sc2621 Semtech Corporation, sc2621 Datasheet

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sc2621

Manufacturer Part Number
sc2621
Description
Sc2621 500 Khz Voltage-mode Pwm Controller With Linear Power Regulator
Manufacturer
Semtech Corporation
Datasheet

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The SC2621 provides the control and protection features
necessary for a synchronous buck converter and a lin-
ear regulator in high performance graphic card applica-
tions.
The SC2621 is designed to directly drive the top and
bottom MOSFETs of the buck converter. It uses an inter-
nal 8.2V supply as the gate drive voltage for minimum
driver power loss and MOSFET switching loss. It allows
the converter to operate at 500kHz switching frequency
with 4V to 16V power rail and as low as 0.5V output. The
SC2621 is capable to drive a N-type MOSFET in a linear
regulator with as low as 0.5V output.
The SC2621 features soft-start, supply power under volt-
age lockout, and hiccup mode over current protection.
The SC2621 monitors the output current by using the
Rdson of the bottom MOSFET in the buck converter that
eliminates the need for a current sensing resistor. The
SC2621 is offered in a SOIC-14 package.
POWER MANAGEMENT
Description
December 17, 2004
Typical Application Circuit
2.5V OUT
12V IN
3.3V IN
+
1
2
3
4
5
6
7
P N
LDOG
LDFB
OCS
FB
COMP
NC
SC2621
GND
DRV
V CC
B ST
500kHz Voltage Mode PWM Controller
DH
NC
DL
14
13
12
11
10
9
8
1
u
u
u
u
u
u
u
u
u
u
u
u
Features
Applications
500kHz switching frequency
4V to 16V power rails
Internal LDO for optimum gate drive voltage
1.5A gate drive current
Programmable output voltages
Internal soft start
Power rail under voltage lockout
Hiccup mode short circuit protection
SOIC-14 package
Graphics processor power supplies on PCI-Express
platform
Embedded, low cost, high efficiency converters
Point of load power supplies
With Linear Power Regulator
1
+
2
www.semtech.com
SC2621
1.5V OUT
+

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sc2621 Summary of contents

Page 1

... MOSFET switching loss. It allows the converter to operate at 500kHz switching frequency with 4V to 16V power rail and as low as 0.5V output. The SC2621 is capable to drive a N-type MOSFET in a linear regulator with as low as 0.5V output. The SC2621 features soft-start, supply power under volt- age lockout, and hiccup mode over current protection ...

Page 2

... BST < < V < SC2621 ...

Page 3

... SC2621 ...

Page 4

... SC2621 ...

Page 5

... POWER MANAGEMENT Block Diagram 2003 Semtech Corp. 8.2V 5 SC2621 www.semtech.com ...

Page 6

... R pn peak ds The soft start time of the SC2621 is fixed at around 5ms. Therefore, the maximum soft start current is determined by the output inductance and output capacitance. The values of output inductor and output bulk capacitors have to be properly selected so that the soft start peak cur- rent does not exceed the load trip point of the short cir- cuit protection ...

Page 7

... MOSFETs are minimized. COMPONENT SELECTION COMPONENT SELECTION COMPONENT SELECTION COMPONENT SELECTION COMPONENT SELECTION General design guideline of switching power supplies can be applied to the component selection for the SC2621. Inductor and MOSFET Induct Induct or and MOSFET or and MOSFETs and MOSFET ...

Page 8

... DC accuracy and a faster transient response for the output voltage, while maintaining the loop stability. The block diagram in Fig. 3 represents the control loop of a buck converter designed with the SC2621. The con- trol loop consists of a compensator, a PWM modulator, and a LC filter. ...

Page 9

... MOSFETs must be as small as pos- sible. Keep the input bulk capacitors close to the drain of the top MOSFETs. bot (2). Place the SC2621 over a quiet ground plane to avoid pulsing current noise. Keep the ground return of the gate drive short. (3). Connect bypass capacitors as close as possible to the decoupling pins (DRV and Vcc) to the ground pin GND ...

Page 10

... SEE DETAIL SIDE VIEW -A- AND - DETERMINED AT DATUM PLANE -H- DIM INCHES Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804 10 SC2621 DIMENSIONS INCHES MILLIMETERS NOM MAX MIN NOM MAX - - .069 1.35 1. .010 0.10 0. .065 1.25 1 ...

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