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ADS7816C Schematic ( PDF Datasheet ) - Burr-Brown Corporation

Teilenummer ADS7816C
Beschreibung 12-Bit High Speed Micro Power Sampling ANALOG-TO-DIGITAL CONVERTER
Hersteller Burr-Brown Corporation
Logo Burr-Brown Corporation Logo 




Gesamt 13 Seiten
ADS7816C Datasheet, Funktion
®
ADS7816
OAPDSA7681568
ADS7816
12-Bit High Speed Micro Power Sampling
ANALOG-TO-DIGITAL CONVERTER
FEATURES
q 200kHz SAMPLING RATE
q MICRO POWER:
1.9mW at 200kHz
150µW at 12.5kHz
q POWER DOWN: 3µA Max
q 8-PIN MINI-DIP, SOIC, AND MSOP
q DIFFERENTIAL INPUT
q SERIAL INTERFACE
APPLICATIONS
q BATTERY OPERATED SYSTEMS
q REMOTE DATA ACQUISITION
q ISOLATED DATA ACQUISITION
DESCRIPTION
The ADS7816 is a 12-bit, 200kHz sampling analog-
to-digital converter. It features low power operation
with automatic power down, a synchronous serial
interface, and a differential input. The reference volt-
age can be varied from 100mV to 5V, with a corre-
sponding resolution from 24µV to 1.22mV.
Low power, automatic power down, and small size
make the ADS7816 ideal for battery operated systems
or for systems where a large number of signals must be
acquired simultaneously. It is also ideal for remote
and/or isolated data acquisition. The ADS7816 is
available in an 8-pin plastic mini-DIP, an 8-lead SOIC,
or an 8-lead MSOP package.
VREF
+In
–In
S/H Amp
SAR
CDAC
Comparator
Control
Serial
Interface
DOUT
DCLOCK
CS/SHDN
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
©1996 Burr-Brown Corporation
PDS-1355B
Printed in U.S.A., March, 1997






ADS7816C Datasheet, Funktion
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, VCC = +5V, VREF = +5V, fSAMPLE = 200kHz, and fCLK = 16 • fSAMPLE, unless otherwise specified.
1.00
0.75
0.50
0.25
0.00
–0.25
–0.50
–0.75
–1.00
0
INTEGRAL LINEARITY ERROR vs CODE
2048
Code
4095
1.00
0.75
0.50
0.25
0.00
–0.25
–0.50
–0.75
–1.00
0
DIFFERENTIAL LINEARITY ERROR vs CODE
2048
Code
4095
CHANGE IN INTEGRAL LINEARITY AND DIFFERENTIAL
LINEARITY vs REFERENCE VOLTAGE
0.10
0.05
0.00
–0.05
Change in Differential
Linearity (LSB)
–0.10
–0.15
Change in Integral
Linearity (LSB)
–0.20
1
234
Reference Voltage (V)
5
450
400
350
300
250
200
150
–55
SUPPLY CURRENT vs TEMPERATURE
fSAMPLE = 200kHz
fSAMPLE = 12.5kHz
–40 –25
0
25
Temperature (°C)
70
85
INPUT LEAKAGE CURRENT vs TEMPERATURE
10
1
0.1
0.01
–55 –40 –25
0
25 70 85
Temperature (°C)
3
2.5
2
1.5
1
0.5
0
–55
POWER DOWN SUPPLY CURRENT
vs TEMPERATURE
–40 –25
0
25
Temperature (°C)
70
85
®
ADS7816
6

6 Page









ADS7816C pdf, datenblatt
sion, the digital output must be updated with the results of the
last bit decision, the capacitor array appropriately switched
and charged, and the input to the comparator settled to a
12-bit level all within one clock cycle.
The basic SAR architecture is sensitive to spikes on the
power supply, reference, and ground connections that occur
just prior to latching the comparator output. Thus, during
any single conversion for an n-bit SAR converter, there are
n “windows” in which large external transient voltages can
easily affect the conversion result. Such spikes might origi-
nate from switching power supplies, digital logic, and high
power devices, to name a few. This particular source of error
can be very difficult to track down if the glitch is almost
synchronous to the converter’s DCLOCK signal—as the
phase difference between the two changes with time and
temperature, causing sporadic misoperation.
With this in mind, power to the ADS7816 should be clean
and well bypassed. A 0.1µF ceramic bypass capacitor should
be placed as close to the ADS7816 package as possible. In
addition, a 1 to 10µF capacitor and a 10series resistor may
be used to lowpass filter a noisy supply.
The reference should be similarly bypassed with a 0.1µF
capacitor. Again, a series resistor and large capacitor can be
used to lowpass filter the reference voltage. If the reference
voltage originates from an op amp, be careful that the op-
amp can drive the bypass capacitor without oscillation (the
series resistor can help in this case). Keep in mind that while
the ADS7816 draws very little current from the reference on
average, there are higher instantaneous current demands
placed on the external reference circuitry.
Also, keep in mind that the ADS7816 offers no inherent
rejection of noise or voltage variation in regards to the
reference input. This is of particular concern when the
reference input is tied to the power supply. Any noise and
ripple from the supply will appear directly in the digital
results. While high frequency noise can be filtered out as
described in the previous paragraph, voltage variation due to
the line frequency (50Hz or 60Hz), can be difficult to
remove.
The GND pin on the ADS7816 should be placed on a clean
ground point. In many cases, this will be the “analog”
ground. Avoid connecting the GND pin too close to the
grounding point for a microprocessor, microcontroller, or
digital signal processor. If needed, run a ground trace di-
rectly from the converter to the power supply connection
point. The ideal layout will include an analog ground plane
for the converter and associated analog circuitry.
The –In input pin should be connected directly to ground. In
those cases where the ADS7816 is a large distance from the
signal source and/or the circuit environment contains large
EMI or RFI sources, the –In input should be connected to the
ground nearest the signal source. This should be done with
a signal trace that is adjacent to the +In input trace. If
appropriate, coax cable or twisted-pair wire can be used.
APPLICATION CIRCUITS
Figures 6, 7, and 8 show some typical application circuits for
the ADS7816. Figure 6 uses an ADS7816 and a multiplexer
to provide for a flexible data acquisition circuit. A resistor
string provides for various voltages at the multiplexer input.
The selected voltage is buffered and driven into VREF. As
shown in Figure 6, the input range of the ADS7816 is
programmable to 100mV, 200mV, 300mV, or 400mV. The
100mV range would be useful for sensors such as the
thermocouple shown.
Figure 7 is more complex variation of Figure 6 with in-
creased flexibility. In this circuit, a digital signal processor
designed for audio applications is put to use in running three
ADS7816s and a DAC56. The DAC56 provides a variable
voltage for VREF—enabling the input range of the ADS7816s
to be programmed from 100mV to 3V.
+5V +5V
D1
TC1
Thermocouple
TC2
TC3
ISO Thermal Block
R1
150k
R2
59k
R4
1k
R6
1M
C4
10µF
R3
500k
C3
0.1µF
R7
10
C2
0.1µF
VREF
ADS7816
DCLOCK
DOUT
CS/SHDN
R5
500
C5
0.1µF
U1
3-Wire
Interface
OPA237
U2
µP
U4
C1
10µF
MUX
A0
A1
U3
FIGURE 6. Thermocouple Application Using a MUX to Scale the Input Range of the ADS7816.
®
ADS7816
12
+5V
R8
46k
R9
1k
R10
1k
R11
1k
R12
1k
0.4V
0.3V
0.2V
0.1V

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