1 www.semtech.com
SC4810A/B/C/D/E
High Performance Current Mode PWM Controller
with Complementary Output, Programmable Delay
POWER MANAGEMENT
Revision: May 5, 2004
Description Features
Applications
Typical Application Circuit
Operation to 1MHz
Accurate programmable maximum duty cycle
Line voltage monitoring
External frequency synchronization
Bi-phase mode of operation for low ripple
Independent programmable delays
Hiccup mode current limit
Under 250µA start-up current
Programmable maximum volt-second clamp
Accessible reference voltage
VDD undervoltage lockout
-40°C to 105°C operating temperature
16 lead TSSOP or MLPQ package
The SC4810A/B/C/D/E is a 16 pin BICMOS primary side
PWM controller for use in Isolated DC-DC and off-line
switching power supplies. It is a highly integrated solution,
requiring few external components. It features a high
frequency of operation, accurately programmable
maximum duty cycle, current mode control, line voltage
monitoring, supply UVLO, low start-up current, and
programmable soft start with user accessible reference.
It operates in a fixed frequency, highly desirable for
Telecom applications. The output for switch is
complementary to each other with programmable delay
between each transition. The active technique allows
single ended converters beyond 50% duty cycle and
greater flux swing for the power transformer while
reducing voltage stresses on the switches. The separate
sync pin simplifies synchronization to an external clock.
Feeding the oscillator of one device to the sync of another
forces biphase operation which reduces input ripple and
filter size.
The SC4810A/D has a turn-on threshold of 4.5V, the
SC4810B/E has a turn-on voltage threshold of 7V, and
the SC4810C has a turn-on threshold of less than 12
volts. In the SC4810A/B/C, OUT2 is inverted to drive
the N-MOSFET. In the SC4810D/E, OUT2 is non-inverted
to drive the P-MOSFET. These devices are available in a
TSSOP-16 or MLPQ-16 lead package.
Telecom equipment and power supplies
Networking power supplies
Power over LAN applications
Industrial power supplies
Isolated power supplies
VoIP phones
Vout
R19
C3
C4
C5
+48V
R5
R2
U3
1
7
2
6
5
U4
SC431L
C10
D3
R17
L1
C13
D2
C16
R1
U1
SC1302A
2 7
6
3
1
8
4 5
C15
R10
R21
R18
R3
U2
SC4810
LUVLO 2
RCT
4
FB 11
SYNC
3
CS 10
PGND
14
OUT1 15
VDD 1
DMAX
5
SS 9
DELAY1
7
RAMP
6
VREF 16
OUT2 13
DELAY2
8
GND
12
R20
Q4
T1
C12
R15
R16
C9
R12 R13
R6
C8
D4
D1
R8
C1
C11
R11
R23
R9
C14
C2
R14
R22
Q1
D5
T2
R4
C6
C7
R7
Q3
Q2
22004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Absolute Maximum Ratings
Electrical Characteristics
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noitceSylppuS
egatloVylppuS 51V
)ylnonoisrevC(pmalCDDVI
DDV
Am01=5.71V
I
DD
V
DD
,V51=N
O
L
OAD
5.35.4Am
I
DD
nwodtuhSSS=V0001052Aµ
noitceSpmaR
egatloVdlohserhTpmalCpmaR 3V
)noisrevD/A(noitceSOLVU
)1(
dlohserhTtratS 5V
siseretsyH 5.0V
)noisrevE/B(noitceSOLVU
dlohserhTtratS 84.88.8V
siseretsyH 2V
)noisrevC(noitceSOLVU
)1(
dlohserhTtratS 21V
siseretsyH 4V
retemaraPlobmySmumixaMstinU
egatloVylppuSV
DD
91V
tnerruCylppuSI
DD
52Am
PMAR,SC,BF,TCR,XAMD,OLVUL,SS VotV3.0-
FER
V3.0+V
FERVtnerruCI
FER
51Am
OLVULtnerruCI
OLVUL
1-Am
egnaRerutarepmeTegarotST
GTS
051+ot56-C°
egnaRerutarepmeTnoitcnuJT
J
051+ot04-C°
.ceS01)gniredloS(erutarepmeTdaeLT
DAEL
003+C°
Unless specified: VDD = 12V, CSS = 1nF, FOSC = 420kHz, RT = 10k, CT = 220pF, DMAX = 2V, RDELAY = 75kΩ, TA = TJ = -40ºC to 105ºC
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.
32004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Electrical Characteristics (Cont.)
retemaraPsnoitidnoCtseTniMpyTxaMtinU
noitceSFERV
)noisrevD/A(FERVAm5-088.3421.4V
)noisrevE/C/B(FERVAm5-058.4551.5V
tuokcoLegatloVrednUeniL
dlohserhTtratS 19.2390.3V
siseretsyH 051Vm
tnerruCsaiBtupnI
)2(
V2.3=OLVUL001-An
noitceSrotarapmoC
tnerruCtupnISC
)2(
002-An
yaleDnoitagaporPTUOotMWP
)daoLoN(
)2(
57sn
noitceStimiLtnerruC
dlohserhTtimiLtnerruC 095526066Vm
I
MIL
yaleDnoitagaporPTUOot
)2(
57sn
noitceStratStfoS
I
SS
V
SS
V0=5.2-5-5.7-Aµ
dlohserhTnwodtuhS 005Vm
noitceSrotallicsO
egnaRycneuqerF 050011zHk
egatloVkaePTCR 00.3V
egatloVyellaVTCR 50.0V
elcyCytuDmumixaM1TUO,V8.2=XAMD58%
elcyCytuDmumixaM1TUO,V52.1=XAMD92%
ycneuqerF 083024064zHk
KCOLC/cnyS
dlohserhTCNYSkcolCdereggirTegdEevitisoP2V
htdiWesluPtupnIcnySmuminiM
)2(
F
CNYS
csoF>05sn
Unless specified: VDD = 12V, CSS = 1nF, FOSC = 420kHz, RT = 10k, CT = 220pF, DMAX = 2V, RDELAY = 75kΩ, TA = TJ = -40ºC to 105ºC
42004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Electrical Characteristics (Cont.)
