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LTM4632

4632fc

For more information www.linear.com/LTM4632

APPLICATIONS INFORMATION

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 VOUT changes, the LTM4632’s PGOOD falling

edge includes a blanking delay of approximately 40μs.

Stability Compensation

The LTM4632 module internal compensation loop is

de-signed and optimized for low ESR ceramic output

capacitors only application. Table 5 is provided for most

application requirements. The LTpowerCAD Design Tool is

available to download for control loop analysis for further

optimization.

RUN Enable

Pulling the RUN pin to ground forces the LTM4632 into

its shutdown state, turning off both power MOSFETs and

most of its internal control circuitry. Tying the RUN pin

voltage above 1.28V will turn on the entire chip.

Low Input Application

The LTM4632 is capable to run from 3.3V input when

the VIN pin is tied to INTVCC pin. See Figure 21 for the

application circuit. Please note the INTVCC pin has 3.6V

ABS max voltage rating.

Pre-Biased Output Start-Up (Channel 1)

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 LTM4632 channel 1 can safely power

up into a pre-biased output without discharging it.

The LTM4632 accomplishes this by forcing discontinuous

mode (DCM) operation until the TRACK/SS1 pin voltage

reaches 80% of the 0.6V reference voltage for channel 1.

This will prevent the BG from turning on during the pre-

biased output start-up which would discharge the out-

put. Do not pre-bias LTM4632 with a voltage higher than

INTVCC (3.3V) voltage.

Overtemperature Protection

The internal overtemperature protection monitors the

junction temperature of the module. If the junction

temperature reaches approximately 170°C, both power

switches will be turned off until the temperature drops

about 10°C cooler.

Input Overvoltage Protection

In order to protect the internal power MOSFET devices

against transient voltage spikes, the LTM4632 constantly

monitors each VIN pin for an overvoltage condition. When

VIN rises above 17.5V, the regulator suspends operation

by shutting off both power MOSFETs on the correspond-

ing channel. Once VIN drops below 16.5V, 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 Configuration

section of the data sheet are consistent with those param-

eters 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 appli-

cation at various electrical and environmental operating

conditions to compliment any FEA activities. Without

FEA software, the thermal resistances reported in the

Pin Configuration section are in-and-of themselves not

relevant to providing guidance of thermal performance;

instead, the derating curves provided in the data sheet can

be used in a manner that yields insight and guidance per-

taining to one’s application-usage, and can be adapted to

correlate thermal performance to one’s own application.

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