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PDF SC1403ITSTR Data sheet ( Hoja de datos )
| Número de pieza | SC1403ITSTR | |
| Descripción | Mobile Multi-Output PWM Controller with Virtual Current SenseTM | |
| Fabricantes | Semtech Corporation | |
| Logotipo |  |
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SC1403
Mobile Multi-Output PWM Controller
with Virtual Current SenseTM
POWER MANAGEMENT
PRELIMINARY
Description
Features
The SC1403 is a multiple-output power supply controller
designed to power battery operated systems. The
SC1403 provides synchronous rectified buck converter
control for two (3.3 V and 5 V) power supplies. An effi-
ciency of 95% can be achieved for the two supplies. The
SC1403 uses Semtech’s proprietary Virtual Current
SenseTM technology along with external error amplifier
compensation to achieve enhanced stability and DC ac-
curacy over a wide range of output filter components
while maintaining fixed frequency operation. The SC1403
also provides a linear regulator for system housekeep-
ing. The 5 V linear regulator takes its input from the
battery; for efficiency, the output is switched to the 5V
output when available.
Control functions include: power up sequencing, soft
start, power-good signaling, and frequency synchroniza-
tion. Line and load regulation is to +/-1% of the output
voltage. The internal oscillator can be adjusted to 200
kHz or 300 kHz or synchronized to an external clock.
The MOSFET drivers provide >1A peak drive current for
fast MOSFET switching.
The SC1403 includes a PSAVE# input to select pulse
skipping mode for high efficiency at light load, or fixed
frequency mode for low noise operation.
3.3V and 5V dual synchronous outputs, resistor
programmable to 2.5V
Fixed frequency or PSAVE for maximum efficiency
over wide load current range
5V / 50mA linear regulator
Virtual Current Sense TM for enhanced stability
Accurate low loss current limiting
Out of phase switching reduces input capacitance
requirements
External compensation supports wide range of
output filter components
Programmable power-up sequence
Power good output
Output overvoltage & overcurrent protection with
output undervoltage shutdown
4µA typical shutdown current
6mW typical quiescent power
Applications
Notebook and subnotebook computers
Automotive electronics
Desktop DC-DC converters
Typical Application Circuit
Revision 3, August 2002
SHDN# V+ SYNC VL
4 COMP3
COMP5 5
BST3
BST5
DH3 DH5
L1
PHASE3
PHASE5
DL3 DL5
PGND
CSH3
CSH5
CSL3
CSL5
FB3 FB5
SEQ
ON3 REF
ON5
PSAV#
RST#
GND
1
L2
www.semtech.com
1 page  
SC1403
POWER MANAGEMENT
PRELIMINARY
Electrical Characteristics (Cont.)
Unless otherwise noted: V+ = 15V, both PWMs on, SYNC = 0V, VL load = 0mA, REF load = 0mA, PSAVE# = 0V, TA =-40 to 85°C. Typical values are at
TA = +25°C. Circuit = Typical Application Circuit
Parameter
Conditions
Min Typ Max Units
Input Leakage Current
ON3, PSAVE#, ON5, SHDN#, SYNC
(SEQ = 0V or VL)
+1 µA
Logic Output Low Voltage
RESET#, ISINK = 4mA
0.4 V
Logic Output High Current
RESET# = 3.5V
1
mA
ON5 Pull-Down Resistance
Gate Driver Sink/Source
Current
ON5, ON3 = 0V, SEQ = REF
DL3, DH3, DL5, DH5, forced to 2.5V
100 Ω
1A
Gate Driver On-Resistance
Non-Overlap Threshold
High or low
PHASE3, PHASE5, DL3, or DL5
1.5 7
1.0
Ω
V
Non-Overlap Delay
Falling edge of DH to rising edge of DL
Falling edge of DL to rising edge of DH
(1V threshold on DH and DL,
no capacitance on DL or DH)
10 17 25 nsec
35 75 115 nsec
Note:
(1) This device is ESD sensitive. Use of standard ESD handling precautions required.
2002 Semtech Corp.
5
www.semtech.com
5 Page 
SC1403
POWER MANAGEMENT
Functional Information (Cont.)
SC1403 Startup Sequence Chart
PRELIMINARY
SEQ
REF
REF
REF
REF
GND
GND
ON3
LOW
LOW
HIGH
HIGH
LOW
HIGH
ON5
LOW
HIGH
LOW
HIGH
X
HIGH/LOW
VL LOW X
VL
HIGH
HIGH/LOW
RESET
Follows 3.3V SMPS.
Low.
Follows 3.3V SMPS.
Follows 3.3V SMPS.
Low.
High after both outputs are
in regulation.
Low.
High after both outputs are
in regulation.
DESCRIPTION
Independant start control mode. Both SMPSs off.
5V SMPS ON, 3.3V SMPS OFF.
3.3V SMPS ON, 5V SMPS OFF.
Both SMPSs on.
Both SMPSs off.
5V starts when ON3 goes high. If ON5 = HIGH,
3V is on. If ON3 = LOW, 3V is off.
Both SMPSs off.
3V starts when ON3 goes high. If ON5 = HIGH,
5V is on. If ON3 = LOW, 5V is off.
Applications Information
Design Guidelines
The schematic for the reference circuit is shown on page 24. The
reference circuit is configured as follows:
Switching Regulator 1
Switching Regulator 2
Linear Regulator
Vout1 = 3.3V @ 6A
Vout2 = 5.0V @ 6A
Vout3 = 5.0V @ 50mA
Designing the Output Filter
Before calculating the output filter inductance and output
capacitance, an acceptable amount of output ripple current is to
be determined. The maximum allowable ripple current depends
on the transient requirement of the power supply. Under normal
situation, the ripple current is usually set at 10 to 20% of the
maximum load. However, in order to speed up the output transient
response, ripple current can be much higher. In this design, we are
going to set the ripple current to be 40% of maximum load. So
once the ripple voltage specification is determined, the capacitor
ESR is chosen. The output ripple voltage is usually specified at +/
- 1% of the output voltage.
For the reference circuit 3.3V switcher, we selected a maximum
ripple voltage of 33mV. Choosing one 180uF, 4V Panasonic SP
Polymer Aluminum Electrolytic Cap, of which ESR is 15 mΩ , sets
the maximum ripple current as follows:
∆IO
=
∆VO _ MAX
ESR
∆IO
=
0.033V
0.015Ω
=
2.2A
Checking to see if the maximum RMS current can be met by the
SP cap.
I1
=
−
∆IO
2
IRMS =
I12 + I1 ⋅I2 + I22
3
I2
=
+
∆IO
2
Irms=0.635 A << Irms_rated=3.0A
The output inductance can now be found by:
LO
=
(VIN _
NOM − VO) ⋅DNOM ⋅ TS
∆IO
2002 Semtech Corp.
11
www.semtech.com
11 Page | ||
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| PDF Descargar | [ Datasheet SC1403ITSTR.PDF ] | |
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