retemaraPsnoitidnoCtseTniMpyTxaMtinU
)2TUOdna1TUO(noitceStuptuO
woLTASVtuptuOI
TUO
gniknisAm5=005Vm
hgiHTASVtuptuOI
TUO
gnicruosAm5=V
FER
6.0-V
emiTesiR
)2(
C
TUO
Fp02=01sn
emiTllaF
)2(
C
TUO
Fp02=01sn
noitceSyaleDmargorP
)B0184CS(esiR2TUOotllaF1TUO 021sn
)B0184CS(esiR1TUOotllaF2TUO 041sn
)E0184CS(llaF2TUOotllaF1TUO 021sn
)E0184CS(esiR1TUOotesiR2TUO 041sn
Notes:
(1) Consult the factory for availability of A, C, and D versions.
(2) Guaranteed by design.
(3) This device is ESD sensitive. Use of standard ESD handling precautions is required.
Unless specified: VDD = 12V, CSS = 1nF, FOSC = 420kHz, RT = 10k, CT = 220pF, DMAX = 2V, RDELAY = 75kΩ, TA = TJ = -40ºC to 105ºC
52004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Pin Configurations Ordering Information
Notes:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices for TSSOP and 3000 parts
for MLP package.
(2) Consult the factory for availability of MLP parts.
(3) Lead free product.
rebmuNtraP
)3(
egakcaP
)1(
T(egnaR.pmeT
J
)
TRTSTIA0184CS
61-POSST
C°501otC°04-
TRTSTIB0184CS
TRTSTIC0184CS
TRTSTID0184CS
TRTSTIE0184CS
TRTLMIA0184CS
61-QPLM
)2(
TRTLMIB0184CS
TRTLMIC0184CS
TRTLMID0184CS
TRLMTIE0184CS
1
2
3
4
5
6
7
8
VREFVDD
TOP VIEW
(16 Pin TSSOP )
13
12
14
15
16
11
10
9
OUT1LUVLO
PGNDSYNC
OUT2RCT
GNDDMAX
CS
RAMP FB
DELAY 1
SSDELAY 2
TOP VIEW
(16 Pin MLPQ)
62004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Pin Descriptions
#niP
POSST
#niP
QPLM
emaNniPnoitcnuFniP
151DDV hcihwV5.71tadetalugertnuhssinipsihT.ecivedsihtrofnoitcennoctupnirewopehT
dluohsDDV.egatsrevirdtuptuoSOMDehtfognitaregatlovehtwolebyltneiciffussi
.roticapaccimarecFµ1ahtiwdessapybeb
261OLVUL ehtmargorplliwredividevitsiserlanretxenA.niptuokcolegatlovrednueniL
ehtdnadelbasidsi1TUOrevirDeht,OLVULehtgniruD.leveltuokcolegatlovrednu
2YALED+1YALEDfoemitnodexifahtiwseunitnoc2TUO.tesersitratstfos
.yletamixorppa
31 CNYS esahP-iBehtnI.V1.2ottesdlohserhtahtiwtupnidereggirtegdeevitisopasiCNYS
fo)roticapaCgnimiT(TCehtotdetcennocebdluohsnipCNYSehtedomnoitarepo
rellortnocelgnisanI.noitarepoesahpfotuoaecroflliwsihT.rellortnocdnoceseht
kcolcnoitazinorhcnyslanretxenaotdetcennocrodednuorgebdluocCNYS,noitarepo
CSOlanretxeehT.ycneuqerfrotallicsodraob-noehtnahtrehgihycneuqerfahtiw
.noitarepoCNYSdeetnaraugrofretaerg%03ebdluohsycneuqerf
42 TCR TCRotFERVmorfTRrotsisergnitcennocybderugifnocsiycneuqerfrotallicsoehT
dnaTRrofseulavwolebnoitauqeehtgnisU.dnuorgotTCRmorfTCroticapacdna
.ycneuqerfTUOderisedehtedivorpotdetcelesebnacTC
egatlovkaepTCR=K-PVerehw
53 XAMD morfredividrotsisereht(21Rdna81Raivdemmargorpebnac%59otpuelcycytuD
elcycytud%001,V3evobanekatsinipXAMDnehW.)tiucriCnoitacilppAehtniferV
.deveihcasi
64 PMAR otPMARehtmorfroticapacadnaegatlovtupniehtotPMARehtmorfrotsiserA
siPMARehT.tcudorpdnoces-tlovelbawollamumixamfolangispmarehtsmrofDNG
A.hgihsi1TUOnehwegrahcotdewolladnawolsi1TUOnehwDNGotdegrahcsid
mumixamehttimilotV3otlangispmarehtserapmocrotarapmocdnoces-tlov
tcudorpdnoces-tloV:tcudorpdnoces-tlovelbawolla
75 1YALED neewtebemityaledpalrevo-nonehtsmargorpDNGotsnipesehtmorfrotsiserA
.2TUOdna1TUO
86 2YALED neewtebemityaledpalrevo-nonehtsmargorpDNGotsnipesehtmorfrotsiserA
.1TUOdna2TUO
−••+−
=
−
REF
KP
V
V
1lnCT)k1RT(
1
F
.CrampRramp3clamp ••=
72004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
#niP
POSST
#niP
QPLM
emaNniPnoitcnuFniP
97 SS sidnaSSotstcennocroticapacgnimittratstfosehT.snoitcnufowtsevresnipsihT
degrahcsidsiSStratstfoslamronrednU.ecruostnerrucAµ5lanretninaybdegrahc
dlehsi1TUOehtemithcihwgnirudV1otevitisopspmarnehtdnaV56.0nahtsselot
gnisaercninaybdetnemelpmisitratstfos,V5.2otV1morfsegrahcSSsA.wol
.woldlehdnadetibihnisirevirdtuptuoeht,V5.0wolebnekatsiSSfI.elcycytudtuptuo
seogoslaecnereferegatlov)EdnaC,B(V5ro)DdnaA(V4elbisseccaresuehT
.Aµ001=DDIdnawol
018 SC esnesamorftupniesnestnerrucehT.nipSCehtaivdedivorpsitupniesnestnerruC
otlangistimiltnerrucdnarotarapmocMWPehtotkcabdeeftnerrucsedivorprotsiser
sdeecxenipsihttadedivorpegatlovkaepeslupanehW.eslupMWPehtetanimret
ehtmorfdeviredsinoitasnepmocepolS.wolloflliwecneuqestratser-tfosa,Vm006
langisllamslanretxenahtiwdereffubebnacdnaroticapacgnimitehttaegatlovgnisir
.rotsisnartPNP
119 BF MWPehtrofSCotderapmocnehwlangisteseraetarenegotdesusinipsihT
