sc4525d

Manufacturer Part Numbersc4525d
Description18v, 3a, 350khz Step-down Switching Regulator
ManufacturerSemtech Corporation
sc4525d datasheet
 


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POWER MANAGEMENT
Features
Input range: 3V to 18V
3A Output Current
350kHz Fixed Switching 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
Applications
XDSL and Cable Modems
Set Top Boxes
Point of Load Applications
CPE Equipment
DSP Power Supplies
LCD and Plasma TVs
Typical Application Circuit
10 V – 16V
V
IN
C4
10mF
BST
IN
SW
SC4525D
SS/ EN
FB
COMP
RSET
GND
C7
R7
R5
C8
11.5k
60.4 k
22 nF
47 pF
C5
2.2 nF
L1 : Coiltronics CD1- 100
C2 : Murata GRM 31CR60J 476 M
C4 : Murata GRM 31CR61E 106 K
Figure 1. 350kHz 10V -16V to 5V/3A Step-down Converter
Jan. 13, 2011
Fig.1a : 350 kHz 10V - 16 V to 5V/3 A Step -
18V, 3A, 350kHz Step-Down
Description
The SC4525D is a 350kHz constant frequency peak
current-mode step-down switching regulator capable of
producing 3A output current from an input ranging from
3V to 18V. The SC4525D is suitable for next generation
XDSL modems, high-definition TVs and various point of
load applications.
Peak current-mode PWM control employed in the
SC4525D 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 SC4525D is available in SOIC-8 EDP package.
Fig.1b: 350kHz 10-16V to 5V/3A Step-Down Converter (Front Page Efficien
SC4525A
D1
1 N 4148
C1
0. 33 mF
L1
OUT
10 mH
5V/3A
R4
33.2k
D2
R6
C2
20BQ030
8.25k
47mF
Efficiency of the 1MHz 10V-28V to 5V/3A Step-Down Converter (Front Pag
Down Converter ( Front Page Schematic
SC4525D
Switching Regulator
Efficiency
90
85
80
V
=12V
IN
75
70
65
60
55
50
45
40
0
0.5
1
1.5
2
2.5
Load Current (A)
www.semtech.com
12 12
3
1
)

sc4525d Summary of contents

  • Page 1

    ... The SC4525D is a 350kHz constant frequency peak current-mode step-down switching regulator capable of producing 3A output current from an input ranging from 3V to 18V. The SC4525D is suitable for next generation XDSL modems, high-definition TVs and various point of load applications. Peak current-mode PWM control employed in the SC4525D achieves fast transient response with simple loop compensation ...

  • Page 2

    ... Lot No. (Example: E9010) © 2011 Semtech Corp. Ordering Information Device SC4525DSETRT BST SC4525DEVB 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. SC4525D Package SOIC-8 EDP (1)(2) Evaluation Board www.semtech.com 2 ...

  • Page 3

    ... 0.8V 0.8V FB COMP V = 1.2V 0.8V FB COMP (Note -3.9A SW SC4525D ……………………………… 36°C/W (1) ………………………………… 5.5°C/W (1) Min Typ Max Units 3 18 2.70 2.82 2.95 225 2 2 ...

  • Page 4

    ... R = 60.4kΩ SET Conditions I = -3. -3. 60.4kΩ SET R = 60.4kΩ SET SS/ 1.5 V SS/EN V Rising SS/EN V Falling SS/EN V Falling SS/EN SC4525D Min Typ Max Units 150 ns 100 150 ns 10 µA 1.8 2.3 V 100 150 mA 275 350 425 kHz 35 65 100 kHz 0.2 0.3 0.4 V 0.95 1.2 1.4 V 1.9 µA 1.6 2.4 3 ...

  • Page 5

    ... The exposed pad serves as a thermal contact to the circuit board soldered to the ground plane of the 9 Exposed Pad PC board. © 2011 Semtech Corp. falls below 0.8V, then the switching frequency will be reduced order to fully enhance the internal NPN power transistor. IN SC4525D www.semtech.com 5 ...

  • Page 6

    ... PWM PWM - - OSCILLATOR OSCILLATOR 1.2V 1. SOFT - START SOFT - START AND AND 1.9V 1.9V OVERLOAD OVERLOAD HICCUP HICCUP FAULT FAULT CONTROL CONTROL Figure 2. SC4525D Block Diagram - - 1.9V 1. 2.4mA 2.4mA B1 B1 1V/2.15V 1V/2.15V 3.9mA 3.9mA SC4525D ISEN ISEN ...

