setup time, CS low to CONVST low
th1
Pulse duration, BUSY signal low
20
ns
ns
0
ns
20
ns
10
Min(tACQ)
Pulse duration, BUSY signal high
Hold time, First data bus data transition (RD low, or CS low for read cycle, or BYTE input
changes) after CONVST low
ns
20
CONVST falling edge jitter
tw3
tw4
ns
35
ps
ns
630
ns
40
ns
0
ns
0
ns
50
ns
td1
tsu2
Delay time, CS low to RD low
tw5
ten
Pulse duration, RD low time
td2
td3
Delay time, data hold from RD high
0
Delay time, BYTE rising edge or falling edge to data valid
2
tw6
th2
RD high
20
ns
Hold time, last RD (or CS for read cycle ) rising edge to CONVST falling edge
50
ns
tpd4
tsu3
Propagation delay time, BUSY falling edge to next RD (or CS for read cycle) falling edge
Max(td5)
0
ns
th3
Hold time, BYTE falling edge to RD falling edge
0
ns
tdis
Disable time, RD High (CS high for read cycle) to 3-stated data bus
Setup time, RD high to CS high
Enable time, RD low (or CS low for read cycle) to data valid
Setup time, BYTE rising edge to RD falling edge
20
td5
Delay time, BUSY low to MSB data valid
(1) All input signals are specified with tr = tf = 5 ns (10% to 90% of +VBD) and timed from a voltage level of (VIL + VIH)/2.
(2) See timing diagrams.
(3) All timings are measured with 20 pF equivalent loads on all data bits and BUSY pins.
ns
ns
20
ns
ns
20
ns
0
ns
5
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
TIMING CHARACTERISTICS
All specifications typical at –40°C to 85°C, +VA = 5 V, +VBD = 3 V (see Notes 1, 2, and 3)
PARAMETER
tCONV
tACQ
Conversion time
tpd1
tpd2
CONVST low to conversion started (BUSY high)
tw1
tsu1
Pulse duration, CONVST low
tw2
Pulse duration, CONVST high
Acquisition time
MIN
TYP
MAX
UNIT
600
610
ns
150
Propagation delay time, end of conversion to BUSY low
Setup time, CS low to CONVST low
th1
Pulse duration, BUSY signal low
20
ns
ns
0
ns
20
ns
10
Min(tACQ)
Pulse duration, BUSY signal high
Hold time, first data bus transition (RD low, or CS low for read cycle, or BYTE or BUS
16/16 input changes) after CONVST low
ns
20
CONVST falling edge jitter
tw3
tw4
ns
40
ps
ns
630
ns
40
ns
0
ns
0
ns
50
ns
td1
tsu2
Delay time, CS low to RD low
tw5
ten
Pulse duration, RD low
td2
td3
Delay time, data hold from RD high
0
Delay time, BUS16/16 or BYTE rising edge or falling edge to data valid
2
tw6
th2
Pulse duration, RD high time
20
ns
Hold time, last RD (or CS for read cycle ) rising edge to CONVST falling edge
50
ns
tpd4
tsu3
Propagation delay time, BUSY falling edge to next RD (or CS for read cycle) falling edge
Max(td5)
ns
Setup time, BYTE rising edge to RD falling edge
0
ns
th3
Hold time, BYTE falling edge to RD falling edge
0
ns
tdis
Disable time, RD High (CS high for read cycle) to 3-stated data bus
Setup time, RD high to CS high
Enable time, RD low (or CS low for read cycle) to data valid
30
td5
Delay time, BUSY low to MSB data valid delay time
(1) All input signals are specified with tr = tf = 5 ns (10% to 90% of +VBD) and timed from a voltage level of (VIL + VIH)/2.
(2) See timing diagrams.
(3) All timings are measured with 10 pF equivalent loads on all data bits and BUSY pins.
