ISL98607

4. Application Information

FN8421 Rev.1.00

Page 18 of 29

Jun.3.19

4.13 Power-ON/OFF Sequence

The boost regulator is activated when the VIN input voltage is higher than the UVLO threshold, and either ENP or

ENN are HIGH. The VP output is activated if ENP is HIGH and VBST has completed its soft-start. The VN charge

pump is activated 2ms after VBST has completed soft-start, and the ENN has been pulled high, whichever comes

later (see Figure 17).

Figure 18 shows power-ON timing for the case when ENN is pulled HIGH after ENP, and after the VBST soft-start

is complete. Figure 19 shows power-ON timing for the case when ENN is pulled HIGH after ENP, but before

VBST has completed its soft-start.

ENP or ENN going LOW shuts down VP or VN, respectively. If both ENP and ENN are pulled low, VP, VN, and

VBST are all turned off even if VIN is still above UVLO, see Figure 20 on page 19. If VIN falls below UVLO while

ENP and ENN are high, VP, VN, and VBST are turned off at the same time (see Figure 21 on page 19).

Figure 17. Power-On Logic Operation

Figure 18. Power-On Sequence - ENN Rising After VP

Soft-Start Finished

Figure 19. Power-On Sequence - Both ENP and ENN

Rising Before VBST Soft-Start Finished

VIN > VUVLO

ENP

ENN

Activate VBST

VBST

Power-Good

Activate

VN

Activate VP

2ms Delay on

Rising Edge

VIN

UVLO

ENP

VBST

0.7ms

ENN

VBST

POWER-GOOD

VP

VN

0.7ms

0.7ms

2ms

VIN

UVLO

ENP

VBST

0.7ms

ENN

VBST

POWER-GOOD

VP

VN

0.7ms

0.7ms

2ms