ADS7825UB [TI]

4 通道、16 位采样 CMOS 模数转换器 | DW | 28 | -40 to 85;
ADS7825UB
型号: ADS7825UB
厂家: TEXAS INSTRUMENTS    TEXAS INSTRUMENTS
描述:

4 通道、16 位采样 CMOS 模数转换器 | DW | 28 | -40 to 85

光电二极管 转换器 模数转换器
文件: 总22页 (文件大小:394K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
®
ADS7825  
ADS7825  
ADS7825  
www.burr-brown.com/databook/ADS7825.html  
4 Channel, 16-Bit Sampling CMOS A/D Converter  
FEATURES  
DESCRIPTION  
25µs max SAMPLING AND CONVERSION  
SINGLE +5V SUPPLY OPERATION  
PIN-COMPATIBLE WITH 12-BIT ADS7824  
PARALLEL AND SERIAL DATA OUTPUT  
28-PIN 0.3" PLASTIC DIP AND SOIC  
±2.0 LSB max INL  
The ADS7825 can acquire and convert 16 bits to  
within ±2.0 LSB in 25µs max while consuming only  
50mW max. Laser-trimmed scaling resistors provide  
the standard industrial ±10V input range and channel-  
to-channel matching of ±0.1%. The ADS7825 is a  
low-power 16-bit sampling A/D with a four channel  
input multiplexer, S/H, clock, reference, and a  
parallel/serial microprocessor interface. It can be con-  
figured in a continuous conversion mode to sequen-  
tially digitize all four channels. The 28-pin ADS7825  
is available in a plastic 0.3" DIP and in a SOIC, both  
fully specified for operation over the industrial –40°C  
to +85°C range.  
50mW max POWER DISSIPATION  
50µW POWER DOWN MODE  
±10V INPUT RANGE, FOUR CHANNEL  
MULTIPLEXER  
CONTINUOUS CONVERSION MODE  
Channel  
A0  
Continuous Conversion  
CONTC  
A1  
40k  
R/C  
CS  
AIN0  
AIN1  
Successive Approximation Register  
and Control Logic  
Clock  
PWRD  
20kΩ  
40kΩ  
8kΩ  
8kΩ  
CDAC  
BUSY  
20kΩ  
40kΩ  
Serial  
DATACLK  
SDATA  
Data  
Out  
AIN2  
AIN3  
Comparator  
or  
20kΩ  
40kΩ  
8kΩ  
8kΩ  
Parallel  
Data  
Out  
8
D7-D0  
BYTE  
20kΩ  
Internal  
+2.5V Ref  
Buffer  
6kΩ  
CAP  
REF  
International Airport Industrial Park  
Mailing Address: PO Box 11400, Tucson, AZ 85734  
FAXLine: (800) 548-6133 (US/Canada Only)  
Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706  
Tel: (520) 746-1111  
Twx: 910-952-1111  
Internet: http://www.burr-brown.com/  
Cable: BBRCORP  
Telex: 066-6491  
FAX: (520) 889-1510  
Immediate Product Info: (800) 548-6132  
©1996 Burr-Brown Corporation  
PDS-1304B  
Printed in U.S.A. October, 1997  
SBAS045  
SPECIFICATIONS  
ELECTRICAL  
At TA = –40°C to +85°C, fS = 40kHz, VS1 = VS2 = VS = +5V ±5%, using external reference, CONTC = 0V, unless otherwise specified.  
ADS7825P, U  
TYP  
ADS7825PB, UB  
PARAMETER  
RESOLUTION  
CONDITIONS  
MIN  
MAX  
MIN  
TYP  
MAX  
UNITS  
(1)  
16  
Bits  
ANALOG INPUT  
Voltage Range  
Impedance  
±10V  
45.7  
35  
V
kΩ  
pF  
Channel On or Off  
Capacitance  
THROUGHPUT SPEED  
Conversion Time  
Acquisition Time  
Multiplexer Settling Time  
Complete Cycle (Acquire and Convert)  
Complete Cycle (Acquire and Convert)  
Throughput Rate  
20  
5
5
µs  
µs  
µs  
µs  
µs  
Includes Acquisition  
CONTC = +5V  
25  
40  
40  
15  
kHz  
DC ACCURACY  
Integral Linearity Error  
No Missing Codes  
Transition Noise(3)  
Full Scale Error(4)  
Full Scale Error Drift  
Full Scale Error(4)  
Full Scale Error Drift  
Bipolar Zero Error  
±3  
±2  
LSB(2)  
16  
0.8  
±7  
±2  
±2  
±5  
LSB  
%
ppm/°C  
%
ppm/°C  
mV  
ppm/°C  
%
Internal Reference  
Internal Reference  
±0.5  
±0.5  
±10  
±0.25  
±0.25  
Bipolar Zero Error Drift  
Channel-to-Channel Mismatch  
Power Supply Sensitivity  
±0.1  
±8  
±0.1  
+4.75 < VS < +5.25  
fIN = 1kHz  
LSB  
AC ACCURACY  
Spurious-Free Dynamic Range(5)  
Total Harmonic Distortion  
Signal-to-(Noise+Distortion)  
Signal-to-Noise  
90  
dB  
dB  
dB  
dB  
dB  
f
IN = 1kHz  
IN = 1kHz  
IN = 1kHz  
fIN = 1kHz  
–90  
f
f
83  
83  
100  
86  
86  
Channel Separation(6)  
–3dB Bandwidth  
Useable Bandwidth(7)  
120  
2
90  
MHz  
kHz  
SAMPLING DYNAMICS  
Aperture Delay  
Transient Response(8)  
Overvoltage Recovery(9)  
40  
5
1
ns  
µs  
µs  
FS Step  
REFERENCE  
Internal Reference Voltage  
Internal Reference Source Current  
(Must use external buffer)  
External Reference Voltage Range  
for Specified Linearity  
2.48  
2.3  
2.5  
1
2.52  
V
µA  
2.5  
2.7  
V
External Reference Current Drain  
VREF = +2.5V  
100  
µA  
DIGITAL INPUTS  
Logic Levels  
VIL  
VIH  
IIL  
–0.3  
+2.4  
+0.8  
VS +0.3V  
±10  
V
V
µA  
µA  
IIH  
±10  
DIGITAL OUTPUTS  
Data Format  
Data Coding  
VOL  
Parallel in two bytes; Serial  
Binary Two's Complement  
ISINK = 1.6mA  
ISOURCE = 500µA  
High-Z State, VOUT = 0V to VS  
High-Z State  
+0.4  
V
V
µA  
pF  
VOH  
+4  
±5  
15  
Leakage Current  
Output Capacitance  
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN  
assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject  
to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not  
authorize or warrant any BURR-BROWN product for use in life support devices and/or systems.  
®
ADS7825  
2
SPECIFICATIONS (CONT)  
ELECTRICAL  
At TA = –40°C to +85°C, fS = 40kHz, VS1 = VS2 = VS = +5V ±5%, using external reference, CONTC = 0V, unless otherwise specified.  
