ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
12-BIT, 3-MSPS
LOW POWER SAR ANALOG-TO-DIGITAL CONVERTER
FEATURES
1
•
•
•
•
•
•
•
•
•
•
•
3-MHz Sample Rate, 12-Bit Resolution
Zero Latency
Unipolar, Pseudo Differential Input, Range:
– 0 V to 2.5 V
High-Speed Parallel Interface
69.5 dB SNR at 100 kHz I/P
Power Dissipation 85 mW at 3 MSPS
Nap Mode (10 mW Power Dissipation)
Power Down (10 µW)
Internal Reference
Internal Reference Buffer
48-Pin TQFP Package
DESCRIPTION
The ADS7882 is a 12-bit 3-MSPS A-to-D converter
with 2.5-V internal reference. The device includes a
capacitor based SAR A/D converter with inherent
sample and hold. The device offers a 12-bit parallel
interface with an additional byte mode that provides
easy interface with 8-bit processors. The device has
a pseudo-differential input stage.
The –IN swing of ±200 mV is useful to compensate
for ground voltage mismatch between the ADC and
sensor and also to cancel common-mode noise. With
nap mode enabled, the device operates at lower
power when used at lower conversion rates. The
device is available in 48-pin TQFP package.
APPLICATIONS
•
•
•
•
•
•
Optical Networking (DWDM, MEMS Based
Switching)
Spectrum Analyzers
High Speed Data Acquisition Systems
High Speed Close-Loop Systems
Telecommunication
Ultra-Sound Detection
BYTE
SAR
+IN
−IN
+
_
Output
Latches
and
3-State
Drivers
CDAC
Comparator
12/8-Bit Parallel
Data Output Bus
REFIN
CLOCK
REFOUT
2.5 V
Internal
Reference
Conversion
and
Control Logic
PWD/RST
CONVST
BUSY
CS
RD
A_PWD
1
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 the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008, Texas Instruments Incorporated
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
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.
ORDERING INFORMATION (1)
MODEL
MAXIMUM
INTEGRAL
LINEARITY
MAXIMUM
DIFFERENTIAL
LINEARITY
NO MISSING
CODES AT
RESOLUTION
(BIT)
PACKAGE
TYPE
PACKAGE
DESIGNATOR
TEMPERATURE
RANGE
ADS7882
±4 LSB at 12 bit
±4 LSB at 12 bit
(±1 LSB at 10 bit)
10
48-Pin
TQFP
PFB
–40°C to 85°C
(1)
ORDERING
INFORMATION
TRANSPORT
MEDIA QUANTITY
ADS7882IPFBT
Tape and reel 250
ADS7882IPFBR
Tape and reel 1000
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
website at www.ti.com.
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range (unless otherwise noted)
(1)
VALUE
UNIT
+IN to AGND
–0.3 to +VA + 0.1
V
-IN to AGND
–0.3 to 0.5
V
+VA to AGND
–0.3 to 7
V
+VBD to BDGND
–0.3 to 7
V
Digital input voltage to GND
–0.3 to (+VBD + 0.3 V)
V
Digital output to GND
–0.3 to (+VBD + 0.3 V)
V
Operating temperature range
–40 to 85
°C
Storage temperature range
–65 to 150
°C
150
°C
Junction temperature (TJmax)
TQFP package
Lead temperature, soldering
(1)
2
(TJ Max–TA)/ θJA
Power dissipation
θJA Thermal impedance
86
°C/W
Vapor phase (60 sec)
215
°C
Infrared (15 sec)
220
°C
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.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
SPECIFICATIONS
TA = –40°C to 85°C, +VA = 5 V, +VBD = 5 V or 3.3 V, Vref = 2.5 V, fsample = 3 MHz (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUT
Full-scale input span (1)
Absolute input range
+IN – (–IN)
0
Vref
+IN
–0.2
Vref +0.2
–IN
–0.2
0.2
Input capacitance
Input leakage current
V
V
27
pF
500
pA
12
Bits
SYSTEM PERFORMANCE
Resolution
No missing codes
10
Integral linearity (2)
–4
±1
4
LSB (3)
Differential linearity
–4
±1
4
LSB (3)
Offset error (4)
Gain error
(4)
Bits
±1
mV
±1.2
mV
Common-mode rejection ratio
With common mode input signal = 200
mVp-p at 1 MHz
60
dB
Power supply rejection
At FF0H output code, +VA = 4.75 V to 5.25
V , Vref = 2.50 V
80
dB
SAMPLING DYNAMICS
Conversion time
Acquisition time
+VDB = 5 V
280
+VDB = 3 V
280
+VDB = 5 V
53
+VDB = 3 V
53
nsec
nsec
Maximum throughput rate
3
MHz
Aperture delay
2
nsec
Aperture jitter
20
psec
Step response
50
nsec
Overvoltage recovery
50
nsec
DYNAMIC CHARACTERISTICS
