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PDF SC4607 Data sheet ( Hoja de datos )
| Número de pieza | SC4607 | |
| Descripción | High Efficiency Synchronous Buck | |
| Fabricantes | Semtech Corporation | |
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POWER MANAGEMENT
Description
SC4607
Very Low Input, MHz Operation,
High Efficiency Synchronous Buck
Features
The SC4607 is a voltage mode step down (buck) regula-
tor controller that provides accurate high efficiency power
conversion from an input supply range of 2.25V to 5.5V.
The SC4607 is capable of producing an output voltage
as low as 0.5V and has a maximum duty cycle of 97%. A
high level of integration reduces external component
count, and makes it suitable for low voltage applications
where cost, size, and efficiency are critical.
www.DataSheet4U.com
The SC4607 drives external, N-channel MOSFETs with a
peak gate current of 1A. The SC4607 prevents shoot
through currents by offering nonoverlap protection for
the gate drive signals of the external MOSFETs. The
SC4607 features lossless current sensing of the voltage
drop across the drain to source resistance of the high
side MOSFET during its conduction period.
Asynchronous start up
BiCMOS voltage mode PWM controller
Operation of frequency to 1MHz
2.25V to 5.5V input voltage range
Output voltages as low as 0.5V
+/-1% reference accuracy
Sleep mode (Icc = 10µA typ)
Adjustable lossless short circuit current limiting
Combination pulse by pulse & hiccup mode
current limit
High efficiency synchronous switching
Up to 97% duty cycle
1A peak current driver
10-pin MSOP package
Applications
The quiescent supply current in sleep mode is typically
lower than 10µA. A 1.2ms soft start is internally provided
to prevent output voltage overshoot during start-up.
The SC4607 is an ideal choice for converting 2.5V, 3.3V,
5V or other low input supply voltages. It’s available in 10
pin MSOP package
Distributed power architecture
Servers/workstations
Local microprocessor core power supplies
DSP and I/O power supplies
Battery-powered applications
Telecommunications equipment
Data processing applications
Typical Application Circuit
R3 C14
0.1u
C1 C2 2.2n
180p
R1
14.3k
R13
1
C3
4.7u
C20
560pF
D2
1u
C71
U1
1 BST
DRVH
2 VCC
PHASE
3 ISET
DRVL
4 COMP
GND
5 FS/SYNC VSENSE
SC4607
10
9
8
7
6
R6
0
R5
0
Vin = 2.25V - 5.5V
C10 C11
C12
220u 22u 22u
M1
L1
1.8u
M2
Vout = 1.5V (as low as 0.5V * ) / 12A
C6
330u
C5 C4 C9
22u 22u 4.7n R7
10k
R8
200
*External components can be modified to provide a Vout as low as 0.5V
R9
4.99k
Revision: June 1, 2005
1
www.semtech.com
1 page  
SC4607
POWER MANAGEMENT
Pin Descriptions (Cont.)
Pin #
Pin Name Pin Function
8 DRVL
9 PHASE
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10 DRVH
Gate drive pin. DRVL drives the gate of the low side (synchronous rectifier) MOSFET. The
output driver is rated for 1A peak current. The PWM circuitry provides complementary drive
signals to the output stages. The cross conduction of the external MOSFETs is prevented
by monitoring the voltage on the DRVH and DRVL driver pins of the MOSFET pair in
conjunction with a time delay optimized for FET turn-off characteristics
The PHASE pin is used to limit current in the high side MOSFET. The SC4607 uses the
voltage across the Vin and ISET pins in order to set the current limit. The current limit
threshold is set by the value of an external resistor (R3 in the Typical Application Circuit
Diagram). Current limiting is performed by comparing the voltage drop across the sense
resistor with the voltage drop across the drain to source resistance of the high side
MOSFET during the MOSFET’s conduction period. The voltage drop across the drain to
source resistance of the high side MOSFET is obtained from the Vin and PHASE pins.
