PM6675AS datasheet(26/48 Pages) STMICROELECTRONICS

26 / 48 page

Device description

PM6675AS

26/48

7.1.4

Mode-of-operation selection

Figure 29.

VSEL and NOSKIP multifunction pin configurations

The PM6675AS has been designed to satisfy the widest range of applications. The device is

provided of some multilevel pins which allow the user to choose the appropriate

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

(user defined) output voltages.

When the VSEL pin is connected to +5 V, the PM6675AS set the switching section output

voltage to 1.5 V without the need of an external divider.

Applications requiring different output voltages can be managed by PM6675AS simply

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

mode is selected. Connecting an external divider to the VSEL pin, it is used as negative

input of the error amplifier and the output voltage is given by expression (20).

Equation 20

The output voltage can be set in the range from 0.6 V to 3.3 V.

The NOSKIP is the power saving algorithm selector: if tied to +5 V, the forced-PWM (fixed

frequency) control is performed. If grounded or connected to VREF pin (1.237 V reference

voltage), the Pulse-Skip or Non-Audible Pulse-Skip Modes are respectively selected.

Table 8.

Mode-of-operation settings summary

VSEL

NOSKIP

VOUT

Operating mode

VVSEL > 4.3V

VNOSKI P > 4.2 V

1.5 V

Forced-PWM

1V < VNOSKIP < 3.5 V

Non-Audible Pulse-skip

< 0.5 V

Pulse-Skip

VVSEL < 3.7V

VNOSKIP > 4.2 V

ADJ

Forced-PWM

1 V < VNOSKIP < 3.5 V

Non-Audible Pulse-skip

VNOSKIP < 0.5 V

Pulse-Skip

PM6675AS

NOSKIP

VSEL

VOUT

+5V

VREF

VOUTADJ

⋅

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