HA16107P Datasheet, PDF (37/40 Pages) Hitachi Semiconductor – PWM Switching Regulator for High-performance Voltage Mode Control

HA16107P/FP, HA16108P/FP
3. IC Heat Emission Problem and Countermeasures (HA16107 Series, HA16114 Series)
While the above ICs can directly drive a power MOS FET gate, if the method of use is not thoroughly investigated,
there will be a tendency for the gate drive power to increase and a problem of heat emission by the IC may occur.
This section should therefore be noted and appropriate measures taken to prevent this kind of problem.
1. Power MOS FET Drive Characteristics
When power MOS FET drive is performed, in order to lower the on-resistance sufficiently, overdrive is normally
performed with a voltage considerably higher than 5 V, for example, such as the 15 V power supply voltage of the
IC.
At this time, the power that should be supplied from the IC to the power MOS FET is determined by gate load Qg in
Figure 9.
2. IC Heat-Emission Power Calculation (Figure 9)
The power that contributes to IC heat emission is calculated by means of the following equation.
Pd = V_IN I_Q + 2Qg V_IN f
Where
V_IN : Power supply voltage of IC
I_Q : Operating current of IC (unloaded)
Qg : Above-mentioned gate load
f : Operating frequency of IC
The coefficient, 2, indicates that gate discharging also contributes to heat emission.
4. Power MOS FET Gate Resistance Design (HA16107 Series, HA16114 Series)
There are the following three purposes in connecting a gate resistance, and the circuit is generally of the kind shown in
Figure 8.
(1) To suppress peak current due to gate charging
(2) To protect IC output pins
(3) To provide drive appropriate to power MOS FET input characteristics
D_G
To transformer
OUT
IC
R_G1
output pin
R_G2
C_S
Power
MOS FET
R_CS
Figure 8 Gate Drive Circuit
Rev.4.00 Jun 15, 2005 page 37 of 39