Datasheet

1
2
3
4
5
AGND2
CAP
REF
AGND1
V
IN
+
+5V
+
Gain
1
2
3
4
5
AGND2
CAP
REF
AGND1
V
IN
+
+
±10V
20kΩ
2.2 µF
2.2 µF
2.2 µF
2.2 µF
30k
Ω
±10V
(a) ±10VWithHardware Trim (b) ±10VWithoutHardware Trim
Note:Use1%metalfilmresistors.
175kΩ
ADS8515
SLAS460D –JUNE 2007–REVISED SEPTEMBER 2010 www.ti.com
APPLICATION INFORMATION
CALIBRATION
The gain of the ADS8515 can be trimmed in software. To achieve optimum performance, several iterations may
be required.
Hardware Calibration
To calibrate the gain of the ADS8515, install the resistors and potentiometer as shown in Figure 25(a). The
calibration range is approximately ±100 mV.
Software Calibration
The offset and gain of the ADS8515 is calibrated with software. See Figure 25(b) for the circuit connections.
Figure 25. Circuit Diagram For Software Trim
REFERENCE
The ADS8515 can operate with its internal 4.096-V reference or an external reference. By applying an external
reference to pin 5, the internal reference can be bypassed. The reference voltage at REF is buffered internally
with the output on CAP (pin 4).
The internal reference has an 8 ppm/°C drift (typical) and accounts for approximately 20% of the full-scale error
(FSE = ±0.5% for low grade, ±0.25% for high grade).
REF
REF (pin 3) is an input for an external reference or the output for the internal 4.096-V reference. A 2.2-mF
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 bandlimit noise on the reference. Using a smaller value capacitor introduces more
noise to the reference degrading the SNR and SINAD. The REF pin should not be used to drive external ac or dc
loads.
The range for the external reference is 3.9 V to 4.2 V and determines the actual LSB size. Increasing the
reference voltage increases the full-scale range and the LSB size of the converter which can improve the SNR.
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