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PDF SC2463 Data sheet ( Hoja de datos )
| Número de pieza | SC2463 | |
| Descripción | High Performance Quad Output Switching Regulator | |
| Fabricantes | Semtech | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de SC2463 (archivo pdf) en la parte inferior de esta página. Total 23 Páginas | ||
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POWER MANAGEMENT
Description
The SC2463 is a high performance controller for multi-
output converters that can be configured for a wide vari-
ety of applications. The SC2463 utilizes PWM synchro-
nous buck topologies where efficiency is most important.
It also provides two dedicated programmable positive
linear regulators using external transistors. Each of the
four outputs is adjustable down to 0.5V. The two PWM
switchers are synchronized 180° out of phase reducing
input ripple, allowing for fewer input capacitors. Power
up sequencing prevents converter latch-up.
The SC2463 can be synchronized to other converters to
prevent beat frequencies. The wide range programmable
operating frequency allows users to optimize a converter
design. The PWM switchers sense the voltage across the
low-side MOSFETs on-resistance to efficiently provide
adjustable current-limit, eliminating costly current-sense
resistors. A POK signal is issued when soft-start is com-
plete on both PWM switchers and their outputs are within
10% of the set point.
Typical Application Circuit
SC2463
High Performance Quad Output
Switcwhwiwn.DgataRSheeegt4uU.cloamtor
Features
Two synchronized converters for low noise
Power up sequencing to prevent latch-up
Out of phase operation for low input ripple
Over current protection
Wide input range, 4.5 to 30V
Programmable frequency up to 700kHz
Low shutdown current 100uA
Two synchronous bucks for high efficiency at high
current
Two programmable positive linear regulators
Output voltage as low as 0.5V
Small package TSSOP-28. This product is fully
WEEE and RoHS compliant
Applications
DSL applications with multiple input voltage
requirements
Mixed-Signal applications requiring 4 positive
output voltages
Cable modem power management
Base station power management
+4.5-30V
Q1 R1
C2
C1
C3
R3
+3.3V
+2.5V
+1.2V
C4
C10
Q4
C6
R4
R7
6 SS/SHDN
9 OSC
7 SY NC
8 POK
4 BD4
C14
5 FB4
R9
R10
11 BD3
C17
Q7
R11
10 FB3
C18
C16 R14
U1 D1 D2
SC2463
BST2
GD2H
PH2
GD2L
FB2
EO2
BST1
GD1H
PH1
GD1L
FB1
EO1
17
18
19
20
13
12
26
25
24
23
2
3
C7
R8 C11
C12
C13
C19
Q2
Q3
Q5
Q6
C20
R15
R16 R17
L1
L2
R18
+3.3V
C8 R5 (as low as 0.5V)
R6
+1.5V
C15 (as low as 0.5V)
R12
R13
Revision: May 16, 2007
1
www.semtech.com
1 page  
SC2463
POWER MANAGEMENT
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Electrical Characteristics (Cont.)
Unless specified:
V = 12V, PVCC = AVCC = 5V, fs = 600KHz, SS/SHDN = 5V, SYNC = 0V,
IN
TA
=
T
J
=
-40°C
to
105°C
Parameter
Test Conditions
Min Typ Max Units
Thermal Protection
Thermal Shutdown Temperature
150 °C
Thermal Shutdown Hysteresis
15 °C
Notes:
(1) Guaranteed by design.
(2) This device is ESD sensitive. Use of standard ESD handling precautions is required.
2007 Semtech Corp.
5
www.semtech.com
5 Page 
SC2463
POWER MANAGEMENT
Applications Information (Cont.)
Shoot through control circuitry provides a 30ns dead time
to ensure both the upper and lower MOSFET will not turn
on simultaneously and cause a shoot through condition.
Error Amplifier and PWM Controller
In closed loop operation, the internal oscillator ramp
ranges from 0.75V to 3.8V. The error amplifier output
ranges determines duty-ratio of a converter. The synchro-
nous continuous-conduction mode of operation allows
the SC2463 to regulate the output irrespective of the
direction of the load current.
The SC2463 uses voltage-mode control for good noise
immunity and ease of compensation. The low-side
MOSFET of each channel is turned off at the falling-edge
of the phase timing clock. After a brief non-overlapping
time interval of 30ns, the high-side MOSFET is turned
on. The phase inductor current ramps up. When the in-
ternal ramp reaches the threshold determined by the
error amplifier output, the high-side MOSFET is turned
off. As long as phase voltage collapses below 1.5V, the
low-side MOSFET is turned on.
Buck Converter
Buck converter design includes the following specifica-
tions:
Input voltage range: Vin ∈ [Vin,min , Vin,max ]
Input voltage ripple
Output voltage: Vo
(peak-to-peak):
∆Vin
Output voltage accuracy: ε
Output voltage ripple (peak-to-peak): ∆Vo
Nominal output (load) current:
Maximum output current limit:
IIoo,max
Output (load) current transient slew rate: dIo (A/s)
Circuit efficiency: η
Selection criteria and design procedures for the
following are described:
1) output inductor (L) type and value
2)
3)
ionuptuptutcacpaapcaictoitror(C(iCn)o)tytpypeeaannddvavlauluee
4) power MOSFETs
5) current sensing and limiting circuit
6) voltage sensing circuit
7) loop compensation network
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Operating Frequency (fs)
The switching frequency in the SC2463 is user-
programmable. The advantages of using constant
frequency operation are simple passive component
selection and ease of feedback compensation. Before
setting the operating frequency, the following trade-offs
should be considered:
1) Passive component size
2) Circuitry efficiency
3) EMI condition
4) Minimum switch on time and
5) Maximum duty ratio
For a given output power, the sizes of the passive
components are inversely proportional to the switching
frequency, whereas MOSFET/Diode switching losses are
proportional to the operating frequency. Other issues
such as heat dissipation, packaging and the cost issues
are also to be considered. The frequency bands for
signal transmission should be avoided because of EM
interference.
Minimum Switch On Time Consideration
In the SC2463, the falling edge of the clock turns on
the top MOSFET. The inductor current and the sensed
voltage ramp up. After the internal ramp voltage crosses
a threshold determined by the error amplifier output,
the top MOSFET is turned off. The propagation delay
time from the turn-on of the controlling FET to its turn-
off is the minimum switch on time. The SC2463 has a
minimum on time of about 50ns at room temperature.
This is the shortest on interval of the controlling FET.
The controller either does not turn on the top MOSFET
at all or turns it on for at least 50ns.
For a synchronous step-down converter, the operating
duty cycle is VO/VIN. So the required on time for the top
MOSFET is VO/(VINfs). If the frequency is set such that
the required pulse width is less than 50ns, then the
converter will start skipping cycles. Due to minimum on
time limitation, simultaneously operating at very high
switching frequency and very short duty cycle is not
practical. If the voltage conversion ratio VO/VIN and
hence the required duty cycle is higher, the switching
frequency can be increased to reduce the size of passive
components.
2007 Semtech Corp.
11
www.semtech.com
11 Page | ||
| Páginas | Total 23 Páginas | |
| PDF Descargar | [ Datasheet SC2463.PDF ] | |
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