XTR111

SBOS375 − NOVEMBER 2006

www.ti.com

10

APPLICATION INFORMATION

The XTR111 is a voltage-controlled current source capa-

ble of delivering currents from 0mA to 36mA. The primary

intent of the device is to source the commonly-used indus-

trial current ranges of 0mA−20mA or 4mA−20mA. The per-

formance is specified for a supply voltage of up to 40V. The

maximum supply voltage is 44V. The voltage-to-current ra-

put voltage range can be freely set in accordance with the

application requirement. The output current is cascoded

by an external P-Channel MOSFET transistor for large

voltage compliance extending below ground, and for easy

power dissipation. This arrangement ensures excellent

suppression of typical interference signals from the indus-

trial environment because of the extremely high output im-

pedance and wide voltage compliance.

An error detection circuit activates a logic output (error

flag) in case the output current cannot correctly flow. It indi-

cates a wire break, high load resistor, or loss of headroom

for the current output to the positive supply.

The output disable (OD) provided can be used during pow-

er-on, multiplexing and other conditions where the output

should present no current. It has an internal pull-up that

causes the XTR111 to come up in output disable mode un-

less the OD pin is tied low.

The onboard voltage regulator can be adjusted between

3V to 15V and delivers up to 5mA load current. It is in-

tended to supply signal conditioning and sensor excitation

in 3-wire sensor systems. Voltages above 3V can be set

by a resistive divider.

Figure 1 shows a basic connection for the XTR111. The in-

of the output current. The I-Mirror has a precise current

gain of 10. This configuration leads to the transfer function:

The output of the voltage regulator can be set over the

ing equation.

3V

REGF

REGS

5V

Signal

Source

(Sensor or

DAC, for

example)

V

I−Mirror

VSP

1

9

8

2

3S

D

G

VG

IS

Q

EXT

P−Channel

MOSFET

(Pull Low for Normal Operation)

0mA or 4mA to 20mA

OD

EF

C

1

R

2

8.2k

Ω

VIN

6

4

5

R

SET

SET

7

10

GND

R

1

5.6k

Ω

V

OUT

Load

I

OUT

(

± Load Ground)

I

()

V

VIN

R

SET

Figure 1. Basic Connection for 0mA to 20mA Related to 0V to 5V Signal Input. The Voltage Regulator is

Set to 5V Output.