ADS7825P, U  
TYP  
ADS7825PB, UB  
PARAMETER  
CONDITIONS  
MIN  
MAX  
MIN  
TYP  
MAX  
UNITS  
DIGITAL TIMING  
Bus Access Time  
Bus Relinquish Time  
Data Clock  
Internal Clock (Output only when  
transmitting data)  
External Clock  
PAR/SER = +5V  
PAR/SER = +5V  
PAR/SER = 0V  
EXT/INT LOW  
83  
83  
ns  
ns  
0.5  
0.1  
1.5  
10  
MHz  
MHz  
EXT/INT HIGH  
POWER SUPPLIES  
VS1 = VS2 = VS  
Power Dissipation  
+4.75  
+5  
50  
+5.25  
50  
V
mW  
µW  
fS = 40kHz  
PWRD HIGH  
TEMPERATURE RANGE  
Specified Performance  
Storage  
–40  
–65  
+85  
+150  
°C  
°C  
Thermal Resistance (θJA  
)
Plastic DIP  
SOIC  
75  
75  
°C/W  
°C/W  
NOTES: (1) An asterik () specifies same value as grade to the left. (2) LSB means Least Significant Bit. For the 16-bit, ±10V input ADS7825, one LSB is 305µV. (3)  
Typical rms noise at worst case transitions and temperatures. (4) Full scale error is the worst case of –Full Scale or +Full Scale untrimmed deviation from ideal first and  
last code transitions, divided by the transition voltage (not divided by the full-scale range) and includes the effect of offset error. (5) All specifications in dB are referred  
to a full-scale ±10V input. (6) A full scale sinewave input on one channel will be attenuated by this amount on the other channels. (7) Useable Bandwidth defined as  
Full-Scale input frequency at which Signal-to-(Noise+Distortion) degrades to 60dB, or 10 bits of accuracy. (8) The ADS7825 will accurately acquire any input step if given  
a full acquisition period after the step. (9) Recovers to specified performance after 2 x FS input overvoltage, and normal acquisitions can begin.  
PACKAGE/ORDERING INFORMATION  
PACKAGE  
DRAWING  
NUMBER(1)  
MINIMUM SIGNAL-  
TO-(NOISE + DISTORTION)  
RATIO (dB)  
TEMPERATURE  
RANGE  
MAXIMUM INTEGRAL  
LINEARITY ERROR (LSB)  
PRODUCT  
PACKAGE  
ADS7825P  
ADS7825PB  
ADS7825U  
ADS7825UB  
Plastic Dip  
Plastic Dip  
SOIC  
246  
246  
217  
217  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
±3  
±2  
±3  
±2  
83  
86  
83  
86  
SOIC  
NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book.  
ABSOLUTE MAXIMUM RATINGS  
PIN CONFIGURATION  
TOP VIEW  
DIP/SOIC  
Analog Inputs: AIN0, AIN1, AIN2, AIN3 .............................................. ±15V  
REF ................................... (AGND2 –0.3V) to (VS + 0.3V)  
CAP ........................................Indefinite Short to AGND2,  
Momentary Short to VS  
1
2
3
4
5
6
7
8
9
28  
27  
VS1  
VS2  
AGND1  
AIN0  
VS1 and VS2 to AGND2........................................................................... 7V  
VS1 to VS2 .......................................................................................... ±0.3V  
Difference between AGND1, AGND2 and DGND ............................. ±0.3V  
Digital Inputs and Outputs.......................................... –0.3V to (VS + 0.3V)  
Maximum Junction Temperature ..................................................... 150°C  
Internal Power Dissipation ............................................................. 825mW  
Lead Temperature (soldering, 10s)................................................ +300°C  
Maximum Input Current to Any Pin ................................................. 100mA  
AIN1  
26 PWRD  
25 CONTC  
24 BUSY  
23 CS  
AIN2  
AIN3  
CAP  
REF  
22 R/C  
ADS7825  
ELECTROSTATIC  
DISCHARGE SENSITIVITY  
This integrated circuit can be damaged by ESD. Burr-Brown  
recommends that all integrated circuits be handled with  
appropriate precautions. Failure to observe proper handling  
and installation procedures can cause damage.  
AGND2  
D7  
21 BYTE  
20 PAR/SER  
19 A0  
TRI-STATE  
TRI-STATE  
TRI-STATE  
EXT/INT  
D6 10  
D5 11  
18 A1  
D4 12  
17 D0  
TAG  
16 D1  
SYNC  
D3 13  
SDATA  
DATACLK  
ESD damage can range from subtle performance degrada-  
tion 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.  
DGND 14  
15 D2  
®
ADS7825  
3
PIN ASSIGNMENTS  
PIN #  
NAME  
I/O  
DESCRIPTION  
1
2
3
4
5
6
7
AGND1  
AIN0  
AIN1  
AIN2  
AIN3  
CAP  
Analog Ground. Used internally as ground reference point.  
Analog Input Channel 0. Full-scale input range is ±10V.  
Analog Input Channel 1. Full-scale input range is ±10V.  
Analog Input Channel 2. Full-scale input range is ±10V.  
Analog Input Channel 3. Full-scale input range is ±10V.  
Internal Reference Output Buffer. 2.2µF Tantalum to ground.  
REF  
Reference Input/Output. Outputs +2.5V nominal. If used externally, must be buffered to maintain ADS7825 accuracy.  
Can also be driven by external system reference. In both cases, bypass to ground with a 2.2µF Tantalum capacitor.  
8
AGND2  
D7  
Analog Ground.  
9
O
O
Parallel Data Bit 7 if PAR/SER HIGH; Tri-state if PAR/SER LOW. See Table I.  
Parallel Data Bit 6 if PAR/SER HIGH; Tri-state if PAR/SER LOW. See Table I.  
Parallel Data Bit 5 if PAR/SER HIGH; Tri-state if PAR/SER LOW. See Table I.  
10  
11  
12  
D6  
D5  
O
D4  
I/O  
Parallel Data Bit 4 if PAR/SER HIGH; if PAR/SER LOW, a LOW level input here will transmit serial data on SDATA from  
the previous conversion using the internal serial clock; a HIGH input here will transmit serial data using an external serial  
clock input on DATACLK (D2). See Table I.  
13  
14  
15  
D3  
DGND  
D2  
O
Parallel Data Bit 3 if PAR/SER HIGH; SYNC output if PAR/SER LOW. See Table I.  
Digital Ground.  
I/O  
Parallel Data Bit 2 if PAR/SER HIGH; if PAR/SER LOW, this will output the internal serial clock if EXT/INT (D4) is LOW;  
will be an input for an external serial clock if EXT/INT (D4) is HIGH. See Table I.  
16  
17  
18  
19  
20  
D1  
D0  
O
I/O  
I/O  
I/O  
I
Parallel Data Bit 1 if PAR/SER HIGH; SDATA serial data output if PAR/SER LOW. See Table I.  
Parallel Data Bit 0 if PAR/SER HIGH; TAG data input if PAR/SER LOW. See Table I.  
Channel Address. Input if CONTC LOW, output if CONTC HIGH. See Table I.  
Channel Address. Input if CONTC LOW, output if CONTC HIGH. See Table I.  
A1  
A0  
PAR/SER  
Select Parallel or Serial Output. If HIGH, parallel data will be output on D0 thru D7. If LOW, serial data will be output on  
SDATA. See Table I and Figure 1.  
21  
22  
23  
24  
25  
26  
BYTE  
R/C  
I
I
Byte Select. Only used with parallel data, when PAR/SER HIGH. Determines which byte is available on D0 thru D7.  
Changing BYTE with CS LOW and R/C HIGH will cause the data bus to change accordingly. LOW selects the 8 MSBs;  
HIGH selects the 8 LSBs. See Figures 2 and 3  
Read/Convert Input. With CS LOW, a falling edge on R/C puts the internal sample/hold into the hold state and starts a  
conversion. With CS LOW, a rising edge on R/C enables the output data bits if PAR/SER HIGH, or starts transmission  
of serial data if PAR/SER LOW and EXT/INT HIGH.  
