ZXGD3102 datasheet(9/15 Pages) DIODES

9 / 15 page

Issue 4, May 2009

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ZXGD3102T8

Component Selection

It is advisable to decouple the ZXGD3102 closely to VCC and ground due to the possibility of high peak

gate currents, as indicated by C1 in Figure 4. In applications where the input voltage is higher than

12V, it is recommended to use a Zener diode, ZD1 as shown in the Typical Application Circuit on page

1, and in Figure 2, in order to limit the VCC supply voltage to the ZXGD3102 and also to limit the

maximum voltage applied to the gate of the MOSFET. A suitable value for the Zener is 10V.

The proper selection of external resistors RREF and RBIAS is important to the optimum device operation.

Select a value for resistor RREF to give a reference current, IREF, of ~2.4mA. The value of RBIAS must

then be selected to give a bias current, IBIAS, of approximately 1.2 times IREF. This set the turn-off

threshold voltage VT of the controller to ‘-24mV’ at VCC =10V.

RREF = (VCC -0.7V)/ 0.0024

RBIAS = (VCC -0.7V)/ 0.0028

Alternatively, RREF and RBIAS can be chosen to be equal to set the turn-off threshold voltage VT to ‘-

29mV’ at VCC =10V. This also reduces the IC current consumption when the gate voltage is off.

External gate resistor to GATEH pin is optional. It can be inserted to control the turn-on gate rise time

which may help with in-rush current protection, EMI issues or power dissipation within the part. The

addition of CBIAS controls the switch-on delay of the MOSFET, and ensures stability. A suitable value

is 1nF.

Layout considerations

The Gate pins should be as close to the MOSFET gate as possible. Also the ground return loop

should be as short as possible. The decoupling capacitor should be close to the VCC and Ground pin,

and should be a X7R type. Trace widths should be maximized in the high current path through the

MOSFET and ground return in order to minimize the effects of circuit inductance and resistance.

For best thermal performance, the PCB heat path from pins 5 and 6 needs attention. The area of

copper connected to pins 5 and 6 should be maximised.

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