Total harmonic distortion (5)
VIN = 2.496 Vp-p at 0.1 MHz/2.5 Vref
–79.5
dB
SNR
VIN = 2.496 Vp-p at 0.1 MHz/2.5 Vref
69.5
dB
SINAD
VIN = 2.496 Vp-p at 0.1 MHz/2.5 Vref
68.5
dB
SFDR
VIN = 2.496 Vp-p at 0.1 MHz/2.5 Vref
80.5
dB
–3 dB Small signal bandwidth
50
MHz
EXTERNAL REFERENCE INPUT
Input VREF range
Resistance
2.4
(6)
2.5
2.6
500
V
kΩ
INTERNAL REFERENCE OUTPUT
Start-up time
From 95% (+VA), with 1-µF storage
capacitor on REFOUT to AGND
VREF range
IOUT = 0
Source current
Static load
Line regulation
+VA = 4.75 V to 5.25 V
Drift
IOUT = 0
(1)
(2)
(3)
(4)
(5)
(6)
120
2.425
2.5
msec
2.575
V
10
µA
1
mV
25
PPM/°C
Ideal input span; does not include gain or offset error.
This is endpoint INL, not best fit.
LSB means least significant bit.
Measured relative to actual measured reference.
Calculated on the first nine harmonics of the input frequency.
Can vary ±20%.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
3
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
SPECIFICATIONS (continued)
TA = –40°C to 85°C, +VA = 5 V, +VBD = 5 V or 3.3 V, Vref = 2.5 V, fsample = 3 MHz (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DIGITAL INPUT/OUTPUT
Logic family
CMOS
Logic level
VIH
IIH = 5 µA
+VBD –1
+VBD +0.3
V
VIL
IIL = 5 µA
–3
0.8
V
VOH
IOH = 2 TTL loads
+VBD –0.6
+VBD
V
VOL
IOL = 2 TTL loads
0
0.4
V
V
Straight
Binary
Data format
POWER SUPPLY REQUIREMENTS
+VBD
Power supply
voltage
+VA
2.7
3.3
5.25
4.75
5
5.25
17
22
mA
85
110
mW
2
3
mA
Supply current, +VA, 3 MHz sample rate
Power dissipation, 3 MHz sample rate
+VA = 5 V
V
NAP MODE
Supply current, +VA
Power-up time
(7)
60
nsec
POWER DOWN
Supply current, +VA
2
2.5
µA
Power down time (8)
From simulation results
10
µsec
Power up time
1-µF storage capacitor on REFOUT to
AGND
25
msec
Invalid conversions after power up or reset
TEMPERATURE RANGE
Operating free-air
(7)
(8)
4
–40
85
°C
Minimum acquisition time for first sampling after the end of nap state must be 60 nsec more than normal.
Time required to reach level of 2.5 µA.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
TIMING REQUIREMENTS
All specifications typical at –40°C to 85°C, +VA = +5 V, +VBD = +5 V
(1) (2) (3) (4)
PARAMETER
t(conv)
Conversion time
t(acq)
Acquisition time
MIN
TYP
MAX
UNIT
REF FIG.
280
ns
5
ns
5
ns
3
ns
1
53
SAMPLING AND CONVERSION START
th1
Hold time CS low to CONVST high (with BUSY high)
td1
Delay CONVST high to acquisition start
10
th2
Hold time, CONVST high to CS high with BUSY low
10
ns
1
th3
Hold time, CONVST low to CS high
10
ns
1
td2
Delay CONVST low to BUSY high
ns
1
tw3
CS width for acquisition or conversion to start
ns
2
td3
Delay CS low to acquisition start with CONVST high
ns
2
tw1
Pulse width, from CS low to CONVST low for acquisition to start
ns
2
td4
Delay CS low to BUSY high with CONVST low
ns
2
2
4
5
40
(3)
Quiet sampling time
20
2
4
5
20
40
25
ns
CONVERSION ABORT
ts1
Setup time CONVST high to CS low with BUSY high
15
ns
4
td5
Delay time CS low to BUSY low with CONVST high
20
ns
4
DATA READ
td6
Delay RD low to data valid with CS low
25
ns
td7
Delay BYTE high to LSB word valid with CS and RD low
25
ns
5
td9
Delay time RD high to data 3-state with CS low
25
ns
5
td11
Delay time end of conversion to BUSY low
20
ns
5
t1
Quiet sampling time RD high to CONVST low
20
ns
5
td8
Delay CS low to data valid with RD low
25
ns
5
td10
Delay CS high to data 3-state with RD low
25
ns
6
t2
Quiet sampling time CS low to CONVST low
25
ns
6
10
BACK-TO-BACK CONVERSION
td12
Delay BUSY low to data valid
ns
7, 8
tw4
Pulse width, CONVST high
63
ns
7, 8
tw5
Pulse width, CONVST low
20
ns
7
ns
10
ns
9
ns
9
POWER DOWN/RESET
tw6
Pulse width, low for PWD/RST to reset the device
tw7
Pulse width, low for PWD/RST to power down the device
td13
Delay time, power up after PWD/RST is high
(1)
(2)
(3)
(4)
45
6140
7200
25
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.
