XRP7720 Datasheet, PDF (25/28 Pages) Exar Corporation – Quad Output Universal Customizable PMIC with PFM

XRP7720
Quad Output Universal Customizable PMIC with PFM
ENABLING XRP7720
XRP7720 has a weak internal pull-up ensuring
it gets enabled as soon as internal voltage
supplies have ramped up and are in
regulation.
Driving the Enable pin low externally will keep
the controller in the shut-down mode. A
simple open drain pull down is the
recommended way to shut the XRP7720
down.
If the Enable pin is driven high externally to
control the XRP7720 coming out of the shut-
down mode care must be taken to ensure the
Enable pin is driven high after Vcc gets
supplied to the controller.
In the configuration, when Vcc = LDO5 =
4.75V to 5.5V, disabling the device by
grounding the Enable pin is not
recommended. It is recommended to leave
the Enable pin floating and place the
controller in the “Standby Mode” instead in
this scenario. The standby mode is defined as
the state when all switching channels are
disabled, all GPIO/PSIOs are programmed as
inputs, and system clock is disabled. In this
state chip consumes 440uA typical.
Short duration Enable pin toggled low
Short duration shutdown pulses to the
ENABLE pin of the XRP7720, which does not
provide sufficient time for the LDO5 voltage
to fall below 3.5V, can result in significant
delay in re-enabling of the device. Some
examples below show LDO5 and ENABLE
pins:
No load on LDO5, blue trace. Recovery time
after ENABLE logic high is approximately
40ms.
Adding a 200 ohm load on LDO5 pulls voltage
below 3.5V and restart is short.
Note that as VCC increases, the restart time
falls as well. 5.5V input is shown as the worst
case.
Since the ENABLE pin has an internal current
source, a simple open drain pull down is the
recommended way to shut down the
XRP7720. A diode in series with a resistor
between the LDO5 and ENABLE pins may
offer a way to more quickly pull down the
LDO5 output when the ENABLE pin is pulled
low.
© 2014 Exar Corporation
25/28
Rev. 1.0.0