PM8908 datasheet, PDF - EEWORLD Datasheet

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PM8908: DescriptionMonolithic buck converter for DDR memory termination; File Size341KB，28 Pages; ManufacturerSTMicroelectronics; Websitehttp://www.st.com/

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PM8908 Overview

Monolithic buck converter for DDR memory termination

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PM8908

Monolithic buck converter for DDR memory termination

Datasheet

production data

Applications



Memory termination regulator for DDR3, DDR4

and low power DDR3/DDR4



Notebook/desktop/server

QFN20 3.5 x 4.0 mm



Low voltage application for 1 V to 3.5 V input

rails

Description

Features



Integrated MOSFETs for high efficiency



Current COT architecture



1 V to 3.5 V input voltage (V

)



5.0 V supply voltage (V

)



Constant frequency mode



1% output voltage accuracy



Two programmable switching frequencies

(0.6 MHz or 1 MHz)



ADJ output voltage from 0.5 V to 2 V



Embedded bootstrap diode



OV/UV/OC and overtemperature protection



Soft-off with integrated discharge resistor



External tracking



Power Good output



QFN20 3.5 x 4.0 mm compact package

The PM8908 is a high efficiency monolithic step-

down switching regulator designed mainly for the

DDR termination.

The IC operates from 1 V to 3.5 V input voltage

The device uses a COT control loop that provides

very good performances in terms of load and line

transients. The current sense is internally

thermally compensated for optimum precision.

The output voltage is adjusted from 0.5 V to 2 V

with ± 1% accuracy overtemperature variations.

The PM8908 also provides external tracking

support.

The PM8908 provides positive and negative

overcurrent protection as well as

over/undervoltage and overtemperature

protection. PGOOD output easily provides real-

time information on the output voltage.

The PM8908 is available in a QFN20

3.5 x 4.0 mm package.

Table 1. Device summary

Order code

PM8908TR

Package

QFN20 (3.5 x 4.0 mm)

Packaging

Tape and reel

November 2015

This is information on a product in full production.

DocID027688 Rev 3

1/28

www.st.com

Contents

PM8908

Contents

Typical application circuit and block diagram . . . . . . . . . . . . . . . . . . . . 4

1.1

1.2

Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Pin description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . . 6

Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.1

4.2

Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5.1

5.2

5.3

5.4

Power section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Device configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Startup and shutdown management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Soft-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Output voltage monitoring and protection . . . . . . . . . . . . . . . . . . . . . . . . 16

5.4.1

5.4.2

5.4.3

5.4.4

5.4.5

Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Undervoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Power Good (PGOOD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Overtemperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

6.1

6.2

6.3

6.4

6.5

6.6

6.7

Output voltage setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Droop setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Non-droop setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Output capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Input capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2/28

DocID027688 Rev 3

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