1 www.semtech.com
SC2442/H
High Performance Wide Input Range
Dual Synchronous Buck Controller
POWER MANAGEMENT
Revision: June, 2007
Description Features
Applications
Typical Application Circuit
Dual output controller
Asynchronous start up mode
Power up sequencing to prevent latch-ups
Out of phase operation for low input ripple
Over current protection
Output down to 0.75V
Wide input range, 4.75 to 30V for SC2442 and
4.75 to 36V for SC2442H
Vcc regulator with external PNP transistor
Programmable clock frequency up to 1.1MHz
Two synchronous bucks for high efficiency at high
current
–40 to +125 Deg C operating temperature
Small package TSSOP-24
SC2442 and SC2442H are high performance dual buck
converter controllers that can be configured for a variety
of synchronous buck applications where efficiency is most
important. Both converters are synchronized to prevent
beat frequencies. The dual buck converters are also
operated out of phase reducing input ripple, allowing for
fewer input capacitors.
High frequency operation up to 1.1 MHz reduces the size
of output inductors and capacitors. The controller has
separate power pins for both VCC and GND to improve
noise immunity. The VCC supplies can be regulated to 7V
using an external PNP transistor. Other features include:
bootstrapping for high side drive supplies, asynchronous
mode start up, power up sequencing to prevent latch-
ups, individual soft start for each convertor, bootstrapped
drivers for high side N-channel MOSFETs, input side
current sensing, dual mode current limit with hiccup,
enable and external frequency synchronization.
The SC2442 operates over the range of 4.75V to 30V
and SC2442H operates over the range of 4.75V to 36V.
Point of load converter applications
DSL applications with multiple output voltages
Power management for mixed signal applications
Cable modems and set top boxes.
R14
C9
R18
D2
R15
L1
C13R17 C1 2
RTN
RTN
PVCC
SS1
ENA
C1 6
C1 1
R1
C8
C6
R10
Q4
Q5
U1
SC2442ITSTR
AVCC
1
BDI
2
VIN
3
OC1
4
EA1
5
FB1
6
SS1
7
BST1
8
GD1H
9
PH1
10
GD1L
11
PGND
12
PVCC
13
GD2L
14
PH2
15
GD2H
16
BST2
17
SS2
18
FB2
19
EA2
20
OC2
21
SYNC/EN
22
ROSC
23
AGND
24
AVCC
RTN
Q3
C1
C7
R11
R9
L2
C10
R3
R5
R4
R2
D1
BST1
C3
R7
Q1
R6
R13
BST2
R8
Q2
C15
R16
R12
C2
PH2
PH1
VIN+
RTN
RTN
C4
C5
VOUT1
FB2
FB1
OC1
VOUT2
SS2
OSC
EA2
MAX 30V/36V (H)
OC2
Fully WEEE and RoHS Compliant
2© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Absolute Maximum Ratings
Electrical Characteristics
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tnerruCevirDIDB I
IDB
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2442CS
H2442CS
V
,1TSB
V
2TSB
83
44
V
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2442CS
H2442CS
NIV
03
63
V
DNGPotIDB V
IDB
NIVV
NIVot2COdna1CO V-NIV
1CO
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2CO
5.0+ot3.0-V
DNGPotCCVA,CCVPCCVA,CCVP8V
2HPot2TSB,1HPot1TSB
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8ot3.0-V
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0-V
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,1HP
V
2HP
1-V
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Unless specified: TA = TJ = -40 to 125°C, VIN = 24V, VCC = 7V, Fc = 550KHz
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© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Electrical Characteristics (Cont.)
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)1(
1Sμ/V
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)1(
08Sn
rotallicsO
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)1(
lanretnI0.3V
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lanretnI5.1V
tupnIelbanE/cnyS
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NEYS
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NEYS
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V8.0<nipNE/CNYS05Sn
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NEYS
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timiLtnerruC
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V
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08Sn
Unless specified: TA = TJ = -40 to 125°C, VIN = 24V, VCC = 7V, Fc = 550KHz
4© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Pin Configuration Ordering Information
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T(
A
)
RTSTI2442CS
42-POSSTC°521+otC°04-
RTSTIH2442CS
TRTSTI2442CS
)1(
42-POSSTC°521+otC°04-
TRTSTIH2442CS
)1(
(24 Pin TSSOP)
Notes:
Only available in tape and reel packaging. A reel
contains 2500 devices.
