SC1302A/B/C/D/E/F
8
General Description
The SC1302A/B/C/D/E/F is a high speed, high peak current
dual MOSFET driver. It is designed to drive power MOSFETs
with ultra-low rise/fall time and propagation delays. As
the switching frequency of PWM controllers is increased
to reduce power converters volume and cost, fast rise and
fall times are necessary to minimize switching losses.
While a discrete solution can achieve reasonable drive
capability, implementing delay and other housekeeping
functions necessary for safe operation can become cum-
bersome and costly. The SC1302A/B/C/D/E/F presents a
total solution for the high-speed, high-power density
applications. Wide input supply range of 4.5V to16.5V
allows use in battery powered applications as well as dis-
tributed power systems.
Supply Bypass and Layout
A 4.7µF to 10µF tantalum bypass capacitor with low ESR
(equivalent series resistance) and an additional 0.1µF
ceramic capacitor in parallel are recommended as a supply
bypass to control switching and supply transients.
As with any high speed, high current circuit, proper layout
is critical in achieving optimum performance of the
SC1302A/B/C/D/E/F. Attention should be paid to the
proper placement of the driver, the switching MOSFET,
and the bypass capacitors.
The driver should be placed as close as possible to the
external MOSFETs to eliminate the possibility of oscillation
caused by trace inductance and the MOSFET gate capaci-
tance. A resistor in the range of 10ohm could be used in
series with the gate drive to damp the ringing if the drive
output path is not short enough. The bypass capacitors
should also be placed closely between V
CC
and GND of the
driver. A Schottky diode may be used to connect the
ground and the output pin to avoid latch-ups in some
applications.
Drive Capability and Power Dissipation
The SC1302A/B/C/D/E/F is able to deliver 1.6A peak
current for driving capacitive loads, such as MOSFETs.
Fast switching of the MOSFETs significantly reduces
switching losses for high frequency applications. Thermal
stress is reduced and system reliability is improved.
For simplicity, it is assumed that the gate capacitance of
a MOSFET is constant. The power delivered from the
power supply can be estimated based on this simpli ca-
tion. The energy needed to charge the capacitor is given
by the following equation
2
ON
VC
2
1
E uu
where C is the load capacitance and V is the output
voltage swing of the driver.
During turn o , the same amount of energy is dumped
to the ground. Therefore, the energy dissipated in one
switching cycle is:
E
TOTAL
= C x V
2
The power dissipation due to the gate driving actions is
given by:
P
GATE
= f x C x V
2
where, f is the switching frequency. With V
CC
= 12V, C =
1nF and f = 200kHz, the power dissipation per output is:
P
GATE
=(200kHz) x (1nF) x (12)
2
= 29mW
The corresponding supply current is:
mA4.2
V12
mW29
V
P
I
CC
GATE
Thermal Information
The driver’s junction temperature must be kept within
the rated limit at any time. The application system has to
e ectively remove the heat generated in the driver in
order for proper functions and performance. If the junc-
tion temperature reaches 150°C, the internal protection
circuit will be triggered to shut down the gate driver.
The power dissipation of the SC1302A/B/C/D/E/F should
be derated according to the following formula:
jA
TC125
pationPowerDissi
A
T
q
where T
A
= ambient temperature.
Applications Information
