Datasheet

LTM4637
9
4637fc
For more information www.linear.com/LTM4637
Decoupling reQuireMenTs
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
C
IN
External Input Capacitor Requirement
(V
IN
= 4.5V to 20V, V
OUT
= 1.5V)
I
OUT
= 20A, 4× 22µF Ceramic X7R Capacitors
(See Table 5)
88 µF
C
OUT
External Output Capacitor Requirement
(V
IN
= 4.5V to 20V, V
OUT
= 1.5V)
I
OUT
= 20A (See Table 5) 400 µF
T
A
= 25°C. Use Figure 1 configuration.
Power Module Description
The LTM4637 is a high performance single output stand-
alone nonisolated
switching mode DC/DC power supply.
It can provide a 20A output with few external input and
output capacitors. This module provides precisely regu
-
lated output voltages programmable via external resistors
from 0.6V
DC
to 5.5V
DC
over a 4.5V to 20V input range.
The typical application schematic is shown in Figure 22.
The LTM4637 has an integrated constant-frequency cur
-
rent mode regulator, power MOSFETs, 0.6µH inductor,
and other supporting discrete components. The switching
frequency range is from 250kHz to 770kHz, and the typical
operating frequency is shown in Table 5 for each V
OUT
. For
switching noise-sensitive applications, it can be externally
synchronized from 250kHz to 800kHz, subject to minimum
on-time limitations. A single resistor is used to program
the frequency. See the Applications Information section.
With current mode control and internal
feedback loop
compensation,
the LTM4637 module has sufficient stabil-
ity margins
and good transient performance with a wide
range
of output capacitors, even with all ceramic output
capacitors.
Current mode control provides cycle-by-cycle fast current
limit in an overcurrent condition. An internal overvoltage
monitor protects the output voltage in the event of an
overvoltage >10%. The top MOSFET is turned off and the
bottom MOSFET is turned on until the output is cleared.
Overtemperature protection will turn off the regulator’s
RUN pin at ~130°C to 137°C. See Applications Information.
operaTion
Pulling the RUN pin below 1.1V forces the regulator into a
shutdown state. The TRACK/SS pin is used for program-
ming the
output voltage ramp and voltage tracking during
start-up. See the Application Information section.
The
LTM4637 is internally compensated to be stable over
all operating conditions. Table 5 provides a guideline for
input and output capacitances for several operating condi
-
tions. L
TpowerCAD™ is available for transient and stability
analysis.
The V
FB
pin is used to program the output voltage
with a single external resistor to ground.
A remote sense amplifier is provided for accurately sensing
output voltages ≤3.3V at the load point.
Multiphase operation can be easily employed with the
synchronization inputs using an external clock source.
See application examples.
High efficiency at light loads can be accomplished with
selectable Burst Mode operation using the MODE_PLLIN
pin. These light load features will accommodate battery
operation. Efficiency graphs are provided for light load op
-
eration in
the Typical Performance Characteristics section.
A
TEMP pin is provided to allow the internal device tem-
perature to
be
monitored using an onboard diode connected
PNP transistor. This diode connected PNP transistor is
grounded in the module and can be used
as a general
temperature
monitor using a device that is designed to
monitor the single-ended connection.