POWER MANAGEMENT
1www.semtech.com
SC2610
Step-Down DC/DC Converter
Features
Applications
January 3, 2005
Description
The SC2610 is a voltage mode switcher and LDO combo
designed for low output voltages and tracking power sup-
plies. The SC2610 is available with fixed switching fre-
quencies of 600kHz (SC2610A). The SC2610 has soft
start and enable functions and is short circuit protected.
The output of the switcher may be set anywhere between
0.8V and 75% of Vin.
The LDO controller drives an external FET to provide an
output voltage which can be set between 1.25V and 90%
of Vin. It is RDS(ON) overcurrent protected. Short circuit
protection is disabled during startup to allow the output
capacitors time to fully charge.
uOperating frequency of 600kHz (SC2610A)
uInput supply of 3V to 15V
u0.5A Drive current for up to 10A output
uOutput voltages down to 0.8V
uOvercurrent protection on both outputs
uSoft Start for switcher output
uMSOP-10 package
C4
L1
Q1
1.5V OUT
C3C5
Q3
3.3V IN
C10
C9R9
R1
12V IN
C2
R5
R2
R8
2.5V OUT
Q2
R3
R10
U1
SC2610
5
8
9
1
7
2
10
4
3
6
VCC
DH
BST
FB
DL
SS/EN
COMP
LDFB
LDOG
GND
C1
R6
C7
uGraphics IC Power supplies
uTracking Power supplies
uVTT Supply and reference
Typical Application Circuit
22003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Absolute Maximum Ratings
retemaraPlobmySmumixaMstinU
egatloVylppuStupnIV
CC
51V
egatloVniPtsooBV
BST
02V
DNGotLD
)1(
DNGotHD,
)1(
V
DLO
V,
DHI
02+ot1-V
egnaRerutarepmeTtneibmAgnitarepOT
A
07ot0C°
erutarepmeTnoitcnuJgnitarepOT
J
521C°
erutarepmeTegarotST
STG
051ot56-C°
s01)gniredloS(erutarepmeTdaeLT
LEAD
003C°
tneibmAotnoitcnuJecnatsiseRlamrehT
)2(
θ
JA
311W/C°
)ledoMydoBnamuH(gnitaRDSEDSE2Vk
retemaraPlobmySsnoitidnoCniMpyTxaMstinU
lareneG
egatloVylppuSCCVV
CC
0.351V
tnerruCtnecseiuQCCVI
QVCC
V
CC
V,V0.5=
BST
V0=NE/SS,V0.21=501Am
egatloVylppuSTSBV
BST
1102V
tnerruCtnecseiuQTSBI
QBST
V
CC
V,V0.5=
BST
V0=NE/SS,V0.21=5Am
tuokcoLegatloVrednUCCVVU
VCC
3.26.29.2V
tuokcoLegatloVrednUTSBVU
BST
0.70.80.9V
noitceSraeniL
egatloVtuptuOV
OL
V=BFDL
OL
,T
A
=52C°132.1052.1962.1V
niaGA
OLL
GODLotBFDL09Bd
noitalugeRdaoLI
O
A4ot0=5.0%
noitalugeReniL 5.0%
ecnadepmItuptuO V5.6=ETAGV15.1kΩ
egatloVpirTtnerrucrevOV
ITL
nipBFDLtA6.08.00.1V
egatlovnwodtuhSNE/SSssV2.04.06.0V
ecnadepmInwodlluPetaGV;DNGotGODL
CC
V=
BST
V0=08003057kΩ
ecnadepmItupnIBFDL 01kΩ
Electrical Characteristics
Unless specified: VCC = 3V to 12V; VFB = VO; BST = Vcc+5V; TA = 0 to 70°C
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied.
3
2003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Notes:
(1) See Gate Resistor selection recommendations
(2) 1 square inch of FR4, double sided, 1oz. minimum copper weight.
