LTM4622A
14
Rev B
For more information
APPLICATIONS INFORMATION
From the equation, we could easily find out that, in the
coincident tracking, the slave regulator’s TRACK/SS pin
resistor divider is always the same as its feedback divider.
R
FB(SL)
R
FB(SL)
+ 60.4k
=
R
TR(BOT)
R
TR(TOP)
+R
TR(BOT)
For example, R
TR(TOP)
= 60.4k and R
TR(BOT)
= 13.3k is a
good combination for coincident tracking for V
OUT(MAX)
= 1.5V and V
OUT(SL)
= 3.3V application.
Power Good
The PGOOD pins are open drain pins that can be used to
monitor valid output voltage regulation. This pin monitors
a ±8% window around the regulation point. A resistor can
be pulled up to a particular supply voltage for monitoring.
To prevent unwanted PGOOD glitches during transients or
dynamic V
OUT
changes, the LTM4622A’s PGOOD falling
edge includes a blanking delay of approximately 40µs.
Stability compensation
The LTM4622A module internal compensation loop is
designed and optimized for low ESR ceramic output
capacitors only application. Table 7 is provided for most
application requirements. The LTpowerCAD Design Tool
is available to down for control loop optimization.
RUN Enable
Pulling the RUN pin to ground forces the LTM4622A into
its shutdown state, turning off both power MOSFETs and
most of its internal control circuitry. Trying the RUN pin
voltage above 1.27V will turn on the entire chip.
Pre-Biased Output Start-Up
There may be situations that require the power supply to
start up with a pre-bias on the output capacitors. In this
case, it is desirable to start up without discharging that
output pre-bias. The LTM4622A can safely power up into
a pre-biased output without discharging it.
The LTM4622A accomplishes this by forcing discontinuous
mode (DCM) operation until the TRACK/SS pin voltage
reaches 0.6V reference voltage. This will prevent the BG
from turning on during the pre-biased output start-up
which would discharge the output.
Overtemperature Protection
The internal overtemperature protection monitors the junc-
tion temperature of the module. If the junction temperature
reaches approximately 160°C, both power switches will be
turned off until the temperature drops about 15°C cooler.
Input Overvoltage Protection
In order to protect the internal power MOSFET devices
against transient voltage spikes, the LTM4622A constantly
monitors each V
IN
pin for an overvoltage condition. When
V
IN
rises above 22.5V, the regulator suspends operation
by shutting off both power MOSFETs on the correspond-
ing channel. Once V
IN
drops below 21.5V, the regulator
immediately resumes normal operation. The regulator
executes its soft-start function when exiting an overvolt-
age condition.
Thermal Considerations and Output Current Derating
The thermal resistances reported in the Pin Configura-
tion section of the data sheet are consistent with those
parameters defined by JESD51-9 and are intended for
use with finite element analysis (FEA) software modeling
tools that leverage the outcome of thermal modeling,
simulation, and correlation to hardware evaluation per-
formed on a µModule package mounted to a hardware test
board—also defined by JESD51-9 (Test Boards for Area
Array Surface Mount Package Thermal Measurements).
The motivation for providing these thermal coefficients in
found in JESD51-12 (Guidelines for Reporting and Using
Electronic Package Thermal Information).
Many designers may opt to use laboratory equipment
and a test vehicle such as the demo board to anticipate
the µModule regulator’s thermal performance in their ap-
plication at various electrical and environmental operating
conditions to compliment any FEA activities. Without FEA
