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 2007 Semtech Corp.

www.semtech.com

SC1301A/B

POWER MANAGEMENT

Applications Information

The SC1301A/B is a high speed, high peak current

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 solutions can achieve reasonable drive

capability, implementing delay and other housekeeping

functions necessary for safe operation can become

cumbersome and costly. The SC1031A/B presents a total

solution for the high-speed, high power density

applications. A wide input supply range of 4.5V - 16.5V

allows operation 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 to con-

trol switching and supply transients. Low ESR (equiva-

lent series resistance) metalized film capacitors may also

be used. As with any high speed, high current circuit,

proper layout is critical in achieving optimum performance

of the SC1301A/B. 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 elimi-

nate the possibility of oscillation caused by trace induc-

tance and the MOSFET gate capacitance. A resistor in

the range of 10

Ω 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 be also

placed closely between Vcc and GND of the driver. A

Schottky diode may be connected between the ground

and the output pin to avoid latch-up in some applica-

tions.

Drive Capability and Power Dissipation

The SC1301A/B is able to deliver 2A peak current typi-

cally for driving a capacitive load, such as a MOSFET.

This high peak current will charge the input capacitance

of the device to turn on quickly. A similar amount of cur-

rent is needed to discharge the capacitance to ground

to turn the device off.

Using the SC1301A/B for fast switching actions, such as

turning on or turning off the capacitive load will signifi-

cantly reduce the device switching loss for high frequency

applications. Accordingly, the thermal stress and reliabil-

ity of the device can be improved.

Due to the non-linear characteristics of the input capaci-

tance of a device, the test load for the SC1301A/B is a

capacitor. Thus, the power from the bias power supply

can be calculated based on this setup. The energy, which

is required to charge the capacitor for turning on pro-

cess, is calculated by:

2

on

V

C

2

1

E

⋅

⋅

=

where, C is the load capacitance and V is the voltage

applied to the driver.

During the turning off process, the same amount of en-

ergy will be dissipated in the resistive elements in the

gate drive. Therefore, the energy for one switching ac-

tion (one turning on and one turning off) will be as

follows:

2

total

V

C

E

⋅

=

The power dissipation due to the gate driving switching is

calculated by:

2

gate

V

C

f

P

⋅

⋅

=

where, f is switching frequency for a given application.

Below is an example to calculate the power dissipation

for the given application.

With V

for the gate switching actions will be as:

() ( ) ( )

mW

29

12

nF

1

kHz

200

P

2

gate

=

⋅

⋅

=

The power supply current will be:

mA

4

.

2

V

12

mW

29

V

P

I

CC

gate

=

=

=