ZXGD3101EV2 Datasheet, PDF (1/8 Pages) Diodes Incorporated – The purpose of this board is to demonstrate synchronous rectification and driving of a MOSFET

ZXGD3101EV2 EVALUATION BOARD USER GUIDE
Description
This document describes how to connect and evaluate the ZXGD3101EV2 evaluation board, Figure 1.
The purpose of this board is to demonstrate synchronous rectification and driving of a MOSFET as a
Schottky/ultra-fast recovery diode replacement in Flyback converters. When the board is used to drive
a synchronous MOSFET, it will yield efficiency improvement, whilst maintaining design simplicity and
incurring minimal component count. The ZXGD3101 senses the voltage across the MOSFET and
generates the gate drive voltage when a negative voltage is detected across the drain-source pin.
This evaluation guide also includes useful guidelines on conditioning of Flyback converters, as well as
a design tip to overcome premature driver turn-off and maximize the effectiveness of synchronous
rectification.
Note: The evaluation board is not recommended to be used with Flyback converters above 100kHz
switching frequency.
Figure 1 Evaluation board layout and connection diagram
Reference design
The ZXGD3101EV2 is configured to the reference design in Figure 2. The target application for the
device is external adapters where the typical output voltage ranges from 12V to 20V. However, the
evaluation board will work with output voltages up to 40V.
Power, which could be sourced directly from the output of the power supply, is applied to the terminal
block P1. At the other end of the board is a location for a three way header, P2. This is not fitted, so
as to allow flexibility of mounting (forward or reverse). The purpose of the header is to allow the board
to be soldered directly across a TO220 packaged synchronous MOSFET.
R4, Q2, D1 and C1 are configured as a simple series regulator to maintain a stable Vcc. The values of
Rref and Rbias in Figure 2 are based on a 10.3V Vcc. For supply voltages below this, these resistor
values need to be reduced proportionally to maintain 5.3mA and 3.2mA into the ‘REF’ and ‘BIAS’ pins
respectively. Refer to the datasheet for further information on selection of the resistor value.
A fixed-bias-point constant current source (Q1, R2, R1//R5 and R3) is included on the board. The
current source is not active in the original board setting and is only intended for elimination of
premature turn-off problem on the controller (refer to the section ‘Overcoming premature turn-off’ for
details).
Issue 1 – December 2009
© Diodes Incorporated, 2009
www.diodes.com