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High Performance Wide Input Range Dual Synchronous Buck Controller
POWER MANAGEMENT Description
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 latchups, 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.
SC2442/H
Features
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 Fully WEEE and RoHS Compliant
Applications
Point of load converter applications DSL applications with multiple output voltages Power management for mixed signal applications Cable modems and set top boxes.
Typical Application Circuit
VIN+ MAX 30V/36V (H)
R1 R2 R3 Q5 R9 C6 C7 OC1 OC2 R4
Q1 R5 L1 Q3 R7 C2
C1
VOUT1
RTN
3 2 C4 AVCC PVCC R10 C5 1 13 7 18 23 SS1 C8 SS2 C9 OSC R12 6 5 19 20 22
VI N BD I AVC C
U1
OC 1 OC 2 G D 1H
4 21 9 11 16 14 10 8 15 17 12 24
D1
D2
Q2 R6 L2 Q4 R8 C3
RTN
VOUT2
SS1 SS2 ROS C FB1 E A1 FB2 E A2
SC2442ITSTR
P VC C
G D 1L G D 2H G D 2L PH1 BS T 1 PH2 BS T 2 P G ND AG ND
PH1 BST1 PH2 BST2 C16 C15
RTN
R13 R14
S YN C /E N
R15
R16
RTN
R11 C10 C11
EA2 C13 FB2
RTN
R17
C12
R18
ENA
FB1
Revision: June, 2007
1
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SC2442/H
POWER MANAGEMENT Absolute Maximum Ratings
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.
Parameter BST1, BST2 to PGND S C 2442 S C 2442H VIN to PGND S C 2442 S C 2442H BD I to PGND OC 1 and OC 2 to VIN PVC C , AVC C to PGND BST1 to PH1, BST2 to PH2 GD 1H to PH1, GD 2H to PH2 GD 1L, GD 2L to PGND PGND to AGND PH1, PH2 -ve swi ng wrt PGND (for 100 nS) All Other Pi ns to AGND Juncti on Temperature Storage Temperature Range Lead Temperature (Solderi ng) 10 Sec.
Sy mbol VBST1, VBST2
Maximum
U nits V
38 44 V 30 36
VIN
V BD I VIN - VOC1, VIN - VOC2 PVC C , AVC C
VIN -0.3 to +0.5 8 -0.3 to 8 -0.3 to PVC C 0.3
V V V V V V V V C C C
VPH1, VPH2
-1 -0.3 to AVC C -40 to +125 -60 to +150 260
Electrical Characteristics
Unless specified: TA = TJ = -40 to 125C, VIN = 24V, VCC = 7V, Fc = 550KHz
Parameter U nderv oltage Lockout Start Threshold UVLO Hysteresi s Power Supply Operati ng C urrent AVC C /PVC C Regulated BD I D ri ve C urrent
Sy mbol
Test C onditions
Min
Ty p
Max
U nit
VUVLO VHYST
AVC C ri si ng AVC C falli ng
4.5
4.6 0.15
4.75
V V
IQSC AVC C , PVC C IBDI
No load, SYNC /EN = Low VIN > 8V VIN > AVC C + 2V 6.7 3
8 7.0 5
13 7.3
mA V mA
(c) 2007 Semtech Corp.
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SC2442/H
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: TA = TJ = -40 to 125C, VIN = 24V, VCC = 7V, Fc = 550KHz
Parameter Soft Start C hargi ng C urrent D i scharge C urrent Error Amplifier Voltage Feedback Reference Input Bi as C urrent Open Loop Gai n (1) Uni ty Gai n Bandwi dth (1) Output Source/Si nk C urrent Output Slew Rate
(1)
Sy mbol
Test C onditions
Min
Ty p
Max
U nit
ISS1, ISS2 ISS1, ISS2
7 -1
10 -2
13 -4
A A
V F B 1, V F B 2 IEABIAS GDC GBW
0.735
0.750 500 70 3 2 1 80
0.765
V nA dB MHz mA V/S nS
PWM to Output D elay (1) Oscillator Frequency Range C lock Frequency Osci llator Peak Voltage Osci llator Valley Voltage Sy nc/Enable Input Enable Thresheld Voltage D i sable Thresheld Voltage D i sable Low to Shut D own D elay (1) Sync Input Hi gh Level Sync Input Low Level C urrent Limit OC 1, OC 2 C urrent Li mi t Sense Feedback Threshold for Hi ccup OC Sense to D ri ve Turn Off D elay (1) VOC1, VOC2 V F B 1, V F B 2 TOCDLY -80 0.450 VSYEN VSYEN VSYEN VSYEN SYNC /EN pi n Voltage ri si ng SYNC /EN pi n Voltage falli ng SYNC /EN pi n < 0.8V 1.8
(1) (1)
Fc Fc ROSC = 60K Internal Internal
0.1 490 550 3.0 1.5
1.1 610
MHz kHz V V
2.0 0.8 50 TTL TTL 1.0
V V nS V V
-105 0.525 80
-125 0.610
mV V nS
(c) 2007 Semtech Corp.
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SC2442/H
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: TA = TJ = -40 to 125C, VIN = 24V, VCC = 7V, Fc = 550KHz
Parameter Gate D riv e Outputs Hi gh Si de Gate D ri ve (1) Low Si de Gate D ri ve Gate D ri ve Ri se Ti me Gate D ri ve Fall Ti me Maxi mum D uty C ycle Mi ni mum D uty C ycle D ead Ti me Between Gate D ri ves
(1)
Sy mbol
Test C onditions
Min
Ty p
Min
U nits
IGDH+, IGDHIGDL+, IGDLTRISE TFALL D max D mi n TDEAD
Soure/Si nk Soure/Si nk C OUT = 1000 pF C OUT = 1000 pF For PWM1 and PWM2 For PWM1 and PWM2 85
+ 0 .5 + 0 .5 30 30 94 0 100
A A nS nS % % nS
NOTES: (1) Guaranteed by design, not tested in production (2) This device is sensitive to ESD. Use of standard ESD handling precautions is required.