Electrical Characteristics (Continued)
Unless specified: VCC = 3V to 12V; VFB = VO; BST = Vcc+5V; TA = 0 to 70°C
retemaraPlobmySsnoitidnoCniMpyTxaMstinU
noitceSgnihctiwS
egatloVtuptuOV
OS
I
O
V;0=
FB
V=
OS
,T
A
C°52=297 008808Vm
egatloVpirTtnerrucrevO V
ITS
4.07.0V
noitalugeRdaoLI
O
A4otA2.0=1%
noitalugeReniL 5.0±%
ycneuqerFrotallicsOf
OSC
A0162CS084006027 zHk
elcyCytuDxaMrotallicsO δ
MAX
A0162CS08%
egatloVnwodtuhSNE/SSV
SS
3.08.0V
tnerruCegrahCNE/SSI
SS
V8.0=ssV52µA
tnerruCecruoS/kniSHDkaeP,V5.4=HD-TSBV3.3=DNG-HD
V5.1=DNG-HD
5.0
05
A
Am
tnerruCecruoS/kniSLDkaeP,V5.4=LD-TSBV3.3=DNG-LD
V5.1=DNG-LD
5.0
05
A
Am
reifilpmArorrE
ecnatcudnocsnarT
gm8.0Sm
niaGreifilpmArorrEA
AE
R
PMOC
nepo=54Bd
kniS/ecruoSreifilpmArorrE
tnerruC
06± µA
niaGrotaludoMA
M
V
CC
V5=91Bd
emiTdaeD 05sn
42003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Block Diagram
Pin Configuration Ordering Information
Pin Descriptions
Note:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
(2). Lead free product. This product is fully WEEE and
RoHS compliant.
srebmuNtraPycneuqerFegakcaP
RTSMA0162CS
)1(
zHk00601-POSM
TRTSMA0162CS
)2()1(
zHk00601-POSM
BST
VCC
DH
GND
DL
FB
LDFB
COMP
1
2
3
4
TOP VIEW
(MSOP-10)
7
8
9
10
5 6
SS/EN
LDOG
#niPemaNniPnoitcnuFniP
1BF.tupnikcabdeeefnoitcesrehctiwS
2NE/SS .etarpmaregatlovtuptuorehctiwsehtslortnoc,nipelbanednatratstfoS
3GODL.TEFODLehtfoetaGehtottcennoC
4BFDL.tupnIkcabdeeFODL
5CCV.egatloVtupnIylppuSpihC
6DNG .senilediugtuoyalees,enalpdnuorgotyltceridtcennoc,dnuorGrewoPdnagolanA
7LD.tuptuoevirdTEFediswoLrehctiwS
8HD.tuptuoevirdTEFedishgiHrehctiwS
9TSBV21yllausu,sevirdTEFrofegatlovylppuS
01PMOC.reifilpmarorreegatlovnoitcesrehctiwSehtfotuptuO
LDOG
SHDN
SSOVER
DH
GND
+
-
R
S
Q
COMP
25u A OS CI LLAT OR
VREF
VREF
R
S
Q
VCC
FB SHOOT-THRU
CONTROL
+
-
+
- UVLO
SS/EN
LEVEL SHIFT AND
HIGH SIDE DRIVE
SY NCHRONOUS
MOSFET DRIVE
+
-
+
-
+
-
UVLO
&
REF
DL
BST
+
-
LDFB
5
2003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Theory of Operation
The SC2610 is a switcher and LDO controller combo,
designed for minimum cost and size without sacrificing
accuracy and protection. Overcurrent protection on both
outputs is implemented by a simple undervoltage detec-
tion scheme and is disabled until soft start has been
completed to eliminate false trips due to output capaci-
tor charging. The LDO does not employ soft start, it’s
output voltage starts up as soon as the VCC and BST
undervoltage lockouts are exceeded. The SS/EN pin is
also held low, as are the DH and DL pins, until the
undervoltage lockout points are exceeded. Once the VCC
and BST pins both rise above their undervoltage lockout
points, the SS capacitor begins to charge, controlling the
duty cycle of the switcher, and therefore slowly ramping
up the switcher output voltage. Once the SS capacitor is
charged, the current limits for both the switcher and the
LDO are enabled. If a short circuit is applied to either
output, that output will be pulled down below it’s trip
point, shutting down both outputs. The device may be
restarted by either cycling power, or momentarily pulling
SS/EN low.