See timing diagram.
Quiet period before conversion start, no data bus activity including data bus 3-state is allowed in this period.
All timings are measured with 20 pF equivalent loads on all data bits and BUSY pin.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
5
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
PWD/RST
A_PWD
BYTE
CONVST
+VA
CS
RD
AGND
AGND
+VA
REFM
REFM
PIN ASSIGNMENTS
48 47 46 45 44 43 42 41 40 39 38 37
REFIN
1
36
BUSY
REFOUT
2
35
BDGND
NC
3
34
+VBD
+VA
4
33
NC
AGND
5
32
NC
+IN
6
31
NC
−IN
7
30
NC
AGND
8
29
+VA
9
28
DB0
DB1
+VA
10
27
DB2
AGND
11
26
DB3
AGND 12
25
BDGND
24
+VBD
DB5
DB4
DB6
DB7
DB8
DB9
DB11
DB10
AGND
AGND
+VA
13 14 15 16 17 18 19 20 21 22 23
NC − No connection
PIN FUNCTIONS
PIN
NAME
NO. PFB
I/O
DESCRIPTION
8-BIT BUS
DATA BUS
16-BIT BUS
BYTE = 0
BYTE = 1
BYTE = 0
DB11
16
O
D11 (MSB)
D3
D11 (MSB)
DB10
17
O
D10
D2
D10
DB9
18
O
D9
D1
D9
DB8
19
O
D8
D0 (LSB)
D8
DB7
20
O
D7
0
D7
DB6
21
O
D6
0
D6
DB5
22
O
D5
0
D5
DB4
23
O
D4
0
D4
DB3
26
O
D3
0
D3
DB2
27
O
D2
0
D2
DB1
28
O
D1
0
D1
DB0
29
O
D0 (LSB)
0
D0 (LSB)
CS
42
I
Chip select. Active low signal enables chip operation like acquisition start, conversion start, bus
release from 3-state. Refer to the timing diagrams for more details.
CONVST
40
I
Conversion start. The rising edge starts the acquisition. The falling edge of this input ends the
acquisition and starts the conversion. Refer to the timing diagrams for more details.
RD
41
I
Active low synchronization pulse for the parallel output. When CS is low, this serves as the
output enable and puts the previous conversion results on the bus.
A_PWD
37
I
Nap mode enable, active low
CONTROL PINS
6
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
PIN FUNCTIONS (continued)
PIN
NAME
NO. PFB
I/O
DESCRIPTION
8-BIT BUS
DATA BUS
BYTE = 0
16-BIT BUS
BYTE = 1
BYTE = 0
PWD/RST
38
I
Active low input, acts as device power down/device reset signal.
BYTE
39
I
Byte select input. Used for 8-bit bus reading.
0: No fold back
1: Lower byte D[3:0] is folded back to high byte so D3 is available in D11 place.
36
O
Status output. High when a conversion is in progress.
+VBD
24, 34
–
Digital power supply for all digital inputs and outputs. Refer to Table 3 for layout guidelines.
BDGND
25, 35
–
Digital ground for all digital inputs and outputs. Short to analog ground plane below the device.
4, 9, 10, 13,
43, 46
–
Analog power supplies. Refer to Table 3 for layout guidelines.
5, 8, 11, 12,
14, 15, 44, 45
–
Analog ground pins. Short to analog ground plane below the device.
+IN
6
I
Noninverting analog input channel
–IN
7
I
Inverting analog input channel
REFIN
1
I
Reference (positive) input. Needs to be decoupled with REFM pin using 0.1-µF bypass capacitor
and 1-µF storage capacitor.