6
ns
ns
30
ns
30
ns
0
ns
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
PIN ASSIGNMENTS
BUSY
BDGND
+VBD
DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
BDGND
PFB PACKAGE
(TOP VIEW)
36 35 34 33 32 31 30 29 28 27 26 25
37
24
38
23
39
22
40
21
41
20
42
19
43
18
44
17
45
16
46
15
47
14
48
3
4 5
6 7 8
13
9 10 11 12
REFIN
REFOUT
NC
+VA
AGND
+IN
–IN
AGND
+VA
+VA
1 2
+VBD
DB8
DB9
DB10
DB11
DB12
DB13
DB14
DB15
AGND
AGND
+VA
AGND
AGND
+VBD
RESET
BYTE
CONVST
RD
CS
+VA
AGND
AGND
+VA
REFM
REFM
NC – No connection
7
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
TERMINAL FUNCTIONS
NAME
AGND
BDGND
NO.
I/O
5, 8, 11, 12,
14, 15, 44, 45
–
Analog ground
DESCRIPTION
25, 35
–
Digital ground for bus interface digital supply
BUSY
36
O
Status output. High when a conversion is in progress.
BYTE
39
I
Byte select input. Used for 8-bit bus reading.
0: No fold back
1: Low byte D[7:0] of the 16 most significant bits is folded back to high byte of the 16 most significant
pins DB[15:8].
CONVST
40
I
Convert start
CS
42
I
Chip select
8-Bit Bus
D t B
Data
Bus
BYTE = 0
16-Bit Bus
BYTE = 1
BYTE = 0
DB15
16
O
D15 (MSB)
D7
D15 (MSB)
DB14
17
O
D14
D6
D14
DB13
18
O
D13
D5
D13
DB12
19
O
D12
D4
D12
DB11
20
O
D11
D3
D11
DB10
21
O
D10
D2
D10
DB9
22
O
D9
D1
D9
DB8
23
O
D8
D0 (LSB)
D8
DB7
26
O
D7
All ones
D7
DB6
27
O
D6
All ones
D6
DB5
28
O
D5
All ones
D5
DB4
29
O
D4
All ones
D4
DB3
30
O
D3
All ones
D3
DB2
31
O
D2
All ones
D2
DB1
32
O
D1
All ones
D1
DB0
33
O
D0 (LSB)
All ones
D0 (LSB)
–IN
7
I
Inverting input channel
+IN
6
I
Non inverting input channel
NC
3
–
No connection
REFIN
1
I
Reference input
REFM
47, 48
I
Reference ground
REFOUT
2
O
Reference output. Add 1 µF capacitor between the REFOUT pin and REFM pin when internal reference
is used.
RESET
38
I
Current conversion is aborted and output latches are cleared (set to zeros) when this pin is asserted low.
RESET works independantly of CS.
RD
41
I
Synchronization pulse for the parallel output.
+VA
4, 9, 10, 13,
43, 46
–
Analog power supplies, 5-V dc
24, 34, 37
–
Digital power supply for bus
+VBD
8
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
TIMING DIAGRAMS
tw2
tw1
CONVST
tpd1
tpd2
tw4
tw3
BUSY
tsu1
CS
CONVERT†
t(CONV)
t(CONV)
SAMPLING†
(When CS Toggle)
t(ACQ)
BYTE
th1
tsu2
tpd4
th2
td1
RD
tdis
ten
DB[15:8]
Hi–Z
Hi–Z
D [15:8]
DB[7:0]
Hi–Z
D [7:0]
Hi–Z
D [7:0]
†Signal internal to device
Figure 1. Timing for Conversion and Acquisition Cycles With CS and RD Toggling
9
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
tw1
tw2
CONVST
tpd1
tpd2
tw4
tw3
BUSY
tsu1
CS
CONVERT†
t(CONV)
t(CONV)
SAMPLING†
(When CS Toggle)
t(ACQ)
BYTE
th1
tpd4
th2
RD = 0
ten
DB[15:8]
DB[7:0]
Hi–Z
Hi–Z
tdis
D [15:8]
D [7:0]
D [7:0]
Hi–Z
Hi–Z
†Signal internal to device
Figure 2. Timing for Conversion and Acquisition Cycles With CS Toggling, RD Tied to BDGND
10
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
tw1
tw2
CONVST
tpd1
tpd2
tw4
tw3
BUSY
CS = 0
CONVERT†
t(CONV)
t(CONV)
t(ACQ)
SAMPLING†
(When CS = 0)
BYTE
th1
tpd4
th2
RD
tdis
ten
DB[15:8]
DB[7:0]
Hi–Z
Hi–Z
D [15:8]
D [7:0]
D [7:0]
Hi–Z
Hi–Z
†Signal internal to device