Gate drive pin. DRVH drives the gate of the high side (main switch) MOSFET. The output
driver is rated for 1A peak current. The PWM circuitry provides complementary drive
signals to the output stages. The cross conduction of the external MOSFETs is prevented
by monitoring the voltage on the DRVH and DRVL driver pins of the MOSFET pair in
conjunction with a time delay optimized for FET turn-off characteristics
2005 Semtech Corp.
5
www.semtech.com
5 Page 
SC4607
POWER MANAGEMENT
Application Information (Cont.)
SC4607 application:
Input Capacitor Selection:
Where:
fs = the switching frequency and
Dmax = maximum duty ratio, 0.97 for the SC4607.
The input capacitor selection is based on its ripple cur-
rent level, required capacitance and voltage rating. This
capacitor must be able to provide the ripple current by
the switching actions. For the continuous conduction
mode, the RMS value of the input capacitor can be cal-
www.DatacSuhelaett4eUd.cofrmom:
ICIN(RMS) = IOMAX ⋅
Vout ⋅ (Vin − Vout )
Vin2
This current gives the capacitor’s power loss as follows:
PCIN
=
I2
CIN( RMS )
⋅ RCIN(ESR)
This capacitor’s RMS loss can be a significant part of the
total loss in the converter and reduce the overall con-
verter efficiency. The input ripple voltage mainly depends
on the input capacitor’s ESR and its capacitance for a
given load, input voltage and output voltage. Assuming
that the input current of the converter is constant, the
required input capacitance for a given voltage ripple can
be calculated by:
CIN
= IOMAX
⋅
fs ⋅ (∆VI
D ⋅ (1− D)
− IOMAX ⋅ RCIN(ESR) )
Where:
D = Vout/Vin , duty ratio and
∆VI = the given input voltage ripple.
Because the input capacitor is exposed to the large surge
current, attention is needed for the input capacitor. If
tantalum capacitors are used at the input side of the
converter, one needs to ensure that the RMS and surge
ratings are not exceeded. For generic tantalum capaci-
tors, it is wise to derate their voltage ratings at a ratio of
2 to protect these input capacitors.
Boost Capacitor Selection:
The boost capacitor selection is based on its discharge
ripple voltage, worst case conduction time and boost
current. The worst case conduction time Tw can be esti-
mated as follows:
Tw
=
1
fs
⋅ Dmax
The required minimum capacitance for boost capacitor
will be:
Cboost
=
IB
VD
⋅ TW
Where:
IB = the boost current and
VD= discharge ripple voltage.
With fs = 300kH, VD=0.3V and IB=50mA, the required
capacitance for the boost capacitor is:
Cboost
=
IB
VD
⋅
1
fs
⋅ Dmax
=
0.05
0.3
⋅
1
300k
⋅
0.97
=
540nF
Power MOSFET Selection:
The SC4607 can drive an N-MOSFET at the high side
and an N-MOSFET synchronous rectifier at the low side.
The use of the high side N-MOSFET will significantly re-
duce its conduction loss for high current. For the top
MOSFET, its total power loss includes its conduction loss,
switching loss, gate charge loss, output capacitance loss
and the loss related to the reverse recovery of the bot-
tom diode, shown as follows:
PTOP _ TOTAL
=
I2
TOP _ RMS
⋅ RTOP _ ON
+
ITOP _PEAK ⋅ Vin
VGATE RG
⋅
fs
⋅
(QGD + QGS2 ) + QGT ⋅ VGATE ⋅ fs + (QOSS + Qrr ) ⋅ Vin ⋅ fs
Where:
RG = gate drive resistor,
QGD = the gate to drain charge of the top MOSFET,
QGS2 = the gate to source charge of the top MOSFET,
QGT = the total gate charge of the top MOSFET,
QOSS = the output charge of the top MOSFET and
Qrr = the reverse recovery charge of the bottom diode.
For the top MOSFET, it experiences high current and high
voltage overlap during each on/off transition. But for the
2005 Semtech Corp.
11
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11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet SC4607.PDF ] | |
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