HPW7095 Datasheet, PDF (18/23 Pages) List of Unclassifed Manufacturers – 6-Channel DC/DC Converter Control IC

HPW7095/A
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:
ON Duty (max) = ^{VDTC - 1.1 V} ⋅100 (%)
0.7 V
VDTC (V) = ^R2 ⋅ VREF
R1 + R2
R1
VDTC
VREF
D TC1
R2
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.
 Copyright HIPAC Semiconductor, Inc.
18
Rev. A.2 - July., 2004
www.hipacsemi.com