APW7095 datasheet(18/23 Pages) ANPEC

18 / 23 page

Rev. A.3 - Jul., 2005

APW7095/A

www.anpec.com.tw

Application Information (Cont.)

Dead-Time Setting

The dead-time control pin (DTC) is designed to set

the maximum ON duty of the main-side MOSFET.

When the device is set for step-up inverted output based

on the step-up or step-up/down Zeta method or flyback

method, the FB pin voltage may reach and exceed

the triangular wave voltage due to load fluctuation. If

this is the case, the output MOSFET is fixed to a ON

duty of 100 %. To prevent this, set the maximum duty

of the output MOSFET. Connecting a resistor- divider

between VREF, DTC and GND pins provides a volt-

age VDTC to DTC pin. When the the voltage at the

DTC pin is higher than the triangular wave voltage (CT1/

2), the output transistor is turned on. The maximum

duty is calculated as the following equation:

DTC1

VREF

VDTC

(%)

100

0.7

1.1

Duty

DTC

(max)

⋅

REF

DTC

(V)

⋅

where VREF is the output of the reference voltage (2.

49V typical) at VREF pin. The amplitude of the trian-

gular waves CT1 and CT2 are typically 0.7V from 1.

1V to 1.8V.

APW7095 Datasheet(PDF) 18 Page - Anpec Electronics Coropration