SC1205HSTR datasheet(6/13 Pages) SEMTECH

6 / 13 page

 2002 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC1205H

PRELIMINARY

Block Diagram

Applications Information

Theory of Operation

SC1205His the higher gate drive voltage version of it

predecessor, the SC1205. It is designed for optimum

enhancement of Low Rds_On power MOS.ETs with ul-

tra-low rise/fall times and propagation delays. Higher

MOS.ET enhancement has been made possible by opti-

mally increasing the gate drive voltage while maintaining

low switching losses at minimum RDS_ON. The SC1205H

is designed for a gate drive voltage of 8V, without com-

promising features that allow fast switching and low propa-

gation delays.

.ast Switching Drives

As the switching frequency of PWM controllers is increased

to reduce power supply volume and cost, fast rise and

fall times are necessary to minimize switching losses (TOP

MOS.ET) and reduce dead-time (BOTTOM MOS.ET)

losses. While low Rds_On MOS.ETs present a power

saving in I2R losses, the MOS.ETs die area is larger and

the effective input capacitance of the MOS.ET is in-

creased. Often a 50% decrease in Rds_On doubles the

effective input gate charge, which must be supplied by

the driver. The Rds_On power savings can be offset by

the switching and dead-time losses with a suboptimum

driver. While discrete solution can achieve reasonable

drive capability, implementing shoot-through, program-

mable delay and other housekeeping functions neces-

sary for safe operation can become cumbersome and

costly. The SC1205H presents a total solution for the

high-speed, high power density applications. Wide input

supply range of 4.5V-18V allows use in battery powered

applications, new high voltage, distributed power serv-

ers.

Shoot Through Protection

The control input (CO) to the SC1205H is typically sup-

plied by a PWM controller that regulates the power sup-

ply output. (See Application Evaluation Schematic, .ig-

ure 6). The timing diagram demonstrates the sequence

of events by which the top and bottom drive signals are

applied. The shoot-through protection is implemented

by holding the bottom .ET off until the voltage at the

phase node (intersection of top .ET source, the output

inductor and the bottom .ET drain) has dropped below

1V. This assures that the top .ET has turned off and

that a direct current path does not exist between the

input supply and ground, a shoot-through condition dur-

ing which both the top and bottom .ETs could be on

momentarily. The top .ET is also prevented from turn-

ing on until the bottom .ET is off. This time is internally

set to 20ns (typical).

The EN (enable) pin may be used to turn both TG and BG

drives off. This would allow lower power operation by

reducing the quiescent current draw of the SC1205H to

less than 10µA.

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