Datasheet

VIN
1N4148
V-Signal
2.2kW
R
SET
2kW
VIN
SET
+100mV
Offset
120kW
5V
Reference
I-VAmp
XTR111
VIN
1Vto5V
R
1
40kW
InputVoltage
0Vto5V
Reference
Voltage
5V
R
2
10kW
XTR111
www.ti.com SBOS375C –NOVEMBER 2006– REVISED JUNE 2011
More protection against negative input signals is LEVEL SHIFT OF 0V INPUT AND
provided using a standard diode and a 2.2kΩ resistor, TRANSCONDUCTANCE TRIM
as shown in Figure 42.
The XTR111 offers low offset voltage error at the
input, which normally does not require cancellation. If
the signal source cannot deliver 0V in a single-supply
circuit, an additional resistor from the SET pin to a
positive reference voltage or the regulator output
(Figure 44) can shift the zero level for the input (V
IN
)
to a positive voltage. Therefore, the signal source can
drive this value within a positive voltage range. The
Figure 42. Enhanced Protection Against Negative
example shows a +100mV (102.04mV) offset
Overload of V
IN
generated to the signal input. The larger this offset,
however, the more influence of its drift and
inaccuracy is seen in the output signal. The voltage at
4mA–20mA OUTPUT
SET should not be larger than 12V for linear
The XTR111 does not provide internal circuits to operation.
generate 4mA with 0V input signal. The most
Transconductance (the input voltage to output current
common way to shift the input signal is a two resistor
ratio) is set by R
SET
. The desired resistor value may
network connected to a voltage reference and the
be found by choosing a combination of two resistors.
signal source, as shown in Figure 43. This
arrangement allows easy adjustment for over-and
under-range. The example assumes a 5V reference
(V
REF
) that equals the full-scale signal voltage and a
signal span of 0V to 5V for 4mA to 20mA (I
MIN
to
I
MAX
) output.
The voltage regulator output or a more precise
reference can be used as V
REF
. Observe the potential
drift added by the drift of the resistors and the voltage
reference.
Figure 44. Input Voltage Level Shift for 0mA
Output Current
Figure 43. Resistive Divider for I
MIN
to I
MAX
Output
(4mA to 20mA) with 0V to V
FS
Signal Source
Copyright © 2006–2011, Texas Instruments Incorporated 17