XTR111 datasheet(17/33 Pages) TI1

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VIN

1N4148

V-Signal

2.2kW

SET

2kW

VIN

SET

+100mV

Offset

120kW

Reference

I-VAmp

XTR111

VIN

1Vto5V

40kW

InputVoltage

0Vto5V

Reference

Voltage

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 2.2k

Ω 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 (VIN)

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

+100mV

(102.04mV)

offset

Overload of VIN

generated to the signal input. The larger this offset,

however,

the

influence

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 RSET. The desired resistor value may

network connected to a voltage reference and the

be found by choosing a combination of two resistors.

signal

source,

shown

Figure

43.

This

arrangement allows easy adjustment for over-and

under-range. The example assumes a 5V reference

(VREF) that equals the full-scale signal voltage and a

signal span of 0V to 5V for 4mA to 20mA (IMIN to

IMAX) output.

The voltage regulator output or a more precise

reference can be used as VREF. 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 IMIN to IMAX Output

(4mA to 20mA) with 0V to VFS Signal Source

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