1
ADS7808
12-Bit 10
s Serial CMOS Sampling
ANALOG-to-DIGITAL CONVERTER
FEATURES
q
100kHz SAMPLING RATE
q
72dB SINAD WITH 45kHz INPUT
q
1/2 LSB INL AND DNL
q
SIX SPECIFIED INPUT RANGES
q
SERIAL OUTPUT
q
SINGLE +5V SUPPLY OPERATION
q
PIN-COMPATIBLE WITH 16-BIT ADS7809
q
USES INTERNAL OR EXTERNAL
REFERENCE
q
100mW MAX POWER DISSIPATION
q
20-PIN 0.3" PLASTIC DIP AND SOIC
q
SIMPLE DSP INTERFACE
ADS7808
DESCRIPTION
The ADS7808 is a complete 12-bit sampling analog-
to-digital using state-of-the-art CMOS structures. It
contains a 12-bit capacitor-based SAR A/D with S/H,
reference, clock, and a serial data interface. Data can
be output using the internal clock, or can be synchro-
nized to an external data clock. The ADS7808 also
provides an output synchronization pulse for ease of
use with standard DSP processors.
The ADS7808 is specified at a 100kHz sampling rate,
and guaranteed over the full temperature range. Laser-
trimmed scaling resistors provide various input ranges
including
10V and 0V to 5V, while an innovative
design operates from a single +5V supply, with power
dissipation under 100mW.
The 20-pin ADS7808 is available in a plastic 0.3" DIP
and in an SOIC, both fully specified for operation over
the industrial 40
C to +85
C range.
10k
CDAC
4k
20k
5k
Internal
+2.5V Ref
Clock
BUSY
Data Clock
Serial Data
Successive Approximation Register and Control Logic
Serial
Data
Out
Comparator
Buffer
20k
R/C
CS
R1
IN
R2
IN
R3
IN
REF
Power Down
CAP
ADS7808
ADS7808
International Airport Industrial Park Mailing Address: PO Box 11400, Tucson, AZ 85734 Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 Tel: (520) 746-1111 Twx: 910-952-1111
Internet: http://www.burr-brown.com/ FAXLine: (800) 548-6133 (US/Canada Only) Cable: BBRCORP Telex: 066-6491 FAX: (520) 889-1510 Immediate Product Info: (800) 548-6132
1992 Burr-Brown Corporation
PDS-1155B
Printed in U.S.A. January 1997
ADS7808
2
SPECIFICATIONS
ELECTRICAL
At T
A
= 40
C to +85
C, f
S
= 100kHz, V
DIG
= V
ANA
= +5V, using internal reference and fixed resistors as shown in Figure 4, unless otherwise specified.
ADS7808P, U
ADS7808PB, UB
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
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.
RESOLUTION
12
T
Bits
ANALOG INPUT
Voltage Ranges
10V, 0V to 5V, etc. (See Table I)
Impedance
See Table I
Capacitance
35
T
pF
THROUGHPUT SPEED
Conversion Time
5.7
8
T
T
s
Complete Cycle
Acquire and Convert
10
T
s
Throughput Rate
100
T
kHz
DC ACCURACY
Integral Linearity Error
0.9
0.45
LSB
(1)
Differential Linearity Error
0.9
0.45
LSB
No Missing Codes
Guaranteed
T
Transition Noise
(2)
0.1
T
LSB
Full Scale Error
(3,4)
0.5
0.25
%
Full Scale Error Drift
7
5
ppm/
C
Full Scale Error
(3,4)
Ext. 2.5000V Ref
0.5
0.25
%
Full Scale Error Drift
Ext. 2.5000V Ref
2
T
ppm/
C
Bipolar Zero Error
(3)
Bipolar Ranges
10
T
mV
Bipolar Zero Error Drift
Bipolar Ranges
2
2
ppm/
C
Unipolar Zero Error
(3)
0V to 10V Range
5
T
mV
0V to 4V Range
3
T
mV
0V to 5V Range
3
T
mV