REFOUT
2
O
Internal reference output. To be shorted to REFIN pin when internal reference is used. Do not
connect to REFIN pin when external reference is used. Always needs to be decoupled with
AGND using 0.1-µF bypass capacitor.
I
Reference ground. Connect to analog ground plane.
–
No connection
STATUS OUTPUT
BUSY
POWER SUPPLY
+VA
AGND
ANALOG INPUT
REFM
NC
47, 48
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
7
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
DESCRIPTION AND TIMING DIAGRAMS
SAMPLING AND CONVERSION START
There are three ways to start sampling. The rising edge of CONVST starts sampling with CS and BUSY being
low (see Figure 1) or it can be started with the falling edge of CS when CONVST is high and BUSY is low (see
Figure 2). Sampling can also be started with an internal conversion end (before BUSY falling edge) with CS
being low and CONVST high before an internal conversion end (see Figure 3). Also refer to the section DEVICE
OPERATION AND DATA READ IN BACK-TO-BACK CONVERSION for more details.
A conversion can be started two ways (a conversion start is the end of sampling). Either with the falling edge of
CONVST when CS is low (see Figure 1) or the falling edge of CS when CONVST is low (see Figure 2). A clean
and low jitter falling edge of these respective signals triggers a conversion start and is important to the
performance of the converter. The BUSY pin is brought high immediately following the CONVST falling edge.
BUSY stays high throughout the conversion process and returns low when the conversion has ended.
th2
th3
CS
CONVST
td1
td2
BUSY
t(acq)
Figure 1. Sampling and Conversion Start Control With CONVST Pin
tw3
tw3
CS
td4
CONVST
td3
tw1
BUSY
t(acq)
Figure 2. Sampling and Conversion Start Control With CS Pin
CS
th1
tw5
CONVST
tw4
BUSY
td2
t(acq)
Figure 3. Sampling Start With CS Low and CONVST High (Back-to-Back)
8
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
CONVERSION ABORT
The falling edge of CS aborts the conversion while BUSY is high and CONVST is high (see Figure 4). The
device outputs FE0 (hex) to indicate a conversion abort.
td5
BUSY
tsu1
CONVST
CS
RD
1111 1110 0000
D11−D0
Figure 4. Conversion Abort
DATA READ
Two conditions need to be satisfied for a read operation. Data appears on the D11 through D0 pins (with D11
MSB) when both CS and RD are low. Figure 5 and Figure 6 illustrate the device read operation. The bus is
3-stated if any one of the signals is high.
t1
td2
tw5
CONVST
t(conv)
td1 + t(acq)
BUSY
td11
CS
RD
BYTE
td6
D11−D0
td7
D11−4 & D3−0
td9
D3−0
Figure 5. Read Control via CS and RD
There are two output formats available. Twelve bit data appears on the bus during a read operation while BYTE
is low. When BYTE is high, the lower byte (D3 through D0 followed by all zeroes) appears on the data bus with
D3 in the MSB. This feature is useful for interfacing with eight bit microprocessors and microcontrollers.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
9
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
t2
CONVST
td1 + t(acq)
BUSY
Conversion No N
td2
CS
BYTE
td7
D11−4 & D3−0
D11−D0
Data For Conv. N−1
td10
D3−0
Data For Conv. N
td8
Figure 6. Read Control Via CS and RD Tied to BDGND
DEVICE OPERATION AND DATA READ IN BACK-TO-BACK CONVERSION
Figure 7 and Figure 8 illustrate device operation in back-to-back conversion mode. It is possible to operate the
device at any throughput in this mode, but this is the only mode in which the device can be operated at
throughputs exceeding 2.83 MSPS (1/t(acq) min + t(conv) max + td11 max)).
A conversion starts on the CONVST falling edge. The BUSY output goes high after a delay (td2). Note that care
must be taken not to abort the conversion (see Figure 4) apart from timing restrictions shown in Figure 7 and
Figure 8. The conversion ends within the conversion time, t(conv), after the CONVST falling edge. The new
acquisition can be immediately started without waiting for the BUSY signal to go low. This can be ensured with a
CONVST high pulse width that is more than or equal to (t0 – t(conv) + 10 nsec) which is tw4 for a 3-MHz operation.
