sc4524a

Manufacturer Part Numbersc4524a
DescriptionSc4524a 28v 2a Step-down Switching Regulator
ManufacturerSemtech Corporation
sc4524a datasheet
 


1
Page 1
2
Page 2
3
Page 3
4
Page 4
5
Page 5
6
Page 6
7
Page 7
8
Page 8
9
Page 9
10
Page 10
11
12
13
14
15
16
17
18
Page 1/18

Download datasheet (739Kb)Embed
Next
POWER MANAGEMENT
Features
Wide input range: 3V to 28V
2A Output Current
200kHz to 2MHz Programmable Frequency
Precision V Feedback Voltage
Peak Current-Mode Control
Cycle-by-Cycle Current Limiting
Hiccup Overload Protection with Frequency Foldback
Soft-Start and Enable
Thermal Shutdown
Thermally Enhanced 8-pin SOIC Package
Fully RoHS and WEEE compliant
Applications
XDSL and Cable Modems
Set Top Boxes
Point of Load Applications
CPE Equipment
DSP Power Supplies
LCD and Plasma TVs
Typical Application Circuit
10V – 28V
V
IN
C4
2.2mF
BST
IN
SW
SC4524A
SS/EN
FB
COMP
ROSC
GND
C7
R7
R5
10nF
18.2k
C8
28.0k
10pF
C5
2.2nF
L1: Coiltronics DR73-8R2
C2: Murata GRM31CR60J226K
C4: Murata GRM31CR71H225K
Figure 1. 1MHz 10V-28V to 5V/2A Step-down Converter
November 2, 2007
28V 2A Step-Down Switching Regulator
Description
The SC4524A is a constant frequency peak current-mode
step-down switching regulator capable of producing 2A
output current from an input ranging from 3V to 28V. The
switching frequency of the SC4524A is programmable
up to 2MHz, allowing the use of small inductors and
ceramic capacitors for miniaturization, and high input/
output conversion ratio. The SC4524A is suitable for
next generation XDSL modems, high-definition TVs and
various point of load applications.
Peak current-mode PWM control employed in the
SC4524A achieves fast transient response with simple loop
compensation. Cycle-by-cycle current limiting and hiccup
overload protection reduces power dissipation during
output overload. Soft-start function reduces input start-
up current and prevents the output from overshooting
during power-up.
The SC4524A is available in SOIC-8 EDP package.
SS270 REV 4
90
D1
85
1N4148
C1
80
0.1mF
L1
OUT
75
8.2mH
5V/2A
70
R4
42.2k
65
60
55
D2
R6
C2
50
20BQ030
10.5k
22mF
45
40
Efficiency of the 1MHz 10V-28V to 5V/2A Step-Down C
SC4524A
Efficiency
V
= 12V
V
= 24V
IN
IN
0
0.5
1
1.5
2
Load Current (A)


sc4524a Summary of contents

  • Page 1

    ... SC4524A achieves fast transient response with simple loop compensation. Cycle-by-cycle current limiting and hiccup overload protection reduces power dissipation during output overload. Soft-start function reduces input start- up current and prevents the output from overshooting during power-up. The SC4524A is available in SOIC-8 EDP package. SS270 REV 1N4148 ...

  • Page 2

    ... Pin SOIC - EDP) Marking Information yyww=Date code (Example: 0752) xxxxx=Semtech Lot No. (Example: E900) Ordering Information Device SC4524ASETRT BST SC4524AEVB FB Notes: COMP () Available in tape and reel only. A reel contains 2,500 devices. (2) Available in lead-free package only. Device is fully WEEE and RoHS SS/EN compliant. Package ...

  • Page 3

    ... 0.8V 0.8V FB COMP V = .2V 0.8V FB COMP (Note ) I = -2.6A SW SC4524A ……………………………… 36°C/W () ………………………………… 5.5°C/W () Min Typ Max Units 3 28 2.70 2.82 2.95 ...

  • Page 4

    Electrical Characteristics (Cont.) Unless otherwise noted 2V 5V BST Parameter Minimum Switch On-time Minimum Switch Off-time Switch Leakage Current Minimum Bootstrap Voltage BST Pin Current Oscillator Switching Frequency Foldback Frequency Soft Start and Overload ...

  • Page 5

    ... V The exposed pad serves as a thermal contact to the circuit board soldered to the ground plane of the 9 Exposed Pad PC board. falls below 0.8V, then the switching frequency will be reduced order to fully enhance the internal NPN power transistor. IN SC4524A 5 ...

