Device description

PM8908

14/28

DocID027688 Rev 3

To properly supply the power section is advised following:



Bypass VIN pins to PGND pins as close as possible to the IC package with high quality

MLCC capacitors.



Connect the bootstrap capacitor (typically a 100 nF ceramic capacitor rated to stand

VIN voltage) from the BOOT pin to the PHASE pin to supply the HS driver.

Caution:

Do not connect an external bootstrap diode. The IC already integrates an active bootstrap

switch to charge the bootstrap capacitor, saving the cost of this external component.

The PM8908 embodies the anti shoot-through and adaptive deadtime control to minimize

low-side body diode conduction time and consequently to reduce power losses:



When the gate driving voltage of the HS drops (to check high-side MOSFET turn-off),

the LS MOSFET is suddenly switched on



When the gate driving voltage of the LS drops (to check low-side MOSFET turn-off),

the HS MOSFET is suddenly switched on.

5.2

Device configuration

switching frequency and the OCL threshold. This programming feature is performed by

selecting the proper resistor, to be mounted between the pin 18 to ground, as summarized

in Table 6.

Note:

The MODE pin must not be left floating.

5.3

Startup and shutdown management

The IC monitors the supply voltage on the VCC pin. Once VCC voltage is above the UVLO

(undervoltage lockout) threshold and the EN pin is above the turn-on threshold:



If the IC is configured for tracking application (see Figure 2 on page 4), the output

voltage is regulated to the REFIN voltage. In order to discriminate between the non-

tracking and the tracking, there is a delay time of 750

s required between the EN or

the VCC UVLO threshold and REFIN voltage. REFIN voltage must be applied within 9

ms (typ.) from the EN high (see Figure 5).



If the IC is configured for non-tracking application, the output voltage is regulated to the

REFIN voltage, and the device provides a precise 2.4 ms soft-start time (see Figure 6).

The power input (VIN) does not have a undervoltage protection function.

Table 6. Switching frequency and OCL (see Figure 1 on page 4)

OCL (A)

47 k



600

7.6

68 k



600

5.4

100 k



1000

5.4