foegatlovtesffonahtiwrotarapmoc kcabdeefehT.noitaunetta2/1dnaVm006
detcennoceblliwrelpuoc-otponaroreifilpmarorrenafotuptuoehtmorflangisgolana
.noitalugeredivorpotnipsihtot
2101DNG.snoitcnufllarofdnuorglangiS
31112TUO otralimis(tiucricrevirdTEFSOMlanretxeehtottuptuoevirdlevelcigolehtsinipsihT
.hctiwsyratnemelpmocehtrof)2031CS
4121DNGP .tniopelgnisataDNGdnaDNGPtcennoC.srevirdetagehtrofnoitcennocdnuorG
51311TUO otralimis(tiucricrevirdTEFSOMlanretxeehtottuptuoevirdlevelcigolehtsinipsihT
.hctiwsniamehtrof)2031CS
6141FERV dnadereffubsiecnerefersihT.tuptuoecnerefer)EdnaC,B(V5/)DdnaA(V4ehT
cimarecFµ0.1-74.0ahtiwdessapybebdluohsFERV.nipFERVehtnoelbaliavasi
.roticapac
Pin Descriptions (Cont.)
82004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Block Diagram
92004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Application Information
Introduction
The SC4810A/B/C/D/E is a 16 pin BICMOS peak current
mode controlled PWM controller for isolated DC-DC and
off-line switching power supplies. It features a high
switching frequency of operation, programmable limits
for both power transformer voltage-second product and
maximum PWM duty cycle, line under-voltage lockout,
auxiliary switch activation complementary to main power
switch drive, programmable leading-edge delay time
between activation of each switch, multiple protection
features with programmable cycle -by-cycle current limit
and hiccup mode over-current protection plus soft-restart.
It operates in a fixed frequency programmed by external
components. The separate sync pin simplifies
synchronization to an external clock. Feeding the oscillator
of one device to the sync of another forces biphase
operation which reduces input ripple and input and output
filter size.
The SC4810 can be applied in an active clamp forward
topology with the input voltage ranging from 36V to 72V.
This topology allows the converter to achieve an efficiency
of 92.4% at normal input voltage of 48V.
Circuit Description
The schematic of the active clamp forward converter is
illustrated in Figure. 1 below. T4 is the power transformer.
M17 is the N-channel main switching MOSFET and M15
is the auxiliary N-channel MOSFET. C35 is the reset
capacitor for resetting the power transformer’s core. M14
and M16 construct the synchronous rectification circuit.
L2 and C32 and C33 construct the low-pass output
filtering circuit. T6 is the current sensing transformer. R62
is the reset resistor for resetting the magnetic core of
the current sensing transformer. D18 is the rectifying
diode. R63 is the current sensing resistor. R60 and C41
construct the low-pass filtering circuit for the sensed
current signal. The primary bias circuit consists of R55,
R58, D17, Q8, C40, C31, D14 and R51. R55 and R58
construct a voltage divider, which limits the bias voltage
to 6.9V until the line voltage reach 36V. D17 is a zener
diode that limits the bias voltage to under 8V. R51, D14
and C31 construct the peak charge circuit. The peak
charge circuit will provide bias to the PWM IC U9 (SC4810)
and the driver U8 (SC1302A) after the converter starts
Figure 1: Active Clamp Forward Converter
R52
10 K
R50
5.11
100uF
C32
C35
3300pF
R78
5.6K
C40
10uF
3.3V/30A
R70
open
C31
0.1uF
C46
open
C43
100pF
R74
4.3K
R77
18 K
D16
open
R53 10 K
M1 6
Si4842DY
45
3
2
1
6
7
8
R80
1.47K
R72
5.11K
L2
1.3uH
R67
50
R64
165k
C47
0.01uF
R76
3.01K
T4
2
4
7
1
6
8
9
10
11
Q9
FMMT718
R62
10K
C49
180pF
R59
10
C44 220pF
C45
open
D17
open T6
P8208T
8
7
1
3
R58
8K
Q8
FZT458
R73
3.01K
R66
open
R57
5.11K
D20
1N5819HW
R79
100K
D14
1N4148WS
C50
1000pF
D13
1N4148WS
C51
0.01uF
R61
1.1M
D18
1N4148WS
M1 4
Si4842DY
4 5
3
2
1
6
7
8
R54
20K
U9
SC4810
2
4
11
3
10
14
15
1
5
9
7
6
16
13
8
12 LUVLO
RCT
FB
SYNC
CS
PG N D
OUT1
VD D
DMAX
SS
DELAY1
RAMP
VREF
OUT2
DELAY2
GND
C42
open
48V
M15
Si4488DY
45
3
2
1
6
7
8
C39
0.1uF
C48
0.1uF
R55
30K
R51
5.11
C33
680uF
Q7
FZT458
C41
330pF
R56
10K
R75
100K U10
SC431
R69
10 K
U8
SC1302A
2 7
6
3
1
8
4 5
R68
1K
U11
MOC207
1
7
2
6
5
R65
100K
T5
PE68386
1
3 4
6
M17
Si4488DY
4 5
3
2
1
6
7
8
C36
0.1uF
R63
6.8
1u , 1 00 V
C34
C37
0.1uF
R81
4.7K
R71
10K
D19
1N5819HW
R82
5.11K
C38
0.1uF
R60
1K
D15
1N4148WS
102004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Application Information (Cont.)
