PM6670AS datasheet(30/54 Pages) STMICROELECTRONICS

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Device description

PM6670AS

30/54

7.1.4

Mode-of-operation selection

Figure 33. MODE and DDRSEL multifunction pin configurations

The PM6670AS has been designed to satisfy the widest range of applications involving

DDR2/3 memories, SSTL15-18 buses termination and I/O supplies for CPU/Chipset. The

device is provided with multilevel pins which allow the user to choose the appropriate

configuration. The MODE pin is used to firstly decide between fixed preset or adjustable

(user defined) output voltages.

When the MODE pin is connected to +5 V, the PM6670AS allows setting the VDDQ voltage

to 1.8 V or 1.5 V just forcing the DDRSEL multilevel pin to +5 V or to ground respectively

(see Figure 33a).

In this condition the Pulse-Skip feature is enabled. This device configuration is suitable for

standard DDR2/3 memory supply applications avoiding the need for an external, high

accuracy, divider for output voltage setting.

Applications requiring different output voltages can be managed by PM6670AS simply

setting the adjustable mode. If MODE pin voltage is higher than 4 V, the fixed output mode is

selected. Connecting an external divider to the MODE pin (Figure 33b), it is used as

negative input of the error amplifier and the output voltage is given by expression (21).

Equation 21

PM6670

DDRSEL

MODE

VDDQ

+5V

VREF

PM6670

DDRSEL

MODE

VDDQ

+5V

(a)

(b)

PM6670

DDRSEL

MODE

VDDQ

+5V

VREF

PM6670

DDRSEL

MODE

VDDQ

+5V

(a)

(b)

PM6670AS

VDDQ

ADJ

⋅

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