Sample N
CONVST
tw4
t(acq)
tw5
Conversion N
BUSY
td12
t(conv) + td11
Data For Conversion N−1
D11−D0
(Data Read without Latency)
t0 = 333 ns for 3 MSPS Operation
Figure 7. Back-To-Back Operation With CS and RD Low
10
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
CS
Sample N
th1
CONVST
tw4
t(acq)
tw3
t(conv) + td11
Conversion N
BUSY
Data For Conversion N−1
td12
D11−D0
(Data Read without Latency)
t0 = 333 ns for 3 MSPS Operation
Figure 8. Back-To-Back operation With CS Toggling and RD Low
NAP MODE
The device can be put in nap mode following the sequences shown in Figure 9. This provides substantial power
saving while operating at lower sampling rates.
While operating the device at throughput rates lower than 2.54 MSPS, A_PWD can be held low (see Figure 9). In
this condition, the device goes into the nap state immediately after BUSY goes low and remains in that state until
the next sampling starts. The minimum acquisition time is 60 nsec more than t(acq) as defined in the timing
requirements section.
Alternately, A_PWD can be toggled any time during operation (see Figure 10). This is useful when the system
acquires data at the maximum conversion speed for some period of time (back-to-back conversion) and it does
not acquire data for some time while the acquired data is being processed. During this period, the device can be
put in the nap state to save power. The device remains in the nap state as long as A_PWD is low with BUSY
being low and sampling has not started. The minimum acquisition time for the first sampling after the nap state is
60 nsec more than t(acq) as defined in the timing requirements section.
A_PWD
(Held Low)
BUSY
SAMPLE
(Internal)
t(acq) + 60 ns
NAP
(Internal Active High)
NOTE: The SAMPLE (Internal) signal is generated as described in the Sampling and Conversion
Start section.
Figure 9. Device Operation While A_PWD is Held Low
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
11
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
A_PWD
BUSY
SAMPLE
(Internal)
t(acq) + 60 ns
NAP
(Internal Active High)
NOTE: The SAMPLE (Internal) signal is generated as described in the Sampling and Conversion
Start section.
Figure 10. Device Operation While A_PWD is Toggling
POWERDOWN/RESET
A low level on the PWD/RST pin puts the device in the powerdown phase. This is an asynchronous signal. As
shown in Figure 11, the device is in the reset phase for the first tw6 period after a high-to-low transition of
PWD/RST. During this period the output code is FE0 (hex) to indicate that the device is in the reset phase. The
device powers down if the PWD/RST pin continues to be low for a period of more than tw7. Data is not valid for
the first four conversions after a power-up (see Figure 11) or an end of reset (see Figure 12). The device is
initialized during the first four conversions.
tw7
Valid Conversions
PWD/RST
First 4 Invalid Conversions
BUSY
1
2
3
4
5
td13
D11−D0
1111 1110 0000
Power Down
Phase
RESET Phase
Invalid Data
Valid Data
Figure 11. Device Power Down
tw6
45 ns
Valid Conversions
PWD/RST
First 4 Invalid Conversions
BUSY
D11−D0
1
2
3
4
5
1111 1110 0000
RESET Phase
Invalid Data
Valid Data
Figure 12. Device Reset
12
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
TYPICAL CHARACTERISTICS (1)
EFFECTIVE NUMBER OF BITS
vs
FREE-AIR TEMPERATURE
HISTOGRAM
(DC CODE SPREAD CLOSE TO ZERO INPUT)
11.24
4692
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
4500
f − Frequency − kHz
4000
ENOB − Effective Number of Bits − Bits
5000
3500
3000
2500
2000
1500
1000
500
308
0
28
11.22
11.20
11.18
11.16
11.14
11.12
11.10
fIN = 100 kHz
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
11.08
−40
29
−20
G001
SIGNAL-TO-NOISE AND DISTORTION
vs
FREE-AIR TEMPERATURE
SIGNAL-TO-NOISE RATIO
vs
FREE-AIR TEMPERATURE
70.5
SNR − Signal-to-Noise Ratio − dB
SINAD − Signal-to-Noise and Distortion − dB
60
80
G002
71.0
fIN = 100 kHz
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
68.5
−20
0
20
40
60
TA − Free-Air temperature − °C
fIN = 100 kHz
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
70.0
69.5
69.0
68.5
68.0
−40
80
G003
Figure 15.
(1)
40
Figure 14.
69.0
68.0
−40
20
Figure 13.
70.0
69.5
0
TA − Free-Air temperature − °C
Bin
−20
0
20
40
60
TA − Free-Air temperature − °C
80
G004
Figure 16.