CS  
I
Chip Select. Internally OR'd with R/C. With CONTC LOW and R/C LOW, a falling edge on CS will initiate a conversion.  
With R/C HIGH, a falling edge on CS will enable the output data bits if PAR/SER HIGH, or starts transmission of serial  
data if PAR/SER LOW and EXT/INT HIGH.  
BUSY  
CONTC  
PWRD  
O
I
Busy Output. Falls when conversion is started; remains LOW until the conversion is completed and the data is latched  
into the output register. In parallel output mode, output data will be valid when BUSY rises, so that the rising edge  
can be used to latch the data.  
Continuous Conversion Input. If LOW, conversions will occur normally when initiated using CS and R/C; if HIGH,  
acquisition and conversions will take place continually, cycling through all four input channels, as long as CS, R/C and  
PWRD are LOW. See Table I. For serial mode only.  
I
Power Down Input. If HIGH, conversions are inhibited and power consumption is significantly reduced. Results from the  
previous conversion are maintained in the output register. In the continuous conversion mode, the multiplexer address  
channel is reset to channel 0.  
27  
28  
VS2  
VS1  
Supply Input. Nominally +5V. Connect directly to pin 28. Decouple to ground with 0.1µF ceramic and 10µF Tantalum  
capacitors.  
Supply Input. Nominally +5V. Connect directly to pin 27.  
®
ADS7825  
4
TYPICAL PERFORMANCE CURVES  
At TA = +25°C, fS = 40kHz, VS1 = VS2 = +5V, using internal reference, unless otherwise noted.  
FREQUENCY SPECTRUM  
(8192 Point FFT; fIN = 1.02kHz, –0.5dB)  
CROSSTALK vs INPUT FREQUENCY  
(Active Channel Amplitude = –0.1dB)  
0
–10  
–60.0  
–70.0  
–20  
Adjacent Channels, Worst Pair  
–30  
–80.0  
–40  
–50  
–90.0  
Adjacent Channels  
–60  
–100.0  
–110.0  
–120.0  
–130.0  
–140.0  
–70  
Non-Adjacent Channels  
–80  
–90  
–100  
–110  
–120  
–130  
Measurement Limit  
0
5
10  
15  
20  
100  
1k  
10k  
100k  
Frequency (kHz)  
Active Channel Input Frequency (Hz)  
ADJACENT CHANNEL CROSSTALK, WORST PAIR  
(8192 Point FFT; AIN3 = 1.02kHz, –0.1dB; AIN2 = AGND)  
ADJACENT CHANNEL CROSSTALK, WORST PAIR  
(8192 Point FFT; AIN3 = 10.1kHz, –0.1dB; AIN2 = AGND )  
0
–10  
0
–10  
–20  
–20  
–30  
–30  
–40  
–40  
–50  
–50  
–60  
–60  
–70  
–70  
–80  
–80  
–90  
–90  
–100  
–110  
–120  
–130  
–100  
–110  
–120  
–130  
0
5
10  
15  
20  
0
5
10  
15  
20  
Frequency (kHz)  
Frequency (kHz)  
SIGNAL-TO-(NOISE + DISTORTION)  
vs INPUT FREQUENCY AND INPUT AMPLITUDE  
SIGNAL-TO-(NOISE + DISTORTION)  
vs INPUT FREQUENCY (fIN = –0.1dB)  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
100  
90  
80  
70  
60  
50  
40  
30  
0dB  
–20dB  
–60dB  
0
2
4
6
8
10 12 14  
16  
18 20  
100  
1k  
10k  
100k  
Input Signal Frequency (kHz)  
Input Signal Frequency (Hz)  
®
ADS7825  
5
TYPICAL PERFORMANCE CURVES (CONT)  
At TA = +25°C, fS = 40kHz, VS1 = VS2 = +5V, using internal reference, unless otherwise noted.  
A. C. PARAMETERS vs TEMPERATURE  
(fIN = 1kHz, –0.1dB)  
110  
105  
100  
95  
–110  
–105  
–100  
–95  
3
2
All Codes INL  
1
SFDR  
0
–1  
–2  
–3  
0
8192  
16384 24576 32768 40960 49152 57344 65535  
Decimal Code  
SNR  
THD  
90  
–90  
3
2
All Codes DNL  
85  
–85  
SINAD  
1
0
80  
–50  
–80  
100  
–1  
–2  
–3  
–25  
0
25  
50  
75  
Temperature (°C)  
0
8192  
16384 24576 32768 40960 49152 57344 65535  
Decimal Code  
ENDPOINT ERRORS  
2
POWER SUPPLY RIPPLE SENSITIVITY  
INL/DNL DEGRADATION PER LSB OF P-P RIPPLE  
BPZ Error  
1
0
1
10–1  
10–2  
10–3  
10–4  
10–5  
–1  
–2  
0.2  
INL  
+FS Error  
0
–0.2  
0.2  
DNL  
–FS Error  
101  
102  
103  
104  
105  
106  
107  
0
Power Supply Ripple Frequency (Hz)  
–0.2  
–50  
–25  
0
25  
50  
75  
100  
Temperature (°C)  
INTERNAL REFERENCE VOLTAGE  
vs TEMPERATURE  
CONVERSION TIME vs TEMPERATURE  
20.4  
20.2  
20  
2.520  
2.515  
2.510  
2.505  
2.500  
2.495  
2.490  
2.485  
2.480  
19.8  
19.6  
–50  
–25  
0
25  
50  
75  
100  
–50  
–25  
0
25  
50  
75  
100  
Temperature (°C)  
Temperature (°C)  
®
ADS7825  
6
BASIC OPERATION  
PARALLEL OUTPUT  
SERIAL OUTPUT  
Figure 1b shows a basic circuit to operate the ADS7825 with  
serial output (Channel 0 selected). Taking R/C (pin 22)  
LOW for 40ns (12µs max) will initiate a conversion and  
output valid data from the previous conversion on SDATA  
(pin 16) synchronized to 16 clock pulses output on  
DATACLK (pin 15). BUSY (pin 24) will go LOW and stay  
LOW until the conversion is completed and the serial data  
has been transmitted. Data will be output in Binary Two’s  
Complement format, MSB first, and will be valid on both the  
rising and falling edges of the data clock. BUSY going  
HIGH can be used to latch the data. All convert commands  
will be ignored while BUSY is LOW.  
Figure 1a shows a basic circuit to operate the ADS7825 with  
parallel output (Channel 0 selected). Taking R/C (pin 22)  
LOW for 40ns (12µs max) will initiate a conversion. BUSY  
(pin 24) will go LOW and stay LOW until the conversion is  
completed and the output register is updated. If BYTE (pin  
21) is LOW, the 8 most significant bits will be valid when  
pin 24 rises; if BYTE is HIGH, the 8 least significant bits  
will be valid when BUSY rises. Data will be output in  
Binary Two’s Complement format. BUSY going HIGH can  
be used to latch the data. After the first byte has been read,  
BYTE can be toggled allowing the remaining byte to be  
read. All convert commands will be ignored while BUSY is  
LOW.  
The ADS7825 will begin tracking the input signal at the end  
of the conversion. Allowing 25µs between convert com-  
mands assures accurate acquisition of a new signal.  
