SC4605IMSTRT datasheet(4/19 Pages) SEMTECH

4 / 19 page

 2004 Semtech Corp.

www.semtech.com

SC4605

POWER MANAGEMENT

Ordering Information

Pin Descriptions

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(

)

(

VCC: Positive supply rail for the IC. Bypass this pin to

GND with a 0.1 to 4.7µF low ESL/ESR ceramic capaci-

tor.

GND: All voltages are measured with respect to this pin.

All bypass and timing capacitors connected to GND should

have leads as short and direct as possible.

FS/SYNC: A capacitor from FS pin to GND sets the PWM

oscillator frequency. Use a high quality ceramic capacitor

with low ESL and ESR for best result. A minimum capaci-

tor value of 200pF ensures good accuracy and less sus-

ceptibility to circuit layout parasitics. When the FS is pulled

and held below 0.2V, its sleep mode operation is invoked.

The Sleepmode supply current is 10µA typical. The oscil-

lator and PWM are designed to provide practical opera-

tion up to 600kHz. In synchronous mode operation, a

low value resistor has to be connected between ground

and the timing capacitor. An external clock is then feed

into the resistor capacitor junction to override the inter-

nal clock.

VSENSE: This pin is the inverting input of the voltage

amplifier and serves as the output voltage feedback point

for the Buck converter. It senses the output voltage through

an external divider.

COMP: This is the output of the voltage amplifier. The

voltage at this output is inverted internally and connected

to the non-inverting input of the PWM comparator. A lead-

lag network around the voltage amplifier compensates for

the two pole LC filter characteristic inherent to voltage mode

control and is required in order to optimize the dynamic

performance of the voltage mode control loop.

ISET / PHASE: PHASE is connected to the junction be-

tween the two external power MOSFET transistors. The

voltage drop across the high side MOSFET during its con-

duction is compared with the voltage drop generated by

the internal 50µA current source and the external cur-

rent limit resistor connected between PHASE and Vin,

and forms the current limit comparator and logic sets

the PWM latch and terminates the output pulse. If the

converter output voltage drops below 68.75% of its nomi-

nal voltage, the controller stops switching and goes

through a soft start sequence. This prevents excess

power dissipation in the low side MOSFET during a short

circuit. The current limit threshold is set by the external

resistor between VCC and ISET.

BST: This pin connects the external charge pump, and

powers the high side MOSFET gate drive.

DRVH, DRVL: The output drivers are rated for 1A peak

currents. The PWM circuitry provides complementary drive

signals to the output stages. The cross conduction of

the external MOSFETs is prevented by monitoring the

voltage on the driver pins of the MOSFET pair in conjunc-

tion with a time delay optimized for FET turn-off charac-

teristics.

Notes:

(1) Only available in tape and reel packaging. A reel

contains 2500 devices.

(2) Lead free product. This product is fully WEEE and

RoHS compliant.

Pin Configuration

DRVH

BST

TOP VIEW

(MSOP-10)

PHASE

VCC

DRVL

ISET

GND

COMP

VSENSE

FS/SYNC

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