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Features
GENERAL
4.5V to 30V input range
Power good function
Input under-voltage lockout
10 µA Shutdown/Recycle for entire chip
Thermal shutdown
TSSOP package
SWITCHING SECTION
Two synchronous buck regulators for fixed 5V/3.3V or adjustable outputs
Outputs adjustable from 1.3V to 5.5V
0.04% (typical) line and load regulation error
Selectable switching frequency 200/300 kHz
Two channels operating 180° out of phase
Separate on/off for each channel
Separate Power Good signals
Current mode control with or without sense resistor
Adjustable cycle-by-cycle current limit
Skip-mode operation available
Negative current limit
Separate soft start for each channel
Output UVP and OVP
Programmable output UVP delay
Self discharge of output capacitors when turned off
LINEAR SECTION
Adjustable (3.3V to 15V) linear regulator with external PNP pass transistor
±2% initial tolerance of set voltage
Output UVP for adjustable linear regulator
Fixed 3.3V/50mA output rail
Fixed 5V reference rail
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° 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 operation at light load achieves high efficiency over a wide load range.
Fixed-frequency operation can be obtained by disabling 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 (Channel
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 circuitry.
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 predictable 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 delayed.
Applications
Notebook and sub-notebook computers
Embedded computer systems
Battery-powered instruments
High end gaming systems
Set-top boxes
WebPAD
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