ADS7810
SBAS014A –MARCH 1992–REVISED SEPTEMBER 2010
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Table 1. Control Line Functions for ‘Read’ and ‘Convert’
CS
1
R/C
X
BUSY
OPERATION
None. Databus in Hi-Z state.
X
1
1
↑
↓
0
Initiates conversion. Databus remains in Hi-Z state.
Initiates conversion. Databus enters Hi-Z state.
0
↓
0
1
Conversion completed. Valid data from the most
recent conversion on the databus.
↓
↓
0
0
1
1
↑
0
1
0
0
↑
Enables databus with valid data from the most recent
conversion.
Conversion in progress. Databus in Hi-Z state,
enabled when the conversion is completed.
Conversion in progress. Databus in Hi-Z state,
enabled when the conversion is completed.
Conversion completed. Valid data from the most
recent conversion in the output register, but output
pins D11-D0 are 3-stated.
X
X
0
New convert commands ignored. Conversion in
progress.
Table 2. Ideal Input Voltages and Output Codes
DESCRIPTION
Full-Scale Range
ANALOG VALUE
±10V
DIGITAL OUTPUT
BINARY TWOS COMPLEMENT
Least Significant Bit (LSB)
4.88mV
BINARY CODE
HEX CODE
+Full-Scale
9.995V
0111 1111 1111
7FF
(10V – 1LSB)
Midscale
0V
0000 0000 0000
1111 1111 1111
000
FFF
One LSB below
Midscale
–4.88mV
–Full-Scale
–10V
1000 0000 0000
800
Software Calibration
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.
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
No Calibration
To calibrate the offset and gain of the ADS7810,
install the proper resistors and potentiometers as
shown in Figure 15. The calibration range is ±50mV
for bipolar zero and ±120mV for full scale.
See Figure 16 for circuit connections. Note that the
actual voltage dropped across the 50Ω 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 specifications of the
external resistors. In most applications, 1% metal-film
resistors will be sufficient.
Potentiometer P1 and resistor R1 form the offset
adjust circuit and P2 and R2 the gain adjust circuit.
The exact values are not critical. R1 and R2 should
not be made any larger than 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.
The external 50Ω resistor shown in Figure 16 may
not be 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 50Ω resistor will cause a
small gain error but will have no effect on the inherent
offset error. Figure 17 shows typical transfer function
characteristics with and without the 50Ω resistor in
the circuit.
P1 and P2 can also be made larger to reduce power
dissipation. However, larger resistances will push the
useful adjustment range to the edges of the
potentiometer. P1 should probably not exceed 20kΩ
and P2 100kΩ in order to maintain reasonable
sensitivity.
12
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