The ADS7825 will begin tracking the input signal at the end  
of the conversion. Allowing 25µs between convert com-  
mands assures accurate acquisition of a new signal.  
Parallel Output  
(a)  
1
2
28  
27  
26  
25  
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
0.1µF 10µF  
+5V  
±10V  
+
+
3
4
BUSY  
5
Convert Pulse  
6
+
R/C  
BYTE  
2.2µF  
7
+
ADS7825  
2.2µF  
8
40ns min  
+5V(1)  
9
10  
11  
12  
13  
14  
(b)  
Serial Output  
Pin 21 D15 D14 D13 D12 D11  
LOW  
D10 D9 D8  
D2 D1 D0  
Pin 21 D7 D6 D5 D4 D3  
HIGH  
1
2
28  
27  
26  
25  
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
0.1µF 10µF  
NOTE: (1) PAR/SER = 5V  
+5V  
±10V  
+
+
3
4
BUSY  
R/C  
5
Convert Pulse  
40ns min  
6
+
2.2µF  
7
+
ADS7825  
2.2µF  
8
(3)  
NC(2)  
NC(2)  
NC(2)  
9
10  
11  
12  
13  
14  
EXT/INT  
SYNC  
SDATA  
DATACLK(1)  
NOTES: (1) DATACLK (pin 15) is an output when EXT/INT (pin 12) is LOW  
and an input when EXT/INT is HIGH. (2) NC = no connection. (3) PAR/SER = 0V.  
FIGURE 1. Basic Connection Diagram, (a) Parallel Output, (b) Serial Output.  
7
®
ADS7825  
STARTING A CONVERSION  
The combination of CS (pin 23) and R/C (pin 22) LOW for  
a minimum of 40ns places the sample/hold of the ADS7825  
in the hold state and starts conversion ‘n’. BUSY (pin 24)  
will go LOW and stay LOW until conversion ‘n’ is com-  
pleted and the internal output register has been updated. All  
new convert commands during BUSY LOW will be ignored.  
CS and/or R/C must go HIGH before BUSY goes HIGH or  
a new conversion will be initiated without sufficient time to  
acquire a new signal.  
initiating a conversion. If, however, it is critical that CS or  
R/C initiates conversion ‘n’, be sure the less critical input is  
LOW at least 10ns prior to the initiating input. If EXT/INT  
(pin 12) is LOW when initiating conversion ‘n’, serial data  
from conversion ‘n – 1’ will be output on SDATA (pin 16)  
following the start of conversion ‘n’. See Internal Data  
Clock in the Reading Data section.  
To reduce the number of control pins, CS can be tied LOW  
using R/C to control the read and convert modes. This will  
have no effect when using the internal data clock in the serial  
output mode. However, the parallel output and the serial  
output (only when using an external data clock) will be  
affected whenever R/C goes HIGH. Refer to the Reading  
Data section and Figures 2, 3, 5, and 6.  
The ADS7825 will begin tracking the input signal at the end  
of the conversion. Allowing 25µs between convert com-  
mands assures accurate acquisition of a new signal. Refer to  
Tables Ia and Ib for a summary of CS, R/C, and BUSY states  
and Figures 2 through 6 and Table II for timing information.  
CS and R/C are internally OR’d and level triggered. There  
is not a requirement which input goes LOW first when  
INPUTS  
OUTPUTS  
CS  
R/C  
BYTE CONTC PWRD BUSY  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
COMMENTS  
1
X
0
X
0
1
X
X
0
X
X
X
X
X
X
X
X
X
Hi-Z  
Hi-Z  
D15  
Hi-Z  
Hi-Z  
D14  
Hi-Z  
Hi-Z  
D13  
Hi-Z  
Hi-Z  
D12  
Hi-Z  
Hi-Z  
D11  
Hi-Z  
Hi-Z  
D10  
Hi-Z  
Hi-Z  
D9  
Hi-Z  
Hi-Z  
D8  
Results from last  
(MSB)  
D7  
completed conversion.  
Results from last  
(LSB) completed conversion.  
0
0
1
1
1
X
X
X
X
X
D6  
D5  
D4  
D3  
D2  
D1  
D0  
X
↑↓  
↑↓  
↑↓  
↑↓  
↑↓  
↑↓  
↑↓  
↑↓  
Data will change at the  
end of a conversion.  
TABLE Ia. Read Control for Parallel Data (PAR/SER = 5V.)  
D4  
D3  
D2  
D1  
D0  
CS  
R/C  
CONTC PWRD BUSY D7, D6, D5 EXT/INT SYNC DATACLK SDATA TAG  
Input  
Input  
Input  
Input  
Output  
Output  
Input Output  
I/O  
Output Input COMMENTS  
1
X
0
X
0
X
X
0
X
X
X
1
1
1
Hi-Z  
Hi-Z  
HI-Z  
LOW  
LOW  
LOW  
LOW  
LOW  
LOW  
Output  
Output  
Output  
Hi-Z  
Hi-Z  
X
X
X
Output  
Starts transmission of data from previous  
conversion on SDATA synchronized to 16  
pulses output on DATACLK.  
0
0
X
1
Hi-Z  
LOW  
LOW  
Output  
Output  
X
Starts transmission of data from previous  
conversion on SDATA synchronized to 16  
pulses output on DATACLK.  
0
0
1
1
0
0
X
X
X
Hi-Z  
Hi-Z  
HIGH  
HIGH  
LOW  
LOW  
Input  
Input  
Output  
Output  
Input The level output on SDATA will be the level  
input on TAG 16 DATACLK input cycles.  
Input At the end of the conversion, when BUSY  
rises, data from the conversion will be shifted  
into the output registers. If DATACLK is HIGH,  
valid data will be lost.  
0
0
1
0
0
0
1
X
X
0
1
1
Hi-Z  
Hi-Z  
Hi-Z  
HIGH  
HIGH  
LOW  
LOW  
LOW  
LOW  
Input  
Input  
Output  
Output  
Output  
X
X
X
Initiates transmission of a HIGH pulse on  
SYNC followed by data from last completed  
conversion on SDATA synchronized to the  
input on DATACLK.  
Initiates transmission of a HIGH pulse on  
SYNC followed by data from last completed  
conversion on SDATA synchronized to the  
input on DATACLK.  
Output  
Starts transmission of data from previous  
conversion on SDATA synchronized to 16  
pulses output on DATACLK  
0
0
1
0
X
X
1
1
X
X
X
X
X
X
X
X
Hi-Z  
Hi-Z  
Hi-Z  
Hi-Z  
HIGH  
HIGH  
LOW  
LOW  
Output  
Output  
LOW  
Input  
Input  
Output  
Output  
Output  
Output  
X
X
X
X
SDATA becomes active. Inputs on DATACLK  
shift out data.  
SDATA becomes active. Inputs on DATACLK  
shift out data.  
Output  
Output  
Restarts continuous conversion mode (n – 1 data  
transmitted when BUSY is LOW).  
LOW  
Restarts continuous conversion mode (n – 1 data  
transmitted when BUSY is LOW).  
TABLE Ib. Read Control for Serial Data (PAR/SER = 0V.)  