Unipolar Zero Error Drift
Unipolar Ranges
2
T
ppm/
C
Recovery to Rated Accuracy
1
F Capacitor to CAP
1
T
ms
after Power Down
Power Supply Sensitivity
+4.75V < V
D
< +5.25V
0.5
T
LSB
(V
DIG
= V
ANA
= V
D
)
AC ACCURACY
Spurious-Free Dynamic Range
f
IN
= 45kHz
80
90
T
T
dB
(5)
Total Harmonic Distortion
f
IN
= 45kHz
90
80
T
T
dB
Signal-to-(Noise+Distortion)
f
IN
= 45kHz
70
73
72
T
dB
Signal-to-Noise
f
IN
= 45kHz
70
73
72
T
dB
Full-Power Bandwidth
(6)
250
T
kHz
SAMPLING DYNAMICS
Aperture Delay
40
T
ns
Aperture Jitter
Sufficient to meet AC specs
T
ns
Transient Response
FS Step
2
T
s
Overvoltage Recovery
(7)
150
T
ns
REFERENCE
Internal Reference Voltage
No Load
2.48
2.5
2.52
T
T
T
V
Internal Reference Source Current
1
T
A
(Must use external buffer)
External Reference Voltage Range
2.3
2.5
2.7
T
T
T
V
for Specified Linearity
External Reference Current Drain
Ext. 2.5000V Ref
100
T
A
DIGITAL INPUTS
Logic Levels
V
IL
0.3
+0.8
T
T
V
V
IH
+2.0
V
D
+0.3V
T
T
V
I
IL
V
IL
= 0V
10
T
A
I
IH
V
IH
= 5V
10
T
A
3
ADS7808
DIGITAL OUTPUTS
Data Format
Data Coding
Pipeline Delay
Data Clock
Internal
EXT/INT LOW
2.3
T
MHz
(Output Only When
Transmitting Data)
External
EXT/INT HIGH
0.1
10
T
T
MHz
(Can Run Continually)
V
OL
I
SINK
= 1.6mA
+0.4
T
V
V
OH
I
SOURCE
= 500
A
+4
T
V
Leakage Current
High-Z State,
5
T
A
V
OUT
= 0V to V
DIG
Output Capacitance
High-Z State
15
15
pF
POWER SUPPLIES
Specified Performance
V
DIG
Must be
V
ANA
+4.75
+5
+5.25
T
*
*
V
V
ANA
+4.75
+5
+5.25
T
*
*
V
I
DIG
0.3
*
mA
I
ANA
16
*
mA
Power Dissipation: PWRD LOW
V
DIG
= V
ANA
= 5V, f
S
= 100kHz
100
*
mW
PWRD HIGH
50
*
W
TEMPERATURE RANGE
Specified Performance
40
+85
*
*
C
Derated Performance
55
+125
*
*
C
Storage
65
+150
*
*
C
Thermal Resistance (
JA
)
Plastic DIP
75
*
C/W
SOIC
75
*
CW
NOTES: (1) LSB means Least Significant Bit. For the
10V input range, one LSB is 4.88mV. (2) Typical rms noise at worst case transitions and temperatures. (3)
As measured with fixed resistors in Figure 4. Adjustable to zero with external potentiometer. (4) For bipolar input ranges, 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. For unipolar input ranges, full scale error is the deviation of the last code transition divided by the transition voltage. It also includes the
effect of offset error. (5) All specifications in dB are referred to a full-scale
10V input. (6) Full-Power Bandwidth defined as Full-Scale input frequency at which Signal-
to (Noise + Distortion) degrades to 60dB. (7) Recovers to specified performance after 2 x FS input overvoltage.
ELECTROSTATIC
DISCHARGE SENSITIVITY
Electrostatic discharge can cause damage ranging from per-
formance degradation to complete device failure. Burr-Brown
Corporation recommends that this integrated circuit be handled
and stored using appropriate ESD protection methods.
SPECIFICATIONS
(CONT)
ELECTRICAL
At T
A
= 40
C to +85
C, f
S
= 100kHz, V
DIG
= V
ANA
= +5V, using internal reference and fixed resistors shown in Figure 4, unless otherwise specified.