OUTPUT INDUCTOROUTPUT INDUCTOR
OUTPUT INDUCTOROUTPUT INDUCTOR
OUTPUT INDUCTOR - A good starting point for output
filter component selection is to choose an inductor value
that will give an inductor ripple current of approximately
20% of max. output current.
Inductor ripple current is given by:-
OSC
IN
O
O
RIPPLE
LfL
V
V
V
I×
÷
÷
ø
ö
ç
ç
è
æ-×
=
1
So choose inductor value from:-
OSCO
IN
O
O
fI
V
V
V
L×
÷
÷
ø
ö
ç
ç
è
æ-××
=
15
OUTPUT CAPOUTPUT CAP
OUTPUT CAPOUTPUT CAP
OUTPUT CAPAA
AA
ACITCIT
CITCIT
CITOR(S) OR(S)
OR(S) OR(S)
OR(S) - The output capacitors should
be selected to meet output ripple and transient response
criteria. Output ripple voltage is caused by the inductor
ripple current flowing in the output capacitor’s ESR (There
is also a component due to the inductor ripple current
charging and discharging the output capacitor itself, but
this component is usually small and can often be ignored).
Given a maximum output voltage ripple requirement, ESR
is given by:-
÷
÷
ø
ö
ç
ç
è
æ-×
××
<
IN
O
O
RIPPLEOSC
ESR
V
V
V
VfL
R
1
Output voltage transient excursions are a function of load
current transient levels, input and output voltages and
inductor and capacitor values.
Capacitance and RESR values to meet a required tran-
sient condition can be calculated from:-
release) (load transients positive for VV
and
n)applicatio (load transients negative for VVV
where
VV
IL
C
I
V
R
OA
OINA
AT
T
T
T
ESR
=
-=
××
×
>
<
2
2
values for positive and negative transients must be cal-
culated seperately and the worst case value chosen. For
Capacitor values, the calculated value should be doubled
to allow for duty cycle limitation and voltage drop issues.
Component Selection
62003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Component Selection (Continued.)
COMPENSATION COMPONENTS - Once the filter com-
ponents have been determined, the compensation com-
ponents can be calculated. The goal of compensation is
to modify the frequency response characteristics of the
error amplifier to ensure that the closed loop feedback
system has the highest gain and bandwidth possible while
maintaining stability.
A simplified stability criteria states that the open loop
gain of the converter should fall through 0dB at 20dB/
decade at a frequency no higher than 20-25% of the
switching frequency.
This objective is most simply met by generating asymp-
totic bode plots of the small signal response of the vari-
ous sections of the converter.
L
VOUT
Co
SC2610 AND FETS
FB
OUT
COMP Ra
MODULATOR
REF +
-
EA
Rb
Resr
Zp
Zf
Zs
It is convenient to split the converter into two sections,
the Error amp and compensation components being one
section and the Modulator, output filter and divider be-
ing the other.
First calculate the DC Filter+Modulator+Divider gain
The DC filter gain is always 0dB, the Modulator gain is
19dB at 5V in and is proportional to Vin, so modulator
gain at any input voltage is.
÷
ø
ö
ç
è
æ
×+=
5
2019 IN
MOD
V
LogG
the divider gain is given by
÷
÷
ø
ö
ç
ç
è
æ
+
×=
85
8
20
RR
R
LogGDIV
So the total Filter+Modulator+Divider DC Gain is
÷
÷
ø
ö
ç
ç
è
æ
+
×+
÷
ø
ö
ç
è
æ
×+=
BA
BIN
FMD RR
R
Log
V
LogG 20
5
2019
Calculate the filter double pole frequency (Fp(lc))
LCo
)lc(Fp
p
=
2
1
and calculate ESR Zero frequency (Fz(esr))
srReCo
)esr(Fz
××p
=
2
1
Choose an open loop crossover frequency (Fco) no higher
than 20% of the switching frequency (Fs).
