INPUT RANGES
SOFTWARE CALIBRATION
The ADS7804 offers a standard ±10V input range. Figure 6
shows the necessary circuit connections for the ADS7804
with and without hardware trim. Offset and full scale error(1)
specifications are tested and guaranteed with the fixed resis-
tors shown in Figure 6b. Adjustments for offset and gain are
described in the Calibration section of this data sheet.
To calibrate the offset and gain of the ADS7804 in software,
no external resistors are required. See the No Calibration
section for details on the effects of the external resistors. Refer
to Table V for range of offset and gain errors with and without
external resistors.
The offset and gain are adjusted internally to allow external
trimming with a single supply. The external resistors com-
pensate for this adjustment and can be left out if the offset
and gain will be corrected in software (refer to the Calibra-
tion section).
NO CALIBRATION
See Figure 6b for circuit connections. The external resistors
shown in Figure 6b may not be necessary in some applica-
tions. These resistors provide compensation for an internal
adjustment of the offset and gain which allows calibration
with a single supply. The nominal transfer function of the
ADS7804 will be bound by the shaded region seen in Figure
7 with a typical offset of –30mV and a typical gain error of
–1.5%. Refer to Table V for range of offset and gain errors
with and without external resistors.
The nominal input impedance of 23kΩ results from the
combination of the internal resistor network shown on the
front page of the product data sheet and the external resistors.
The input resistor divider network provides inherent overvolt-
age protection guaranteed to at least ±25V. The 1% resistors
used for the external circuitry do not compromise the accuracy
or drift of the converter. They have little influence relative to
the internal resistors, and tighter tolerances are not required.
WITH
EXTERNAL
RESISTORS
WITHOUT
EXTERNAL
RESISTORS
UNITS
NOTE: (1) Full scale error includes offset and gain errors measured at both +FS
and –FS.
BPZ
–10 < BPZ < 10
–2 < BPZ < 2
–45 < BPZ < 5
–8 < BPZ < 1
mV
LSBs
Gain
Error
–0.5 < error < 0.5
–0.6 < error < –0.55
–0.45 < error < –0.3(1)
% of FSR
–0.25 < error < 0.25(1)
CALIBRATION
NOTE: (1) High Grade.
The ADS7804 can be trimmed in hardware or software. The
offset should be trimmed before the gain since the offset
directly affects the gain. To achieve optimum performance,
several iterations may be required.
TABLE VII. Bipolar Offset and Gain Errors With and
Without External Resistors.
HARDWARE CALIBRATION
To calibrate the offset and gain of the ADS7804, install the
proper resistors and potentiometers as shown in Figure 6a. The
calibration range is ±15mV for the offset and ±60mV for the
gain.
a)
±10V With Hardware
b)
±10V Without Hardware
Trim
Trim
200Ω
200Ω
1
2
3
4
5
1
±10V
±10V
VIN
VIN
2
33.2kΩ
AGND1
REF
AGND1
+5V
2.2µF
576kΩ
2.2µF
2.2µF
2.2µF
+
+
33.2kΩ
+
+
3
4
5
REF
50kΩ
Gain
Offset
CAP
CAP
50kΩ
AGND2
AGND2
NOTE: Use 1% metal film resistors.
FIGURE 6. Circuit Diagram With and Without External Resistors.
®
ADS7804
8
BB [ BURR-BROWN CORPORATION ]