up so that the total power loss is less. D19, R59, C37,
T5, C36, D15 and R53 construct the driving circuit for
the auxiliary reset switch M15. The secondary side bias
circuit composed of R50, D13 and C38 is regulated to
about 7.5V via a linear regulator composed of R57, Q7
D16 and C39. The feedback of the converter is composed
of U10 (SC431), U11, R73, C47, C45, R72, R76, R70
and C46.
SC4810 is the PWM controller which processes the
voltage feedback plus current signal and generates
driving signals to drive the main switch and auxiliary reset
switch. SC1302A is a dual driver IC which is capable of
sourcing 3A peak current. To obtain the best performance,
SC1302A is adopted to drive M17 and M15 in the
Semtech application circuits. SC4810 features dual
complementary driving signals. And SC4810 also provides
adjustable leading-edge delay time for the driving signals,
which helps to achieve zero-voltage switching in active
clamp forward converter. R75 and R79 are the two
resistors available to adjust the delay for the
complementary driving. C50 is the soft-start capacitor.
R61 and R65 construct the voltage divider for the line
under voltage lock out protection. R64 and C44 construct
the circuit for the programmable power transformer
voltage-second production protection limits. This special
protection function provide the voltage-second balance
for the power transformer under different input line
conditions. R78 and R74 also provide an extra maximum
duty cycle protection for the power converter.
The clock signal is generated by C49 and R77. When VDD
of SC4810 hits the threshold voltage, VREF jumps up to
5.0V. VREF charges C49 via R77. C49 will be discharged
via an internal FET whenever the voltage on C49 reaches
3.0V. The selection of C49 and R77 is described in the
“Set Clock Frequency” section on the following page. Q9
works as a buffer between the clock signal and the slope
compensation signal to minimize the interference on the
system clock signal. R80 is a pull-up resistor tied to VREF.
Since SYNC function is not utilized, SYNC pin is grounded
via R71.
Power Transformer Design
A power transformer with the turns ration of 6 to 1 was
designed for this application. With the turns ratio of 6:1,
the duty ratio under different input line and load conditions
were calculated to verify feasibility.
A self-driven configuration was adopted on the secondary
side for driving the synchronous rectification FETs. One
extra winding (Pin8~Pin9) was added at the bottom side
of the power transformer’s secondary side to drive the
freewheeling FET. The forward FET was driven directly
from the top of the power winding. Primary side auxiliary
winding was used to generated primary side bias to
improve the converter’s efficiency.
The final configuration of the power transformer is
illustrated as Fig. 2.
6T(PRI)
2T(PRI AUX)
1T(SEC)
1T(SEC AUX)
1T(SEC)
2
6
1
4
11
10
9
8
7
Fig.2 Illustration of the power transformer
PA0576 (PUSLE ENGINEERING)
For detailed information about PA0576, please check the
appendix on page 17.
Power MOSFET Selection
The selection of the switching power MOSFET is based
on the peak & RMS current rating, the total gate charge,
Rds and drain to source voltage rating. In this application,
SI4842 was chosen for the secondary side synchronous
rectification MOSFET. And SI4488 was chosen for the
primary side main switching and reset MOSFET.
Output Filter Design
The output filtering circuit consists of the output inductor
and output capacitors. The design of the output capacitor
usually depends on the specification of the requirement
of the output ripple. Given the worst case output ripple
requirement and peak to peak output current ripple plus
the duty ratio under the different line and load condition,
output capacitance is calculated to meet the output ripple
requirement. After all, ESR and ESL of the output
capacitor under certain switching frequency should also
be considered during the calculation. The value of the
112004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
output inductance would affect the peak to peak value
of the output current, which would also influence the
output voltage ripple. The designer needs to take the
output inductance and output capacitance and the ESL
and ESR of the output capacitor into consideration during
the design.
For this application, one Panasonic power choke output
inductor was selected and three 6.3V, 100uF TDK
ceramic capacitors were adopted in the design.
Selection of the Current Sensing Resistor
The selection of the current sensing resistor is based on
the over-current protection triggering point. SC4810
employs a Hiccup mode over-current protection with an
overcurrent threshold of 600mV. A voltage signal above
600mV on the CS pin will trigger hiccup mode overcurrent
protection. Suppose the over-current protection setpoint
is set to be Iov. The threshold voltage of SC4810 is
Vthreshold. The turns ratio of the power transformer is
Ns/Np. The turns ratio of the current sensing transformer
is Ncs:1. Then the Rsense would be calculated as:
)1......(
NI
NNV
R
SOV
CSPThreshold
sense ×××
=
Set Clock Frequency
The SC4810 uses a pair of resistors and capacitors to
generate a triangle signal as the clock signal, as illustrated
in Fig. 3.
R
C
RCT
VREF
VRCT
Fig. 3 Configuration for Clock Signal
The voltage waveform on the RCT pin is illustrated as in
Fig. 4.
Application Information (Cont.)
VRCT
t
3V
0V
Fig.4 Voltage Waveform on RCT Pin
VPK
As illustrated, the capacitor C is charged via the resistor
R from VREF. Whenever the voltage on the RCT pin
reaches 3V, the capacitor C will be discharged through
an internal FET shorted to ground. When the clock signal
circuit is connected as in Fig.3, the frequency of the clock
signal is defined, as in equation 2.
