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SC4524Programmable Frequency, 2A Output 30V Step-Down Switching Regulator
POWER MANAGEMENT
Revision: December 30th, 2006
Description Features
Applications
Typical Application Circuit
Up to 1.5 MHz Programmable Switching Frequency 2.3A Integrated Switch Wide Input Voltage Range 2.8V to 30V Peak Current-Mode Control with Cycle-by-Cycle
Current Limiting Hiccup Overload Protection Soft-Start and Enable Thermal Shutdown Thermally Enhanced 8-Pin SOIC Package Fully WEEE and RoHS Compliant
The SC4524 is an adjustable frequency peak current-mode step-down switching regulator with an integrated2.3A, 30V switch. The SC4524 can be programmed upto 1.5MHz. This allows the use of small inductor andceramic capacitors, resulting in very compact powersupplies. The SC4524 is suitable for next generation XDSLmodems, set-top boxes and point of load applications.
The SC4524 uses peak current-mode PWM control forease of compensation. Cycle-by-cycle current limit andhiccup overload protection reduce power dissipationduring overload. Combined soft start and enable pin notonly eliminates output start up overshoot but also allowspower sequencing.
The SC4524 is available in SOIC-8 EDP package.
XDSL and Cable Modems Set-top Boxes Point of Load Applications CPE Equipment DSP Power Supplies Disk Drives
SC4524
GND
IN
SW
BST L1
4.7H
C2 0.1F
SS
COMP FB D2 20BQ030 5.49k R2
R1 22.1k
22nF
C6 22pF
R5 15.4k
C5 470pF
L1: Coiltronics FP3-4R7
OUT 5V/2A
D1 1N4148
24V
ROSC
C1: Murata GRM21BR60J226M
C3 10F
17.4k R3
C7
C3: Murata GRM32ER71H106K
V IN
C1 22F
Efficiency
50
55
60
65
70
75
80
85
90
0.0 0.5 1.0 1.5 2.0
Load Current (A)
Effic
ienc
y (%
)
Figure 1. 1MHz 24V to 5V/2A Step-down Converter.
2 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTAbsolute Maximum Ratings
Electrical Characteristics
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specifiedin the Electrical Characteristics section is not implied.
Unless specified: -40°C < TA < 85°C, -40°C < TJ< 105°C, ROSC = 12.1kΩ, VIN = 5V, VBST = 8V
Notes: This device is ESD sensitive. ESD handling precaution is required.
retemaraP lobmyS xaM stinU
egatloVtupnI V NI 23ot3.0- V
niPTSB V TSB 24 V
WSevobAniPTSB V TSB V- WS 42 V
niPSS V SS 3 V
niPBF V BF Vot3.0- NI V
egatloVWS V WS Vot6.0- NI V
)noitaruDsn01<(sekipStneisnarTWS V WS
V NI 5.1+V
5.2-
egnaRerutarepmeTtneibmAgnitarepO TA 58ot04- C°
tneibmAotnoitcnuJecnatsiseRlamrehT θ AJ 63 W/C°
esaCotnoitcnuJecnatsiseRlamrehT θ CJ 5.5 W/C°
erutarepmeTnoitcnuJmumixaM TJ 051 C°
egnaRerutarepmeTegarotS T GTS 051+ot56- C°
ces01)gniredloS(erutarepmeTdaeL T DAEL 003 C°
)ledoMydoBnamuH(gnitaRDSE DSE 0051 V
retemaraP snoitidnoC niM pyT xaM stinU
VgnitarepOmumixaM NI 03 V
V NI egatloVtratS 54.2 26.2 87.2 V
V NI siseretsyHtratS 57 Vm
V NI tnerruCtnecseiuQ gnihctiwstoN 5.3 5 Am
V NI nwodtuhSnitnerruCtnecseiuQ V SS V0= 04 06 Aµ
egatloVkcabdeeF 089.0 000.1 020.1 V
