Keysight Technologies RP7900 Series, Operating And Service Manual

Page: 77 / 318

Lead Inductance Considerations in Current Priority Mode
For operation of the RPS units in current priority mode, the setup typically resembles that in the
following figure where the DUT is of a low impedance or voltage source nature. Sense lead
measurements are still utilized to detect over/under voltage protection events and when cross-over
into CV operation occurs.
In current priority mode, large inductive leads have the potential to create ringing in the output current
when undergoing current programming steps or load voltage changes. This effect increases as
inductance increases and lead resistance decreases. The
Inductive Load Boundary graph in the
Characteristics section shows the minimum amount of lead resistance to mitigate programming
overshoot and unstable programming response under two sets of load lead conditions. This is a
function of the current
compensation mode . Note that lead and DUT resistance are indistinguishable
in this context, so any resistance in the DUT is added to the effective lead resistance as specified in the
graphs.
Dynamic Current Programming with Large Inductive Loads
Additional constraints may be required when programming current steps with high inductance DUTs or
leads. Programming speed decreases with inductive loads greater than 1 μH. When programming
large current steps, further speed degradation and overshoots may occur due to inherent voltage
limitations of the RPS. Without lowering the inductance, the speed degradation cannot be improved.
However, the overshoot aspect can be mitigated or removed by gradually decreasing the
programming pole or slew rate setting until the desired level of performance is achieved.
Excessive Current in Current Priority Mode
Excessive output current may damage the device under test under certain conditions.
This can occur, for example, if the DUT shorts the output of the instrument when the
lower voltage limit is set substantially above zero.
When operating in current priority mode, if the voltage of a low-impedance DUT, such as a battery or
short circuit, rises above the upper voltage limit setting or falls below the lower voltage limit setting,
current flow exceeding the RPS unit's steady state rating can occur, potentially damaging the DUT.
After a short delay, the excessive current flow will cause over-current protection to engage - disabling
the output of the RPS.
Keysight RP7900 Series Operating and Service Guide 77
2 Installing the Instrument