-SCS Pulse Card (PGU and PMU) User's Manual Section 2:
4200A-PMU-900-01 Rev. B March 2023 2-25
Methods to compensate for load-line effect
The methods to compensate for load-line effect include:
• Use the built-in load-line effect compensation (LLEC) in the PMU for the standard 2-level pulse
mode. Ideally (when LLEC is enabled), the PMU adjusts its output levels such that the
programmed output voltage appears at the DUT. For ITMs, see Load-line effect compensation
(on page 2-24). For UTMs, use the LPT pulse_meas_sm function to control LLEC.
• Manual adjustment of the PMU output until the target pulse level is measured across the DUT.
For a pulse sweep, this manual process must be repeated for every step in the sweep.
If you are not using LLEC, you can manually set the output impedance to match the impedance of the
DUT. For example, if the impedance of the DUT is 1 kΩ, set the output impedance to 1 kΩ. Maximum
power transfer is achieved when the DUT impedance matches the output impedance setting. In a real
test environment, you may not know the exact resistance value of the DUT, and you will have the
added affect of cabling and pin-to-pad resistance. The output impedance can be set from an ITM (see
Disable LLEC and set the output impedance (on page 2-30
)) or from a UTM (see the LPT
pulse_load function).
How LLEC adjusts pulse output to the target levels
LLEC is an algorithm that adjusts the output of a PMU channel. When enabled, the algorithm
performs a set number of iterations in an attempt to output the target voltage to the DUT.
The algorithm used for LLEC is shown in the following figure. The diagram shows that the PMU
standard pulse source (with measure) uses a burst-measure-analyze-reburst method. This method
allows for range changing, threshold comparison, load-line effect compensation, and pulse timing.
This means there is separation between each set, or burst, of pulses. The number of pulses output
for each attempt is controlled by the Number of Pulses setting for ITMs or the pulse_meas_timing
function for UTMs. Note that LLEC is available only in the standard 2-level pulse mode. LLEC is not
available in the Segment Arb mode.
Note that after the first action, "Output Pulse Burst," all pulse channels in the test stop pulsing and
output 0 V while performing the actions in the remaining boxes in the diagram. The time between
pulses is determined by the time required to process the measurements and perform the calculations
and comparisons shown in the previous figure. Wider pulses, longer pulse periods, and a higher
number of pulses increases the time between pulses where the output is at 0 V. Note that both Pulse
I-V and Waveform Capture Test modes use this algorithm and both will output 0 V between pulses for
each step in a sweep. For strict control over the pulse voltage versus time, see the Segment Arb
feature of the PMU.
The "Get Good Measurement" step shown in the previous figure also must ensure that the current
measure range is correct (if ranging is enabled) and check the measured voltage and current against
the thresholds. See PMU - all terminal parameters (on page 3-6
).
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