Figure 3. Timing for Conversion and Acquisition Cycles With CS Tied to BDGND, RD Toggling
11
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
tw2
tw1
CONVST
tpd1
tpd2
tw4
tw3
BUSY
CS = 0
CONVERT†
t(CONV)
t(CONV)
t(ACQ)
SAMPLING†
(When CS = 0)
BYTE
th1
RD = 0
th1
tdis
td3
td5
DB[15:8]
Previous D [7:0]
Next D [15:8]
D [7:0]
D [15:8]
DB[7:0]
Next D [7:0]
D [7:0]
†Signal internal to device
Figure 4. Timing for Conversion and Acquisition Cycles With CS and RD Tied to BDGND—Auto Read
CS
RD
BYTE
ten
tdis
tdis
ten
DB[15:0]
td3
Hi–Z
Valid
Hi–Z
Valid
Valid
Figure 5. Detailed Timing for Read Cycles
12
Hi–Z
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
TYPICAL CHARACTERISTICS†
HISTOGRAM (DC Code Spread)
NEAR POSITIVE FULL SCALE
196608 CONVERSIONS
SIGNAL-TO-NOISE RATIO
vs
FREE-AIR TEMPERATURE
120000
fi = 50 kHz
(+IN– –IN) = Full Scale
+VA = 5 V,
Code = 61383
SNR – Signal-To- Noise Ratio – dB
100000
90.9
80000
60000
40000
20000
61385
61383
61380
90.7
90.6
90.5
90.4
90.3
–40
0
Figure 6
90.8
SFDR – Spurious Free-Dynamic Range – dB
SINAD – Signal-To-Noise Plus Distortion – dB
102
fi = 50 kHz
(+IN– –IN) = Full Scale
90
89.8
89.6
89.4
89.2
–25
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
Figure 8
80
SPURIOUS FREE-DYNAMIC RANGE
vs
FREE-AIR TEMPERATURE
90.4
89
–40
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
Figure 7
SIGNAL-TO-NOISE PLUS DISTORTION
vs
FREE-AIR TEMPERATURE
90.2
–25
80
101
fi = 50 kHz
(+IN– –IN) = Full Scale
100
99
98
97
96
95
94
–40
–20
0
20
40
60
80
TA – Free-Air Temperature – °C
Figure 9
† At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 1.25 MHz (unless otherwise noted)
13
ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
TOTAL HARMONIC DISTORTION
vs
FREE-AIR TEMPERATURE
SIGNAL-TO-NOISE RATIO
vs
INPUT FREQUENCY
92
91.8
–95
SNR – Signal-To- Noise Ratio – dB
THD – Total Harmonic Distortion – dB
–94
–96
–97
–98
–99
–100
fi = 50 kHz
(+IN– –IN) = Full Scale
–101
–102
–40
–25
–10
5
20
35
50
TA = 25°C
(+IN– –IN) = Full Scale
91.6
91.4
91.2
91
90.8
90.6
90.4
90.2
90
65
89.8
80
0
20
TA – Free-Air Temperature – °C
Figure 10
60
14.9
TA = 25°C
(+IN– –IN) = Full Scale
Vref = 4.096 V
14.85
14.8
14.75
ENOB – Bit
90.5
90
89.5
14.7
14.65
14.6
14.55
14.5
89
14.45
14.4
88.5
0
20
40
60
80
fi – Input Frequency – kHz
Figure 12
100
0
20
40
60
80
fi – Input Frequency – kHz
Figure 13
† At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 1.25 MHz (unless otherwise noted)
14
100
ENOB
vs
INPUT FREQUENCY
91.5
91
80
Figure 11
SIGNAL-TO-NOISE PLUS DISTORTION
vs
INPUT FREQUENCY
SINAD – Signal-To-Noise Plus Distortion – dB
40
fi – Input Frequency – kHz
100
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
SPURIOUS FREE-DYNAMIC RANGE
vs
INPUT FREQUENCY
TOTAL HARMONIC DISTORTION
vs
INPUT FREQUENCY
–94
TA = 25°C
(+IN– –IN) = Full Scale
100
THD – Total Harmonic Distortion – dB
SFDR – Spurious Free-Dynamic Range – dB
101
99
98
97
96
95
TA = 25°C
(+IN– –IN) = Full Scale
–95
–96
–97
–98
–99
–100
94
–101
0
20
40
60
80
fi – Input Frequency – kHz
0
100
Figure 14
0.0073
TA = 25°C
Current of +VA only
0.0061
TA = 25°C
External Reference = 4.096 V (REFIN)
0.0048
31
EG – Gain Error – %FS
