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6 Advanced Source, Measurement, and Control
Downprogrammming
As shown by the dashed line on the left in the figures, the power analyzer is capable of sinking current
over the output voltage range from zero volts to the rated voltage. This negative current sinking
capability provides fast downprogramming of the output. The negative current is not programmable.
CC Mode Delay
The power supply may momentarily cross into constant-current (CC) mode when it is turned on, when
an output value is programmed, or when the output load is connected. In most cases these temporary
conditions would not be considered an over-current protection fault, and having an OCP condition
disable the output when the CC status bit is set would be a nuisance. Specifying an OCP delay will
ignore the CC status bit during the specified delay period. For example, if the OCP delay is 100 ms, and
the output goes into CC mode for 80 ms and then back to CV mode, the output will not shut down, If
the CC mode persists for more than 100 ms, the output will shut down.
To program a delay time, press the Settings key to access the Source Settings. Navigate to and select
Protection. Then press Enter.
You can specify if the delay timer is started by any transition of the output into CC mode (select CC
Transition), or if the delay timer is started at the end of a settings change in voltage, current, or output
state (select Settings Change).
Factors that influence how long the settings or load change lasts may include: the difference between
the old and new output value, the current limit setting, load capacitance in CV mode, load inductance
in CC mode, the slew rate, and bandwidth setting. The delay required must be determined empirically;
the power module programming-response time characteristics may be used as guidelines.
Note that the time it takes the output to go into CC mode varies - depending on the magnitude of the
over-current condition compared to the current limit setting. For example, if the over-current is only
slightly greater than the current limit setting, it may take several tens of milliseconds, depending on
the power module type, for the output to set the CC status bit. If the over-current is significantly
greater than the current limit setting, it may only take a few milliseconds or less, depending on power
module type, for the output to set the CC status bit. To determine when the output will shut down, you
must add the time it takes to set the CC status bit to the over-current protection delay time. If the
over-current persists beyond the sum of these two time intervals, the output will shut down.
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Keysight N6705C User's Guide
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