At sample rate = 3 MSPS, Vref = 2.5 V external, unless otherwise specified.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
13
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
TOTAL HARMONIC DISTORTION
vs
FREE-AIR TEMPERATURE
SPURIOUS-FREE DYNAMIC RANGE
vs
FREE-AIR TEMPERATURE
82.0
fIN = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
−78.5
SFDR − Spurious-Free Dynamic Range − dB
THD − Total Harmonic Distortion − dB
−78.0
−79.0
−79.5
−80.0
−80.5
−81.0
−40
−20
0
20
40
60
81.0
80.5
fIN = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
80.0
−40
80
−20
20
40
60
G005
Figure 17.
Figure 18.
EFFECTIVE NUMBER OF BITS
vs
INPUT FREQUENCY
SIGNAL-TO-NOISE AND DISTORTION
vs
INPUT FREQUENCY
80
G006
72
SINAD − Signal-to-Noise and Distortion − dB
11.5
11.3
11.1
10.9
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
10.7
1
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
71
70
69
68
67
10.5
10
fIN − Input Frequency − kHz
100
1
10
fIN − Input Frequency − kHz
G007
Figure 19.
14
0
TA − Free-Air temperature − °C
TA − Free-Air temperature − °C
ENOB − Effective Number of Bits − Bits
81.5
100
G008
Figure 20.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
SIGNAL-TO-NOISE RATIO
vs
INPUT FREQUENCY
TOTAL HARMONIC DISTORTION
vs
INPUT FREQUENCY
72.0
−78.0
THD − Total Harmonic Distortion − dB
SNR − Signal-to-Noise Ratio − dB
71.5
71.0
70.5
70.0
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
69.5
69.0
−78.5
−79.0
−79.5
−80.0
−80.5
−81.0
1
10
100
fIN − Input Frequency − kHz
1
10
100
fIN − Input Frequency − kHz
G009
Figure 21.
Figure 22.
SPURIOUS-FREE DYNAMIC RANGE
vs
INPUT FREQUENCY
OFFSET ERROR
vs
FREE-AIR TEMPERATURE
G010
2.0
87.0
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
86.5
86.0
1.5
85.5
85.0
84.5
0.5
0.0
−0.5
84.0
−1.0
83.5
−1.5
83.0
1
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
1.0
Offset Error − mV
SFDR − Spurious-Free Dynamic Range − dB
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
10
fIN − Input Frequency − kHz
100
−2.0
−40
G011
Figure 23.
−20
0
20
40
60
TA − Free-Air temperature − °C
80
G012
Figure 24.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
15
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
GAIN ERROR
vs
FREE-AIR TEMPERATURE
INTEGRAL NONLINEARITY
vs
FREE-AIR TEMPERATURE
2.0
3
INL − Integral Nonlinearity − LSB
1.5
4
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
Gain Error − LSB
1.0
0.5
0.0
−0.5
−1.0
−1.5
−2.0
−40
−20
0
20
40
60
0
−1
Min
−2
−20
0
20
40
60
G013
Figure 25.
Figure 26.
DIFFERENTIAL NONLINEARITY
vs
FREE-AIR TEMPERATURE
REFERENCE OUTPUT DRIFT
vs
FREE-AIR TEMPERATURE
80
G014
7
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
2
1
Max
0
−1
Throughput = 3 MSPS
VA = 5 V
6
Min
−2
−3
5
4
3
2
1
0
−1
−20
0
20
40
60
TA − Free-Air temperature − °C
−2
−40
80
G015
Figure 27.
16
Max
TA − Free-Air temperature − °C
Reference Output Drift − mV
DNL − Differential Nonlinearity − LSB
1
−4
−40
80
4
−4
−40
2
−3
TA − Free-Air temperature − °C
3
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
−20
0
20
40
60
TA − Free-Air temperature − °C
80
G016
Figure 28.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
POWER DISSIPATION
vs
SAMPLE RATE
90
PD − Power Dissipation − mW
80
70
60
50
40
30
20
TA = 25°C
VA = 5 V
VREF = 2.5 V
10
0
0
500
1000
1500
2000
2500
3000
Sample Rate − KSPS
G017
Figure 29.
DIFFERENTIAL NONLINEARITY
DNL − Differential Nonlinearity − LSB
1.0
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
0.8
0.6
0.4
0.2
0.0
−0.2
−0.4
−0.6
−0.8
−1.0
0
1024
2048
3072
4096
Code
G018
Figure 30.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
17
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
INTEGRAL NONLINEARITY
INL − Integral Nonlinearity − LSB
1.0
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
0.8
0.6
0.4
0.2
0.0
−0.2
−0.4
−0.6
−0.8
−1.0
0
1024
2048
3072
4096
Code
G019
Figure 31.
