LTM4622
9
Rev F
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OPERATION
APPLICATIONS INFORMATION
The LTM4622 is a dual output standalone non-isolated
switch mode DC/DC power supply. It can deliver two 2.5A
DC, 3A peak output current with few external input and
output ceramic capacitors. This module provides dual
precisely regulated output voltage programmable via
two external resistor from 0.6V to 5.5V over 3.6V to 20V
input voltage range. With INTV
CC
tied to V
IN
, this module
is able to operate from 3.3V input. The typical application
schematic is shown in Figure24.
The LTM4622 contains an integrated controlled on-time
valley current mode regulator, power MOSFETs, inductor,
and other supporting discrete components. The default
switching frequency is 1MHz. For output voltages between
2.5V and 5.5V, an external resistor is required between
FREQ and GND pins to set the operating frequency to
higher frequency to optimize inductor current ripple.
For switching noise-sensitive applications, the switch-
ing frequency can be adjusted by external resistors and
the μModule regulator can be externally synchronized
to a clock within ±30% of the set frequency. See the
Applications Information section.
With current mode control and internal feedback loop
compensation, the LTM4622 module has sufficient
stability 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 cur-
rent limiting. An internal overvoltage and undervoltage
comparators pull the open-drain PGOOD output low if
the output feedback voltage exits a ±8% window around
the regulation point. Furthermore, an input overvoltage
protection been utilized by shutting down both power
MOSFETs when V
IN
rises above 22.5V to protect internal
devices.
Multiphase operation can be easily employed by connect-
ing SYNC pin to an external oscillator. Up to 6 phases can
be paralleled to run simultaneously a good current sharing
guaranteed by current mode control loop.
Pulling the RUN pin below 1V forces the controller into
its shutdown state, turning off both power MOSFETs and
most of the internal control circuitry. At light load cur-
rents, Burst Mode operation can be enabled to achieve
higher efficiency compared to continuous mode (CCM) by
setting MODE pin to INTV
CC
. The TRACK/SS pin is used
for power supply tracking and soft-start programming.
See the Applications Information section.
The typical LTM4622 application circuit is shown in
Figure24. External component selection is primarily deter-
mined by the input voltage, the output voltage and the
maximum load current. Refer to Table7 for specific exter-
nal capacitor requirements for a particular application.
V
IN
to V
OUT
Step-Down Ratios
There are restrictions in the maximum V
IN
and V
OUT
step
down ratio that can be achieved for a given input voltage
due to the minimum off-time and minimum on-time limits
of the regulator. The minimum off-time limit imposes a
maximum duty cycle which can be calculated as
D
MAX
= 1 – t
OFF(MIN)
• f
SW
where t
OFF(MIN)
is the minimum off-time, 45ns typical for
LTM4622, and f
SW
is the switching frequency. Conversely
the minimum on-time limit imposes a minimum duty
cycle of the converter which can be calculated as
D
MIN
= t
ON(MIN)
• f
SW
where t
ON(MIN)
is the minimum on-time, 20ns typical for
LTM4622. In the rare cases where the minimum duty
cycle is surpassed, the output voltage will still remain
in regulation, but the switching frequency will decrease
from its programmed value. Note that additional thermal
derating may be applied. See the Thermal Considerations
and Output Current Derating section in this data sheet.