®
ADS7825  
8
t1  
t1  
R/C  
t3  
t3  
t4  
BUSY  
t5  
t6  
t6  
t7  
t8  
Convert  
Acquire  
Convert  
t12  
Acquire  
MODE  
t12  
t11  
t10  
Parallel  
Data Bus  
Previous  
High Byte Valid  
Previous High  
Byte Valid  
Previous Low  
Byte Valid  
High Byte  
Valid  
Low Byte  
Valid  
High Byte  
Valid  
Hi-Z  
Not Valid  
Hi-Z  
t9  
t2  
t12  
t12  
t21  
t21  
t9  
t12  
t12  
BYTE  
FIGURE 2. Conversion Timing with Parallel Output (CS LOW).  
t21  
t21  
t21  
t21  
t21  
R/C  
CS  
t1  
t3  
t4  
BUSY  
BYTE  
t21  
t21  
t21  
DATA  
BUS  
Hi-Z State  
High Byte Hi-Z State Low Byte  
t12 t9 t12  
Hi-Z State  
t9  
FIGURE 3. Using CS to Control Conversion and Read Timing with Parallel Outputs.  
t7 + t8  
CS or R/C(1)  
t14  
1
2
3
15  
16  
1
2
t13  
DATACLK  
t16  
t15  
SDATA  
BUSY  
MSB Valid  
Bit 14 Valid  
Bit 13 Valid  
Bit 1 Valid  
LSB Valid  
MSB Valid  
Bit 14 Valid  
Hi-Z  
Hi-Z  
t25  
(Results from previous conversion.)  
t26  
NOTE: (1) If controlling with CS, tie R/C LOW. If controlling with R/C, tie CS LOW.  
FIGURE 4. Serial Data Timing Using Internal Data Clock (TAG LOW).  
®
ADS7825  
9
®
ADS7825  
10  
®
ADS7825  
11  
after the start of conversion ‘n’. Do not attempt to read data  
beyond 12µs after the start of conversion ‘n’ until BUSY  
(pin 24) goes HIGH; this may result in reading invalid data.  
Refer to Table II and Figures 2 and 3 for timing constraints.  
READING DATA  
PARALLEL OUTPUT  
To use the parallel output, tie PAR/SER (pin 20) HIGH. The  
parallel output will be active when R/C (pin 22) is HIGH and  
CS (pin 23) is LOW. Any other combination of CS and R/C  
will tri-state the parallel output. Valid conversion data can be  
read in two 8-bit bytes on D7-D0 (pins 9-13 and 15-17). When  
BYTE (pin 21) is LOW, the 8 most significant bits will be  
valid with the MSB on D7. When BYTE is HIGH, the 8 least  
significant bits will be valid with the LSB on D0. BYTE can  
be toggled to read both bytes within one conversion cycle.  
SERIAL OUTPUT  
When PAR/SER (pin 20) is LOW, data can be clocked out  
serially with the internal data clock or an external data clock.  
When EXT/INT (pin 12) is LOW, DATACLK (pin 15) is an  
output and is always active regardless of the state of CS (pin  
23) and R/C (pin 22). The SDATA output is active when  
BUSY (pin 24) is LOW. Otherwise, it is in a tri-state  
condition. When EXT/INT is HIGH, DATACLK is an input.  
The SDATA output is active when CS is LOW and R/C is  
HIGH. Otherwise, it is in a tri-state condition. Regardless of  
the state of EXT/INT, SYNC (pin 13) is an output and always  
active, while TAG (pin 17) is always an input.  
Upon initial power up, the parallel output will contain  
indeterminate data.  
PARALLEL OUTPUT (After a Conversion)  
After conversion ‘n’ is completed and the output registers  
have been updated, BUSY (pin 24) will go HIGH. Valid data  
from conversion ‘n’ will be available on D7-D0 (pins 9-13  
and 15-17). BUSY going HIGH can be used to latch the  
data. Refer to Table II and Figures 2 and 3 for timing  
constraints.  
INTERNAL DATA CLOCK (During A Conversion)  
To use the internal data clock, tie EXT/INT (pin 12) LOW.  
The combination of R/C (pin 22) and CS (pin 23) LOW will  
initiate conversion ‘n’ and activate the internal data clock  
(typically 900kHz clock rate). The ADS7825 will output 16  
bits of valid data, MSB first, from conversion ‘n – 1’ on  
SDATA (pin 16), synchronized to 16 clock pulses output on  
PARALLEL OUTPUT (During a Conversion)  
After conversion ‘n’ has been initiated, valid data from  
conversion ‘n – 1’ can be read and will be valid up to 12µs  
SYMBOL  
t1  
DESCRIPTION  
MIN  
TYP  
MAX  
12  
UNITS  
µs  
µs  
ns  
µs  
ns  
ns  
µs  
µs  
µs  
ns  
ns  
µs  
ns  
µs  
µs  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
ns  
Convert Pulse Width  
0.04  
t2  
Start of Conversion to New Data Valid  
Start of Conversion to BUSY LOW  
BUSY LOW  
20  
21  
t3  
85  
t4  
20  
90  
40  
20  
4
21  
t5  
End of Conversion to BUSY HIGH  
Aperture Delay  
t6  
t7  
Conversion Time  
21  
5
t8  
Acquisition Time  
t7 + t8  
t9  
Throughput Time  
25  
83  
Bus Relinquish Time  
10  
20  
12  
t10  
t11  
t12  
t13  
t14  
t15  
t16  
t17  
t18  
t19  
t20  
t21  
t22  
t23  
t24  
t25  
t26  
t27  
t28  
t29  
t30  
Data Valid to BUSY HIGH  
60  
20  
Start of Conversion to Previous Data Not Valid  
Bus Access Time and BYTE Delay  
Start of Conversion to DATACLK Delay  
DATACLK Period  
83  
1.4  
1.1  
75  
Data Valid to DATACLK HIGH  
DATACLK LOW to Data Not Valid  
External DATACLK Period  
20  
400  
100  
50  
600  
External DATACLK HIGH  
External DATACLK LOW  
40  
CS LOW and R/C HIGH to External DATACLK HIGH (Enable Clock)  
R/C to CS Setup Time  
25  
10  
CS HIGH or R/C LOW to External DATACLK HIGH (Disable Clock)  
DATACLK HIGH to SYNC HIGH  
DATACLK HIGH to Valid Data  
Start of Conversion to SDATA Active  
End of Conversion to SDATA Tri-State  
CS LOW and R/C HIGH to SDATA Active  
CS HIGH or R/C LOW to SDATA Tri-State  
BUSY HIGH to Address Valid  
Address Valid to BUSY LOW  
25  
15  
35  
55  
83  
83  
83  
83  
20  
25  
500  
TABLE II. Conversion, Data, and Address Timing. TA = –40°C to +85°C.  
®
ADS7825  
12  
DATACLK (pin 15). The data will be valid on both the  
rising and falling edges of the internal data clock. The rising  
edge of BUSY (pin 24) can be used to latch the data. After  
the 16th clock pulse, DATACLK will remain LOW until the  
next conversion is initiated, while SDATA will go to what-  
ever logic level was input on TAG (pin 17) during the first  
clock pulse. The SDATA output will tri-state when BUSY  
returns HIGH. Refer to Table II and Figure 4 for timing  
information.  
The first bit input on TAG will be valid on SDATA on the  
18th falling edge and the 19th rising edge of DATACLK; the  
second input bit will be valid on the 19th falling edge and the  
20th rising edge, etc. With a continuous data clock, TAG  
data will be output on DATA until the internal output  
registers are updated with the results from the next conver-  
sion. Refer to Table II and Figure 5 for timing information.  