I CC – Supply Current – mA
100
GAIN ERROR
vs
SUPPLY VOLTAGE
32
30.5
30
29.5
0.0036
0.0024
0.0012
29
0
28.5
–0.0012
28
250
40
60
80
fi – Input Frequency – kHz
Figure 15
SUPPLY CURRENT
vs
SAMPLE RATE
31.5
20
500
750
1000
Sample Rate – KSPS
Figure 16
1250
–0.0024
4.75
5
+VA – Supply Voltage – V
5.25
Figure 17
† At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 1.25 MHz (unless otherwise noted)
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
INTERNAL REFERENCE VOLTAGE
vs
FREE-AIR TEMPERATURE
OFFSET ERROR
vs
SUPPLY VOLTAGE
0.25
Vref – Internal Reference Voltage – V
4.098
EO – Offset Error – mV
0.2
0.15
0.1
TA = 25°C
External Reference = 4.096 V (REFIN)
0.05
0
4.75
5
+VA – Supply Voltage – V
4.096
4.094
4.092
4.090
4.088
–40
5.25
–25
–10
5
20
35
50
65
80
TA – Free-Air Temperature – °C
Figure 18
Figure 19
OFFSET ERROR
vs
FREE-AIR TEMPERATURE
GAIN ERROR
vs
FREE-AIR TEMPERATURE
0.018
0.6
0.4
0.012
EO – Offset Error – mV
EG – Gain Error – %FS
0.2
0.006
0
0
–0.2
–0.4
–0.6
–0.006
–0.8
External Reference = 4.096 V (REFIN)
–0.012
–40 –25
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
Figure 20
External Reference = 4.096 V (REFIN)
80
–1
–40
–25
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
80
Figure 21
† At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 1.25 MHz (unless otherwise noted)
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
DIFFERENTIAL NONLINEARITY (MAX)
vs
FREE-AIR TEMPERATURE
SUPPLY CURRENT
vs
FREE-AIR TEMPERATURE
1.4
DNL – Differential Nonlinearity (Max) – LSB
30.75
I CC – Supply Current – mA
30.70
30.65
30.60
30.55
30.50
30.45
30.40
30.35
30.30
–40
External Reference = 4.096 V (REFIN)
Current of +VA only
–25
–10
5
20
35
50
65
1.2
1
0.8
0.6
0.4
External Reference = 4.096 V (REFIN)
0.2
0
–40
80
–25
TA – Free-Air Temperature – °C
Figure 22
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
80
Figure 23
DIFFERENTIAL NONLINEARITY (MIN)
vs
FREE-AIR TEMPERATURE
INTEGRAL NONLINEARITY (MAX)
vs
FREE-AIR TEMPERATURE
3
–0.68
–0.69
INL – Integral Nonlinearity (MAX) – LSB
DNL – Differential Nonlinearity (MIN) – LSB
External Reference = 4.096 V (REFIN)
–0.70
–0.71
–0.72
–0.73
–0.74
–0.75
–0.76
2.5
2
1.5
1
External Reference = 4.096 V (REFIN)
0.5
–0.77
–0.78
–40
–25
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
Figure 24
80
0
–40
–25
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
80
Figure 25
† At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 1.25 MHz (unless otherwise noted)
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
INTEGRAL NONLINEARITY
vs
REFERENCE VOLTAGE
INTEGRAL NONLINEARITY (MIN)
vs
FREE-AIR TEMPERATURE
3.0
0
2.5
INL – Integral Nonlinearity – LSB
INL – Integral Nonlinearity (MIN) – LSB
External Reference = 4.096 V (REFIN)
–0.5
–1
–1.5
–2
Max
2.0
1.5
1.0
+VA = +VBD = 5 V,
TA = 25°C
0.5
0.0
–0.5
Min
–1.0
–1.5
–2.0
–2.5
–40
–25
–10
5
20
35
50
65
TA – Free-Air Temperature – °C
–2.5
2.0
80
2.5
3.0
3.5
4.0
Vref – Reference Voltage – V
Figure 26
Figure 27
DIFFERENTIAL NONLINEARITY
vs
REFERENCE VOLTAGE
3.5
+VA = +VBD = 5 V,
TA = 25°C
DNL – Differential Nonlinearity – LSB
3.0
2.5
2.0
Max
1.5