)2........(
V
V
1lnCT)k1RT(
1
F
REF
KP
−••+−
=
−
VREF is the reference voltage of the SC4810, 4V for
SC4810A/D and 5V for SC4810B/C/E.
In this application, to get 600kHz, C = 180pF,
(R + 1k) = 10k ohms and VP-K = 3V.
Maximum Duty Ratio Limit
SC4810 features maximum duty ratio limitation for ex-
tra protection. The maximum duty ratio is determined by
the voltage on DMAX pin. As illustrated as in Fig. 5, VDMAX
will be compared with VRCT and DMAX is determined by
the comparison of the two signals.
122004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Application Information (Cont.)
Clock Signal of SC4810
DMAX
Fig. 5 Illustration for DMAX
VRCT
t
3V
0V
0V
VDMAX
t
In this application, VDMAX was designed to be 2.8V. So the
DMAX = 90%.
Limit for Power Transformer
Voltage Second Product
The SC4810 also features programmable limits for power
transformer voltage-second product. As illustrated in Fig.
6 and Fig. 7 RAMP pin is charged up via a resistor R from
the input line voltage. The capacitor C will be discharged
via an internal FET shorted to ground and the output
OUT1 will be pulled low whenever the voltage on RAMP
pin hits 3V. By adjusting the values of the resistor R and
the value of the capacitor C, the maximum voltage-sec-
ond product imposed on the power transformer is pre-
set. The maximum voltage-second product limitation helps
prevent saturation of the power transformer.
Voltage waveform on RAMP pin
Maximum OUT1 of SC4810
Fig. 6 Illustration of the programmable limits for power
transformer voltage-second product
VRAMP
t
3V
0V
0V
t
OUT1
R
C
RAMP
Fig. 7 Illustration for Maximum voltage-
second product on the power transformer
VIN
The selection of the R and C should consider the maxi-
mum voltage rating of the main switching FET. In this
application, the voltage rating of SI4488 is 150V. Since
Vin*D/(1-D) = 150V, D = 0.8 for low line 36V. So to get
80% at low line, R = 165kOhms and C = 220pF were
selected using volt-second product equation:
3 • Ramp • Cramp.
132004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Application Information (Cont.)
VDD and LUVLO
SC4810 features three different input turn-on voltage
thresholds, as specified in the Electrical Characteristics
on page 2. VREF starts to regulate when the supply voltage
on the VDD pin is above the turn-on voltage threshold.
VREF drops to ground when VDD is lower than the turn-on
threshold minus the hysteresis value. The soft start cap
remains grounded as long as LUVLO is below the thresh-
old voltage 3V. The soft start cap will be charged up
through an internal 5uA current source when LUVLO is
above the threshold voltage.
Soft Start
The soft-start function is implemented by charging the
soft-start cap through an internal 5uA current source.
Under normal soft-start, the SS pin is discharged below
0.65V and ramps up to 1V, during which time the output
driving signals OUT1 and OUT2 are held low. During the
time when the SS pin is charged from 1V to 2.5V, soft-
start is implemented by an increasing output duty ratio.
The duty ratio is completely under the control of the
feedback after the SS pin is above 2.5V.
When the SS pin is pulled down below 0.5V, OUT1 and
OUT2 will be held low and the VREF pin will be grounded
via an internal FET.
Complementary Driving with Programmable Delays
The SC4810 features dual driving signals to drive two
power switches complementarily. This feature makes the
SC4810 suitable for a variety of applications in which
dual complimentary driving signals are needed. The
SC4810 even provides programmable driving delay as
an extra feature for applications such as active-clamp
forward topology. The users can program the driving delay
by adjusting the resistors tied to pin DELAY1 and pin
DELAY2 respectively to achieve the optimum delay for
each output. The delay of OUT1 is controlled by the
resistor tied to pin DELAY1 and the delay of OUT2 is
controlled by the resistor tied to pin DELAY2. For
illustration, see Fig. 8.
Over Current Protection
The SC4810 provides Hiccup mode over-current
protection when the sensed current signals are beyond
0.6V. When the hiccup mode over-current protection is
triggered, the soft-start cap will be discharged
immediately by an internal grounded FET. When the soft-
start pin SS is pulled down below 1V, OUT1 and OUT2 will
be disabled, and a soft re-start sequence will follow.
SC4810 can also be configured to implement cycle-by-
cycle over-current limit. As illustrated in Fig. 9, cycle-by-
cycle over-current limitation can be achieved by adjusting
the values of R1 and R2 to limit the voltage of FB pin to
less than the threshold voltage (0.6Volt) of the hiccup
over-current protection, using equations (3) and (4).
142004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Application Information (Cont.)
FB
GND
R1
VREF
R2
V
out
V
Bias
R3
R4
R5 SC431
Fig.9 Cycle-by-cycle over-current limitation
)3........(V3.1V2V CSFB +•=
)4........(
RR
R
VV
21
2
REFFB +
•=
Synchronization
SC4810 features a special synchronization function
which is leading-edge triggered with a threshold set to
2.1V. Applications like multi-phase interleaving can be
achieved using the SYNC pin. When the SYNC pin is con-
nected to the RCT pin of the master SC4810, the out-
puts of the two SC4810’s will be out of phase. The fre-
quency of the master SC4810 clock signal should be at
least 30% faster than that of the slave SC4810 for the
guaranteed synchronization. SYNC pin should be
grounded if synchronization is unused. (The patent for
the synchronization scheme is pending).
The synchronous function is illustrated as in Fig. 10.