EXTERNAL DATA CLOCK (During a Conversion)  
After conversion ‘n’ has been initiated, valid data from  
conversion ’n-1’ can be read and will be valid up to 12µs  
after the start of conversion ‘n’. Do not attempt to clock out  
data from 12µs after the start of conversion ‘n’ until BUSY  
(pin 24) rises; this will result in data loss.  
EXTERNAL DATA CLOCK  
To use an external clock, tie EXT/INT (pin 12) HIGH. The  
external clock is not a conversion clock; it can only be used  
as a data clock. To enable the output mode of the ADS7825,  
CS (pin 23) must be LOW and R/C (pin 22) must be HIGH.  
DATACLK must be HIGH for 20% to 70% of the total data  
clock period; the clock rate can be between DC and 10MHz.  
Serial data from conversion ‘n’ can be output on SDATA  
(pin 16) after conversion ‘n’ is completed or during conver-  
sion ‘n + 1’.  
NOTE: For the best possible performance when using an  
external data clock, data should not be clocked out during a  
conversion. The switching noise of the asynchronous data clock  
can cause digital feedthrough degrading the converter’s perfor-  
mance. Refer to Table II and Figure 6 for timing information.  
An obvious way to simplify control of the converter is to tie  
CS LOW while using R/C to initiate conversions. While this  
is perfectly acceptable, there is a possible problem when  
using an external data clock. At an indeterminate point from  
12µs after the start of conversion ‘n’ until BUSY rises, the  
internal logic will shift the results of conversion ‘n’ into the  
output register. If CS is LOW, R/C is HIGH and the external  
clock is HIGH at this point, data will be lost. So, with CS  
LOW, either R/C and/or DATACLK must be LOW during  
this period to avoid losing valid data.  
TAG FEATURE  
TAG (pin 17) inputs serial data synchronized to the external  
or internal data clock.  
When using an external data clock, the serial bit stream input  
on TAG will follow the LSB output on SDATA (pin 16)  
until the internal output register is updated with new conver-  
sion results. See Table II and Figures 5 and 6.  
The logic level input on TAG for the first rising edge of the  
internal data clock will be valid on SDATA after all 16 bits  
of valid data have been output.  
EXTERNAL DATA CLOCK (After a Conversion)  
MULTIPLEXER TIMING  
After conversion ‘n’ is completed and the output registers  
have been updated, BUSY (pin 24) will go HIGH. With CS  
LOW (pin 23) and R/C HIGH (pin 22), valid data from  
conversion ‘n’ will be output on SDATA (pin 16) synchro-  
nized to the external data clock input on DATACLK (pin  
15). Between 15 and 35ns following the rising edge of the  
first external data clock, the SYNC output pin will go HIGH  
for one full data clock period (100ns minimum). The MSB  
will be valid between 25 and 55ns after the rising edge of the  
second data clock. The LSB will be valid on the 17th falling  
edge and the 18th rising edge of the data clock. TAG (pin  
17) will input a bit of data for every external clock pulse.  
The four channel input multiplexer may be addressed manu-  
ally or placed in a continuous conversion mode where all  
four channels are sequentially addressed.  
CONTINUOUS CONVERSION MODE (CONTC = 5V)  
To place the ADS7825 in the continuous conversion mode,  
CONTC (pin 25) must be tied HIGH. In this mode, acquisi-  
tion and conversions will take place continually, cycling  
through all four channels as long as CS, R/C and PWRD are  
LOW (See Table III). Whichever address was last loaded  
CONTC  
CS  
R/C  
BUSY  
PWRD  
A0 and A1 OPERATION  
0
X
X
X
X
Inputs  
Initiating conversion n latches in the levels input on A0 and A1 to select the channel for  
conversion 'n + 1'.  
0
0
0
0
X
0
X
0
1
1
X
0
0
0
1
Inputs  
Inputs  
Inputs  
Inputs  
Conversion in process. New convert commands ignored.  
Initiates conversion on channel selected at start of previous conversion.  
Initiates conversion on channel selected at start of previous conversion.  
0
X
X
All analog functions powered down. Conversions in process or initiated will yield  
meaningless data.  
1
X
X
X
X
Outputs  
The end of conversion 'n' (when BUSY rises) increments the internal channel latches and  
outputs the channel address for conversion 'n + 1' on A0 and A1.  
1
1
1
1
X
0
X
0
1
1
X
0
0
0
1
Outputs  
Outputs  
Outputs  
Outputs  
Conversion in process.  
Restarts continuous conversion process on next input channel.  
Restarts continuous conversion process on next input channel.  
0
X
X
All analog functions powered down. Conversions in process or initiated will yield  
meaningless data. Resets selected input channel for next conversion to AIN0.  
TABLE III. Conversion Control.  
®
ADS7825  
13  
into the A0 and A1 registers (pins 19 and 18, respectively)  
prior to CONTC being raised HIGH, becomes the first  
address in the sequential continuous conversion mode (e.g.,  
if Channel 1 was the last address selected then Channel 2  
will follow, then Channel 3, and so on). The A0 and A1  
address inputs become outputs when the device is in this  
mode. When BUSY rises at the end of a conversion, A0 and  
A1 will output the address of the channel that will be  
converted when BUSY goes LOW at the beginning of the  
next conversion. Data will be valid for the previous channel  
when BUSY rises. See Table IVa and Figure 7 for channel  
selection timing in continuous conversion mode.  
conversions will proceed through each higher channel, cy-  
cling back to zero after Channel 3.  
If PWRD is held HIGH for a significant period of time, the  
REF (pin 7) bypass capacitor may discharge (if the internal  
reference is being utilized) and the CAP (pin 6) bypass  
capacitor will discharge (for both internal and external  
references). The continuous conversion mode should not be  
enabled until the bypass capacitor(s) have recharged and  
stabilized (1ms for 2.2µF capacitors recommended). In  
addition, the continuous conversion mode should not be  
enabled even with a short pulse on PWRD until the mini-  
mum acquisition time has been met.  
PWRD (pin 26) can be used to reset the multiplexer address  
to zero. With the ADS7825 configured for no conversion,  
PWRD can be taken HIGH for a minimum of 200ns. When  
PWRD returns LOW, the multiplexer address will be reset  
to zero. When the continuous conversion mode is enabled,  
the first conversion will be done on channel 0. Subsequent  
MANUAL CHANNEL SELECTION (CONTC= 0V)  
The channels of the ADS7825 can be selected manually by  
using the A0 and A1 address pins (pins 19 and 18, respec-  
tively). See Table IVb for the multiplexer truth table and  
Figure 8 for channel selection timing.  
ADS7825 TIMING AND CONTROL  
DATA AVAILABLE  
FROM CHANNEL  
CHANNEL TO BE OR  
BEING CONVERTED  
A1  
A0  
DESCRIPTION OF OPERATION  
0
0
1
1
0
1
0
1
AIN3  
AIN0  
AIN1  
AIN2  
AIN0  
AIN1  
AIN2  
AIN3  
Channel being acquired or converted is output on these  
address lines. Data is valid for the previous channel. These  
lines are updated when BUSY rises.  
TABLE IVa. A0 and A1 Outputs (CONTC HIGH).  
CHANNEL SELECTED  
A1  
A0  
WHEN BUSY GOES HIGH  
DESCRIPTION OF OPERATION  
0
0
1
1
0
1
0
1
AIN0  
AIN1  
AIN2  
AIN3  
Channel to be converted during conversion 'n + 1' is latched  
when conversion 'n' is initiated (BUSY goes LOW). The selected  
input starts being acquired as soon as conversion 'n' is done  
(BUSY goes HIGH).  
