LM2648 National Semiconductor, LM2648 Datasheet
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LM2648
Manufacturer Part Number
LM2648
Description
Synchronous Step-Down 3-Channel Switching Regulator Controller
Manufacturer
National Semiconductor
Datasheet
1.LM2648.pdf
(23 pages)
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© 2004 National Semiconductor Corporation
LM2648
Two-Phase, Synchronous Step-Down 3-Channel
Switching Regulator Controller
General Description
The LM2648 consists of two current mode and two voltage
mode synchronous buck regulator controllers providing 3
outputs at a switching frequency of 300kHz.
Each pair of 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 current mode regulator outputs operate as a dual-
phase, single output regulator for high current applications.
Current-mode feedback control on Channel 3 assures supe-
rior line and load regulation and wide loop bandwidth as-
sures excellent response to fast load transients. Channels 1
and 2 employ voltage-mode feedback control.
The LM2648 features analog soft-start circuitry that is inde-
pendent of the output load and output capacitance. This
makes the soft-start behavior more predictable than tradi-
tional soft-start circuits. Sequential startup is built in and
requires a single capacitor to set the timing.
The LM2648 has over-voltage protection and under-voltage
protection for all outputs. Two additional comparator inputs
(analog and logic level) are provided to shut down the IC for
any user defined protection. The FAULT_DELAY pin allows
delayed shut off time for the IC during an under-voltage or
PROT-IN2 fault. The LM2648 also features an adjustable
UVLO feature.
Block Diagram
DS200596
Features
n Four synchronous buck regulators
n Channel 3: Two-phase, current mode controller
n 4.5V to 18V input range
n Built in sequential startup
n Channels 1 and 2: Independent, 180˚ out of phase
n Single soft start for channels 1 and 2
n Adjustable cycle-by-cycle current limit for each channel
n Adjustable reference current
n Adjustable input under-voltage lockout
n Output over-voltage latch protection
n Output under-voltage protection with delay
n Two comparator inputs for user defined protection - one
n Thermal shutdown
n Self-discharge of output capacitors when the regulator is
n TSSOP package
Applications
n Embedded Computer Systems
n Interactive Games
n Set-top Boxes/Home Gateways
voltage mode controllers
with delay
off
20059690
December 2004
www.national.com