5B39

Rev. 0 | Page 2 of 8

GENERAL DESCRIPTION

The 5B39 is a single-channel signal conditioning module that

converts a high-level analog input voltage into a floating,

isolated proportional output current of 4 to 20 mA or 0 to 20

mA across loads from 0Ω to 750Ω. The module provides high

accuracy of +0.05%, low nonlinearity of +0.02%, and the

protection of 1500V rms isolation between output-to-input and

output-to power supply. The input common must be held to

within +1V of power common.

Signal isolation by transformer coupling uses a proprietary

modulation technique for linear, stable and reliable

performance. A demodulator on the output side of the signal

transformer recovers the original signal, which is then filtered

and converted to an accurate current output by a current (V-to-

I) converter output stage. Output protection enables the 5B39 to

withstand accidental connection to 240V rms power lines

without damage, while isolating computer-side circuitry. In

addition, the 5B39 is mix-and-match and hot-swappable with

all 5B Series modules, so can be inserted or removed from any

socket in the same backplane without disrupting system power.

Track-and-Hold for DAC Applications

– In applications where

a single system digital-to-analog converter (DAC) is used to

drive a number of current output channels, the 5B39 includes a

track-and-hold input circuit. Selected by a high Write Enable

input, the hold mode exhibits an output droop rate of 80 uA/s.

This corresponds to a refresh interval of 25 ms for 0.01% span

droop. On power-up, the module’s output remains at 0 mA for

about 100 ms to allow the user to initialize the track-and-hold

circuit.

In applications using one DAC per channel, where the track-

and-hold feature of the 5B39 is not used, the Write Enable input

should be set to low by grounding it to power common, as on

the 5B01 and 5B08 backplanes. The module current output will

then track its input signal.

Generating A Voltage Output Signal

– The 0 to 20 mA output

of the 5B39-04 and the 5B39-03, can produce a 0 to +10V

output by connecting a 500Ω conversion resistor across the

modules’ output terminals,. This approach should be used with

caution because the output lacks the low impedance of a true

voltage source. This means that the tolerance and size of the

load impedance relative to the conversion resistor can introduce

significant error. For example, a load impedance < 500kΩ would

contribute <0.1% error.

.

.

Figure 2