An external bias ranging 4.75V to 5.3V can
be connected to VCC/VDRV pin and power the device. This enhances the efficiency of the
converter because the VCC and VRDV power supply current now runs from this internal bias
instead of the internal LDO.
Considerations when using an external bias
on the VCC and VDRV pin are shown below
- Connect the external bias to VCC/VDRV
pin.
- When the external bias is applied on the
VCC/VDRV pin earlier than PVIN rail, the internal LDO is be always forced off and the
internal analog circuits have a stable power supply rail at their power enable.
- (Not recommended) When the external bias
is applied on the VCC/VRDV pin late (for example, after PVIN rail ramp-up), any power-up
and power-down sequencing can be applied as long as there is excess current pulled out of
the VCC/VDRV pin. Understand that an external discharge path on the VCC/VDRV pin, which
can pull a current higher than the current limit of the internal LDO, can potentially turn
off VCC LDO, thereby shutting off the converter output.
- A good power-up sequence is: The external
bias is applied first, then the 12V bus is applied on PVIN and then EN signal goes
high.