noitalugeReniLegatloVkcabdeeF V NI V03otV3= 500.0 V/%
tnerruCsaiBtupnIniPBF V BF V,V1= PMOC V5.1= 51- 03- An
ecnatcudnocsnarTreifilpmArorrE 082 µΩ 1-
3 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTElectrical Characteristics (Cont.)Unless specified: -40°C < TA < 85°C, -40°C < TJ< 105°C, ROSC = 12.1kΩ, VIN = 5V, VBST = 8V
retemaraP snoitidnoC niM pyT xaM stinU
niaGpooL-nepOreifilpmArorrE 35 Bd
tnerruCecruoSPMOC V BF V,V8.0= PMOC V5.1= 02 Aµ
tnerruCkniSPMOC V BF V,V2.1= PMOC V5.1= 02 Aµ
niaGtnerruChctiwSotniPPMOC 8 V/A
dlohserhTgnihctiwSPMOC 7.0 1.1 3.1 V
egatloVmumixaMPMOC V BF V9.0= 2.2 V
ycneuqerFgnihctiwS 2.1 4.1 6.1 zHM
elcyCytuDmumixaM )2etoN( 08 09 %
timiLtnerruChctiwS )1etoN( 3.2 2.3 A
egatloVnoitarutaShctiwS I WS A2-= 3.0 V
tnerruCegakaeLhctiwS 01 Aµ
egatloVTSBmuminiM I WS A2-= 8.1 5.2 V
tnerruCniPTSBI WS A5.0-= 02 Am
I WS A2-= 06 Am
tixEotegatloVtratS-tfoSmuminiMnwodtuhS 2.0 4.0 7.0 V
tnerruCgnigrahCtrats-tfoSV SS V0= 2 Aµ
V SS V5.1= 8.1 Aµ
tnerruCgnigrahcsiDtrats-tfoS V SS V5.1= 8.0 Aµ
otegatloVtrats-tfoSmuminiMffotuhSdaolrevOelbanE V SS gnisiR 2 V
dlohserhTdaolrevOBF V SS V,V3.2= BF gnillaF 7.0 V
tratseRotegatloVtrats-tfoSffotuhSdaolrevOretfAgnihctiwS V SS gnillaF 7.0 1 3.1 V
erutarepmeTnwodtuhSlamrehT 551 C°
siseretsyHnwodtuhSlamrehT 01 C°
Notes: (1) Guaranteed by design, not tested in production.(2) The maximum duty cycle specified corresponds to 1.4MHz switching frequency. Duty cycles higher than those specified can be
achieved by lowering the operating frequency.
4 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTPin Configuration
Pin Descriptions
PDE8-OS emaNniP noitcnuFniP
1 WS ehtdnarotcudniehtotnipsihttcennoC.rotsisnartrewopNPNlanretniehtforettimeehT.edoidgnileehweerf
2 NIV rewopNPNlanretniehtforotcellocehtotdetcennocoslasitI.4254CSehtotylppusrewoP.dnuorgotroticapaccimarecahtiwdessapybebtsumtI.rotsisnart
3 CSOR .ycneuqerfrotallicsoehtstesdnuorgehtotnipsihmorfrotsiserlanretxenA.nipgnittesycneuqerF
4 DNG .nipdnuorG
5 SS
.nipelbanednatratstfoStfoS.snoitcnufpuccihdaolrevodnatrats-tfossedivorpdnuorgehtotnipSSmorfroticapacA.)1(
.snoitacilppallarofdednemmocersitratsottnerrucylppustupniehtsecuderdnarotalugerehtffostuhsV4.0wolebnipSSgnilluP.)2(
.V5taAu04
6 PMOC.reifilpmarorrelanretniehtfotuptuoehtoslasitI.nipnoitasnepmoC
.poollortnocehtsetasnepmocnipsihttakrowtenCRA.)1(.hctiwslanretniehtfotnerruckaepehtslortnocnipsihttaegatlovehT.)2(
7 BF .reifilpmarorreehtfotupnignitrevniehtoslasitI.nipkcabdeefegatlovtuptuoehT
8 TSB lacolaetarenegottiucricpartstooblanretxeoteiT.revirdrotsisnartrewopehtotnipylppuS.rotsisnartrewoplanretniehtnonrutyllufotredroniegatlovtupniehtnahtrehgihegatlovylppus
lateMdaP
ehtfonipdnuorgehtotdetcennocyllacirtcelesiegakcapehtfomottobehttadapdesopxeehTgolanaehtotderedlosebotsahtI.draobtiucricehtottcatnoclamrehtasedivorposlatI.4254CS
.draobCPehtfodnuorg
Underside metal must be soldered to ground.