The proximity of Fz(esr) to the crossover frequency Fco
determines the type of compensation required, if
Fz(esr)>Fco/4, use type 3 compensation, otherwise use
type 2. Type 1 compensation is not appropriate and is
not discussed here.
Type 2 Example
As an example of type 2 compensation, we will use the
Evaluation board schematic.
3.3uH
VOUT
3000uF
SC2610 AND FETS
FB
OUT
COMP 6.98k
MODULATOR
REF +
-
EA
8.06k
22mOhm
Cs Cp
Rs
Vin=5V
The total Filter+Modulator+Divider DC Gain is
dB.
..
.
LogLogGFMD 613
068986
068
20
5
5
2019 =
÷
ø
ö
ç
è
æ
+
×+
÷
ø
ö
ç
è
æ
×+=
This is drawn as the line A-B in Fig2
kHz.
.
LCo
)lc(Fp 61
10300010332
1
2
1
66
»
×××p
=
p
=
--
This is point B in Fig2.
kHz.)esr(Fz 42
10221030002
1
36 =
××××p
=
--
This is point C in Fig2., the line joining B-C slopes at -
40dB/decade, the line joining C-D slopes at -20dB/de-
cade.
For 600kHz switching frequency, crossover is designed
for 100kHz.
Since Fz(esr)<<Fco/4 Type 2 compensation is appropri-
ate.
7
2003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Having plotted the line ABCD, and confirmed the type of
compensation necessary, compensation component val-
ues can be determined.
At Fco, the line ABCD shows a gain of -27.5dB and a
slope of -20dB/decade. In order for the total open loop
gain to be 0dB with a -20dB/decade slope at this fre-
quency, the compensated error amp gain at Fco must be
+27.5dB with a 0dB slope. This is the line FG on the plot
below.
Since open loop DC gain should be as high as possible to
minimize errors, a zero is placed at F and to minimize
high frequency gain and switching interference a pole is
placed at G.
The zero at F should be no higher than Fco/4 and the
pole at G no lower than 4*Fco. The equations to set the
gain and the pole and zero locations are:
dB) (in Fco at gain A where
gm
Rs
A
==
20
10
RsFz
Cs
××p
=
12
1
RsFp
Cp
××p
=
12
1
For this example, this results in the following values.
W»W== kk.
.
Rs
.
30629
80
10 20
527
nF.Cs 220
103010256
1
33
=
××××
»
) rolloffEA to duey (unecessar pFCp 14
1030104006
1
33
=
××××
»
Fco
Fz(esr)
Fp(lc)
-60
-40
-20
0
20
40
60
80
100
100.0E+0 1.0E+3 10.0E+3 100.0E+3 1.0E+6
Frequency (Hz)
Gain (dB)
A B
C
D
E
FG
H
Fp1
Fz1
Filter+modulator
+divider gain
Compensated
Error Amp gain
Total open
loop gain
Fig2: Type 2 Error Amplifier Compensation
Component Selection (Continued.)
