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PDF SC4812 Data sheet ( Hoja de datos )
| Número de pieza | SC4812 | |
| Descripción | Current Mode PWM Controller | |
| Fabricantes | Semtech Corporation | |
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SC4812
Current Mode PWM Controller with
Integrated Start-up Circuit and Op Amp
POWER MANAGEMENT
Description
Features
The SC4812 is a highly integrated current mode PWM
controller designed for isolated or non-isolated dc-dc con-
verters in telecommunication and data communication
applications. It minimizes the amount of external discrete
components needed and leads to substantial cost and
space saving converter designs.
The circuitry of the SC4812 includes an integrated high
voltage start-up circuit suitable for telecom/industrial
www.DatavSohelteat4gUe.caompplications. It is disabled during regular opera-
tion and improves efficiency. Current mode control with
leading-edge blanking simplifies control loop design and
internal ramp compensation circuit stabilizes the current
loop when operating above 50% duty cycle. Internal er-
ror amplifier could be used for non-isolated applications.
Wide input range 12V to 90V
High-voltage start-up circuit
Current mode control
Transconductance error amplifier
Leading-edge blanking
Cycle by cycle current limit
Programmable external soft-start
Thermal shutdown
SO-8 package. Fully WEEE and RoHS compliant
Applications
IP phones, PoE
Telecom isolated converters
Off-line isolated power supplies
Instrumentation power supplies
Battery chargers
Typical Application Circuit
Vin
C2
R2
T1
R1
C3
C4
U1
D1 Vout
C1
2 FB
OUT 7
SC4812
3 COMP
CS 5
C5
R3 4 SS/SHDN GND 6
R4
C6
Q1
R5
Revision: February 6, 2007
1
www.semtech.com
1 page  
SC4812
POWER MANAGEMENT
Pin Descriptions
Pin #
1
Pin Name
VIN
2 FB
3 COMP
www.DataSheet4U.com
4 SS/SHDN
5 CS
6 GND
7 OUT
8 VCC
Pin Function
High voltage startup input. Connect directly to an input voltage between 12 to 90V. Connects
internally to a high voltage linear regulator that generates VCC during startup.
Feedback input to the internal transconductance error amplifier. VFB sensed the regulated
output voltage through an external resistor divider.
Internal transconductance error amplifier output. Compensation network of the overall loop is
placed between this pin and GND.
Soft start timing capacitor connection. Ramp time to full current limit is approximately TBD
ms/nF. This pin is also the reference voltage output. Bypass with a minimum 10nF capacitor
to GND. The device goes into shutdown when VSS_SHDN is pulled below 0.25V.
Current sense input. Turns power switch off if VCS rises above 465mV for cycle-by-cycle
current limiting. CS is also the feedback for the current mode controller. CS is connected to
the PWM comparator through a leading edge blanking circuit.
Ground.
Gate drive. Drives a high voltage external N-channel power MOSFET.
Supply voltage. Provides power for entire IC. VCC is regulated from VIN during startup. Bypass
VCC with a 10uF tantalum capacitor in parallel with 0.1uF ceramic capacitor to GND.
2007 Semtech Corp.
5
www.semtech.com
5 Page 
POWER MANAGEMENT
SC4812 Evaluation Board - Schematics( Non-Isolated Flyback )
SC4812
www.DataSheet4U.com
2007 Semtech Corp.
11
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11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet SC4812.PDF ] | |
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