sc4524c Semtech Corporation, sc4524c Datasheet

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sc4524c

Manufacturer Part Number
sc4524c
Description
28v 2a Step-down Switching Regulator
Manufacturer
Semtech Corporation
Datasheet
POWER MANAGEMENT
Features
Applications
Typical Application Circuit
Dec. 2, 2010
V
Wide input range: 3V to 28V
2A 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
IN
C7
10nF
C4
2.2 F
10V – 28V
L1: Coiltronics DR73-8R2
C8
22pF
SS/EN
COMP
IN
R7
28.0k
C5
2.2nF
SC4524C
ROSC
R5
15.8k
GND
Figure 1. 1MHz 10V-28V to 5V/2A Step-down Converter
BST
SW
FB
C2: Murata GRM31CR60J226K
C4: Murata GRM31CR71H225K
C1
0.33 F
D2
20BQ030
8.2 H
1N4148
L1
D1
28V 2A Step-Down Switching Regulator
10.5k
R4
42.2k
R6
C2
22 F
5V/2A
SS270 REV 4
OUT
Description
The SC4524C 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 SC4524C is programmable
up to 2MHz, allowing the use of small inductors and
ceramic capacitors for miniaturization, and high input/
output conversion ratio. The SC4524C is suitable for
next generation XDSL modems, high-definition TVs and
various point of load applications.
Peak current-mode PWM control employed in the
SC4524C 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 SC4524C is available in SOIC-8 EDP package.
Fig.1 Efficiency of the 1MHz 10V-28V to 5V/2A Step-Do
90
85
80
75
70
65
60
55
50
45
40
0
0.5
V
Load Current (A)
IN
= 12V
Efficiency
1
V
SC4524C
IN
1.5
= 24V
2
1

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sc4524c Summary of contents

Page 1

... SC4524C 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 SC4524C 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: E9010) Ordering Information Device SC4524CSETRT BST SC4524CEVB 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 -2.6A SW SC4524C ……………………………… 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 SC4524C 5 ...

Page 6

... PWM CLK OSCILLATOR 1. SOFT - START - AND 1V 1.9V OVERLOAD HICCUP REFERENCE FAULT CONTROL & THERMAL SHUTDOWN Figure 2. SC4524C Block Diagram - - 1. 1V/2.15V 3.9 A SC4524C ISEN - - 5. 18mV ILIM - - BST 8 8 POWER TRANSISTOR GND ...

Page 7

Curve 2 Typical Characteristics SC4524A/B Efficiency =3. =2. =1. 1MHz, V =12V Curve =20BQ030 0.5 ...

Page 8

... C 2.0 o -40 C 1.5 1.0 0.5 Curve 15 0.0 0 0.5 1 1 Shutdown Threshold vs Temperature IN 0.40 0.35 0.30 0.25 0.20 30 -50 - Temperature ( C) SC4524C 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 ...

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 SC4524C turns on and the SC4524C 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 SC4524C is set with an external resistor from the ROSC pin to ground. Table 3 lists standard resistor values for typical frequency setting ⋅ ⋅ − − ...

Page 11

... least 2.6A. The maximum deliverable load current for the SC4524C is 2.6A 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 by ...

Page 12

... Inc.), SS13, SS23 (Vishay), CMSH1-40M, CMSH1- 40ML and CMSH2-40M (Central-Semi.) are all suitable. The freewheeling diode should be placed close to the SW pin of the SC4524C 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 1 ...

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 SC4524C. The inner loop (current     C1   loop) consists of a current sensing resistor (R  ...

Page 14

... ω ω =0.3mA/V is the EA gain of the SC4524C and F =600kHz. From Equation (9), the log log 18.5 18.5 5.5 5 ...

Page 15

... TOTAL TOTAL BST BST The temperature rise of the SC4524C 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

... Table 5 lists the recommended inductance (L voltages. The inductance is determined by assuming that the ripple current is 35% of load current I parameters are calculated by assuming a 22mF low ESR ceramic output capacitor and a loop gain crossover frequency of F /10. SW Table 5. Recommended inductance (L SC4524C Compensator Parameters Typical Applications Vin(V) Vo(V) Io(A) 1 1.5 ...

Page 17

... Figure 11. 700kHz 10V-26V to 3.3V/2A Step-down Converter D1 D3 18V Zener 1N4148 C1 0.33 F BST IN SW SC4524C SS/EN FB COMP ROSC GND R7 R5 69.8k C8 5.49k 47pF C5 3.3nF C2: Murata GRM31CR60J226K C4: Murata GRM32ER71H475K C1 0.33 F BST IN SW SC4524C SS/EN FB COMP ROSC GND 25.5k C8 10.7k 20BQ030 33pF C5 1nF C2: Murata GRM31CR60J226M C4: Murata GRM32ER71H475K L1 OUT 8.2 H 1.5V/2A R4 33. 66.5k 20BQ030 D1 ...

Page 18

... Inductor Current (1A/DIV) 40us/DIV Figure 12(c). Load Transient Response (I = 0.3A to 2A) O Fig.12( 2.5 3 Fig.12(d) OCP Figure 12(b). V Figure 12(d). Output Short Circuit (Hiccup) SC4524C 24V Input (10V/DIV) 5V Output (2V/DIV) SS Voltage (1V/DIV) 10ms/DIV Start up Transient ( Output Short (5V/DIV) Retry Inductor Current (2A/DIV) SS Voltage (2V/DIV) 20ms/DIV =2A) O ...

Page 19

... e aaa bbb A1 ccc bxN bbb C A GAGE PLANE 0.25 SEE DETAIL SIDE VIEW TO BE DETERMINED AT DATUM PLANE SC4524C DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX - - .053 .069 1.35 1. .000 .005 0.00 0. .049 .065 1.25 1. .012 ...

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 SC4524C DIMENSIONS DIM INCHES MILLIMETERS (.205) (5.20 .134 3.40 E .201 5 ...

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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