ADS7807 Burr-Brown Corporation, ADS7807 Datasheet - Page 14

• Manufacturer Part Number: ADS7807
• Description: Low-Power 16-Bit Sampling CMOS ANALOG-to-DIGITAL CONVERTER
• Manufacturer: Burr-Brown Corporation

The external resistors shown in Figure 7b may not be
necessary in some applications. These resistors provide
compensation for an internal adjustment of the offset and
gain which allows calibration with a single supply. Not
using the external resistors will result in offset and gain
errors in addition to those listed in the electrical specifica-
tions section. Offset refers to the equivalent voltage of the
digital output when converting with the input grounded. A
positive gain error occurs when the equivalent output volt-
age of the digital output is larger than the analog input. Refer
to Table VIII for nominal ranges of gain and offset errors
with and without the external resistors. Refer to Figure 8 for
typical shifts in the transfer functions which occur when the
external resistors are removed.
To further analyze the effects of removing any combination
of the external resistors, consider Figure 9. The combination
of the external and the internal resistors form a voltage
TABLE VIII. Range of Offset and Gain Errors with and without External Resistors.
FIGURE 8. Typical Transfer Functions With and Without External Resistors.
INPUT
RANGE
(V)
0 to 5
0 to 4
Note: (1) High Grade.
10
+Full Scale
®
W/ RESISTORS
–10
–3
–3
RANGE (mV)
ADS7807
(a) Bipolar
Digital Output
UPO
UPO
BPZ
10
–Full Scale
3
3
OFFSET ERROR
–10.5
–12
RANGE (mV)
0
W/OUT RESISTORS
BPZ
UPO
UPO
35
–3
–1.5
Analog Input
Typical Transfer Functions
With External Resistors
Typical Transfer Functions
Without External Resistors
TYP (mV)
–7.5
15
–6
14
–Full Scale
–0.15
divider which reduces the input signal to a 0.3125V to
2.8125V input range at the CDAC. The internal resistors are
laser trimmed to high relative accuracy to meet full scale
specifications. The actual input impedance of the internal
resistor network looking into pin 1 or pin 3 however, is only
accurate to 20% due to process variations. This should be
taken into account when determining the effects of removing
the external resistors.
REFERENCE
The ADS7807 can operate with its internal 2.5V reference or
an external reference. By applying an external reference to
pin 5, the internal reference can be bypassed; REFD (pin 26)
tied HIGH will power-down the internal reference reducing
0.15
0.15
W/ RESISTORS
RANGE (% FS)
–0.4
–0.4
–0.4
+Full Scale
G
G
G
G
G
G
(1)
(1)
(1)
(b) Unipolar
Digital Output
0.4
0.4
0.4
0.15
0.15
0.15
–0.55
–0.55
–0.1
RANGE (% FS)
–0.3
–1.0
–1.0
GAIN ERROR
G
G
G
G
G
G
(1)
(1)
(1)
W/OUT RESISTORS
0.5
0.1
0.1
–0.05
–0.05
0.2
+0.05
+0.05
TYP
–0.2
–0.2
–0.2
–0.2
Analog Input