  • Page 6

    ... PWM PWM - - R R CLK CLK OSCILLATOR OSCILLATOR 1.23V 1.23V + + - - R R SOFT-START SOFT-START AND AND 1.9V 1.9V OVERLOAD OVERLOAD HICCUP HICCUP FAULT FAULT CONTROL CONTROL Figure 2. SC4524A Block Diagram - - 1.9V 1. 1V/2.15V 1V/2.15V 3.5mA 3.5mA SC4524A ISEN ISEN - - 6.1mW 6.1mW + + ...

  • Page 7

    ... IN 100 10 ( 0.5 1 1.5 Frequency (MHz) Switch Saturation Voltage vs Switch Current 300 250 200 o - 125 150 100 50 0.0 0.5 1.0 1.5 Switch Current (A) (3) SC4524A Efficiency (6) 1MHz =20BQ030 1 0.5 Load Current (A) SS270 REV 6-7 Frequency vs Temperature 1.2 R =93.1k OSC 1.1 1.0 R =12.1k OSC 0 ...

  • Page 8

    ... Soft-Start Voltage 2.5 o 125 C 2.0 o -40 C 1.5 1.0 0.5 (15) 0.0 0 0.5 1 1 Shutdown Threshold vs Temperature IN 0.40 0.35 0.30 0.25 0.20 -50 - Temperature ( C) SC4524A SS270 REV 6-7 V Shutdown Current 100 - (V) IN SS270 REV 6-7 Soft-Start Charging Current vs Soft-Start Voltage 0.0 -0.5 -1.0 o 125 C -1.5 -2.0 -2.5 -3.0 ...

  • Page 9

    ... When the SS/EN pin is released, the soft-start capacitor is charged with an internal .6µA current source (not shown in Figure 3). As the SS/EN voltage exceeds 0.4V, the internal bias circuit of the SC4524A turns on and the SC4524A draws 2mA from V turns off and the 2µA current source I charges the soft-start capacitor. ...

  • Page 10

    ... V Setting the Switching Frequency = = − − CESAT CESAT The switching frequency of the SC4524A is set with an external resistor from the ROSC pin to ground ⋅ ⋅ − − ...

  • Page 11

    ... ⋅ D ⋅ ⋅ ⋅ CESAT CESAT The peak current limit of SC4524A power transistor least 2.6A. The maximum deliverable load current for the       ⋅ ...

  • Page 12

    ... Inc.), SS3, SS23 (Vishay), CMSH-40M, CMSH- 40ML and CMSH2-40M (Central-Semi.) are all suitable. The freewheeling diode should be placed close to the SW pin of the SC4524A on the PCB to minimize ringing due to trace inductance. Bootstrapping the Power Transistor The typical minimum BST-SW voltage required to fully saturate the power transistor is shown in Figure 5, which is about  ...

  • Page 13

    ...     buck converter with the SC4524A. The inner loop (current loop) consists of a current sensing resistor (     and a current amplifier (CA) with gain ( − − ...

  • Page 14

    ... operation, the size of the loop formed by these components . C should be minimized. Since the power switch is already , to cancel the ESR zero, integrated within the SC4524A, connecting the anode ≈ ≈ ω ω the freewheeling diode close to the negative terminal of ...

  • Page 15

    ... SC4524A , for common input and output The compensator Recommended Parameters R7(k) C5(nF) C8(pF) 4.32 2.2 12.4 1.0 15 0.82 20 0.68 43.2 0.47 20 0.68 10 43.2 0.47 35.7 0.68 63.4 0.47 35.7 0.68 63.4 0.47 43.2 ...

  • Page 16

    ... C4 C1 4.7mF 0.1mF BST IN SW SC4524A SS/EN FB COMP ROSC GND 10nF C8 13.0k 23.7k 22pF C5 2.2nF L1: Coiltronics DR73-8R2 C2: Murata GRM31CR60J226M C4: Murata GRM32ER71H475K 800kHz 10V-26V to 3.3V/2A Step-Down Converter L1 OUT 8.2mH 1.5V/2A R4 33. 20BQ030 66.5k 22mF D1 1N4148 L1 OUT 8.2mH 3.3V/2A R4 3.65k SS23 1.58k 22mF SC4524A 6 ...

  • Page 17

    Typical Performance Characteristics (For A 24V to 5V/2A Step-down Converter with 1MHz Switching Frequency) SS270 REV 6-7 Load Characteristic 0.5 1 1.5 Load Current (A) Figure 12(a). Load Characteristic 5V Output Response ...

  • Page 18

    ... SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. FAILURE MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE. Semtech Corporation Power Mangement Products Division 200 Flynn Road, Camarillo, CA 9302 Phone: (805) 498-2 Fax: (805) 498-3804 SC4524A DIMENSIONS INCHES MILLIMETERS DIM MIN MAX ...