SC4525A

Manufacturer Part NumberSC4525A
Description28V 3A Step-Down Switching Regulator
ManufacturerSemtech Corporation
SC4525A datasheet
 
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POWER MANAGEMENT
Features
Wide input range: 8V to 28V
3A 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
www.DataSheet4U.com
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
4.7mF
IN
SC4525A
SS/EN
COMP
ROSC
C7
R7
10nF
C8
24.3k
10pF
C5
1nF
L1: Coiltronics CD1-5R2
November 8, 2007
28V 3A Step-Down Switching Regulator
Description
The SC4525A is a constant frequency peak current-mode
step-down switching regulator capable of producing 3A
output current from an input ranging from 8V to 28V. The
switching frequency of the SC4525A is programmable
up to 2MHz, allowing the use of small inductors and
ceramic capacitors for miniaturization, and high input/
output conversion ratio. The SC4525A is suitable for
next generation XDSL modems, high-definition TVs and
various point of load applications.
Peak current-mode PWM control employed in the
SC4525A 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 SC4525A is available in SOIC-8 EDP package.
SC4525A
D1
1N4148
C1
0.1mF
BST
L1
OUT
SW
5.2mH
5V/3A
R4
33.2k
FB
GND
D2
R6
C2
R5
20BQ030
8.25k
10mFX3
18.2k
C2: Murata GRM31CR60J106K
C4: Murata GRM32ER71H475K
Figure 1. 1MHz 10V -28V to 5V/3A Step-down Converter
Efficiency of the 1MHz 10V-28V to 5V/3A Step-Down Conve
SC4525A
Efficiency
90
80
V
= 24V
IN
V
= 12V
IN
70
60
50
40
0.0
0.5
1.0
1.5
2.0
2.5
Load Current (A)
3.0


SC4525A Summary of contents

  • Page 1

    ... SC4525A 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 SC4525A is available in SOIC-8 EDP package. SC4525A D1 1N4148 C1 0.1mF ...

  • Page 2

    ... Lot No. (Example: E900) Ordering Information 8 BST 7 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 5 SS/EN compliant. Device Package SC4525ASETRT SOIC-8 EDP ()(2) SC4525AEVB Evaluation Board SC4525A 2 ...

  • Page 3

    ... OSC Min Typ 8 2.70 2.82 225 2 40 0.980 .000 0.005 -70 280 60 2 2. 0.8V 25 3.9 5. 380 SC4525A 5.5°C/W Max Units µA V .020 %/V nA -340 µ Ω A/V V µA 6.6 A ...

  • Page 4

    ... V SS/EN V Rising SS/EN V Falling SS/EN V Falling SS/EN Min Typ 50 00 .8 00 .04 .3 240 300 = 0 0 230 0 FB 0.2 0.3 .0 .3 .7 .2 2.0 .5 2.5 .9 0.6 .0 65 0 SC4525A Max Units ns  µA 2.3 V 50 mA .56 MHz 360 kHz 350 kHz 70 0.4 V .3 V µA 2.8 µ .2 V °C °C 4 ...

  • 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 SC4525A 5 ...

  • Page 6

    ... SOFT-START AND AND 1V 1V 1.9V 1.9V OVERLOAD OVERLOAD HICCUP HICCUP REFERENCE REFERENCE FAULT FAULT CONTROL CONTROL & THERMAL & THERMAL SHUTDOWN SHUTDOWN Figure 2. SC4525A Block Diagram - - 1.9V 1. 2mA 2mA B1 B1 1V/2.15V 1V/2.15V 3.5mA 3.5mA Figure 3. Soft-start and Overload Hiccup Control Circuit ...

  • Page 7

    ... Temperature ( Foldback Frequency =93.1k OSC 0.75 0.5 0.25 R =12.1k OSC 0 0.0 0.2 0.4 75 100 125 BST Pin Current vs Switch Current 100.0 V =12V IN V =5V BST-SW 75.0 o 50.0 -40 C 25.0 0.0 75 100 125 0 0.5 1 1.5 o Switch Current (A) C) SC4525A 50 75 100 125 = 0.6 0.8 1.0 (V) o 125 C 2 2 ...

  • Page 8

    ... Temperature ( SS270 REV 6-7 V Shutdown Current 100 - 1 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 -3 100 125 0 0 SC4525A 125 ( - 1 ...

