National Instruments cFP-PWM-520, FP-PWM-520 Short-Circuit Protection

FP-PWM-520 and cFP-PWM-520 6 ni.com

In the ON state, the effective resistance between VOUT and VSUP

causes a voltage drop between the external supply voltage and the

output voltage. Forexample, if the external supply voltage is 5 V

and the output current is 1 A, calculate the output voltage as

follows:

5 V – (1 A × RON) = VOUT

where RON is the ON resistance and VOUT is the output voltage.

Refer to the Specifications section for the value of the ON

resistance.

Short-Circuit Protection

If the protection circuitry detects a short-circuit condition on an

output channel, it disables the output. If the protection circuitry

disables an output that would otherwise be in the ON state, the

status indicator for that channel is still lit, but the output transistor

is turned off.

To determine whether a channel is in a short-circuit condition,

complete the following steps:

1. In FieldPoint software, set the duty cycle to 100% for the

channel in question. Refer to the Configuring the Output

Channels section for more information about configuring the

duty cycle.

2. Measure the voltage between the VOUT and VSUP terminals for

that channel.

Under normal load conditions, the VOUT-to-VSUP voltage is

less than 1V when the output is ON continuously. Any voltage

higher than 1V indicates a short circuit. Typically, the

VOUT-to-COM voltage is almost zero if the protection circuitry

is activated.

To reset a channel in a short-circuit condition, determine the cause

of the condition and disconnect the load from the channel. The

channel resets automatically when the load is removed.

Alternatively, if completely removing the channel load is not

convenient, reset the channel in any of the following ways:

• In FieldPoint software, set the duty cycle to 0%. Thechannel

resets immediately.