MINIMUM-SCALE CURRENT
MAXIMUM OUTPUT CURRENT
The quiescent current of the XTR115/6 (typically 200µA)
is the lower limit of its output current. Zero input current
(IIN = 0) will produce an IO equal to the quiescent current.
Output current will not begin to increase until IIN > IQ /100.
Current drawn from VREF or VREG 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.
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.
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 VREF (Figure 2), or by generating offset in the input
drive circuitry.
XTR115
XTR116
VREG
VREF
RIN
VO
D/A
XTR115
VREG
XTR115
XTR116
VREG
VREF
IIN
2.5V
40µA
VREF
Voltage
Reference
R0
62.5kΩ
Digital
Control
IO
D/A
Optical
Isolation
IIN
IRET
A1
0 to 160µA
XTR115
XTR116
5V
VREG
RIN
Filter
PWM
Out
Digital
Control
IRET
µC
R1
2.475kΩ
Optical
Isolation
IRET
FIGURE 2. Creating Low-Scale Offset.
FIGURE 3. Digital Control Methods.
XTR115, XTR116
6
SBOS124A
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