PM6670ASTR datasheet(19/54 Pages) STMICROELECTRONICS

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PM6670AS

Device description

19/54

Device description

The PM6670AS is designed to satisfy DDR2-3 power supply requirements combining a

synchronous buck controller, a 15 mA buffered reference and a high-current Low-Drop Out

(LDO) linear regulator capable of sourcing and sinking up to 2 Apk. The switching controller

section is a high-performance, pseudo-fixed frequency, Constant-On-Time (COT) based

regulator specifically designed for handling fast load transient over a wide range of input

voltages.

The DDR2-3 supply voltage VDDQ can be easily set to 1.8 V (DDR2) or 1.5 V (DDR3)

without additional components. The output voltage can also be adjusted in the 0.9 V to 2.6 V

range using an external resistor divider. The Switching Mode Power Supply (SMPS) can

handle different modes of operation in order to minimize noise or power consumption,

depending on the application needs.

A lossless current sensing scheme, based on the Low-Side MOSFET’s on resistance avoids

the need for an external current sense resistor.

The output of the linear regulator (VTT) tracks the memory’s reference voltage VTTREF

within ±30 mV over the full operating load conditions. The input of the LDO can be either

VDDQ or a lower voltage rail in order to reduce the total power dissipation. Linear regulator

stability is achieved by filtering its output with a ceramic capacitor

(20 µF or greater).

The reference voltage (VTTREF) section provides a voltage equal to one half of VSNS with

an accuracy of 1 %. This regulator can source and sink up to ±15 mA. A 10 nF to 100 nF

bypass capacitor is required between VTTREF and SGND for stability.

According to DDR2/3 JEDEC specifications, when the system enters the Suspend-To-RAM

state the LDO output is left in high impedance while VTTREF and VDDQ are still alive.

When the Suspend-To-Disk state (S3 and S5 tied to ground) is entered, all outputs are

actively discharged when either tracking or non-tracking discharge is selected.

PM6670ASTR データシート(PDF) 19 Page - STMicroelectronics