TABLE IVb. A0 and A1 Inputs (CONTC LOW).  
Conversion Currently in Progress:  
n – 2  
n – 1  
n
n + 1  
n + 1  
n + 2  
n + 3  
n + 3  
n + 4  
n + 4  
BUSY  
Channel Address for Conversion:  
n – 2 n – 1  
A0, A1  
(Output)  
n
n + 2  
t29  
n + 5  
n + 4  
Results from Conversion:  
n – 3 n – 2  
D7-D0  
n – 1  
n
n + 1  
n + 2  
n + 3  
FIGURE 7. Channel Addressing in Continuous Conversion Mode (CONTC HIGH, CS and R/C LOW).  
R/C  
Conversion Currently in Progress:  
n – 2  
n – 1  
n
n + 1  
n + 2  
n + 3  
n + 3  
n + 4  
n + 4  
n + 5  
BUSY  
Channel Address for Conversion:  
n – 1 n + 1  
A0, A1  
(Input)  
n
n + 2  
t30  
Results from Conversion:  
n – 3 n – 2  
D7-D0  
n – 1  
n
n + 1  
n + 2  
n + 3  
n + 4  
FIGURE 8. Channel Addressing in Normal Conversion Mode (CONTC and CS LOW).  
®
ADS7825  
14  
CDAC. Capacitor values larger than 2.2µF will have little  
CALIBRATION  
affect on improving performance.  
The ADS7825 has no internal provision for correcting the  
individual bipolar zero error or full-scale error for each  
individual channel. Instead, the bipolar zero error of each  
channel is guaranteed to be below a level which is quite  
small for a 16-bit converter with a ±10V input range (slightly  
more than ±32 LSBs). In addition, the channel errors should  
match each other to within 16 LSBs.  
The output of the buffer is capable of driving up to 1mA of  
current to a DC load. Using an external buffer will allow the  
internal reference to be used for larger DC loads and AC  
loads. Do not attempt to directly drive an AC load with the  
output voltage on CAP. This will cause performance degra-  
dation of the converter.  
For the full-scale error, the circuit of Figure 9 can be used.  
This will allow the reference to be adjusted such that the  
full-scale error for any single channel can be set to zero.  
Again, the close matching of the channels will ensure that  
the full-scale errors on the other channels will be small.  
PWRD  
PWRD (pin 26) HIGH will power down all of the analog  
circuitry including the reference. Data from the previous  
conversion will be maintained in the internal registers and  
can still be read. With PWRD HIGH, a convert command  
yields meaningless data. When PWRD is returned LOW,  
adequate time must be provided in order for the capacitors  
on REF (pin 7) and CAP (pin 6) to recharge. For 2.2µF  
capacitors, a minimum recharge/settling time of 1ms is  
recommended before the conversion results should be con-  
sidered valid.  
AIN2  
AIN3  
CAP  
+5V  
+
R1  
1MΩ  
2.2µF  
2.2µF  
P1  
50kΩ  
REF  
LAYOUT  
POWER  
+
AGND2  
The ADS7825 uses 90% of its power for the analog cir-  
cuitry, and the converter should be considered an analog  
component. For optimum performance, tie both power pins  
to the same +5V power supply and tie the analog and digital  
grounds together.  
FIGURE 9. Full Scale Trim.  
REFERENCE  
The ADS7825 can operate with its internal 2.5V reference or  
an external reference. By applying an external reference to  
pin 7, the internal reference can be bypassed.  
The +5V power for the converter should be separate from  
the +5V used for the system’s digital logic. Connecting VS1  
and VS2 (pins 28 and 27) directly to a digital supply can  
reduce converter performance due to switching noise from  
the digital logic. For best performance, the +5V supply can  
be produced from whatever analog supply is used for the rest  
of the analog signal conditioning. If +12V or +15V supplies  
are present, a simple +5V regulator can be used. Although it  
is not suggested, if the digital supply must be used to power  
the converter, be sure to properly filter the supply. Either  
using a filtered digital supply or a regulated analog supply,  
both VS1 and VS2 should be tied to the same +5V source.  
REF  
REF (pin 7) is an input for an external reference or the output  
for the internal 2.5V reference. A 2.2µF capacitor should be  
connected as close to the REF pin as possible. This capacitor  
and the output resistance of REF create a low pass filter to  
bandlimit noise on the reference. Using a smaller value  
capacitor will introduce more noise to the reference degrad-  
ing the SNR and SINAD. The REF pin should not be used  
to drive external AC or DC loads.  
GROUNDING  
Three ground pins are present on the ADS7825. DGND is  
the digital supply ground. AGND2 is the analog supply  
ground. AGND1 is the ground which all analog signals  
internal to the A/D are referenced. AGND1 is more suscep-  
tible to current induced voltage drops and must have the path  
of least resistance back to the power supply.  
The range for the external reference is 2.3V to 2.7V and  
determines the actual LSB size. Increasing the reference  
voltage will increase the full scale range and the LSB size of  
the converter which can improve the SNR.  
CAP  
All the ground pins of the A/D should be tied to an analog  
ground plane, separated from the system’s digital logic  
ground, to achieve optimum performance. Both analog and  
digital ground planes should be tied to the ‘system’ ground  
as near to the power supplies as possible. This helps to  
prevent dynamic digital ground currents from modulating  
the analog ground through a common impedance to power  
ground.  
CAP (pin 6) is the output of the internal reference buffer. A  
2.2µF capacitor should be placed as close to the CAP pin as  
possible to provide optimum switching currents for the  
CDAC throughout the conversion cycle. This capacitor also  
provides compensation for the output of the buffer. Using a  
capacitor any smaller than 1µF can cause the output buffer  
to oscillate and may not have sufficient charge for the  
®
ADS7825  
15  
SIGNAL CONDITIONING  
CROSSTALK  
The FET switches used for the sample hold on many CMOS  
A/D converters release a significant amount of charge injec-  
tion which can cause the driving op amp to oscillate. The  
amount of charge injection due to the sampling FET switch  
on the ADS7825 is approximately 5-10% of the amount on  
similar ADCs with the charge redistribution DAC (CDAC)  
architecture. There is also a resistive front end which attenu-  
ates any charge which is released. The end result is a  
minimal requirement for the drive capability on the signal  
conditioning preceding the A/D. Any op amp sufficient for  
the signal in an application will be sufficient to drive the  
ADS7825.  
The worst-case channel-to-channel crosstalk versus input  
frequency is shown in the Typical Performance Curves  
section of this data sheet. With a full-scale 1kHz input  
signal, worst case crosstalk on the ADS7825 is better than  
–115dB. This should be adequate for even the most de-  
manding applications. However, if crosstalk is a concern,  
the following items should be kept in mind: The worst case  
crosstalk is generally from channel 3 to 2. In addition,  
crosstalk from Channel 3 to any other channel is worse than  
from those channels to Channel 3. The reason for this is that  
Channel 3 is nearer to the reference on the ADS7825. This  
allows two coupling modes: channel-to-channel and Chan-  
nel 3 to the reference. In general, when crosstalk is a  
concern, avoid placing signals with higher frequency com-  
ponents on Channel 3.  
The resistive front end of the ADS7825 also provides a  
guaranteed ±15V overvoltage protection. In most cases, this  
eliminates the need for external overvoltage protection  
circuitry.  
