Datasheet

10kW
OPA333
±10mV
AdjustmentRange
100 W
100 W
100 Am
1/2REF200
100 Am
1/2REF200
V+
V-
R
G
INA826
REF
V
O
V
IN-
V
IN+
INA826
www.ti.com SBOS562E –AUGUST 2011–REVISED APRIL 2013
OFFSET TRIMMING
Most applications require no external offset adjustment; however, if necessary, adjustments can be made by
applying a voltage to the REF terminal. Figure 59 shows an optional circuit for trimming the output offset voltage.
The voltage applied to the REF terminal is summed at the output. The op amp buffer provides low impedance at
the REF terminal to preserve good common-mode rejection.
Figure 59. Optional Trimming of Output Offset Voltage
INPUT COMMON-MODE RANGE
The linear input voltage range of the INA826 input circuitry extends from the negative supply voltage to 1 V
below the positive supply, while maintaining 84-dB (minimum) common-mode rejection throughout this range.
The common-mode range for most common operating conditions is described in the typical characteristic curves
(Input Common-Mode Voltage vs Output Voltage, Figure 9 through Figure 16) and Offset Voltage vs Common-
Mode Voltage (Figure 41 through Figure 44). The INA826 can operate over a wide range of power supplies and
V
REF
configurations, making it impractical to provide a comprehensive guide to common-mode range limits for all
possible conditions.
The most commonly overlooked overload condition occurs when a circuit exceeds the output swing of A
1
and A
2
,
which are internal circuit nodes that cannot be measured. Calculating the expected voltages at the output of A
1
and A
2
(see Figure 60) provides a check for the most common overload conditions. The designs of A
1
and A
2
are
identical and the outputs can swing to within approximately 100 mV of the power-supply rails. For example, when
the A
2
output is saturated, A
1
may continue to be in linear operation, responding to changes in the noninverting
input voltage. This difference may give the appearance of linear operation but the output voltage is invalid.
A single-supply instrumentation amplifier has special design considerations. To achieve a common-mode range
that extends to single-supply ground, the INA826 employs a current-feedback topology with PNP input
transistors; see Figure 60. The matched PNP transistors Q
1
and Q
2
shift the input voltages of both inputs up by a
diode drop, and through the feedback network, shift the output of A
1
and A
2
by approximately +0.8 V. With both
inputs and V
REF
at single-supply ground (negative power supply), the output of A
1
and A
2
is well within the linear
range, allowing users to make differential measurements at the GND level. As a result of this input level-shifting,
the voltages at pin 2 and pin 3 are not equal to the respective input terminal voltages (pin 1 and pin 4). For most
applications, this inequality is not important because only the gain-setting resistor connects to these pins.
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Product Folder Links: INA826