LTM4686BIVPBF datasheet(62/130 Pages) AD

62 / 130 page

LTM4686B

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

It is recommended that all command writes (write byte,

write word, etc.) be preceded with a polling loop to avoid

the extra complexity of dealing with busy behavior and

unwanted ALERT notification. A simple way to achieve this

is by creating SAFE_WRITE_BYTE() and SAFE_WRITE_

WORD() subroutines. The above polling mechanism

allows one’s software to remain clean and simple while

robustly communicating with the part. For a detailed dis-

cussion of these topics and other special cases please

refer to the Analog Devices Application Note section.

When communicating using bus speeds at or below

100kHz, the polling mechanism shown here provides a

simple solution that ensures robust communication with-

out clock stretching. At bus speeds in excess of 100kHz,

it is strongly recommended that the part be configured to

enable clock stretching. This requires a PMBus master that

supports clock stretching. System software that detects

and properly recovers from the standard PMBus NACK/

BUSY faults as described in the PMBus Specification v1.2,

Part II, Section 10.8.7 is required to communicate above

100kHz without clock stretching. Clock stretching will not

extend the PMBus speed beyond the specified 400kHz.

THERMAL CONSIDERATIONS AND

OUTPUT CURRENT DERATING

The thermal resistances reported in the Pin Configuration

section of this data sheet are consistent with those param-

eters defined by JESD51-12 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 performed on a

µModule package mounted to a hardware test board.

The motivation for providing these thermal coefficients

is 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 predict the µModule

regulator’s thermal performance in their application 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 this data sheet can be used in a man-

ner that yields insight and guidance pertaining to one’s

application-usage, and can be adapted to correlate thermal

performance to one’s own application.

The Pin Configuration section gives four thermal coeffi-

cients explicitly defined in JESD51-12; these coefficients

are quoted or paraphrased below:

1. θJA, the thermal resistance from junction to ambient, is

the natural convection junction-to-ambient air thermal

resistance measured in a one cubic foot sealed enclo-

sure. This environment is sometimes referred to as “still

air” although natural convection causes the air to move.

This value is determined with the part mounted to a

JESD51-9 defined test board, which does not reflect

an actual application or viable operating condition.

2. θJCbottom, the thermal resistance from junction to the

bottom of the product case, is determined with all of

the component power dissipation flowing through the

bottom of the package. In the typical µModule regulator,

the bulk of the heat flows out the bottom of the pack-

age, but there is always heat flow out into the ambient

environment. As a result, this thermal resistance value

may be useful for comparing packages but the test

conditions don’t generally match the user’s application.

3. θJCtop, the thermal resistance from junction to top of

the product case, is determined with nearly all of the

component power dissipation flowing through the top

of the package. As the electrical connections of the

typical µModule regulator are on the bottom of the

package, it is rare for an application to operate such

that most of the heat flows from the junction to the top

of the part. As in the case of θJCbottom, this value may

be useful for comparing packages but the test condi-

tions don’t generally match the user’s application.

4. θJB, the thermal resistance from junction to the printed

circuit board, is the junction-to-board thermal resis-

tance where almost all of the heat flows through the

bottom of the µModule regulator and into the board,

and is really the sum of the θJCbottom and the thermal

resistance of the bottom of the part through the solder

LTM4686BIVPBF 数据表(PDF) 62 Page - Analog Devices

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