1.0
0.5
0.0
Min
–0.5
–1.0
2.0
2.5
3.0
3.5
4.0
Vref – Reference Voltage – V
4.5
Figure 28
† At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 1.25 MHz (unless otherwise noted)
18
4.5
ADS8402
www.ti.com
SLAS154B – DECEMBER 2002 – REVISED MAY 2003
DNL – LSB
DNL
2.5
2
1.5
1
0.5
0
–0.5
–1
–1.5
–2
–2.5
32768
16384
0
49152
65536
49152
65536
Code
TA = 25°C, External Reference = 4.096 V (REFIN)
Figure 29
INL
5
4
INL – LSB
3
2
1
–0
–1
–2
–3
–4
–5
0
16384
32768
Code
TA = 25°C, External Reference = 4.096 V (REFIN)
Figure 30
FFT SPECTRUM RESPONSE
Magnitude – dB of Full Scale
0
–20
–40
–60
–80
–100
–120
–140
–160
–180
–200
0
100
32768 Points, fS = 1.25 MHz,
Internal Reference = 4.096 V (REFIN),
TA = 25°C, fi = 100 kHz, (+IN– –IN) = Full Scale
200
300
400
500
600
Frequency – kHz
Figure 31
† At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 1.25 MHz (unless otherwise noted)
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
APPLICATION INFORMATION
MICROCONTROLLER INTERFACING
ADS8402 to 8-Bit Microcontroller Interface
Figure 32 shows a parallel interface between the ADS8402 and a typical microcontroller using the 8-bit data bus.
The BUSY signal is used as a falling-edge interrupt to the microcontroller.
Analog 5 V
0.1 µF
AGND
10 µF
Ext Ref Input
0.1 µF
1 µF
Micro
Controller
–IN
+VA
REFIN
REFM
AGND
+IN
Analog Input
Digital 3 V
ADS8402
GPIO
CS
GPIO
P[7:0]
BYTE
DB[15:8]
RD
CONVST
BUSY
RD
GPIO
INT
0.1 µF
BDGND
BDGND
+VBD
Figure 32. ADS8402 Application Circuitry (using external reference)
Analog 5 V
0.1 µF
AGND
10 µF
0.1 µF
AGND
REFM
REFIN
REFOUT
+VA
1 µF
ADS8402
Figure 33. Use Internal Reference
20
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ADS8402
www.ti.com
SLAS154B – DECEMBER 2002 – REVISED MAY 2003
PRINCIPLES OF OPERATION
The ADS8402 is a high-speed successive approximation register (SAR) analog-to-digital converter (ADC). The
architecture is based on charge redistribution, which inherently includes a sample/hold function. See Figure 32 for
the application circuit for the ADS8402.
The conversion clock is generated internally. The conversion time of 610 ns is capable of sustaining a 1.25-MHz
throughput.
The analog input is provided to two input pins: +IN and –IN. When a conversion is initiated, the differential input on
these pins is sampled on the internal capacitor array. While a conversion is in progress, both inputs are disconnected
from any internal function.
REFERENCE
The ADS8402 can operate with an external reference with a range from 2.5 V to 4.2 V. A 4.096-V internal reference
is included. When internal reference is used, pin 2 (REFOUT) should be connected to pin 1 (REFIN) with an 0.1 µF
decoupling capacitor and 1 µF storage capacitor between pin 2 (REFOUT) and pins 47 and 48 (REFM) (see
Figure 33). The internal reference of the converter is double buffered. If an external reference is used, the second
buffer provides isolation between the external reference and the CDAC. This buffer is also used to recharge all of
the capacitors of the CDAC during conversion. Pin 2 (REFOUT) can be left unconnected (floating) if external
reference is used.
