Datasheet

A3
A1
A2
Gain
Clamp
Clamp
MUX
SwitchNetwork,
CurrentSource
andSink,
andBuffer
DigitalI/O
Error:
Inputover-voltage
Error:
Inputampsaturation
Error:
Outputamplifier
Error:
Gainnetwork
overload
VSP
VSOP
VSN VSON
VSP
VSN
VSP
VSN
VSOP
VSON
Error:
Clampcondition
PGA280
SBOS487A –JUNE 2009–REVISED SEPTEMBER 2009................................................................................................................................................ www.ti.com
Note: The signal path is observed for possible limitations; flags are stored and indicated in Register 4.
Figure 49. Diagnostic Points for Error Detection
ERROR INDICATORS
Input Clamp Conduction (ICAerr)
The input clamp protects the precision input amplifier from large voltages between the inputs that occur from a
fast signal slew rate in the input. This clamp circuit pulls current from the input pins while active. Current flowing
through the clamp can influence the signal source and cause long settling delays on passive signal filters. The
current is limited by internal resistors of approximately 2.4kΩ. Dynamic overload can result from the difference
signal as well as the common-mode signal.
The input clamp turns on when the input signal slew rate is faster than the amplifier slew rate (see the Electrical
Characteristics specification) and larger than ±1V. Appropriate input filtering avoids the activation. However,
transients from MUX switching, internal switches, and gain switching action cannot be filtered; therefore, to avoid
these transients, it is recommended that the current buffer (BUF) be activated. The buffer isolates the signal input
from the clamp, and therefore avoids the current pulse (see Figure 44).
Input Overvoltage (IOVerr)
The input amplifier can only operate at high performance within a certain input voltage range to the supply rail.
The IOVerr flag indicates a loss of performance because of the input voltage or the amplifier output approaching
the rail.
Gain Network Overload (GAINerr)
The gain setting network is protected against overcurrent conditions that arise because of an improper gain
setting. The current into the resistors is proportional to the voltage between both inputs and the internal resistor;
a low resistor value results in high gains. This error flag indicates such an overload condition that is the result of
an improper gain setting.
Output Amplifier (OUTerr)
The output stage is monitored for signal clipping to the supply rail and for overcurrent conditions.
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