PM8903A

Device description

Doc ID 024147 Rev 1

17/33

Caution:

Do not connect together the synchronization pin of two master devices in order to avoid any

damage to the ICs.

When two PM8903As are synchronized together they act as follows:

●

Master mode

The SYNCH pin is configured as clock output. The device provides, on the SYNCH pin,

its internal switching clock information with a 180 ° time shifting.

●

Slave mode

The SYNCH pin is configured as clock input. The device uses the clock information

received on the SYNCH pin to synchronize its internal switching clock.

5.7

Pulse-skipping

The PM8903A implements an ST proprietary adaptive pulse-skipping algorithm which

requires no configuration by the user and is independent from application setup and

parasites.

The algorithm allows to strongly increase the overall system efficiency skipping some

switching cycles (so reducing the equivalent switching frequency of the converter) when the

load current is low.

In many applications, MLCCs (multi layer ceramic capacitors) are used as the input or

output filter, or both. MLCCs can produce audible noise if the switching frequency is in the

human hearing range. To avoid audible noise, the PM8903A pulse-skipping algorithm limits

the minimum equivalent switching frequency above the audio band.

Pulse-skipping mode is enabled connecting a resistor between the PSKIP/MS pin and

ground, and selects the resistor value according to

Table 7.

5.8

Multifunction pin PSKIP/MS

With this pin it is possible to:

●

Enable/disable the pulse-skipping management

●

Assign to the IC master or slave status

●

Select the switching frequency.

functionality according to

Table 7.

Table 7.

PSKIP/MS pin configuration

Pulse-skipping

Synch mode

Switching frequency

0

Ω

Disabled

Slave

1.1 MHz

24 k

Ω

Enabled

Slave

1.1 MHz

56 k

Ω

Disabled

Slave

0.8 MHz

110 k

Ω

Disabled

Master

1.0 MHz

180 k

Ω

Enabled

Master

1.1 MHz

240 k

Ω

(or pin floating)

Disabled

Master

1.1 MHz