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PDF SC4609 Data sheet ( Hoja de datos )
| Número de pieza | SC4609 | |
| Descripción | High Efficiency Synchronous Buck | |
| Fabricantes | Semtech Corporation | |
| Logotipo |  |
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POWER MANAGEMENT
Description
SC4609
Low Input, MHz Operation,
High Efficiency Synchronous Buck
Features
The SC4609 is a voltage mode step down (buck) regula-
tor controller that provides accurate high efficiency power
conversion from an input supply range of 2.7V to 5.5V. A
high level of integration reduces external component
count, and makes it suitable for low voltage applications
where cost, size and efficiency are critical. The SC4609
is capable of producing an output voltage as low as 0.5V.
www.DataTpSheheeaektS4gUCa.4cto6em0c9urdrerinvet sofe1xtAe.rnAanl,oNn--ochvearnlanpelpMroOteScFtEioTns
with a
is pro-
vided for the gate drive signals to prevent shoot through
of the MOSFET pair. The SC4609 features lossless cur-
rent sensing of the voltage drop across the drain to
source resistance of the high side MOSFET during its
conduction period. Its switching frequency can be pro-
grammed up to 1MHz.
Asynchronous start up
Programmable switching frequency up to 1MHz
BiCMOS voltage mode PWM controller
2.7V to 5.5V input voltage range
Output voltage 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
1A peak current driver
External soft start
12-pin MLP Lead-free package, fully WEEE and RoHS
compliant
The quiescent supply current in sleep mode is typically
lower than 10µA. A external soft start is provided to pre-
vent output voltage overshoot during start-up.
The SC4609 is an ideal choice for converting 3.3V, 5V or
other low input supply voltages. It’s available in 12 pin
MLP package.
Typical Application Circuit
Applications
Distributed power architecture
Servers/workstations
Local microprocessor core power supplies
DSP and I/O power supplies
Battery-powered applications
Telecommunications equipment
Data processing applications
C1
180p
D2
1u
C17
R13
R3 1
C2 2.2n
R1
14.3k
C3
4.7u
12
1
2
3
C16
4
560pF 5
U1
BST
VCC
ISET
DRVH
PHASE
DRVL
11
10
9
COMP
FSET
VSENSE
PGND
AGND
SS
8
7
6
SC4609
Css
22u
R6
1
R5
1
M11
M2
C10
220u
Vin=2.7V - 5.5V
C13 C14
22u 22u
L1
1.8u
C6
330u
Vout=1.5V (as low as 0.5V*) / 12A
C9
C5 C4
4.7n
22u 22u
R7
10k
R8
200
*External components can be modified to provide a Vout as low as 0.5V
R9
4.99k
Revision: February 8, 2006
1
www.semtech.com
1 page  
SC4609
POWER MANAGEMENT
Pin Descriptions (Cont.)
Pin #
Pin Name Pin Function
7
AGND
Analog ground.
8 PGND
9 DRVL
www.DataSheet4U.com
10
PHASE
11 DRVH
Power ground.
DRVL drives the gate of the low side (synchronous rectifier) MOSFET. The output drivers
are rated for 1A peak currents. 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 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 SC4609 uses the
voltage across the VIN and ISET pin 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 pin.
DRVH drives the gate of the high side (main switch) MOSFET. The output drivers are rated
for 1A peak currents. 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 driver pins of the MOSFET pair in conjunction with a time delay
optimized for FET turn-off characteristics.
12
BST
This pin enables the converter to drive an N-Channel high side MOSFET. BST connects to
the external charge pump circuit. The charge pump circuit boosts the BST pin voltage to a
sufficient gate-to-source voltage level for driving the gate of the high side MOSFET.
THERMAL PAD Pad for heatsinking purposes. Connect to ground plane using multiple vias. Not connected
internally.
2006 Semtech Corp.
5
www.semtech.com
5 Page 
SC4609
POWER MANAGEMENT
Application Information (Cont.)
For a low voltage and high output current application such
as the 3.3V/1.5V@12A case, the conduction loss is of-
ten dominant and selecting low RDS(ON) MOSFETs will no-
ticeably improve the efficiency of the converter even
though they give higher switching losses.
The gate charge loss portion of the top/bottom MOSFET’s
total power loss is derived from the SC4609. This gate
charge loss is based on certain operating conditions (fs,
www.DataVSGhAeTeE,t4aUn.cdomIO).
The thermal estimations have to be done for both
MOSFETs to make sure that their junction temperatures
do not exceed their thermal ratings according to their
total power losses PTOTAL, ambient temperature TA and their
thermal resistance RθJA as follows:
Figure 4. Compensation network provides 3 poles and
2 zeros.
For voltage mode step down applications as shown in
Figure 4, the power stage transfer function is:
TJ(max)
<
TA
+
PTOTAL
RθJA
Loop Compensation Design
For a DC/DC converter, it is usually required that the
converter has a loop gain of a high cross-over frequency
for fast load response, high DC and low frequency gain
for low steady state error, and enough phase margin for
its operating stability. Often one can not have all these
properties at the same time. The purpose of the loop
compensation is to arrange the poles and zeros of the
compensation network to meet the requirements for a
specific application.
The SC4609 has an internal error amplifier and requires
the compensation network to connect among the COMP
pin and VSENSE pin, GND, and the output as shown in
Figure 4. The compensation network includes C1, C2,
R1, R7, R8 and C9. R9 is used to program the output
voltage according to
VO
=
0.5 ⋅ (1+
R7
R9
)
1+
s
1
GVD (s)
=
VI
1+
s
RC
L1
R
+
⋅ C4
s2L1C4
Where:
R = load resistance and
RC = C4’s ESR.
The compensation network will have the characteristic
as follows:
Where
1+ s 1+ s
GCOMP (s) =
ωI
s
⋅
1+
ωZ1
s
⋅
⋅1+
ωZ2
s
ωP1 ωP2
1
ωI = R7 ⋅ (C1 + C2 )
1
ωZ1 = R1 ⋅ C2
1
ωZ2 = (R7 + R8 ) ⋅ C9
ωP1
=
C1 + C2
R1 ⋅ C1 ⋅ C2
2006 Semtech Corp.
11
www.semtech.com
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet SC4609.PDF ] | |
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