ADS7808P/U
ADS7808PB/UB
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
Analog Inputs: R1
IN
..........................................................................
25V
R2
IN
..........................................................................
25V
R3
IN
..........................................................................
25V
CAP ..................................... V
ANA
+0.3V to AGND2 0.3V
REF ....................................... Indefinite Short to AGND2,
Momentary Short to V
ANA
Ground Voltage Differences: DGND, AGND2 .................................
0.3V
V
ANA
...................................................................................................... 7V
V
DIG
to V
ANA
....................................................................................... +0.3
V
DIG
....................................................................................................... 7V
Digital Inputs ............................................................. 0.3V to V
DIG
+0.3V
Maximum Junction Temperature .................................................. +165
C
Internal Power Dissipation ............................................................ 700mW
Lead Temperature (soldering, 10s) .............................................. +300
C
ABSOLUTE MAXIMUM RATINGS
ORDERING INFORMATION
MINIMUM
MAXIMUM
SIGNAL-TO-
SPECIFICATION
LINEARITY
(NOISE + DISTORTION)
TEMPERATURE
PRODUCT
ERROR (LSB)
RATIO(dB)
RANGE (
C)
PACKAGE
ADS7808P
0.9
70
40
C to +85
C
20-Pin Plastic DIP
ADS7808PB
0.45
72
40
C to +85
C
20-Pin Plastic DIP
ADS7808U
0.9
70
40
C to +85
C
20-Pin SOIC
ADS7808UB
0.45
72
40
C to +85
C
20-Pin SOIC
PACKAGE INFORMATION
PACKAGE DRAWING
PRODUCT
PACKAGE
NUMBER
(1)
ADS7808P
20-Pin Plastic DIP
222
ADS7808PB
20-Pin Plastic DIP
222
ADS7808U
20-Pin SOIC
221
ADS7808UB
20-Pin SOIC
221
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
Serial 12 bits
Binary Two's Complement or Straight Binary
Conversion results only available after completed conversion.
Selectable for internal or external data clock
ADS7808
4
PIN #
NAME
DESCRIPTION
PIN ASSIGNMENTS
PIN CONFIGURATION
V
DIG
V
ANA
PWRD
BUSY
CS
R/C
TAG
DATA
DATACLK
SYNC
R1
IN
AGND1
R2
IN
R3
IN
CAP
REF
AGND2
SB/BTC
EXT/INT
DGND
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
ADS7808
ANALOG
CONNECT R1
IN
CONNECT R2
IN
INPUT
VIA 200
VIA 100
CONNECT R3
IN
RANGE
TO
TO
TO
IMPEDANCE
10V
V
IN
AGND
CAP
22.9k
5V
AGND
V
IN
CAP
13.3k
3.33
V
IN
V
IN
CAP
10.7k
0V to 10V
AGND
V
IN
AGND
13.3k
0V to 5V
AGND
AGND
V
IN
10.0k
0V to 4V
V
IN
AGND
V
IN
10.7k
TABLE I. Input Range Connections. See Figure 4 for
complete information.
1
R1
IN
Analog Input. See Table I and Figure 4 for input range connections.
2
AGND1
Analog Ground. Used internally as ground reference point. Minimal current flow.
3
R2
IN
Analog Input. See Table I and Figure 4 for input range connections.
4
R3
IN
Analog Input. See Table I and Figure 4 for input range connections.
5
CAP
Reference Buffer Capacitor. 2.2
F Tantalum to ground.
6
REF
Reference Input/Output. Outputs internal 2.5V reference. Can also be driven by external system reference. In both cases,
bypass to ground with a 2.2
F Tantalum capacitor.
7
AGND2
Analog Ground.
8
SB/BTC
Select Straight Binary or Binary Two's Complement data output format. If HIGH, data will be output in a Straight Binary format. If
LOW, data will be output in a Binary Two's complement format.
9
EXT/INT
Select External or Internal Clock for transmitting data. If HIGH, data will be output synchronized to the clock input on DATACLK. If
LOW, a convert command will initiate the transmission of the data from the previous conversion, along with 12 clock pulses output
on DATACLK.