  • 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 SC4525A turns on and the SC4525A 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 SC4525A is set with an external resistor from the ROSC pin to ground ⋅ ⋅ − − ...

  • Page 11

    ... ⋅ D ⋅ ⋅ ⋅ CESAT CESAT The peak current limit of SC4525A power transistor least 3.6A. The maximum deliverable load current for the       ⋅ ...

  • Page 12

    ... Rectifier), B320A, B330A (Diodes Inc.), SS33 (Vishay), CMSH3-20MA and CMSH3-40MA (Central-Semi.) are all suitable. The freewheeling diode should be placed close to the SW pin of the SC4525A on the PCB to minimize ringing due to trace inductance. Bootstrapping the Power Transistor The minimum BST-SW voltage required to fully saturate the power transistor is shown in Figure 4, which is about  ...

  • Page 13

    ...     buck converter with the SC4525A. The inner loop (current loop) consists of a current sensing resistor (R     and a current amplifier (CA) with gain ( − − ⋅ ⋅ A ...

  • Page 14

    ... BST BST BST BST 3 3 ⋅ ⋅ The temperature rise of the SC4525A is the product of the total power dissipation (Equation (2)) and which is the thermal impedance from junction to ambient = = − − ⋅ ⋅ ⋅ ⋅ ...

  • Page 15

    ... For jitter-free operation, the size of the loop formed by these components should be minimized. Since the power switch is already integrated within the SC4525A, connecting the anode of the freewheeling diode close to the negative terminal of www.DataSheet4U.com the input bypass capacitor minimizes size of the switched current loop ...

  • Page 16

    ... Fsw(kHz) C2(uF) L1(uH) 500 3.3 500 4.7 1000 2.2 500 6.8 1000 3.3 3 500 47 6.8 1000 3.3 500 6.8 1000 3.3 500 3.3 1000 2.2 300 6.8 500 6.8 1000 2.2 500 6.8 1000 3 500 8.2 1000 4.7 500 10 1000 4.7 500 15 1000 6.8 SC4525A , for common input and output The compensator Recommended Parameters R7(k) C5(nF) C8(pF) 10 2.2 16.2 2.2 29.4 0.47 23.2 2.2 39.2 0.47 29.4 2.2 10 69.8 0.47 43.2 2.2 90.9 0.47 69.8 2.2 133 0.47 6.81 2.2 12.4 2.2 29.4 0.47 23.2 2.2 43.2 ...

  • Page 17

    ... IN BST SW SC4525A SS/EN FB COMP ROSC GND 10nF C8 43.2k 18.2k 10pF C5 0.47nF L1: Coiltronics DR74-3R3 C2: Murata GRM31CR60J476M C4: Murata GRM32ER71H475K Figure 11. 1MHz 10V-26V to 3.3V/3A Step-down Converter 1MHz 10V-26V to 3.3V/3A Step-Down Converter C1 0.33mF L1 OUT 6.8mH 1.5V/3A R4 33. B330A 66.5k 47mF D1 1N4148 C1 0.1mF L1 OUT 3.3mH 3.3V/3A R4 33. B330A 14.3k 47mF SC4525A 7 ...

  • Page 18

    ... Inductor Current (1A/DIV) 40us/DIV Figure 12(c). Load Transient Response (I = 0. 2.5 3 3.5 4 4.5 OCP 12V Input (5V/DIV) 5V Output (2V/DIV) SS Voltage (1V/DIV) 10ms/DIV Figure 12(b). V Start up Transient ( Output Short (5V/DIV) Retry Inductor Current (2A/DIV) SS Voltage (2V/DIV) 20ms/DIV Figure 12(d). Output Short Circuit (Hiccup) SC4525A =3A ...

  • Page 19

    ... BSC 6.00 BSC .050 BSC 1.27 BSC .120 .130 2.95 3.05 3.30 .095 .099 2.15 2.41 2. .020 0.25 0.50 .028 .041 0.40 0.72 1.04 (.041) (1.05 8° 0° 8° .004 0.10 .010 0.25 .008 0. (L1) A DETAIL DIMENSIONS DIM INCHES MILLIMETERS (.205) (5.20 .134 3.40 E .201 5.10 F .101 2.56 G .118 3.00 P .050 1.27 X .024 0.60 Y .087 2.20 Z .291 7.40 SC4525A 9 ...