ANALOG INPUT
When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs is captured on the
internal capacitor array. Both +IN and –IN input has a range of –0.2 V to Vref + 0.2 V. The input span
(+IN – (–IN)) is limited to –Vref to Vref.
The input current on the analog inputs depends upon a number of factors: sample rate, input voltage, and source
impedance. Essentially, the current into the ADS8402 charges the internal capacitor array during the sample period.
After this capacitance has been fully charged, there is no further input current. The source of the analog input voltage
must be able to charge the input capacitance (25 pF) to an 16-bit settling level within the acquisition time (150 ns)
of the device. When the converter goes into the hold mode, the input impedance is greater than 1 GΩ.
Care must be taken regarding the absolute analog input voltage. To maintain the linearity of the converter, the +IN
and –IN inputs and the span (+IN – (–IN)) should be within the limits specified. Outside of these ranges, the
converter’s linearity may not meet specifications. To minimize noise, low bandwidth input signals with low-pass filters
should be used.
Care should be taken to ensure that the output impedance of the sources driving +IN and –IN inputs are matched.
If this is not observed, the two inputs could have different setting time. This may result in offset error, gain error and
linearity error which varies with temperature and input voltage.
A typical input circuit using TI’s THS4503 is shown in Figure 34. Input from a single-ended source may be converted
into differential signal for ADS8402 as shown in the figure. In case the source itself is differential then THS4503 may
be used in differential input and differential output mode.
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
68 pF
RS
RG
RT
1 kΩ
50 Ω
VCC+
+ _
20 pF
THS4503
IN–
ADS8402
_ +
+
_
IN+
OCM
VCC–
1 kΩ
1 kΩ
50 Ω
68 pF
RG, RS, and RT should be chosen such that
RG + RS || RT = 1 k Ω
VOCM = 2 V, +VCC = 7 V, and –VCC = –7 V
Figure 34. Using THS4503 With ADS8402
DIGITAL INTERFACE
Timing and Control
See the timing diagrams in the specifications section for detailed information on timing signals and their requirements.
The ADS8402 uses an internal oscillator generated clock which controls the conversion rate and in turn the
throughput of the converter. No external clock input is required.
Conversions are initiated by bringing the CONVST pin low for a minimum of 20 ns (after the 20 ns minimum
requirement has been met, the CONVST pin can be brought high), while CS is low. The ADS8402 switches from the
sample to the hold mode on the falling edge of the CONVST command. A clean and low jitter falling edge of this signal
is important to the performance of the converter. The BUSY output is brought high after CONVST goes low. BUSY
stays high throughout the conversion process and returns low when the conversion has ended.
Sampling starts with the falling edge of the BUSY signal when CS is tied low or starts with the falling edge of CS when
BUSY is low.
Both RD and CS can be high during and before a conversion with one exception (CS must be low when CONVST
goes low to initiate a conversion). Both the RD and CS pins are brought low in order to enable the parallel output bus
with the conversion.
Reading Data
The ADS8402 outputs full parallel data in two’s complement format as shown in Table 1. The parallel output is active
when CS and RD are both low. There is a minimal quiet zone requirement around the falling edge of CONVST. This
is 100 ns prior to the falling edge of CONVST and 40 ns after the falling edge. No data read should be attempted
within this zone. Any other combination of CS and RD sets the parallel output to 3-state. BYTE is used for multiword
read operations. BYTE is used whenever lower bits of the conversion result are output on the higher byte of the bus.
Refer to Table 1 for ideal output codes.
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
Table 1. Ideal Input Voltages and Output Codes
DESCRIPTION
ANALOG VALUE
FULL SCALE RANGE
Least significant bit (LSB)
DIGITAL OUTPUT TWOS COMPLEMENT
2Vref
2Vref/65536
BINARY CODE
HEX CODE
0111 1111 1111 1111
7FFF
Midscale
Vref
0
0000 0000 0000 0000
0000
Zero
–Vref
1000 0000 0000 0000
8000
Full scale
The output data is a full 16-bit word (D15–D0) on DB15–DB0 pins (MSB–LSB) if BYTE is low.