Pin Configuration
Top View
AVCC BDI VIN OC1 EA1 FB1 SS1 BST1 GD1H PH1 GD1L PGND AGND ROSC SYNC/EN OC2 EA2 FB2 SS2 BST2 GD2H PH2 GD2L PVCC
Ordering Information
Temp. Range (T A) -40C to +125C
Part Number SC2442ITSTR
Package
TSSOP-24 SC2442HITSTR SC2442ITSTRT
(1)
TSSOP-24 SC2442HITSTRT
(1)
-40C to +125C
Notes: Only available in tape and reel packaging. A reel contains 2500 devices. (1) Lead free devices
(24 Pin TSSOP)
(c) 2007 Semtech Corp.
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SC2442/H
POWER MANAGEMENT Pin Descriptions
Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Pin Name AVCC BDI VIN OC1 EA1 FB1 SS1 BST1 GD1H PH1 GD1L PGND PVCC GD2L PH2 GD2H BST2 SS2 FB2 EA2 OC2 SY NC/EN ROSC AGND Pin Function Supply voltage for analog circuit. Regulated by the BDI pin to 7V from VIN using an external PNP transistor. Base drive for AVCC/PVCC regulator. Input supply voltage. Maximum is 30V for SC2442 and 36V for SC2442H. High side current sense for VOUT1. Threshold is 100 mV. Error amplifier output for compensation for the VOUT1. Feedback input for the VOUT1. Soft start pin for VOUT1. A capacitor to AGND sets the soft start period. Boost capacitor connection for the VOUT1 high side gate drive. Connect an external capacitor and a diode as show n in the Typical Application Circuit. Gate drive for the high side MOSFET of VOUT1. 180 degrees out of phase w ith GD2H. Sw itching node for VOUT1 external inductor connection. Gate drive for low side MOSFET of VOUT1. Pow er ground for gate drive return currents. Supply voltage for output drivers. Gate drive for low side MOSFET of VOUT2. Sw itching node for VOUT2 external inductor connection. Gate drive for the high side MOSFET of VOUT2. 180 degrees out of phase w ith GD1H. Boost capacitor connection for the VOUT2 high side gate drive. Connect an external capacitor and a diode as show n in the Typical Application Circuit. Soft start pin for VOUT2. A capacitor to AGND sets the soft start period. Feedback input for the VOUT2. Error amplifier output for compensation for the VOUT2. High side current sense for VOUT2. Threshold is 100 mV. Oscillator synchronization and PWM Enable pin. Oscillator frequency programming pin. Connect a resistor to AGND to set clock frequency. Analog signal ground.
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SC2442/H
POWER MANAGEMENT Block Diagram
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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 lockout 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 A internal current source. The error amplifier outputs are clamped by the respective 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 A. The 2 A of sink current will slowly discharge the SS capacitor until its voltage reaches 1V, which will trigger the SS pin to begin sourcing 10 A. The convertor will operate in the asynchronous mode during hiccup.
(c) 2007 Semtech Corp. 7
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.
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SC2442/H
POWER MANAGEMENT Application Information (Contd)
VIN J1-1 R2 56 uF 10V C2
2.2 uF
4.75-6V
R1
0.075R, 1/4W
0.06R, 1/4W
QD1
FDS6982S
8
7
6
5 TP2 L1 P1166.473T 2 C3 100 uF 4V
RTN
C7
2.2 uF
R3 C8 C22
10 nF 100R
R4
100R
***
QB
3.3V/0.6A VOUT1
2.2 uF
J1-2
OC1 OC2
R7 3.3R R5 2R QD2
FDS6982S
*
1 2 3
QT
1
4
C14
J2-1
J1-3 TP1
RTN
C23 PVCC 3 2 1
10 nF
VIN BD I AVCC
SCH
C10 15 uF C11 15 uF SS1 C16 C17
0.22 uF
OC 2 G D 1H
SCH
U1
OC 1
4 21 9 11 16 14 10 8 15 17 12 24
D1
D2
8
7
6
5
J2-2
***
QB
TP3 L2 P1166.223T 2 C4 100 uF 4V 1.8V/1A VOUT2
2.2 uF
J2-4
R9
10K
R10
5R
13 7 18 23 6 5 19 20 22
*
1 2 3
1
QT
C15
SS1 SS2 ROS C FB1 E A1 FB2 E A2
SC2442ITSTR
P VC C
G D 1L G D 2H G D 2L PH1 BS T 1 PH2 BS T 2 P G ND AG ND
R6 2R R8 3.3R PH1 BST1 PH2 BST2 C13 C12
4
J2-3
RTN 1 nF 2.2 uF
C24
C25
1 nF
SS2
0.1 uF
R16
100R
R17
14K
R18
34K
R19
100R
OSC R11 40.2K
2.2 uF
S YN C /E N
R14
10K
R15
10K
ENA C20 R12
220K 47 pF
EA1 R13
100K
C21 47 pF C19
10 nF
EA2
C18 FB1
4.7 nF
FB2
Fig 1) Application Circuit for 5V to 3.3V/1.8V Low Power Dual Synchronous Buck Convertor
Input 5V
3.3V Output
1.8V Output
Fig 2) Input and output rise times with full load
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SC2442/H
POWER MANAGEMENT Application Information (Contd)
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
Fig 5) 1.8V Transient response for 10% to 100% step load
Fig 6) 3.3V Transient response for 10% to 100% step load
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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
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