LM27212 Datasheet, PDF (1/23 Pages) National Semiconductor (TI) – Two-Phase Current-Mode Hysteretic Buck Controller

March 2006
LM27212
Two-Phase Current-Mode Hysteretic Buck Controller
General Description
The LM27212 is a two-phase synchronous buck regulator
controller that is designed to support high-current loads such
as microprocessors.
The IC employs a two-phase current-mode hysteretic control
mechanism. During normal operation, the two switching
channels operate 180˚ out of phase, helping reduce the
number of input capacitors.
Inductor currents are sensed through low value sense resis-
tors. Current sharing between the two channels is automati-
cally guaranteed by multiplexing the feedback comparator.
The regulator input voltage range supported by the LM27212
is 5V to 30V. The output voltage is programmed through six
voltage identification pins and ranges from 0.700V to 1.708V
in 64 steps.
The IC provides accurate load-line characteristic. The regu-
lator can be programmed to lower its output voltage linearly
with increasing load current, so that the power generated by
the load can be significantly reduced.
Since the error in the output voltage directly sets the inductor
currents, the dynamic response to a large and fast load
transient is close to a square wave. This is optimal for
meeting CPU supply voltage specifications.
Due to the intrinsic input voltage feed forward characteristic
of a peak current-mode controller, the IC has a superior line
transient response.
The IC provides a cycle-by-cycle peak current limit, over-
voltage protection, and a power good signal.
The LM27212 fully supports the Stop CPU mode and Sleep
mode required by some mobile CPUs. In the Sleep mode,
the IC enters single-phase power-saving operation which
significantly enhances the light load efficiency.
The LM27212 also has a soft start pin for the external
adjustment of soft start speed.
The LM27212 combined with the LM27222 series of MOS-
FET drivers, provides a layout-friendly, thermally optimized
and noise-immune power solution for the mobile platform.
Features
n 5V to 30V input range
n Two channels operating 180˚ out of phase
n Ideal load and line transient responses
n Dynamic output voltage swing supported
n Excellent inductor current sharing
n High efficiency Sleep mode
n Soft start and soft shutdown
n Cycle-by-cycle current limit
n Adjustable over-voltage protection
n Accurate load-line supported
n ±1% reference over temperature
n On/off pin and power good signal
n TSSOP package or tiny LLP package
Applications
n Power Supply For Mobile CPUs
n Low Output Voltage Buck Regulators Up To 50A
Typical Application
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