VRCT
t
3V
0V
Clock Signal of the Master SC4810
0V
2.1V
0V
t
t
OUT1 of the Master SC4810
OUT1 of the Slave SC4810
Fig. 10 Illustration for Synchronization
152004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
PCB Layout Guidelines
PCB layout is very critical, and the following should be
used to insure proper operation of the SC4810. High
switching currents are present in applications and their
effect on ground plane must be understood and
minimized.
1) The high power parts of the circuit should be placed
on a board first. A ground plane should be used. Isolated
or semi-isolated areas of the ground plane may be delib-
erately introduced to constrain ground currents to par-
ticular areas, for example the input capacitor and the
main switch FET ground.
2) The loop formed by the Input Capacitor(s) (Cin), the
main transformer and the main switch FET must be kept
as small as possible. This loop contains all the high fast
transient switching current. Connections should be as
wide and as short as possible to minimize loop induc-
tance. Minimizing this loop area will a) reduce EMI, b)
lower ground injection currents, resulting in electrically
“cleaner” grounds for the rest of the system and c) mini-
mize source ringing, resulting in more reliable gate switch-
ing signals.
3) The connection between FETs and the main trans-
former should be a wide trace or copper region. It should
be as short as practical. Since this connection has fast
voltage transitions, keeping this connection short will
minimize EMI.
4) The output capacitor(s) (Cout) should be located as
close to the load as possible. Fast transient load cur-
rents are supplied by Cout only. Connections between
Cout and the load must be short, wide copper areas to
minimize inductance and resistance.
5) A 0.1uF to 1uF ceramic capacitor should be directly
connected between VDD and PGND and a 1uF to 4.7uF
ceramic capacitor between VREF and PGND. The SC4810
is best placed over a quiet ground plane area. Avoid pulse
currents in the Cin and the main switch FET loop flowing
in this area. GND should be returned to the ground plane
close to the package and close to the ground side of
(one of) the VDD supply capacitor(s). Under no
circumstances should GND be returned to a ground inside
the Cin and the main switch FET loop. This can be
achieved by making a star connection between the quiet
GND planes that the SC4810 will be connected to and
the noisy high current GND planes connected to the FETs.
6) The feed back connection between the error ampli-
fier and the FB pin should be kept as short as possible,
and the GND connections should be to the quiet GND
used for the SC4810.
7) If an opto-coupler is used for isolation, quiet primary
and secondary ground planes should be used. The same
precautions should be followed for the primary GND plane
as mentioned in item 5. For the secondary GND plane,
the GND plane method mentioned in item 4 should be
followed.
8) All the noise sensitive components such as VDD by-
pass capacitor, RCT oscillator resistor/capacitor network,
DMAX resistive divider, VREF by pass capacitor, delay
setting resistors, current sensing circuitry and feedback
circuitry should be connected as close as possible to the
SC4810. The GND return should be connected to the
quiet SC4810 GND plane.
9) The connection from the OUT of the SC4810 should
be minimized to avoid any stray inductance. If the layout
can not be optimized due to constraints, a small Schottky
diode may be connected from the OUT pin to the ground
directly at the IC. This will clamp excessive negative volt-
ages at the IC.
10) If the SYNC function is not used, the SYNC pin should
be grounded at the SC4810 GND to avoid noise pick up.
Applications Information (Cont.)
162004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
