National Instruments cFP-PWM-520 用户手册

In the ON state, the effective resistance between V

OUT

 and V

SUP

 

causes a voltage drop between the external supply voltage and the 
output voltage. For example, 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 

× R

) = V

where R

 is the ON resistance and V

 is the output voltage.

Refer to the 

 section for the value of the ON 

resistance.

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 

 section for more information about configuring the 

duty cycle.

2. Measure the voltage between the V

OUT

 and V

SUP

 terminals for 

that channel.

Under normal load conditions, the V

OUT

-to-V

SUP

 voltage is 

less than 1 V when the output is ON continuously. Any voltage 
higher than 1 V indicates a short circuit. Typically, the 
V

OUT

-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%. The channel 
resets immediately.