(1) Lead free devices
Top View
Electrical Characteristics (Cont.)
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)1(
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+LDG
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kniS/eruoS+5.0A
emiTesiRevirDetaG T
ESIR
C
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C
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Fp0001=03Sn
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DAED
001Sn
AVCC
BDI
VIN
OC1
EA1
FB1
SS1
BST1
GD1H
PH1
GD1L
PGND PVCC
GD2L
PH2
GD2H
BST2
SS2
FB2
EA2
OC2
SYNC/EN
ROSC
AGND
Unless specified: TA = TJ = -40 to 125°C, VIN = 24V, VCC = 7V, Fc = 550KHz
NOTES:
(1) Guaranteed by design, not tested in production
(2) This device is sensitive to ESD. Use of standard ESD handling precautions is required.
5© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Pin Descriptions
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81TSB.evirdet
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6© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Block Diagram
7© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Application Information
Undervoltage Lockout
The undervoltage lockout circuitry monitors the AVCC pin.
During undervoltage lockout all output drives are turned
off and both SS pins are discharged to ground. Typically,
for AVCC increasing, normal operation will not occur until
AVCC reaches 4.6V. For AVCC falling, undervoltage lock-
out will not occur until AVCC falls below 4.5V.
Voltage Regulator
Using an external PNP transistor as shown in the Typical
Applications Circuit, the SC2442/H provide a regulated
AVCC supply. The same AVCC with adequate filtering can
be connected to PVCC to provide power for the output
drives. The AVCC is regulated at 7V typical which provides
optimum drive for most low Voltage power MOSFETs. The
BDI pin will provide at least 3 mA to regulate the external
PNP.
For VIN voltages below 8V, the PNP pass transistor will
always be operating in saturation and it is recommended
to connect VIN directly to AVCC and PVCC so long as
maximum input voltage is below 8V. The BDI pin may be
left unconnected. Alternately if an additional supply <8V is
available in addition to VIN, it can be used for separately
powering both the VCCs.
Soft Start and Hiccup Mode
The SC2442/H controllers utilize asynchronous start up
to provide glitch free output rise times. During start up, the
SS1 and SS2 pins are held low and the gate drive signals
are also pulled low. Once AVCC reaches 4.6V and above,
the SS capacitors are charged by a 10 μA internal current
source. The error amplifier outputs are clamped by the re-
spective SSx voltages. As the SSx pin voltage goes above
the oscillator valley voltage of 1.5V, the high-side driver
will begin switching. The low-side driver will not begin
switching until the SSx voltage has reached 3.3V.
During normal operation, the SC2442/H will enter hiccup
mode if the SS pin voltage is above 3.3V and the FB pin
voltage is below 0.525V (70% of 0.750V). If this occurs
the GDxH and GDxL signals will go low and the SS pin will
begin to sink 2 μA. The 2 μA of sink current will slowly
discharge the SS capacitor until its voltage reaches 1V,
which will trigger the SS pin to begin sourcing 10 μA. The
convertor will operate in the asynchronous mode during
hiccup.
Sync and Enable
When the SYNC/EN pin is pulled below 1V, all output
drives are turned off and both SS pins are discharged to
ground. When the SYNC/EN pin is pulled high above
1.8V, normal operation occurs. When an external clock
signal is applied that is marginally higher in frequency to
that set by the ROSC resistor, the internal oscillator will
synchronize to this signal. The external signal should have
TTL compatible transition.
Operating Frequency
The operating frequency is set by a resistor from ROSC
pin to AGND. ROSC sets the clock frequency Fc that is
twice the operating frequency of each converter. The
clock frequency is given by
Fc = 33,000 / ROSC
Fc is in kHz and ROSC is in kOhm.