The result may also be read on an 8-bit bus for convenience. This is done by using only pins DB15–DB8. In this case
two reads are necessary: the first as before, leaving BYTE low and reading the 8 most significant bits on pins
DB15–DB8, then bringing BYTE high. When BYTE is high, the low bits (D7–D0) appears on pins DB15–D8.
These multiword read operations can be done with multiple active RD (toggling) or with RD tied low for simplicity.
DATA READ OUT
BYTE
DB15–DB8
DB7–DB0
High
D7–D0
All one’s
Low
D15–D8
D7–D0
RESET
RESET is an asynchronous active low input signal (that works independantly of CS). Minimum RESET low time is
20 ns. Current conversion will be aborted no later than 50 ns after the converter is in the reset mode. In addition, all
output latches are cleared (set to zero’s) after RESET. The converter goes back to normal operation mode no later
than 20 ns after RESET input is brought high.
The converter starts the first sampling period 20 ns after the rising edge of RESET. Any sampling period except for
the one immediately after a RESET is started with the falling edge of the previous BUSY signal or the falling edge
of CS, whichever is later.
POWER-ON INITIALIZATION
One RESET pulse followed by three conversion cycles must be given to the converter after powerup to ensure proper
operation. The next pulse can be issued once both +VA and +VBD reach 95% of the minimum required value.
LAYOUT
For optimum performance, care should be taken with the physical layout of the ADS8402 circuitry.
As the ADS8402 offers single-supply operation, it is often used in close proximity with digital logic, microcontrollers,
microprocessors, and digital signal processors. The more digital logic present in the design and the higher the
switching speed, the more difficult it is to achieve good performance from the converter.
The basic SAR architecture is sensitive to glitches or sudden changes on the power supply, reference, ground
connections and digital inputs that occur just prior to latching the output of the analog comparator. Thus, driving any
single conversion for an n-bit SAR converter, there are at least n windows in which large external transient voltages
can affect the conversion result. Such glitches might originate from switching power supplies, nearby digital logic,
or high power devices.
The degree of error in the digital output depends on the reference voltage, layout, and the exact timing of the external
event.
On average, the ADS8402 draws very little current from an external reference, as the reference voltage is internally
buffered. If the reference voltage is external and originates from an op amp, make sure that it can drive the bypass
capacitor or capacitors without oscillation. A 0.1-µF bypass capacitor and 1-µF storage capacitor are recommended
from pin 1 (REFIN) directly to pin 48 (REFM). REFM and AGND should be shorted on the same ground plane under
the device.
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ADS8402
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SLAS154B – DECEMBER 2002 – REVISED MAY 2003
The AGND and BDGND pins should be connected to a clean ground point. In all cases, this should be the analog
ground. Avoid connections which are close to the grounding point of a microcontroller or digital signal processor. If
required, run a ground trace directly from the converter to the power supply entry point. The ideal layout consists of
an analog ground plane dedicated to the converter and associated analog circuitry.
As with the AGND connections, +VA should be connected to a 5-V power supply plane or trace that is separate from
the connection for digital logic until they are connected at the power entry point. Power to the ADS8402 should be
clean and well bypassed. A 0.1-µF ceramic bypass capacitor should be placed as close to the device as possible.
See Table 2 for the placement of the capacitor. In addition, a 1-µF to 10-µF capacitor is recommended. In some
situations, additional bypassing may be required, such as a 100-µF electrolytic capacitor or even a Pi filter made up
of inductors and capacitors—all designed to essentially low-pass filter the 5-V supply, removing the high frequency
noise.
Table 2. Power Supply Decoupling Capacitor Placement
POWER SUPPLY PLANE
SUPPLY PINS
CONVERTER ANALOG SIDE
CONVERTER DIGITAL SIDE
Pin pairs that require shortest path to decoupling capacitors
(4,5), (8,9), (10,11), (13,15),
(43,44), (45,46)
(24,25), (34, 35)
Pins that require no decoupling
12, 14
37
24
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