82003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Typical Characteristics
LDO
Switcher
-0.3%
-0.2%
-0.1%
0.0%
0.1%
0.2%
0.3%
0.4%
02468101214
VCC (V)
VCC Line Reg. (%)
VCC < 7V; VBST=12V
VCC > 7V; VBST = VCC + 5V
T
A
= 25
O
C
LDO
Switcher
-0.4%
-0.3%
-0.2%
-0.1%
0.0%
0.1%
0.2%
5 7 9 1113151719
VBST (V)
VBST Line Reg. (%)
VCC = 5V
T
A
= 25
O
C
LDO
Switcher
-0.10%
-0.08%
-0.06%
-0.04%
-0.02%
0.00%
0.02%
0.0 0.5 1.0 1.5 2.0 2.5
IOL (A)
Load Reg (%)
Linear Output Loaded
VCC = 5V
IOS = 0A
T
A
= 25
O
C
60%
70%
80%
90%
100%
024681012
IOS (A)
Efficiency (%)
VCC = 5V
VBST = 12V
VOS = 1.5V
T
A
= 25
O
C
Switcher
LDO
-1.0%
-0.8%
-0.6%
-0.4%
-0.2%
0.0%
024681012
IOS (A)
Load Reg (%)
Switcher Output Loaded
VCC = 5V
VBST = 12V
IOS = 0A
T
A
= 25
O
C
Typical VCC Line Regulation Typical VBST Line Regulation
Typical Load Regulation with Linear loaded Typical Load Regulation with Switcher loaded
Typical Switcher Efficiency Typical Switcher Ripple Voltage
9
2003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
0%
20%
40%
60%
80%
100%
0.0 0.2 0.4 0.6 0.8 1.0 1.2
SS/EN Voltage (V)
Duty Cycle (%) (No Feedback)
SS/EN control of duty cycle
Typical Characteristics (Continued)
0
20
40
60
80
100
0.8 1.0 1.2 1.4 1.6 1.8 2.0
Vcomp (V)
Duty Cycle (%)
COMP Pin control of duty cycle
102003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Evaluation Board Schematic & Layout
R2 2.2
12V IN
J1
C10
1500uF
R3 2.2
R6
8.06k
L1 3.3uH
Q1
Si4410DY
R9
No Stuff
C13
No Stuff
Q3
Si4410DY
GND
J7
D1
No Stuff
C9
0.1uF
C7
220uF
3.3V - 5V IN
J2
C1
0.1uF
C8
220pF
C6
1500uF
C12
1uF
GND
J5
C3
1500uF
C4
1500uF
C11
C11 = NO STUFF
2.5V OUT
J3
R11 0
C5
1500uF
GND
J6 Q2
Si4410DY
1.5V OUT
J4
R4
8.06k
C2
10uF
R7
30k
R5
6.98k
R8
8.06k
U1
SC2610
5
8
9
1
7
2
10
4
3
6
VCC
DH
BST
FB
DL
SS/EN
COMP
LDFB
LDOG
GND
R1 10
GND
J8
11
2003 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC2610
Outline Drawing - MSOP-10
Land Pattern - MSOP-10
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
bbb CA-B D
DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
3.
OR GATE BURRS.
DATUMS AND TO BE DETERMINED AT DATUM PLANE
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
-B-
NOTES:
1.
2. -A- -H-
SIDE VIEW
A
B
C
D
H
PLANE
0°
.010
.004
-
.016
.003
.024
(.037)
-
.000
.030
-
-
-
-
0.25
0.10
8° 0° -8°
0.60
(.95)
.032
.009
0.40
0.08
.043
.006
.037 0.75
0.00
-
0.80
0.23
-
0.95
1.10
0.15
-
-
-
e
.193 BSC
.020 BSC
DETAIL
aaa C
SEATING
INDICATOR
ccc C
2X N/2 TIPS
PIN 1
2X E/2
10
SEE DETAIL
A1
A
A2
bxN
D
0.25
A
PLANE
GAGE
.003
E1
12
N
.114
.114
.118
.118
.007 -
10
01
c
(L1)
L
A
0.08
3.00
3.00
4.90 BSC
0.50 BSC
.122
.122
2.90
2.90
.011 0.17
3.10
3.10
0.27
-
REFERENCE JEDEC STD MO-187, VARIATION BA.
4.
DIM
ccc
A1
e
bbb
aaa
01
L1
N
L
D
E1
E
A2
b
c
A
MILLIMETERS
NOM
INCHES
DIMENSIONS
MIN NOM MAX MIN MAX
E
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
NOTES:
1.
P
(C)
X
ZG
Y
.063
.224
.011
.020
.098
(.161)
5.70
1.60
0.30
0.50
2.50
(4.10)
MILLIMETERS
DIMENSIONS
DIM INCHES
Y
Z
G
P
X
C