FAN5037M Datasheet, PDF(6/11 Page) Fairchild Semiconductor – Adjustable Switching Regulator Controller

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FAN5037M Datasheet, PDF (6/11 Pages) Fairchild Semiconductor – Adjustable Switching Regulator Controller

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FAN5037

Table1. Bill of Materials for a FAN5037 3.3V, 13A Application

Qty. Reference

Manufacturer

Part Order #

Description

3 C1, C7-8 Any

100nF, 25V Capacitor

3 C2-4

Sanyo

10MV1200GX

1200ÂµF, 10V Aluminum Capacitor

6 C9-14

Any

Sanyo

6MV1500GX

1ÂµF, 25V Capacitor

180pF, 50V Capacitor

1500ÂµF, 6.3V Aluminum Capacitor

1 R1

Any

1 R2

Any

47.5â¦

4.75â¦

1 R3

N/A

5.2mâ¦, 1W Resistor

1 R4

1 R5

1 D1

1 D2

1 D3

1 Q1

Optional L1

1 L2

1 U1

Any

Motorola

MBRB1545CT

Fairchild

MMBD4148

Motorola

1N4735A

Fairchild

FDB6030L

Any

Fairchild

FAN5037M

3.48Kâ¦

2Kâ¦

15A, 45V Schottky

Signal Diode

6.2V Zener

30V, 14mâ¦ Logic Level MOSFET

2.5ÂµH Inductor

4.7ÂµH Inductor

PWM Controller

PRODUCT SPECIFICATION

Requirements

and Comments

IRMS = 2A , See Equation

(2) in Applications

C0G

ESR = 44mâ¦

PCB Trace Resistor, see

Equation (3) Applications

ISAT > 8A

ISAT > 13A

Application Information

The FAN5037 contains a precision trimmed zero TC voltage

reference, a constant-on-time architecture controller, a high

current output driver, and a low offset error amp. The

detailed block diagram in Figure 1 shows how the FAN5037

works together with external components to achieve a high-

performance switching power supply.

Switch-Mode Control Loop

The main control loop for the switch-mode converter consists

of a current conditioning ampliï¬er and a voltage conditioning

ampliï¬er. The voltage ampliï¬er compares the voltage from the

internal reference with the converterâs output voltage divided

by an external resistor divider. The current ampliï¬er senses the

current by comparing the voltages at the IFBH and IFBL pins,

which are attached to either side of the current sense resistor.

The signals from the voltage and current ampliï¬ers are

summed together, the result being used to control the off-time

of the oscillator. The current feedback signal is also used as

part of the FAN5037 short-circuit protection.

High Current Output Drivers

The FAN5037 high current output driver (DRV) contains

high speed bipolar power transistors conï¬gured in a

push-pull conï¬guration. The output driver is capable of sup-

plying 0.5A of current in less than 100ns. The driverâs power

and ground are separated from the overall chip power and

ground for added switching noise immunity.

Internal Reference

The reference in the FAN5037 is a precision band-gap type

reference. Its temperature coefï¬cient is trimmed to provide a

near zero TC.

Constant-On-Time Oscillator

The FAN5037 switch-mode oscillator is designed as a ï¬xed

on-time, variable off-time oscillator. The constant-on-time

oscillator consists of a comparator, an external capacitor, a

ï¬xed current source, a variable current source, and an analog

switch that selects between two threshold voltages for the

comparator. The external timing capacitor is alternately

REV. 1.0.3 9/26/01

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