R12
5.1K
M7 SI2308
M9 SI2308
U1 MOCD207
1
2
8
7
3
4
6
5
C50
0.1uF
D2
1N4148WS
D20
MMSZ4697(10V)
R61
200K
D21
1N4148WS
R54 5.1
C4
0.1uF
C3
0.1uF
C2
0.1uF
C5
0.1uF
R50
open
C51
open
R52
51
R15
open
R25
5.1K
R29
6.34K
C1 2.2nF/630V
R1
5.11
10Vbias
R62
4.75K
R63
10K
R60
open
Vin=48V
R44
1.5K
R17
1K
100uF
C8
100uF
C9
M13
Si4488DY
4 5
3
2
1
6
7
8
C52
0.1uF
U6
SC431
C53
1uF
R13
open
Vout=3.3V/20A
Q3
FZT853
Q1 FMMT618
C16
47uF/16V
R18
1K
D11
1N5819HW
R33
100K
T2
PE68386
1
3 4
6
M1 Open
4 5
3
2
1
6
7
8
R35
10K
D7
1N4148WS
R31
7.5K
D6
1N4148WS
1u,100V
C11
M12 Open
4 5
3
2
1
6
7
8
C23 open
D1
1N4148WS
R34 1K
M6 Open
45
3
2
1
6
7
8
Q6
FMMT718
R20
8.2(16//16)
TP2
TP3
R38
1.47K
R14
open
TP4
C22 220pF
C15
0.1uF
C19
1uF
C18
0.1uF
L1
1.3uH
1u,100V
C12
TP5
M2 Open
4 5
3
2
1
6
7
8
TP7
R36
7.5K
C21
100pF
TP8
TP9
R8
10K
TP10
TP11 TP12 TP13
100uF
C7
C27
0(short)
1u,100V
C10
TP14
R42 2.4K
R22
10
T3
P8208T
8
7
1
3
R37
100K
R24
100K
M10Si4842DY
45
3
2
1
6
7
8
D9
1N5819HW
C24
1uF
R32
5.1K
TP6
R2
5.1K
R30
10K
D3
MMSZ4702(15V)
D4
MMSZ4698(11V)
C13
22nF/100V
Q5
FMMT718
C26
47nF
D8
MMSZ4698(11V)
U3
SC4810
LUVLO 2
RCT
4
FB 11
SY N C
3
CS 10
PGND
14
OUT1 15
VDD 1
DMAX
5
SS 9
DELAY1
7
RAMP
6
VREF 16
OUT2 13
DELAY2
8
GND
12
10Vbias
U2
SC1302A
2 7
6
3
1
8
4 5
R16 1K
R21
1.1M
C14
open
M4 Si4842DY
4 5
3
2
1
6
7
8
R28
10K
R43
10K
R19
10K
R3
5.11K
C25
220pF
C6
680uF
M11 Open
4 5
3
2
1
6
7
8
Q2
FMMT718
R10 10K
R23
160K
R57
5.1
T1
PA0944G
2
4
7
1
6
8
9
10
11
D5 1N4148WS
M14 SI2308
M5
Si4488DY
45
3
2
1
6
7
8
M8 Si4842DY
45
3
2
1
6
7
8
R56
5.1
C17
180pF
R40
15.8K
C20
1uF
M3 Si4842DY
4 5
3
2
1
6
7
8
R9 10K
U4
SC431
D10 1N4148WS
Q10
FMMT493
SC4810B Evaluation Board - Schematic
172004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Item Quantity Reference Part Package Manufacturer P/N
1 1 C1 2.2nF/630V SM0805 TDK C3216X7R2J222K
211
C2,C3,C4,C5,
C15,C18,C19,
C20,C50,C52,C53
0.1uF SM0805
3 1 C6 680uF SM/CT_7343_12 Sanyo 4TPB680M
4 3 C7,C8,C9 100uF SM/C_1812 TDK C4532X5ROJ107MT
5 3 C10,C11,C12 1u,100V SM/C_1210 TDK C3225X7R2A105K
6 1 C13 22nF/100V SM1206 TDK C3216X7R2J223M
8 1 C16 47uF/16V SM/CT_7343 Sanyo 16TQC47M
9 1 C17 180pF SM0805
10 1 C21 100pF SM0805
11 2 C25,C22 220pF SM0805
12 1 C24 1uF SM0805
13 1 C26 47nF SM0805
14 1 C27 0(short) SM0805
15 7 D1,D2,D5,
D6,D7,D10,D21 1N4148WS SOD123 Vishay 1N4148WS
16 1 D3 MMSZ4702(15V) SOD123 On Semi MMSZ4702T1
17 2 D4,D8 MMSZ4698(11V) SOD123 On Semi MMSZ4698T1
18 2 D9,D11 SL04 SOD123 Vishay SL04
19 1 D20 MMSZ4697(10V) SOD123 On Semi MMSZ4697T1
20 1 L1 1.3uH PCC-S1 Panasonic ETQPAF1R3EFA
22 4 M3,M4,M8,M10 Si4842DY SO-8 Vishay Si4842DY
23 2 M5,M13 Si4488DY SO-8 Vishay Si4488DY
24 3 M7,M9,M14 SI2308 SOT-23 Vishay SI2308
25 1 Q1 FMMT618 SOT-23 Zetex FMMT618
26 3 Q2,Q5,Q6 FMMT718 SOT-23 Zetex FMMT718
27 1 Q3 FZT853 SM/SOT223_BCEC Zetex FZT853
28 1 Q10 FMMT493 SOT-23 Zetex FMMT493
29 1 R1 5.11 SM0805
30 4 R2,R12,R25,R32 5.1K SM0805
31 1 R3 5.11K SM0805
32 9 R8,R9,R10,R19,
R28,R30,R35,R43,R63 10K SM0805
33 1 R13 open SM1206
34 1 R16 1K RC0805
35 3 R17,R18,R34 1K SM0805
SC4810B Evaluation Board - BOM
182004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
36 1 R20 8.2 SM0805
37 1 R21 1.1M SM0805
38 1 R22 10 SM0805
39 1 R23 160K SM0805
40 1 R24 100K SM0805
41 1 R29 6.34K SM0805
42 2 R31,R36 7.5K SM0805
43 2 R33,R37 100K SM0805
44 1 R38 1.47K SM0805
45 1 R40 15.8K SM0805
46 1 R42 2.4K SM0805
47 1 R44 1.5K SM0805
48 1 R52 51 SM0805
49 3 R54,R56,R57 5.1 SM0805
50 1 R61 200K SM0805
51 1 R62 4.75K SM0805
53 1 T1 PA0944G PA0646 Pulse PA0944G
54 1 T2 PE68386 PE68386 Pulse PE68386
55 1 T3 P8208T P8208 Pulse P8208T
56 1 U1 MOCD207 SO-8 Fairchild MOCD207
57 1 U2 SC1302A MSOP-8 Semtech SC1302A
58 1 U3 SC4810 TSSOP16 Semtech SC4810
59 2 U4,U6 SC431 SOT-23 Semtech SC431
SC4810B Evaluation Board - BOM
(Cont.)
