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LM2645 Datasheet

  • LM2645

  • Advanced Two-Phase Switching Controller With Two Linear Outp...

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LM2645 Advanced Two-Phase Switching Controller With Two Linear Outputs
April 2001
LM2645
Advanced Two-Phase Switching Controller With Two
Linear Outputs
General Description
The LM2645 is a feature-rich IC that combines two current
mode synchronous buck regulator controllers, an adjustable
linear regulator controller and a fixed 3.3V standby output
rail.
The two switching regulator controllers operate 180藲 out of
phase. This feature reduces the input ripple RMS current,
thereby significantly reducing the required input capacitance.
The two switching regulator outputs can also be paralleled to
operate as a dual-phase regulator.
The use of synchronous rectification and pulse-skip opera-
tion at light load achieves high efficiency over a wide load
range. Fixed-frequency operation can be obtained by dis-
abling the pulse-skip mode. The switching frequency of the
LM2645 is user selectable between 200 kHz or 300 kHz.
The first switching controller (Channel 1) features a fixed 5V
output, and the second switching controller controller (Chan-
nel 2) features a fixed 3.3V output. Both channels can also
be independently adjusted from 1.3 to 5.5V. The adjustable
linear regulator can be adjusted from 3.3V to 15V. An internal
5V rail is also available externally for driving bootstrap cir-
cuitry. This rail also serves as the input for an internal LDO
that provides the fixed 3.3V/50mA output rail.
Current-mode feedback control assures excellent line and
load regulation and a wide loop bandwidth for excellent
response to fast load transients. Current is sensed across
either the Vds of the top FET or across an external sense
resistor connected in series with the drain of the top FET.
Current limit is independently adjustable for each channel.
The analog soft-start for the switching controllers uses an
innovative new approach. It is independent of the input
voltage which makes the soft-start behavior more predict-
able and controllable.
Independant PGOOD signals monitor each of the switching
regulator outputs. The switching outputs have under-voltage
and over-voltage latch protection, while the output of the
external linear regulator has undervoltage latch protection.
The undervoltage latch can be disabled or adjustably de-
layed.
Features
GENERAL
n
4.5V to 30V input range
n
Power good function
n
Input under-voltage lockout
n
10 碌A(chǔ) Shutdown/Recycle for entire chip
n
Thermal shutdown
n
TSSOP package
SWITCHING SECTION
n
Two synchronous buck regulators for fixed 5V/3.3V or
adjustable outputs
n
Outputs adjustable from 1.3V to 5.5V
n
0.04% (typical) line and load regulation error
n
Selectable switching frequency 200/300 kHz
n
Two channels operating 180藲 out of phase
n
Separate on/off for each channel
n
Separate Power Good signals
n
Current mode control with or without sense resistor
n
Adjustable cycle-by-cycle current limit
n
Skip-mode operation available
n
Negative current limit
n
Separate soft start for each channel
n
Output UVP and OVP
n
Programmable output UVP delay
n
Self discharge of output capacitors when turned off
LINEAR SECTION
n
Adjustable (3.3V to 15V) linear regulator with external
PNP pass transistor
n
鹵
2% initial tolerance of set voltage
n
Output UVP for adjustable linear regulator
n
Fixed 3.3V/50mA output rail
n
Fixed 5V reference rail
Applications
n
n
n
n
n
n
Notebook and sub-notebook computers
Embedded computer systems
Battery-powered instruments
High end gaming systems
Set-top boxes
WebPAD
漏 2001 National Semiconductor Corporation
DS200159
www.national.com

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