sc4525c Semtech Corporation, sc4525c Datasheet

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sc4525c

Manufacturer Part Number
sc4525c
Description
28v 3a Step-down Switching Regulator
Manufacturer
Semtech Corporation
Datasheet
POWER MANAGEMENT
Features
Applications
Typical Application Circuit
Jan. 13, 2011
Wide input range: 3V to 28V
3A Output Current
200kHz to 2MHz Programmable Frequency
Precision 1V 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
XDSL and Cable Modems
Set Top Boxes
Point of Load Applications
CPE Equipment
DSP Power Supplies
LCD and Plasma TVs
V IN
22nF
C7
L1: Coiltronics CD1- 5R2
C4
4.7mF
10V – 28V
C8
22pF
SS/EN
COMP
IN
12.7k
R7
C5
2.2nF
SC4525C
ROSC
Figure 1. 1MHz 10V -28V to 5V/3A Step-down Converter
R5
15.8k
GND
BST
SW
FB
C2: Murata GRM31CR60J106K
C4: Murata GRM32ER71H475K
C1
0.33mF
D2
20BQ030
5.2mH
1N4148
L1
D1
28V 3A Step-Down Switching Regulator
8.25k
R4
33.2k
R6
Efficiency of the 1MHz 10V-28V to 5V/3A Step-Down Conve
C2
10mFX3
Description
The SC4525C is a constant frequency peak current-mode
step-down switching regulator capable of producing 3A
output current from an input ranging from 3V to 28V. The
switching frequency of the SC4525C is programmable
up to 2MHz, allowing the use of small inductors and
ceramic capacitors for miniaturization, and high input/
output conversion ratio. The SC4525C is suitable for
next generation XDSL modems, high-definition TVs and
various point of load applications.
Peak current-mode PWM control employed in the
SC4525C 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 SC4525C is available in SOIC-8 EDP package.
SC4525A
5V/3A
OUT
90
80
70
60
50
40
0.0
0.5
V
IN
Load Current (A)
1.0
= 12V
Efficiency
1.5
V
IN
2.0
SC4525C
= 24V
2.5
3.0
1

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sc4525c Summary of contents

Page 1

... SC4525C 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 SC4525C is available in SOIC-8 EDP package. SC4525A D1 1N4148 C1 0.33mF ...

Page 2

... Pin SOIC - EDP) Marking Information yyww=Date code (Example: 0752) xxxxx=Semtech Lot No. (Example: E9010) Ordering Information Device SC4525CSETRT BST SC4525CEVB FB Notes: COMP (1) 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 and halogen-free. ...

Page 3

... 0.8V 0.8V FB COMP V = 1.2V 0.8V FB COMP (Note -3.9A SW SC4525C ……………………………… 36°C/W (1) ………………………………… 5.5°C/W (1) Min Typ Max Units 3 28 2.70 2.82 2.95 225 2 2 ...

Page 4

Electrical Characteristics (Cont.) Unless otherwise noted 12V 15V 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 SC4525C 5 ...

Page 6

... SS/EN SS/EN FAULT FAULT Figure 3. Soft-start and Overload Hiccup Control Circuit SLOPE + COMP PWM CLK 1.2V R SOFT - START AND OVERLOAD HICCUP FAULT CONTROL Figure 2. SC4525C Block Diagram - - 1.9V 1. 2.4mA 2.4mA B1 B1 1V/2.15V 1V/2.15V 3.9mA 3.9mA ISEN - 3.53m W ...

Page 7

Eff Typical Characteristics Efficiency =3. =2. =1. 1MHz, V =12V Curve =B320A 0.5 ...

Page 8

... Temperature ( SS270 REV 6-7 V Shutdown Current 100 - 1.5 2 SS270 REV 6-7 Soft-Start Charging Current vs Soft-Start Voltage 0.0 -0.5 -1.0 125 -1.5 -2.0 -2.5 -3 100 125 0 0 SC4525C 125 ( - 1 ( ...

Page 9

... When the SS/EN pin is released, the soft-start capacitor is charged with an internal 1.9µA current source (not shown in Figure 3). As the SS/EN voltage exceeds 0.4V, the internal bias circuit of the SC4525C turns on and the SC4525C draws 2mA from V turns off and the 2.4µA current source I charges the soft-start capacitor. ...

Page 10

... CESAT CESAT The switching frequency of the SC4525C is set with an external resistor from the ROSC pin to ground. Table 3 lists the standard resistor values for typical frequency setting ⋅ ⋅ − − ...

Page 11

...   SC4525C is 3.9A minus one half of the inductor ripple current Input Decoupling Capacitor L L The input capacitor should be chosen to handle the RMS ripple current of a buck converter. This value is given The input capacitance must also be high enough to keep input ripple voltage within specification ...

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 SC4525C 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 5, which is about 2V at room temperature ...

Page 13

... COMP COMP Figure 7. Block diagram of control loops The block diagram in Figure 7 shows the control loops of a buck converter with the SC4525C. The inner loop (current     C1   loop) consists of a current sensing resistor (R  ...

Page 14

... C Thermal Considerations       ⋅ ⋅ (   For the power transistor inside the SC4525C, the between 10% and conduction loss ω ω ...

Page 15

... TOTAL TOTAL BST BST The temperature rise of the SC4525C is the product of the = = ⋅ ⋅ ⋅ ⋅ CESAT CESAT O O total power dissipation (Equation (12)) and q which is the thermal impedance from junction to ambient ...

Page 16

... Fsw(kHz) C2(uF) L1(uH) 500 3.3 500 4.7 1000 2.2 500 6.8 1000 3.3 47 500 6.8 1000 3.3 500 6.8 1000 3.3 500 3.3 300 6.8 500 6.8 500 6.8 1000 3.3 500 47 8.2 1000 4.7 500 10 1000 4.7 500 15 SC4525C , for common input and output The compensator Recommended Parameters R7(k) C5(nF) C8(pF) Snubber 5.23 3.9 8.45 3.9 15.4 0.82 12.1 3.9 20.5 0.82 no 15.4 3.9 36.5 0.82 22.6 3.9 47.5 0.82 36.5 3.9 22 3.57 3.9 6.49 3.9 12.1 3.9 1 +220pF 22 ...

Page 17

Typical Application Schematics 24V 4.7mF Coiltronics DR74- 6R8 Figure 10. 300kHz 24V to 1.5V/3A Step-down Converter 10V – 26V 4.7m F Fig10 : 300 kHz 1.5V/3 ...

Page 18

... Inductor Current (1A/DIV) 40us/DIV Figure 12(c). Load Transient Response (I = 0. 3.5 4 4.5 OCP Figure 12(d). Output Short Circuit (Hiccup) 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 SC4525C =3A ...

Page 19

... DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. REFERENCE JEDEC STD MS -012, VARIATION BA e bxN bbb C A SEE DETAIL SIDE VIEW - DETERMINED AT DATUM PLANE SC4525C DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM - - .053 .069 1. .000 .005 0. ...

Page 20

... REFERENCE IPC-SM-782A, RLP NO. 300A. 3. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. FAILURE MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE. E SOLDER MASK D DIM SC4525C DIMENSIONS INCHES MILLIMETERS (.205) (5.20 .134 3.40 E .201 5.10 F ...

Page 21

... Semtech products for any such unauthorized application, the customer shall indemnify and hold Semtech and its officers, em- ployees, subsidiaries, affiliates, and distributors harmless against all claims, costs damages and attorney fees which could arise. Contact Information Semtech Corporation Power Mangement Products Division 200 Flynn Road, Camarillo, CA 93012 ...

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