192004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
R12
5.1K
M7 SI2308
M9 SI2308
U1 MOCD207
1
2
8
7
3
4
6
5
C50
0.1uF
D2
1N4148WS
D20
MMSZ4697(10V)
R61
200K
D21
1N4148WS
R54 5.1
C4
0.1uF
C3
0.1uF
C2
0.1uF
C5
0.1uF
D6
1N5819HW
R22
2
R50
open
C51
open
R52
51
R15
open
R25
5.1K
R29
6.34K
C1 2. 2nF/630V
R1
5.11
R62
4.75K
10Vbias
R63
10K
R60
open
Vin=48V
R44
1.5K
R17
1K
100uF
C8
100uF
C9
M13
Si4488D Y
4 5
3
2
1
6
7
8
C52
0.1uF
U6
SC431
R13
open
C53
1uF
Vout=3.3V/20A
Q3
FZT853
Q1 F MMT6 18
C16
47uF/16V
R18
1K
D11
1N5819HW
R33
80.6K
M1 Op en
4 5
3
2
1
6
7
8
R35
10K
R31
7.5K
1u,100V
C11
M12
Open
4 5
3
2
1
6
7
8
C23 open
D1
1N4148WS
R34 1K
M6 Op en
45
3
2
1
6
7
8
Q6
F MMT7 18
TP2
R20
8.2(16// 16)
R38
1.47K
TP3
TP4
R14
open
C22 220pF
C19
1uF
C18
0.1uF
L1
1.3uH
1u,100V
C12
TP5
M2 Op en
4 5
3
2
1
6
7
8
TP7
R36
7.5K
C21
100pF
TP8
R8
10K
TP9
TP10
TP11 TP12 TP13
C27
0(short)
100uF
C7
1u,100V
C10
TP14
R42 2.4K
T3
P8208T
8
7
1
3
R37
80.6K
R24
100K
M10Si4842DY
45
3
2
1
6
7
8
D9
1N5819HW
C24
1uF
TP6
R32
5.1K
R2
5.1K
D3
MMSZ4702(15V)
R30
10K
D4
MMSZ4698(11V)
C13
22nF/100V
Q5
F MMT7 18
C26
47nF
D8
MMSZ4698(11V)
U3
SC4810
LUVLO 2
RCT
4
FB 11
SYNC
3
CS 10
PGND
14
OUT1 15
VDD 1
DMAX
5
SS 9
DELAY1
7
RAMP
6
VREF 16
OUT2 13
DELAY2
8
GND
12
10Vbias
U2
SC1302A
2 7
6
3
1
8
4 5
R16 1K
R21
1.1M
C14
open
M4 Si4842DY
4 5
3
2
1
6
7
8
R28
10K
R43
10K
R19
10K
R3
5.11K
C25
220pF
C6
680uF
R10
10K
R23
160K
R57
5.1
T1
PA0944G
2
4
7
1
6
8
9
10
11
D5 1N 4148WS
M1 4 S I 23 08
M8 Si4842DY
45
3
2
1
6
7
8
R56
5.1
C17
180pF
R40
15.8K
C20
1uF
M3 Si4842DY
4 5
3
2
1
6
7
8
M5
IR F6216
4 5
3
2
1
6
7
8
R9 10K
U4
SC431
D10 1N4148WS
Q10
F MMT4 93
SC4810E Evaluation Board - Schematic
202004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
SC4810E Evaluation Board - BOM
Item Quantity Reference Part Package Manufacturer P/N
1 1 C1 2.2nF/630V SM0805 TDK C3216X7R2J222K
210 C2,C3,C4,C5,C18,
C19,C20,C50,C52,C53 0.1uF SM0805
3 1 C6 680uF SM/CT_7343 Sanyo 4TPB680M
4 3 C7,C8,C9 100uF SM/C_1812 TDK C4532X5ROJ107MT
5 3 C10,C11,C12 1u,100V SM/C_1210 TDK C3225X7R2A105K
6 1 C13 22nF/100V SM1206 TDK C3216X7R2J223M
8 1 C16 47uF/16V SM/CT_7343 Sanyo 16TQC47M
9 1 C17 180pF SM0805
10 1 C21 100pF SM0805
11 2 C25,C22 220pF SM0805
12 1 C24 1uF SM0805
13 1 C26 47nF SM0805
14 1 C27 0(short) SM0805
15 5 D1,D2,D5,D10,D21 1N4148WS SOD123 Vishay 1N4148WS
16 1 D3 MMSZ4702(15V) SOD123 On Semi MMSZ4702T1
17 2 D4,D8 MMSZ4698(11V) SOD123 On Semi MMSZ4698T1
18 3 D6,D9,D11 SL04 SOD123 Vishay SL04
19 1 D20 MMSZ4697(10V) SOD123 On Semi MMSZ4697T1
20 1 L1 1.3uH PCC-S1 Panasonic ETQPAF1R3EFA
22 4 M3,M4,M8,M10 Si4842DY SO-8 Vishay Si4842DY
23 1 M5 IRF6216 SO-8 I. R. IRF6216
24 3 M7,M9,M14 SI2308 SOT-23 Vishay SI2308
25 1 M13 Si4488DY SO-8 Vishay Si4488DY
26 1 Q1 FMMT618 SOT-23 Zetex FMMT618
27 1 Q3 FZT853 SM/SOT223 Zetex FZT853
28 2 Q5,Q6 FMMT718 SOT-23 Zetex FMMT718
29 1 Q10 FMMT493 SOT-23 Zetex FMMT493
30 1 R1 5.11 SM0805
31 4 R2,R12,R25,R32 5.1K SM0805
32 1 R3 5.11K SM0805
33 9 R8,R9,R10,R19,
R28,R30,R35,R43,R63 10K SM0805
35 1 R16 1K SM0805
212004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
SC4810E Evaluation Board - BOM
36 3 R17,R18,R34 1K SM0805
37 1 R20 8.2 SM0805
38 1 R21 1.1M SM0805
39 1 R22 2 SM0805
40 1 R23 160K SM0805
41 1 R24 100K SM0805
42 1 R29 6.34K SM0805
43 2 R31,R36 7.5K SM0805
44 2 R33,R37 80.6K SM0805
45 1 R38 1.47K SM0805
46 1 R40 15.8K SM0805
47 1 R42 2.4K SM0805
48 1 R44 1.5K SM0805
49 1 R52 51 SM0805
50 3 R54,R56,57 5.1 SM0805
51 1 R61 200K SM0805
52 1 R62 4.75K SM0805
54 1 T1 PA0944G PA0646 Pulse PA0944G
55 1 T3 P8208T P8208 Pulse P8208T
56 1 U1 MOCD207 SO-8 Fairchild MOCD207
57 1 U2 SC1302A MSOP-8 Semtech SC1302A
58 1 U3 SC4810 TSSOP16 Semtech SC4810
59 2 U4,U6 SC431 SOT-23 Semtech SC431
222004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Outline Drawing - TSSOP-16
Land Pattern - TSSOP-16
232004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Land Pattern MLPQ-16, 4 x 4
242004 Semtech Corp. www.semtech.com
SC4810A/B/C/D/E
POWER MANAGEMENT
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
Contact Information
Land Pattern MLPQ-16, 4 x 4