The worst case crosstalk occurs from Channel 3 to Channel  
2 as shown in the Crosstalk vs Input Frequency graph in the  
Typical Performance Curves section. Other adjacent chan-  
nels are typically several dB better than this while non-  
adjacent channels are typically 10dB better. If a particular  
channel should be as immune as possible from crosstalk,  
channel 0 would be the best channel for the signal and  
channel 1 should have the signal with the lowest frequency  
content. If two signals are to have as little crosstalk as  
possible, they should be placed on Channel 0 and Channel  
2 with lower frequency, less-sensitive inputs on the other  
channels.  
INTERMEDIATE LATCHES  
The ADS7825 does have tri-state outputs for the parallel  
port, but intermediate latches should be used if the bus will  
be active during conversions. If the bus is not active during  
conversions, the tri-state outputs can be used to isolate the  
A/D from other peripherals on the same bus.  
Intermediate latches are beneficial on any monolithic A/D  
converter. The ADS7825 has an internal LSB size of 38µV.  
Transients from fast switching signals on the parallel port,  
even when the A/D is tri-stated, can be coupled through the  
substrate to the analog circuitry causing degradation of  
converter performance.  
If crosstalk is a concern for all channels, keep in mind that the  
crosstalk graph shows crosstalk between any two channels.  
Total crosstalk to any given channel is the sum of the  
crosstalk contributions from all the other channels. Since non-  
adjacent channels contribute very little, their contribution can  
generally be ignored. A good approximation for absolute  
worst case crosstalk would be to add 6dB to the highest curve  
shown in the Crosstalk vs Input Frequency graph.  
For an ADS7825 with proper layout, grounding, and bypass-  
ing, the effect can be a few LSBs of error. In some cases, this  
error can be treated as an increase in converter noise and  
simply averaged out. In others, the error may not be random  
and will produce an error in the conversion result, even with  
averaging. Poor grounding, poor bypassing, and high-speed  
digital signals will increase the magnitude of the errors—  
possibly to many tens of LSBs.  
®
ADS7825  
16  
PACKAGE OPTION ADDENDUM  
www.ti.com  
14-Oct-2022  
PACKAGING INFORMATION  
Orderable Device  
Status Package Type Package Pins Package  
Eco Plan  
Lead finish/  
Ball material  
MSL Peak Temp  
Op Temp (°C)  
Device Marking  
Samples  
Drawing  
Qty  
(1)  
(2)  
(3)  
(4/5)  
(6)  
ADS7825U  
ADS7825U/1K  
ADS7825UB  
ACTIVE  
ACTIVE  
ACTIVE  
SOIC  
SOIC  
SOIC  
DW  
DW  
DW  
28  
28  
28  
20  
RoHS & Green  
Call TI  
Level-3-260C-168 HR  
Level-3-260C-168 HR  
Level-3-260C-168 HR  
-40 to 85  
-40 to 85  
-40 to 85  
ADS7825U  
Samples  
Samples  
Samples  
1000 RoHS & Green  
20 RoHS & Green  
1000 RoHS & Green  
Call TI  
Call TI  
ADS7825U  
ADS7825U  
B
ADS7825UB/1K  
ACTIVE  
SOIC  
DW  
28  
Call TI  
Level-3-260C-168 HR  
-40 to 85  
ADS7825U  
B
Samples  
(1) The marketing status values are defined as follows:  
ACTIVE: Product device recommended for new designs.  
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.  
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.  
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.  
OBSOLETE: TI has discontinued the production of the device.  
(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance  
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may  
reference these types of products as "Pb-Free".  
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.  
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based  
flame retardants must also meet the <=1000ppm threshold requirement.  
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.  
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.  
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation  
of the previous line and the two combined represent the entire Device Marking for that device.  
(6)  
Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two  
lines if the finish value exceeds the maximum column width.  
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information  
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and  
Addendum-Page 1  
PACKAGE OPTION ADDENDUM  
www.ti.com  
14-Oct-2022  
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  
PACKAGE MATERIALS INFORMATION  
www.ti.com  
9-Aug-2022  
TAPE AND REEL INFORMATION  
REEL DIMENSIONS  
TAPE DIMENSIONS  
K0  
P1  
W
B0  
Reel  
Diameter  
Cavity  
A0  
A0 Dimension designed to accommodate the component width  
B0 Dimension designed to accommodate the component length  
K0 Dimension designed to accommodate the component thickness  
Overall width of the carrier tape  
W
P1 Pitch between successive cavity centers  
Reel Width (W1)  
QUADRANT ASSIGNMENTS FOR PIN 1 ORIENTATION IN TAPE  
Sprocket Holes  
Q1 Q2  
Q3 Q4  
Q1 Q2  
Q3 Q4  
User Direction of Feed  
Pocket Quadrants  
*All dimensions are nominal  
Device  
Package Package Pins  
Type Drawing  
SPQ  
Reel  
Reel  
A0  
B0  
K0  
P1  
W
Pin1  
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant  
(mm) W1 (mm)  
ADS7825U/1K  
SOIC  
SOIC  
DW  
DW  
28  
28  
1000  
1000  
330.0  
330.0  
32.4  
32.4  
11.35 18.67  
11.35 18.67  
3.1  
3.1  
16.0  
16.0  
32.0  
32.0  
Q1  
Q1  
ADS7825UB/1K  
Pack Materials-Page 1  
PACKAGE MATERIALS INFORMATION  
www.ti.com  
9-Aug-2022  
TAPE AND REEL BOX DIMENSIONS  
Width (mm)  
H
W
L
*All dimensions are nominal  
Device  
Package Type Package Drawing Pins  
SPQ  
Length (mm) Width (mm) Height (mm)  
ADS7825U/1K  
SOIC  
SOIC  
DW  
DW  
28  
28  
1000  
1000  
367.0  
367.0  
367.0  
367.0  
55.0  
55.0  
ADS7825UB/1K  
Pack Materials-Page 2  
PACKAGE MATERIALS INFORMATION  
www.ti.com  
9-Aug-2022  
TUBE  
T - Tube  
height  
L - Tube length  
W - Tube  
width  
B - Alignment groove width  
*All dimensions are nominal  
Device  
Package Name Package Type  
Pins  
SPQ  
L (mm)  
W (mm)  
T (µm)  
B (mm)  
ADS7825U  
DW  
DW  
SOIC  
SOIC  
28  
28  
20  
20  
507  
507  
12.83  
12.83  
5080  
5080  
6.6  
6.6  
ADS7825UB  
Pack Materials-Page 3  
IMPORTANT NOTICE AND DISCLAIMER  
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATA SHEETS), DESIGN RESOURCES (INCLUDING REFERENCE  
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”  
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY  
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD  
PARTY INTELLECTUAL PROPERTY RIGHTS.  
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate  
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable  
standards, and any other safety, security, regulatory or other requirements.  
These resources are subject to change without notice. TI grants you permission to use these resources only for development of an  
application that uses the TI products described in the resource. Other reproduction and display of these resources is prohibited. No license  
is granted to any other TI intellectual property right or to any third party intellectual property right. TI disclaims responsibility for, and you  
will fully indemnify TI and its representatives against, any claims, damages, costs, losses, and liabilities arising out of your use of these  
resources.  
TI’s products are provided subject to TI’s Terms of Sale or other applicable terms available either on ti.com or provided in conjunction with  
such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable warranties or warranty disclaimers for  
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TI objects to and rejects any additional or different terms you may have proposed. IMPORTANT NOTICE  
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265  
Copyright © 2022, Texas Instruments Incorporated  

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