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In CV operation, large capacitive loads and high inductance leads have the potential to create ringing
and dynamically unstable voltage at the DUT when undergoing sudden load or voltage changes. ESR
tends to mitigate this by dampening the resonance that occurs between the load capacitance and lead
inductance. Lead resistance contributes to the damping effects of ESR but also increases voltage drop
and power dissipation in the load leads. The
guidelines for minimum required ESR as a function of DUT capacitance. This is a function of the
voltage
compensation
mode.
For a DUT that has internal capacitance with low ESR as shown in the Capacitive Load Boundary
graphs, such as film capacitor or ceramic capacitors, additional capacitance and series resistance can
be added in parallel to dampen the effects of ringing, as shown in the following figure. The additional
capacitance should be at least 1 to 4 times the value of C
based on the Capacitive Load Boundary plots for C
of a high-voltage film capacitor and a series resistor. The parallel capacitance and ESR must be able to
handle DUT-specific requirements such as current or voltage ripple. In addition, parallel capacitance
will limit the ability of the power supply to measure fast current edges sourced directly from the DUT,
as well as slow down the voltage programming speed and bandwidth.
Typical external
damping network
The specified voltage transient response to a load current step for the power supply may become
degraded when remote sensing with long load leads, especially with low bypass capacitance at the
DUT. This can be manifested as a poorly dampened ringing or even as a well dampened response with
very large peak deviation. This issue can be most problematic when operating at lower voltage with
higher current. To mitigate this, parallel capacitance can be added at the terminals of interest to
reduce the amplitude of voltage deviation. It is likely an external parallel damping network, as
previously illustrated, would be needed in place of or in addition to a pure capacitor. Generally, a
capacitor with low ESR in parallel with a capacitor with high ESR allows for good stability, minimized
transient response voltage deviation, as well as good voltage noise filtering.
Lead Inductance Considerations in Constant Current (CC) Operation
In CC operation, both in current priority mode and in voltage priority mode (when in current limit), 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.
Keysight RP7970 & RP7980 Series Operating and Service Guide
Capacitive Load Boundary
and the desired ESR should be chosen
DUT
. This can be implemented through the addition
DUT
2 Installing the Instrument
characteristic graphs have
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