ADS7810 Burr-Brown Corporation, ADS7810 Datasheet - Page 10

• Manufacturer Part Number: ADS7810
• Description: 12-Bit 800kHz Sampling CMOS ANALOG-to-DIGITAL CONVERTER
• Manufacturer: Burr-Brown Corporation

CALIBRATION
The ADS7810 can be trimmed in hardware or software. The
offset should be trimmed before the gain since the offset
directly affects the gain.
Hardware Calibration
To calibrate the offset and gain of the ADS7810, install the
proper resistors and potentiometers as shown in Figure 4a.
The calibration range is 50mV for bipolar zero and 120mV
for full scale.
Potentiometer P
circuit and P
are not critical. R
the value shown. They can easily be made smaller to provide
increased adjustment range. Reducing these below 15% of
the indicated values could begin to adversely affect the
operation of the converter.
P
tion. However, larger resistances will push the useful adjust-
ment range to the edges of the potentiometer. P
probably not exceed 20k
tain reasonable sensitivity.
Software Calibration
To calibrate the offset and gain of the ADS7810, no external
resistors are required. See the No Calibration section for
details on the effects of the external resistor.
No Calibration
See Figure 4b for circuit connections. Note that the actual
voltage dropped across the 50 resistor is nearly two orders
of magnitude lower than the voltage dropped across the
internal resistor divider network. This should be taken into
consideration when choosing the accuracy and drift specifi-
cations of the external resistors. In most applications, 1%
metal-film resistors will be sufficient.
FIGURE 5. Comparison of the ADS7810 Transfer Function With and Without the 50
1
and P
2
can also be made larger to reduce power dissipa-
2
®
and R
ADS7810
1
1
and R
and resistor R
2
the gain adjust circuit. The exact values
2
–10.0V
should not be made any larger than
and P2 100k
–9.84V
1
form the offset adjust
in order to main-
Output
Digital
+ Full Scale
– Full Scale
1
should
9.84V
10
The external 50
necessary in some applications. This resistor provides trim
capability for the offset and compensates for a slight gain
adjustment internal to the ADS7810. Not using the 50
resistor will cause a small gain error but will have no effect
on the inherent offset error. Figure 5 shows typical transfer
function characteristics with and without the 50 resistor in
the circuit.
REFERENCE
The ADS7810 can operate with its internal 2.5V reference or an
external reference. By applying an external reference to pin 3,
the internal reference can be bypassed. The reference voltage at
REF is buffered internally and output on CAP (pin 4).
REF
REF (pin 3) is an input for an external reference or the
output for the internal 2.5V reference. A 0.1 F capacitor
should be connected as close to the REF pin as possible. The
capacitor and the output resistance of REF create a low pass
filter to band limit noise on the reference. Using a smaller
value capacitor will introduce more noise to the reference
degrading the SNR and SINAD. The internal reference
should not be used to sink or source currents greater than
100 A. In addition, all external loads should be static.
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.
10.0V
Analog
Input
Typical Transfer Function
with 50 Resistor
Typical Transfer Function
without 50 Resistor
resistor shown in Figure 4b may not be
Series Resistor on V
IN
.