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PDF SC1402 Data sheet ( Hoja de datos )
| Número de pieza | SC1402 | |
| Descripción | Multi-Output/ Low-Noise Power Supply Controller for Notebook Computers | |
| Fabricantes | Semtech Corporation | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de SC1402 (archivo pdf) en la parte inferior de esta página. Total 18 Páginas | ||
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Multi-Output, Low-Noise Power Supply
Controller for Notebook Computers
SC1402
December 15, 2000
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1402 is pin compatible with the MAX1632 with
improved load regulation performance. The SC1402 is
a multiple-output power supply controller designed to
power logic supply components in battery operated
systems. The SC1402 utilizes synchronous rectified
buck topologies to generate two voltages, (3.3V and
5V) with up to 95% efficiency. It also provides two lin-
ear regulators for system housekeeping functions. The
12V linear regulator output is generated from a coupled
inductor of the 5V switching regulator.
Control functions include: power up sequencing, soft
start, power-good signaling, automatic bootstrapping
for high side MOSFETs, and frequency synchroniza-
tion. An internal precision 2.5V reference ensures ±2%
output voltage. The internal oscillator can be adjusted
to 200kHz, 300kHz or synchronized to an external
clock. The MOSFET drivers provide 1A peak drive
current for fast MOSFET switching.
The SC1402 includes a PSAVE enable input to select
a pulse skipping mode for high efficiency or a fixed fre-
quency mode for low noise operation.
FEATURES
•= 6V to 30V Input range
•= 3.3V and 5V dual synchronous rectified outputs
•= Fixed frequency or PSAVE for maximum efficiency
over wide load current range
•= 5V/50mA linear regulator
•= 12V/120mA linear regulator
•= Precision 2.5V reference output
•= Programmable power-up sequence
•= Power good output (RESET)
•= Output over current protection
•= Output over voltage protection
•= Output under voltage shut down
•= 4µA typical shut down current
•= 7mW typical quiescent power
APPLICATIONS
•= Notebook and subnotebook computers
•= PDAs and Mobile communicators
•= Desktop DC-DC converters
ORDERING INFORMATION:
DEVICE
PACKAGE(1)
SC1402ISS
SSOP-28
TEMP. (TA)
-40 - +85°C
TYPICAL APPLICATION CIRCUIT
Note:
(1) Only available in tape and reel packaging. (Suffix ‘.TR’).
© 2000 SEMTECH CORP.
1
652 MITCHELL ROAD NEWBURY PARK CA 91320
1 page  
December 15, 2000
BLOCK DIAGRAM
Multi-Output, Low-Noise Power Supply
Controller for Notebook Computers
SC1402
VL
© 2000 SEMTECH CORP.
5
652 MITCHELL ROAD NEWBURY PARK CA 91320
5 Page 
Multi-Output, Low-Noise Power Supply
Controller for Notebook Computers
SC1402
December 15, 2000
APPLICATION INFORMATION
Introduction
The SC1402 is a versatile dual switching regulator ad-
justable from 2.5V to 5.5V with fixed 5V and 3.3V
modes. In addition, there are two on-chip 12V & 5V lin-
ear regulators capable of supplying 120mA & 50mA of
output current, respectively. The SC1402 is designed
for notebook applications but has applications any-
where high efficiency, small size and low cost are re-
quired.
The Semtech SC1402 EVAL board consists of a 3.3V,
3A switcher, a 5.0V, 3A switcher, an onboard 12V lin-
ear regulator. A 15V flyback supply developed off the
5V SMPS inductor delivers the input voltage to the on-
board 12V linear regulator.
Design Guidelines
The schematic for the EVAL board is shown on page
18. The EVAL board is configured as follows:
Switching Regulator 1
Vout1 = 3.3V, 3A
Switching Regulator 2
Vout2 = 5.0V, 3A
Linear Regulator 1
Linear Regulator 2
Vout3 = 12V, 120mA
Vout4 = 5V, 50mA
Designing the Output Filter
Before calculating the output filter inductance and out-
put capacitor, an acceptable amount of output ripple
current is to be determined. The ESR of the output ca-
pacitor multiplied by the ripple current sets the maxi-
mum allowable ripple voltage. So once the ripple volt-
age specification is selected, the capacitor ESR is cho-
sen usually based on capacitor cost and size con-
straints. This then sets the maximum output ripple cur-
rent through the capacitor and inductor.
For the EVAL board 3.3V switcher, we selected a max-
imum ripple voltage of 50mV. Choosing two 330uF,
6.3V tantalum capacitors C21 & C22, each having an
ESR of 100mΩ, their combined ESR equaling 50mΩ,
sets the maximum ripple current as follows:
∆ IO
=
∆VO
ESR
∆IO
=
0.05
0.05
= 1Amp
Be sure that the two output capacitors can handle this
ripple current. Ripple current specifications are found
in the capacitor data sheet for high quality capacitors
intended for use in switching power supplies.
The inductance can now be found:
L1 =
(VINMAX
− VO ) • D • t
∆IO
These inductance and duty cycle equations exclude
any resistive drops due to winding resistance and
MOSFET on resistance.
Where:
For f = 300KHz, t = 1/f
D=
VO
VIN
(28
;L1 =
−
3.3)
•
3.3
28
1
• 3.33
• 10 −6
From this calculation we choose L1 to be 10uH.
For a 200kHz operating frequency, L1 calculates to be
14.5uH.
Choosing Inductor & FET Current Rating
The current carrying capability of the inductor and
MOSFETs should be sized to handle the maximum
current of the supply set by the current sense resistor,
Rsense = R9. Here we use the minimum current
threshold value:
R9
=
80mV
IPEAK
Where Ipeak equals:
IPEAK
= IOUT
+
∆IO
2
Ipeak = 3.5 Amps
R9
=
0.080
3.5
= 0.023 Ω
Here we chose a sense resistor of 20mΩ. Now we can
determine FET and inductor current carrying capability
© 2000 SEMTECH CORP.
11
652 MITCHELL ROAD NEWBURY PARK CA 91320
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet SC1402.PDF ] | |
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