MINIMUM-SCALE CURRENT
The quiescent current of the XTR115/6 (typically 200µA)
is the lower limit of its output current. Zero input current
(I
IN
= 0) will produce an I
O
equal to the quiescent current.
Output current will not begin to increase until I
IN
> I
Q
/100.
Current drawn from V
REF
or V
REG
will add to this minimum
output current. This means that more than 3.7mA is avail-
able to power external circuitry while still allowing the
output current to go below 4mA.
OFFSETTING THE INPUT
A low scale of 4mA is produced by creating a 40µA input
current. This can be created with the proper value resistor
from V
REF
(Figure 2), or by generating offset in the input
drive circuitry.
MAXIMUM OUTPUT CURRENT
The XTR115/6 provides accurate, linear output up to 25mA.
Internal circuitry limits the output current to approximately
32mA to protect the transmitter and loop power/measure-
ment circuitry.
It is possible to extend the output current range of the
XTR115/6 by connecting an external resistor from pin 3 to
pin 5, to change the current limit value. Since all output
current must flow through internal resistors, it is possible to
damage with excessive current. Output currents greater than
45mA may cause permanent damage.
V
REG
V
REF
R
IN
XTR115
XTR116
XTR115
V
REG
V
O
D/A
V
REG
2.5V
40µA
R
0
62.5kΩ
V
REF
Voltage
Reference
XTR115
XTR116
V
REF
I
IN
Digital
Control
I
O
D/A
I
IN
0 to 160µA
A1
≈
Optical
Isolation
I
RET
5V
V
REG
XTR115
XTR116
I
RET
R
1
2.475kΩ
Digital
Control
µC
PWM
Out
≈
Filter
R
IN
Optical
Isolation
I
RET
FIGURE 2. Creating Low-Scale Offset.
FIGURE 3. Digital Control Methods.
6
XTR115, XTR116
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