International Rectifier
IRDC2085S-S DEMO BOARD EVALUATION PROCEDURE
International Rectifier • 233 Kansas Street, El Segundo, CA 90245 USA
Overview
This document describes how to connect and evaluate the supplied IRDC2085S-DF demo board. The demo board
incorporates a new DC Bus Converter chipset in a fixed-frequency, open-loop isolated half-bridge DC-DC
converter with 6:1 input to output voltage conversion ratio. The chipset consists of a primary side IC (IR2085S),
two 80V primary side FETs (IRF7493), two 30V secondary side FETs (IRF7832), a primary side biasing FET
(IRF7380) and a secondary side gate clamp FET (IRF9956). The front side of the demo board is shown in Fig. 1.
Fig. 1 Front side of the DC Bus Converter demo board with IR2085S ChipSet with marked input and output pins.
This version of the Demo Board employs IRF7832 Power MOSFETs for secondary synchronous rectification *
IRDC2085S-S Quick Evaluation Procedure
To evaluate the operation and performance of the IRDC2085S-S demo board, connect a power supply to its input
terminals, and a power load to its output terminals. Input and output terminals are marked in Fig. 1. To duplicate
the performance data reported on page two, approximately 400 LFM of airflow is needed across the module.
The circuit will start to operate as soon as the primary Vcc reaches about 9V – typically at 12Vin. At this low
input voltage, the output voltage will be only about 2V, and the secondary Vcc will be insufficient to fully
enhance the secondary side synchronous rectifier MOSFETs. To avoid excessive body diode conduction losses,
output current during slow input voltage ramp-up should be set at less than 2A.
IRDC2085S-S Demo Board Description and circuit capability
The circuit is designed to deliver continuous 20A output current in 36V – 60V input voltage range, with 400 LFM
of airflow. Output voltage for this input voltage range will vary from 6V to 10V, and the total available output
power from the module will range from around 120W at 36V to up to 200W at 60V input.
The circuit design is optimized in order to demonstrate true performance of the IR2085S control IC, IRF7493
primary FETs and IRF7832 secondary FETs. Therefore, no test pins are available on the board. To probe the
circuit waveforms use an oscilloscope probe with minimal length for the ground pin and connect directly to the
pins of the IC / MOSFET device.
To measure circuit efficiency, voltage and current at the input and output of the demo board need to be accurately
measured. Use of calibrated shunts for input and output current measurements is strongly recommended, as is use
of a thermal camera for thermal performance evaluation.
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