FFT
0
TA = 25°C
Throughput = 3 MSPS
VA = 5 V
VREF = 2.5 V
−20
P − Power − dB
−40
−60
−80
−100
−120
−140
−160
−180
0
300
600
900
1200
1500
f − Frequency − kHz
G020
Figure 32.
PRINCIPLES OF OPERATION
The ADS7882 is a member of a family of high-speed successive approximation register (SAR) analog-to-digital
converters (ADC). The architecture is based on charge redistribution, which inherently includes a sample/hold
function.
The conversion clock is generated internally. The conversion time is 200 ns max (at 5 V +VBD).
The analog input is provided to two input pins: +IN and –IN. (Note that this is pseudo differential input and there
are restrictions on –IN voltage range.) When a conversion is initiated, the difference voltage between 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 ADS7882 has a built-in 2.5-V (nominal value) reference but can operate with an external reference. When
an internal reference is used, pin 2 (REFOUT) should be connected to pin 1 (REFIN) with an 0.1-µF decoupling
capacitor and a 1-µF storage capacitor between pin 2 (REFOUT) and pins 47, 48 (REFM). The internal reference
of the converter is buffered . There is also a buffer from REFIN to CDAC. This buffer provides isolation between
the external reference and the CDAC and also recharges the CDAC during conversion. It is essential to decouple
REFOUT to AGND with a 0.1-µF capacitor while the device operates with an external reference.
18
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
PRINCIPLES OF OPERATION (continued)
ANALOG INPUT
When the converter enters hold mode, the voltage difference between the +IN and -IN inputs is captured on the
internal capacitor array. The voltage on the –IN input is limited to between –0.2 V and 0.2 V, thus allowing the
input to reject a small signal which is common to both the +IN and -IN inputs. The +IN input has a range of –0.2
V to (+Vref +0.2 V). The input span (+IN – (–IN)) is limited from 0 V to VREF.
The input current on the analog inputs depends upon a number of factors: sample rate, input voltage, signal
frequency, and source impedance. Essentially, the current into the ADS7882 charges the internal capacitor array
during the sample period. After this capacitance has been fully charged, there is no further input current (this
may not happen when a signal is moving continuously). The source of the analog input voltage must be able to
charge the input capacitance (27 pF) to better than a 12-bit settling level with a step input within the acquisition
time of the device. The step size can be selected equal to the maximum voltage difference between two
consecutive samples at the maximum signal frequency. (Refer to Figure 35 for the suggested input circuit.) When
the converter goes into 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, both
–IN and +IN inputs should be within the limits specified. Outside of these ranges, the converter's linearity may
not meet specifications.
Care should be taken to ensure that +IN and -IN see the same impedance to the respective sources. (For
example, both +IN and –IN are connected to a decoupling capacitor through a 21-Ω resistor as shown in
Figure 35.) If this is not observed, the two inputs could have different settling times. This may result in an offset
error, gain error, or linearity error which changes with temperature and input voltage.
DIGITAL INTERFACE
TIMING AND CONTROL
Refer to the SAMPLING AND CONVERSION START section and the CONVERSION ABORT section.
READING DATA
The ADS7882 outputs full parallel data in straight binary format as shown in Table 1. The parallel output is active
when CS and RD are both low. There is a minimal quiet sampling period requirement around the falling edge of
CONVST as stated in the timing requirements section. Data reads or bus three-state operations should not be
attempted within this period. Any other combination of CS and RD 3-states the parallel output. Refer to Table 1
for ideal output codes.
Table 1. Ideal Input Voltages and Output Codes (1)
DESCRIPTION
ANALOG VALUE
BINARY CODE
HEX CODE
Full scale
Vref – 1 LSB
1111 1111 1111
FFF
Midscale
Vref/2
1000 0000 0000
800
Midscale – 1 LSB
Vref/2 – 1 LSB
0111 1111 1111
7FF
Zero
0V
0000 0000 0000
000
(1)
Full-scale range = Vref and least significant bit (LSB) = Vref/4096
The output data appears as a full 12-bit word (D11–D0) on pins DB11–DB0 (MSB–LSB) if BYTE is low.
READING THE DATA IN BYTE MODE
The result can also be read on an 8-bit bus for convenience by using pins DB11–DB4. In this case two reads are
necessary; the first as before, leaving BYTE low and reading the 8 most significant bits on pins DB11–DB4, and
then bringing BYTE high. When BYTE is high, the lower bits (D3–D0) followed by all zeros are on pins
DB11–DB4 (refer to Table 2).