Ordering Information
rebmuNtraP egakcaP
TRTES4254CS )2()1( PDE8-CIOS
BVE4254CS draoBnoitaulavE
Notes:(1) Only available in tape and reel packaging. A reel contains2500 devices.(2) Lead free product. This product is fully WEEE and RoHS
compliant.
1234
BSTSW
TOP V IEW
(8 Pin SOIC -EDP)
76
8
5
FBVINCOMPROSCSSGND
5 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTBlock Diagrams
Figure 3. Details of the Soft-Start and Overload Hiccup Control Circuit
Figure 2. SC4524 Functional Diagram
COMP
TRANSISTOR
ROSC
VIN2
FB
SW
EA RQ
SPWM-
+
+
- POWER
SLOPECOMP
+
+ +
-ISEN
ILIM+
-20m V
6.3m
BST
SS
CLKOSCILLATOR
SLOPE COMP
SLOPECOMP
REFERENCE & THERMAL SHUTDOWN
1V
FAULT
OVLD
Soft-Start And
Overload Hiccup Control
0.7V
FB
8
1
7
3
5
6
GND4
FAULT
SSOVLD
1V/2 V
S
Q
R
+-
1.8A
2.6A
FB0.7V
FAULT
SSOVLD
1V/2 V
S
Q
R
+-
1.8A
2.6A
FB0.7V
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13 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTApplications Information
cycle is
ONINSW TVIfor a power loss of
OUTSWINSW VIVDI.
If DBST is tied to the output, then the charge drawn from
the output capacitor will still be
ONSWTI. The energy loss
due to base charge per cycle is
ONOUTSW TVI for a power
loss of
OUTSW VDI.
Since VOUT < VIN, DBST should always be tied to VOUT (if>2.5V) to maximize efficiency. In general efficiencypenalty increases as D decreases.
Figure 7 summarizes various ways of bootstrapping theSC4524. A fast switching PN diode (such as 1N4148 or
MAX VBST = 2VINMAX VBST = VIN + VOUT
MAX VBST = 2VIN - VZ
MAX VBST = VS
MAX VBST = VIN + VS
Figure 7. Methods of Bootstrapping the SC4524.
(a)
SC4524
BST
GND
IN
SW
DBST
VOUT CBST
VIN
D RECT
(b)
(c)
SC4524
BST
GND
IN
SW
DBST
VOUT CBST
VIN
VS > 2.5V
D RECT
(d)
SC4524
BST
GND
IN
SW
DBST
VOUT CBST
VIN
D RECT
(d)
SC4524
BST
GND
IN
SW
DBST
VOUT VIN
VS > VIN + 2.5V
D RECT
SC4524
BST
GND
IN
SW
DBST
VOUT CBST
VIN
D RECT
DZ
+ VZ -
14 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTApplications Information1N914) and a small (0.1µF – 0.47µF) ceramic capacitorcan be used. In Figure 7(a) the power switch isbootstrapped from the output. This is the most efficientconfiguration and it also results in the least voltage stressat the BST pin. The maximum BST pin voltage is about
OUTIN VV + . If the output is below 2.8V, then DBSTT willpreferably be a small Schottky diode (such as BAT-54) tomaximize bootstrap voltage. A 0.33-0.47µF bootstrapcapacitor may be needed to reduce droop. Benchmeasurement shows that using Schottky bootstrappingdiode has no noticeable efficiency benefit.
