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 2005 Semtech Corp.

www.semtech.com

SC1302A/B/C/D/E/F

PRELIMINARY

POWER MANAGEMENT

Applications Information

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 discrete solution can achieve reasonable

drive capability, implementing delay and other

housekeeping functions necessary for safe operation can

become cumbersome and costly. The SC1032A/B/C/

D/E/F presents a total solution for the high-speed, high

power density applications. Wide input supply range of

4.5V - 16.5V allows use in battery powered applications

as well as distributed 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 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 capacitance. A resistor in the range of 10W 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 Vcc 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, we assume that the gate capacitance of a

MOSFET is constant. The power delivered from the power

supply can be estimated based on this simplification. The

energy needed to charge the capacitor is given by:

2

ON

V

C

2

1

E

⋅

⋅

=

where C is the load capacitance and V is the output

voltage swing of the driver.

During turn off, the same amount of energy is dumped to

the ground. Therefore, the energy dissipated in one

switching cycle is:

The power dissipation due to the gate driving actions is

given by:

2

GATE

V

C

f

P

⋅

⋅

=

where, f is the switching frequency.

with V

dissipation per output is:

() ( ) ( )

mW

29

12

nF

1

kHz

200

P

2

GATE

=

⋅

⋅

=

The corresponding supply current is:

mA

4

.

2

V

12

mW

29

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

effectively remove the heat generated in the driver in order

for proper functions and performance. If the junction

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:

where T

A

= ambient temperature.

2

TOTAL

V

C

E

⋅

=

jA

T

C

125

n

Dissipatio

Power

A

θ

−

°

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