These multi-word read operations can be performed with multiple active RD signals (toggling) or with RD tied low
for simplicity.
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
19
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
Table 2. Conversion Data Read Out
DATA READ OUT
BYTE
DB11–DB4
DB3–DB0
High
D3–D0, 0000
All zeroes
Low
D11–D4
D3–D0
Also refer to the DATA READ and DEVICE OPERATION AND DATA READ IN BACK-TO-BACK CONVERSION
sections for more details.
Reset
Refer to the POWERDOWN/RESET section for the device reset sequence.
It is recommended to reset the device after power on. A reset can be issued once the power has reached 95% of
its final value.
PWD/RST is an asynchronous active low input signal. A current conversion is aborted no later than 45 ns after
the converter is in the reset mode. In addition, the device outputs a FE0 code to indicate a reset condition. The
converter returns back to normal operation mode immediately after the PWD/RST input is brought high.
Data is not valid for the first four conversions after a device reset.
Powerdown
Refer to the POWERDOWN/RESET section for the device powerdown sequence.
The device enters powerdown mode if a PWD/RST low duration is extended for more than a period of tw7.
The converter goes back to normal operation mode no later than a period of td13 after the PWD/RST input is
brought high.
After this period, normal conversion and sampling operation can be started as discussed in previous sections.
Data is not valid for the first four conversions after a device reset.
Nap Mode
Refer to the NAP MODE section in the DESCRIPTION AND TIMING DIAGRAMS section for information.
20
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
APPLICATION INFORMATION
LAYOUT
For optimum performance, care should be taken with the physical layout of the ADS7882 circuitry.
As the ADS7882 offers single-supply operation, it is often used in close proximity with digital logic,
micro-controllers, 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 acceptable 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 the end of sampling (within quiet sampling time) and just
prior to latching the output of the analog comparator during the conversion phase. Thus, driving any single
conversion for an n-bit SAR converter, there are n+1 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 ADS7882 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 REFIN (pin 1) directly to REFM (pin 48).
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 too close to the grounding point of a micro-controller 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 that is separate from the
connection for +VBD and digital logic until they are connected at the power entry point onto the PCB. Power to
the ADS7882 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 3 for the placement of capacitor. In addition to a 0.1-µF capacitor, a 1-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 3. Power Supply Decoupling Capacitor Placement
POWER SUPPLY PLANE
CONVERTER ANALOG SIDE
SUPPLY PINS
Pairs of pins that require a shortest path to decoupling
capacitors
(4,5), (9,8), (10,11), (13, 15), (43, 44) (46, 45)
Pins that require no decoupling
14, 12
Analog 5 V
CONVERTER
DIGITAL SIDE
(24, 25), (34, 35)
+VA
0.1 µF
1 µF
ADS7882
AGND
AGND
0.1 µF
REFOUT
External Reference from
REF5025 or REF3225
REFIN
1 µF
0.1 µF
REFM
AGND
21 Ω
Analog Input
Circuit
+IN
21 Ω
−IN
Figure 33. Using External Reference
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
21
ADS7882
SLAS630 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
Analog 5 V
+VA
0.1 µF
1 µF
ADS7882
AGND
AGND
REFOUT
REFIN
0.1 µF
1 µF
REFM
AGND
21 Ω
+IN
Analog Input
Circuit
21 Ω
−IN
Figure 34. Using Internal Reference
130 pF
604 Ω
Signal Input,
Bipolar, "1.25 V
2.5 V DC
3 kΩ
604 Ω
_
100 Ω
THS4031
12 Ω
21 Ω
+IN
+
21 Ω
150 pF
ADS7882
−IN
1 kΩ
1 nF
AGND
AGND
Figure 35. Typical Analog Input Circuit for Bipolar Signal
50 W
_
Signal Input
Unipolar 0 V–2.5 V
THS4031
+
12 W
21 W
150 pF
21 W
+IN
ADS7882
–IN
Figure 36. Typical Application Input Circuit for Unipolar Signal
22
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
ADS7882
www.ti.com ........................................................................................................................................................................................... SLAS630 – DECEMBER 2008
GPIO
CS
GPIO
BYTE
GPIO
CONVST
ADS7882
Microcontroller
P[7:0]
DB[11:4]
RD
RD
INT
BUSY
Figure 37. Interfacing With Microcontroller
Submit Documentation Feedback
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS7882
23
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
ADS7882IPFBR
ACTIVE
TQFP
PFB
48
1000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS7882
ADS7882IPFBT
ACTIVE
TQFP
PFB
48
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS7882
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
