Page 63 - PEN eBook July 2023

Test & Measurement

is needed to settle quickly, enabling a measurement of the clamped V and I 50 to 500 ns
ds d
after the switching event. These techniques will provide the best R measurement to
DS(on)
compare against stress voltages and timeframes to characterize the current collapse in

the GaN FET structure.
▶ Switching loss (i.e., t , t , E , t , t , E ): These parameters are specified in the IEC
d(on) r (on) d(off) f (off)
60747-8 standard and are typically specified in power FET datasheets. The ability to
measure and extract these parameters repeatably and reliably is highly dependent on the
design of the fixture and the minimization of parasitics. Test conditions typically include
V , I , V and sometimes the L but almost always the gate resistor (R ). R is one of the
ds d gs load g g
main controls of the gate-drive speed and ultimately how hard the device is turned on.
Most ideally, R is a small value, allowing for a fast-switching transition. However, if the DPT
g
fixture design is not optimized and has unwanted parasitics, then a larger Rg is needed to

slow down the switching waveforms to minimize ringing.
▶ Drive loss (i.e., Q ): Drive loss is typically the smallest of the losses. Repeatable and reliable
g
measurement and calculation of gate charge (Q ) requires clean switching waveforms,
g
specifically V and I . Minimal gate-loop parasitics are critical for clean waveforms.
gs g

REPEATABLE, RELIABLE
DYNAMIC CHARACTERIZATION
OF LOW-VOLTAGE GaN FETS

The key to obtaining repeatable and reliable
dynamic characterization of small GaN FETs is
attention to detail in the DPT fixture design.
The EPC2045A described in Figure 1 was used
as the target DUT. This part exemplifies the
100-V GaN FET and the challenges discussed
previously.

DESIGN MODIFICATIONS TO
KEYSIGHT’S CUSTOMIZED GaN
SOLUTION

Keysight’s solderless DUT connection
technology (Figure 3 and Figure 9) for the
PD1500A Dynamic Power Analyzer/Double
Pulse Tester is presented. However, this

connection technology had not been tested
with as small a device as the EPC2045A
(1.5 × 2.5 mm), requiring repeatable connections
to the gate, a single 44.5-µm round solder-
2
ball target. Fixturing and registration of these
Figure 3: Customized GaN board for EPC2045A

JULY 2023 | www.powerelectronicsnews.com 63