The SC4524 can also be bootstrapped from the input(Figure 7(b)). This configuration is not as efficient as Figure7(a). However this may be only option if the outputvoltage is less than 2.5V and there is no other supplywith voltage higher than 2.5V. Voltage stress at the BSTpin can be somewhat higher than 2VIN. The Zener diodein Figure 7(c) reduces the maximum BST pin voltage. TheBST pin voltage should not exceed its absolute maximumrating of 42V.
Figures 7(d) and (e) show how to bootstrap the SC4524from a second power supply VS with voltage > 2.5V.
Since the inductor current charges CBST, the bootstrapcircuit requires some minimum load current to get going.Figures 8(a) and 8(b) show the dependence of theminimum input voltage required to properly bootstrap a
5V and a 3.3V converters on the load current. Oncestarted the bootstrap circuit is able to sustain itself downto zero load.
Shutdown and Soft-Start
Pulling the soft-start pin below 0.8V with an open-collector NPN or an open-drain NMOS transistor turnsoff the regulator. In “Typical Characteristics”, the soft-start pin current is plotted against the soft-start voltagewith VIN = 5V. When the soft-start pin is pulled below 1V,105µA current flows out of the pin. Pulling the soft-startpin below 0.2V shuts off the internal bias circuit of theSC4524. The total VIN current decreases to 40µA. Inshutdown the SS pin sources only 2µA. A fast chargingcircuit (enabled by the internal bias circuit), which chargesthe soft-start capacitor below 1V, causes the differencein the soft-start pin currents.
If the SS pin is released in shutdown, the internal currentsource pulls up on the SS pin. When this SS voltagereaches 0.4V, the SC4524 turns on and the VIN quiescentcurrent increases to 3.5mA. The fast charging circuitquickly pulls the released soft-start capacitor to 1V(slightly below the switching threshold). The fast chargingcircuit is then disabled. A 1.8µA current source continuesto charge the soft-start capacitor (Figure 3). The soft-
Figure 8. Minimum Input Voltage Required to Start and to Maintain Bootstrap.(TA = 25°C).
Minimum Starting andSustaining VIN vs Load Current
4.5
5.0
5.5
6.0
6.5
7.0
7.5
1 10 100 1000
Load Current (mA)
Min
imu
m In
pu
t V
olt
age
(V)
DBST TIEDTO OUTPUT
DBST TIEDTO INPUT
VOUT = 5V
STARTING
SUSTAINING
MA729
(a) (b)
Minimum Starting andSustaining VIN vs Load Current
3.5
4.0
4.5
5.0
5.5
0.1 1.0 10.0 100.0 1000.0
Load Current (mA)
Min
imu
m In
pu
t V
olt
age
(V)
DBST TIEDTO OUTPUT
DBST TIEDTO INPUT
VOUT = 3.3V
STARTING
SUSTAINING
MA729
15 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTApplications Information
start voltage ramp at the SS pin clamps the error amplifieroutput (Figure 2). During regulator start-up, COMP voltagefollows the SS voltage. The converter starts to switchwhen its COMP voltage exceeds 1.1V. The peak inductorcurrent gradually increases until the converter outputcomes into regulation. Proper soft-start prevents outputovershoot during start-up. Current drawn from the inputsupply is also well controlled. Notice that the inductorcurrent, not the converter output voltage, is rampedduring soft-start.
The soft-start capacitor is charged to a final voltage ofabout 2.4V.
Overload / Short-Circuit Protection
The current limit comparator in the SC4524 limits thepeak inductor current to 3.2A (typical). The regulatoroutput voltage will fall if the load is increased above thecurrent limit. If overload is detected (the output voltagefalls below 70% of the set voltage), then the regulatorwill be shut off. An internal 0.8µA current sink starts todischarge the soft-start capacitor. As the soft-startcapacitor is discharged below 1V, the discharge currentsource turns off and the soft-start capacitor is rechargedwith a 1.8µA current source. The regulator undergoessoft-start. During soft-start (1V < VSS < 2V), the overloadshutdown latch in Figure 3 cannot be set. When VSS
exceeds 2V, the set input of the overload latch is no
Figure 9(a). Normal Soft-start.