Current Limiting
The SC2442/H provide cycle-by-cycle current limiting by
sensing the current in the input line. A non inductive resistor
should be used for precise current sensing and limiting.
When the voltage drop across a sense resistor in the input
line exceeds 105 mV, the PWM pulse is latched off and is
not reset until the next clock cycle. Overcurrent condition
affects only the high side driver. An RC filter should be
placed across the sense resistor as shown in the Typical
Application Circuit to reduce noise due to turn-on spikes.
The filter capacitor should be connected between VIN and
respective OCx pins for proper filtering. Typically a ceramic
or similar low esr capacitor is placed between the current
sense resistor and the switching circuit. If this capacitor
value is large, it can significantly distort the current
feedback waveform aross the sense resistors. This should
be taken into account while designing the overcurrent
protection circuit.
Gate Drive Considerations
The SC2442/H provide high side gate drive with
bootstrapping as shown in the Typical Application Circuit.
A ceramic capacitor is recommended between each BSTx
pin to the corresponding Phase Node. Each gate drive can
source and sink a minimum of 0.5A current with 100 nS
dead time between transistions to prevent shoot throughs.
8© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Application Information (Contd)
Fig 1) Application Circuit for 5V to 3.3V/1.8V Low Power Dual Synchronous Buck Convertor
Fig 2) Input and output rise times with full load
Input 5V
3.3V Output
1.8V Output
J2-3
C13
2.2 uF
C21
47 pF
J2-2
C16
0.22 uF
R10
5R
C22
10 nF
PH1
C15
2. 2 uF
J2-1
U1
SC2442ITSTR
AVCC
1
BDI
2
VIN
3
OC1
4
EA1
5
FB1
6
SS1
7
BST1
8
GD1H
9
PH1
10
GD1L
11
PGND
12
PVCC
13
GD2L
14
PH2
15
GD2H
16
BST2
17
SS2
18
FB2
19
EA2
20
OC2
21
SYNC/EN
22
ROSC
23
AGND
24
R16
100R
TP 2
C14
2.2 uF
C8
2. 2 uF
C23
10 nF
R9
10K
C7
2. 2 uF
C20
47 pF
SS1
TP 3
R3
100R
R5
2R
TP 1
R4
100R
C4
100 uF 4V
D1
SCH
R7
3.3R
R6
2R
J1-1
R17
14K
R8
3.3R
C12
2.2 uF
R15
10K
R11
40.2K
C3
100 uF 4V
J2-4
R18
34K
C17
0.1 uF
R13
100K
D2
SCH
C24
1 nF
R14
10K
R19
100R
C19
10 nF
C25
1 nF
R12
220K
C18
4.7 nF
RTN
RTN
RTN
BST1
PH2
BST2
VIN
C10
15 uF
C11
15 uF
VOUT2
FB2
PVCC
FB1
OC1
ENA
R1
0.075R, 1/4W
R2
0.06R, 1/4W
L1
P1166.473T
1 2
L2
P1166.223T
1 2
••
QB QT
•
•
QD1
FDS6982S
1 2 3 4
5678
••
QB QT
•
•
QD2
FDS6982S
1 2 3 4
5678
SS2
OSC
1.8V/1A
3.3V/0.6A
4.75-6V
EA1
EA2
C2
56 uF 10V
VOUT1
OC2
J1-2
J1-3
9© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Application Information (Contd)
Fig 5) 1.8V Transient response for 10% to 100% step load Fig 6) 3.3V Transient response for 10% to 100% step load
Fig 3) Switching waveforms at Phase Node with full load.
Top trace: 1.8V/1A Bottom trace: 3.3V/0.6A
Fig 4) Output ripple and noise at full load
Top trace: 3.3V Output Bottom trace: 1.8V Output
10© 2007 Semtech Corp. www.semtech.com
SC2442/H
POWER MANAGEMENT
Outline Drawing - TSSOP-24
Land Pattern - TSSOP-24
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