10
DGND
Digital Ground.
11
SYNC
Synch Output. If EXT/INT is HIGH, either a rising edge on R/C with CS LOW or a falling edge on CS with R/C HIGH will output a
pulse on SYNC synchronized to the external DATACLK.
12
DATACLK
Either an input or an output depending on the EXT/INT level. Output data will be synchronized to this clock. If EXT/INT is LOW,
DATACLK will transmit 12 pulses after each conversion, and then remain LOW between conversions.
13
DATA
Serial Data Output. Data will be synchronized to DATACLK, with the format determined by the level of SB/BTC. In the external clock
mode, after 12-bits of data, the ADS7808 will output the level input on TAG as long as CS is LOW and R/C is HIGH (see Figure 3.) If
EXT/INT is LOW, data will be valid on both the rising and falling edges of DATACLK, and between conversions DATA will stay at the
level of the TAG input when the conversion was started.
14
TAG
Tag Input for use in external clock mode. If EXT/INT is HIGH, digital data input on TAG will be output on DATA with a delay of 12
DATACLK pulses as long as CS is LOW and R/C is HIGH. See Figure 3.
15
R/C
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.
When EXT/INT is LOW, this also initiates the transmission of the data results from the previous conversion. If EXT/INT is HIGH, a
rising edge on R/C with CS LOW, or a falling edge on CS with R/C HIGH, transmits a pulse on SYNC and initiates the transmission of
data from the previous conversion.
16
CS
Chip Select. Internally OR'ed with R/C.
17
BUSY
Busy Output. Falls when a conversion is started, and remains LOW until the conversion is completed and the data is latched into the
output shift register. CS or R/C must be HIGH when BUSY rises, or another conversion will start without time for signal acquisition.
18
PWRD
Power Down Input. If HIGH, conversions are inhibited and power consumption is significantly reduced. Results from the previous
conversion are maintained in the output shift register.
19
V
ANA
Analog Supply Input. Nominally +5V. Connect directly to pin 20, and decouple to ground with 0.1
F ceramic and 10
F Tantalum
capacitors.
20
V
DIG
Digital Supply Input. Nominally +5V. Connect directly to pin 19. Must be
V
ANA
.
5
ADS7808
FIGURE 1. Basic Conversion Timing.
MODE Acquire
t
4
t
5
t
1
t
3
t
7
t
6
Convert
Acquire
t
2
BUSY
CS, R/C
TABLE II. Conversion and Data Timing T
A
= 40
C to
+85
C.
FIGURE 2. Serial Data Timing Using Internal Clock. (CS, EXT/INT and TAG Tied LOW.)
SYMBOL
DESCRIPTION
MIN
TYP
MAX UNITS
t
1
Convert Pulse Width
40
4500
ns
t
2
BUSY Delay
65
ns
t
3
BUSY LOW
8
s
t
4
BUSY Delay after
220
ns
End of Conversion
t
5
Aperture Delay
40
ns
t
6
Conversion Time
5.7
8
s
t
7
Acquisition Time
2
s
t
6
+ t
7
Throughput Time
9
10
s
t
8
R/C LOW to DATACLK Delay
450
ns
t
9
DATACLK Period
440
ns
t
10
Data Valid to DATACLK
20
75
ns
HIGH Delay
t
11
Data Valid after
100
125
ns
DATACLK LOW Delay
t
12
External DATACLK Period
100
ns
t
13
External DATACLK HIGH
20
ns
t
14
External DATACLK LOW
30
ns
t
15
DATACLK HIGH
20
t
12
+ 5
ns
Setup Time
t
16
R/C to CS
10
ns
Setup Time
t
17
SYNC Delay After
15
35
ns
DATACLK HIGH
t
18
Data Valid Delay
25
55
ns
t
19
CS to Rising Edge Delay
25
ns
t
20
Data Available after CS LOW
4.5
s
1
MSB Valid
R/C
DATACLK
SDATA
t
8
t
11
t
10
t
9
2
3
11
12
Bit 10 Valid
Bit 1 Valid
Bit 9 Valid
LSB Valid
t
2
t
3
BUSY
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