Broadcom ACPL-C740 User Manual page 8

ACPL-C740 Evaluation Kit Board User Guide Isolated Sigma-Delta Modulator
Isolated DC-DC Converter
The isolated DC-DC converter circuitry is designed based on the push-pull transformer method to provide isolated Vdd1=5V
for the Broadcom ACPL-C740 sigma-delta modulator from the 5V power supply directly from the micro-USB type B
connector of the FPGA-EVBD board. The design incorporates the push-pull transformer driver, PE22100 from pSemi, which
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is built in a small form factor of 2 x 2 x 0.5 mm QFN package and can operate from –40°C to +125°C. The device consists
of an on-chip oscillator where switching frequency can be set by an external capacitor. The oscillator output is divided by
two in frequency to create anti-phase clock signals that drive two power switches. In this design, Cset of the PE22100 is
selected as 100 pF, which results in a switching frequency of around 200 kHz. This frequency is outside the operating
bandwidth of the ACPL-C740 sigma-delta modulator and the Sinc3 filter FFT bandwidth used for filtering and decimating the
sigma-delta bitstream from the ACPL-C740.
The PE22100 drives the Wurth push-pull transformer coil (PN 750313638). The transformer coil can withstand isolation
voltage of Viso = 5 kVrms per 1 min., and built into a package with creepage and clearance distance of 8 mm. The
transformer coil operates at an ambient temperature from –40°C to +125°C. The two outputs of the transformer coil are then
combined after the Schottky diodes. The output voltage must be regulated through a 5V/5V LDO regulator. The plot below
shows measurement conversion efficiency versus output load current.
Figure 5: Vout and Conversion Efficiency of the Isolated DC-DC Converter
For further technical support and pricing enquiries, contact pSemi at sales_europe@psemi.com or Wurth at midcom@we-
online.com.
Broadcom ACPL-C740-EvalKit-UG100
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