FastCharge
Output must be atleast 70% of its set
voltage in thisinterval or theregulator will
undergo shutdownand restart
(hiccup).
HiccupEnabled
0.3V 1V
0
2V 2.4V
Switching Starts
V SS
1V 0.7V
V FB
0
1V
1V
2V
0.3V 0 Switching Not Switching Switching Not Switching
0
0.7V 1V
V FB
V SS V COMP
Figure 9(b). Start-up Fails due to (i) Short Soft-start Duration or (ii) Output Overload or (iii)Output Short-circuited.
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17 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTApplications Information
POWER STAGE
GMP = 8Ω
REFERENCE
VOLTAGE
1V
+
-
R5
C5
C6 RO R2
R1
FB
C11
ESR C1
R
OUT
V OUT
V IN
I OUT
-1
GMA = 280µΩ
-1
COMP V
1.6MΩ
Figure 10. Simplified Control Loop Equivalent Circuit
Bode Plots of Control-to-Ouput, Output-to-Control and the Overall LoopGain. Control-to-output transfer function is shown with two poles nearhalf the switching frequency ωS.
Figure 11.
2pω
1OUTCRn
5OCR1
1pω 3pω
65CR1
55CR1
1ZωCω
ω
Gain
2Sω
OUTMPRG
+ 21
2OMA RR
RRG
+ 21
25MA RR
RRG
nRC OUT1Cω
)j(T ω
OUT
COMP
vv
Control-to-OutputTransfer Function
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21 2006 Semtech Corp. www.semtech.com
SC4524
POWER MANAGEMENTOutline Drawing - SOIC-8 EDP
Land Pattern - SOIC-8 EDP
SEE DETAILDETAIL A
A
.050 BSC
.236 BSC
8
.010
.150
.189.154.193
.012 -
8
0.25
1.27 BSC6.00 BSC
3.904.90
-
.157
.1973.804.80
.020 0.31
4.005.00
0.51
bxN
2X N/2 TIPS
SEATING
aaa C
E/22X
1 2
N
A
D
A1
E1
bbb C A-B D
ccc Ce/2
E
A2
(.041)
.004
.008
-
.028
-
--
-
0°
.016
.007
.049
.000
.053
8° 0°
0.20
0.10- 8°
0.40
0.17
1.250.00
.041
.010
.069
.065
.0051.35
(1.05)0.72
-
1.04
0.25
--- 1.75
1.650.13
0.25-.010 .020 0.50-
c
L(L1) 01
0.25
GAGEPLANE
h
3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONSOR GATE BURRS.
-B-
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
DATUMS AND TO BE DETERMINED AT DATUM PLANE
NOTES:1.
2. -A- -H-
SIDE VIEW
A
B
C
De
H
PLANE
EXPOSED PAD
L1N01
bbbaaa
ccc
A
bA2A1
D
EE1
Lh
e
c
DIM MINMILLIMETERS
NOM
DIMENSIONSINCHES
MIN MAX MAXNOM
F
h
H
F
H
.085.120.095
.116 .130.099
2.952.15
3.052.41
3.302.51
4. REFERENCE JEDEC STD MS-012, VARIATION BA.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOURCOMPANY'S MANUFACTURING GUIDELINES ARE MET.
NOTES:1.
REFERENCE IPC-SM-782A, RLP NO. 300A.2.
3. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PADSHALL BE CONNECTED TO A SYSTEM GROUND PLANE.FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE.
E
Z(C) G
PØ 0.36mmTHERMAL VIA
X
Y
SOLDER MASK
(5.20)C (.205)
XYZ
FGP
DE
.024
.087
.291
.101
.118
.050
.201
.134
0.602.207.40
2.563.001.27
5.103.40
MILLIMETERSINCHESDIMDIMENSIONS
D
F
Semtech CorporationPower Management Products Division
200 Flynn Road, Camarillo, CA 93012-8790Phone: (805)498-2111 FAX (805)498-3804
Contact Information
