ZXGD3105N8_15 datasheet(7/14 Pages) DIODES

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ZXGD3105N8

Document Number DS35101 Rev. 3 - 2

7 of 14

www.diodes.com

March 2013

A Product Line of

Diodes Incorporated

ZXGD3105N8

Application Information

The purpose of the ZXGD3105 is to drive a MOSFET as a low-VF Schottky diode replacement in isolated AC/DC converter. When combined with

a low RDS(ON) MOSFET, the controller can yield significant power efficiency improvement, whilst maintaining design simplicity and incurring

minimal component count. Figure 1 shows the typical configuration of ZXGD3105 for synchronous rectification in a low output voltage Flyback

converter.

A typical circuit configuration of synchronous rectification with ZXGD3105 for use in resonant converter is shown in Figure 2. Two ZXGD3105

together with two synchronous MOSFETs should be used on the secondary side of the center tapped transformer winding.

Figure 1 Typical Flyback application schematic

Figure 2 Synchronous rectification in resonant converter

Threshold Voltage and Resistor Setting

The correct selection of external resistors RREF and RBIAS is important for optimum device operation. RREF and RBIAS supply fixed current into the

IREF and IBIAS pin of the controller. IREF and IBIAS combines to set the turn-off threshold voltage level, VT. In order to set VT to -10mV, the

recommended IREF and IBIAS are 1.02mA and 0.54mA respectively.

The values for RREF and RBIAS are selected based on the VCC voltage. If the VCC pin is connected to the power converter’s output, the resistors

should be selected based on the nominal converter’s output voltage. Table 1 provides the recommended resistor values for different Vcc voltages.

Supply, VCC

(V)

Bias Resistor, RBIAS

(kΩ)

Reference Resistor, RREF

(kΩ)

9.6

4.3

9.1

Table 1 Recommended resistor values for different VCC voltages

ZXGD3105N8 Datasheet(PDF) 7 Page - Diodes Incorporated