  • Page 7

    ... Foldback Frequency vs V 1.25 1 0.75 0.5 0. 100 125 0.00 0. BST Pin Current vs Switch Current 100.0 V =12V IN V =15V BST 75.0 o 50.0 -40 C 25.0 0 100 125 Switch Current ( www.semtech.com SC4525D Efficiency =3. =B320A 2 1 0.40 0.60 0.80 1. 125 C 1.5 2 2.5 3 3.5 ...

  • Page 8

    ... SS270 REV 6-7 V Shutdown Current - 1 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 SC4525D 125 ( - 1 (V) SS www.semtech.com 8 ...

  • Page 9

    ... Semtech Corp. 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 SC4525D turns on and the SC4525D draws 2mA from V turns off and the 2.4µA current source I charges the soft-start capacitor. ...

  • Page 10

    ... I ). The COMP pin is C Closed-loop measurement shows that the SC4525D Fig.4: Min On-Time vs Temp Fig.4: Min On-Time vs Temp minimum on time is about 120ns at room temperature (Figure 4). If the required switch on time is shorter than the minimum on time, the regulator will either skip cycles ...

  • Page 11

    ... − − ⋅ D ⋅ ⋅ ⋅ CESAT CESAT The peak current limit of SC4525D power transistor ⋅ ⋅ − − least 3.9A. 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 SC4525D on the PCB to minimize ringing due to trace inductance. Bootstrapping the Power Transistor Fig.6: Methods of BST Fig ...

  • Page 13

    ... The block diagram in Figure 7 shows the control loops buck converter with the SC4525D. The inner loop (current loop) consists of a current sensing resistor ( and a current amplifier (CA) with gain ( outer loop (voltage loop) consists of an error amplifier D ⋅ ...

  • Page 14

    ... ⋅ ⋅ ⋅ ⋅ The total power loss of the SC4525D is therefore ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ...

  • Page 15

    ... The temperature rise of the SC4525D is the product of the = = ⋅ ⋅ ⋅ ⋅ total power dissipation (Equation (13)) and q ...

  • Page 16

    ... Table 4 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 47mF low ESR ceramic output capacitor and a loop gain crossover frequency of F /10. SW Table 4: SC4525D Compensator Parameters Table 4. Recommended inductance (L Typical Applications Vin(V) Vo(V) Io(A) 1 ...

  • Page 17

    ... D2 60.4k 6.49 k CMSH3 - 20M C5 4.7nF C2 : Murata GRM 31CR60J476M C4 : Murata GRM 31CR60J475K D1 BAT-54 C1 0.33 mF BST IN SW SC4525D FB RSET GND B320A 3.74k 60.4k C5 6.8nF C2 : Murata GRM 31CR60J476 Murata GRM 32ER71H475 K SC4525D D1 BAT OUT 4.7mH 2.5V/3A R4 33. .1k 47mF L1 OUT 3.3 mH 1.5V/3A R4 33. 66.5 k 47mF www.semtech.com 17 ...

  • Page 18

    ... Figure 12(c). Load Transient Response (I = 0.3A to 3A) O © 2011 Semtech Corp. Fig.12b: SS 12V Input (5V/DIV) 5V Output (2V/DIV) SS Voltage (1V/DIV) 3 3.5 4 Fig.12d: OCP Figure 12(b). V Figure 12(d). Output Short Circuit (Hiccup) SC4525D 5ms/DIV Start up Transient (I =3A Output Short (5V/DIV) Retry Inductor Current (2A/DIV) SS Voltage (2V/DIV) 10ms/DIV www.semtech.com 18 ...

  • Page 19

    ... BSC 6.00 BSC e .050 BSC 1.27 BSC .116 .120 .130 2.95 3. .085 .095 .099 2.15 2. .010 .020 0.25 L .016 .028 .041 0.40 0.72 (.041) (1.05 0° 8° 0° aaa .004 0.10 bbb .010 0.25 ccc .008 0. GAGE PLANE 0.25 L (L1) A DETAIL A -H- www.semtech.com SC4525D MAX 1.75 0.13 1.65 0.51 0.25 5.00 4.00 3.30 2.51 0.50 1.04 8° ...

  • Page 20

    ... 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. © 2011 Semtech Corp. E SOLDER MASK D DIM SC4525D DIMENSIONS INCHES MILLIMETERS (.205) (5.20 .134 3.40 E .201 5.10 F ...

  • Page 21

    ... Contact Information © 2011 Semtech Corp. Semtech Corporation Power Mangement Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805) 498-2111 Fax: (805) 498-3804 SC4525D www.semtech.com 21 ...