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Número de pieza | SC2602 | |
Descripción | Synchronous Voltage Mode Controller | |
Fabricantes | Semtech Corporation | |
Logotipo | ||
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SC2602/SC2602A
Synchronous Voltage Mode Controller
for Distributed Power Supply Applications
POWER MANAGEMENT
Description
Features
The SC2602 and SC2602A are low-cost, full featured,
synchronous voltage-mode controllers designed for use
in single ended power supply applications where efficiency
is of primary concern. Synchronous operation allows for
the elimination of heat sinks in many applications. The
SC2602s are ideal for implementing DC/DC converters
needed to power advanced microprocessors in low cost
systems, or in distributed power applications where effi-
ciency is important. Internal level-shift, high-side drive
circuitry, and preset shoot-thru control, allows the use of
inexpensive N-channel power switches.
SC2602s features include temperature compensated
voltage reference, triangle wave oscillator and current
sense comparator circuitry. Power good signaling, shut-
down, and over voltage protection are also provided.
Synchronous operation for high efficiency (95%)
RDS(ON) current sensing
On-chip power good and OVP functions
Small size with minimum external components
Soft Start
Enable function
Applications
Microprocessor core supply
Low cost synchronous applications
Voltage Regulator Modules (VRM)
DDR termination supplies
Networking power supplies
Sequenced power supplies
The SC2602 operates at a fixed 200kHz and the
SC2602A at 500kHz, providing a choice for optimum
compromise between efficiency, external component size,
and cost.
Two SC2602s can be used together to sequence power up
of telecom systems. The power good of the first SC2602
connected to the enable of the second SC2602 makes
this possible.
Typical Application Circuit
Typical Distributed Power Supply
+5V
R1 R2
1k
PWRGD
0.1
OVP
C1
0.1 C2
0.1
R3
1k
R4
10 U1
SC2602
1 VCC
GND
2 PWRGD SS/SHDN
3 OVP
COMP
14
C3
13 0.1
4.99K
12
4 OCSET
SENSE
11
5
D1
MBR0520 6
PHASE
DRVH
BST H
BST L
10
9
7 PGND
DRVL
8
820pF
C4
1.0
SHDN
+12V
R5
3.9
R6
2.2
Figure 1.
+
VinC5 C6 C7 C8
10.0 680/6.3V 680/6.3V 680/6.3V
_ 5V
Q1
STP40NE
Q2
STP40NE
R8
124*
R7
127
L2u1H
+
C9
180/4V
C10
180/4V
C11
180/4V
C12
180/4V
C13
180/4V
Vout=2.5V
_*
NOTE:
*) Vout = 1.265 x (1+R8/R7)
Revision: October 13, 2004
1
www.semtech.com
1 page POWER MANAGEMENT
Block Diagram
SC2602/SC2602A
Theory of Operation
Synchronous Buck Converter
Pagriem-maroydVeCOpRuElspeowweidr tihs
provided by a synchronous,
modulated (PWM) controller.
volt-
This
section has all the features required to build a high effi-
ciency synchronous buck converter, including “Power
Good” flag, shut-down, and cycle-by-cycle current limit.
The output voltage of the synchronous converter is set
and controlled by the output of the error amplifier. The
external resistive divider reference voltage is derived from
an internal trimmed-bandgap voltage reference (See Fig.
1). The inverting input of the error amplifier receives its
voltage from the SENSE pin.
The internal oscillator uses an on-chip capacitor and
trimmed precision current sources to set the oscillation
frequency to 200kHz/500kHz. The triangular output of
the oscillator sets the reference voltage at the inverting
input of the comparator. The non-inverting input of the
comparator receives it’s input voltage from the error am-
plifier. When the oscillator output voltage drops below
the error amplifier output voltage, the comparator out-
put goes high. This pulls DL low, turning off the low-side
FET, and DH is pulled high, turning on the high-side FET
(once the cross-current control allows it). When the oscil-
lator voltage rises back above the error amplifier output
voltage, the comparator output goes low. This pulls DH
low, turning off the high-side FET, and DL is pulled high,
turning on the low-side FET (once the cross-current con-
trol allows it).
As SENSE increases, the output voltage of the error
amplifier decreases. This causes a reduction in the on-
time of the high-side MOSFET connected to DH, hence
lowering the output voltage.
Under Voltage Lockout
The under voltage lockout circuit of the SC2602 assures
that the high-side MOSFET driver outputs remain in the off
state whenever the supply voltage drops below set param-
eters. Lockout occurs if VCC falls below 4.1V. Normal opera-
tion resumes once VCC rises above 4.2V.
Over-Voltage Protection
The over-voltage protection pin (OVP) is high only when
the voltage at SENSE is 20% higher than the target value
programmed by the external resistor divider. The OVP pin
is internally connected to a PNP’s collector.
Power Good
The power good function is to confirm that the regulator
outputs are within +/-10% of the programmed level.
PWRGD remains high as long as this condition is met.
PWRGD is connected to an internal open collector NPN
transistor.
2004 Semtech Corp.
5
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5 Page POWER MANAGEMENT
Typical Characteristics (Cont.)
Math Cad Close Loop Stability Analysis
SC2602/SC2602A
Output Filter Schematic:
2004 Semtech Corp.
11
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11 Page |
Páginas | Total 16 Páginas | |
PDF Descargar | [ Datasheet SC2602.PDF ] |
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