Datasheet

ADM1063
Rev. C | Page 13 of 32
POWERING THE ADM1063
The ADM1063 is powered from the highest voltage input on
either the positive-only supply inputs (VPx) or the high voltage
supply input (VH). This technique offers improved redundancy
because the device is not dependent on any particular voltage
rail to keep it operational. The same pins are used for supply
fault detection (see the Supply Supervision section). A V
DD
arbi-
trator on the device chooses which supply to use. The arbitrator
can be considered an OR’ing of five low dropout regulators (LDOs)
together. A supply comparator chooses the highest input to provide
the on-chip supply. There is minimal switching loss with this
architecture (~0.2 V), resulting in the ability to power the
ADM1063 from a supply as low as 3.0 V. Note that the supply
on the VXx pins cannot be used to power the device.
An external capacitor to GND is required to decouple the on-chip
supply from noise. This capacitor should be connected to the
VDDCAP pin, as shown in Figure 18. The capacitor has another
use during brownouts (momentary loss of power). Under these
conditions, when the input supply (VPx or VH) dips transiently
below V
DD
, the synchronous rectifier switch immediately turns
off so that it does not pull V
DD
down. The V
DD
capacitor can
then act as a reservoir to keep the device active until the next
highest supply takes over the powering of the device. A 10 μF
capacitor is recommended for this reservoir/decoupling function.
The VH input pin can accommodate supplies up to 14.4 V, which
allows the ADM1063 to be powered using a 12 V backplane supply.
In cases where this 12 V supply is hot swapped, it is recommended
that the ADM1063 not be connected directly to the supply. Suitable
precautions, such as the use of a hot swap controller, should be
taken to protect the device from transients that could cause
damage during hot swap events.
When two or more supplies are within 100 mV of each other,
the supply that first takes control of V
DD
keeps control. For
example, if VP1 is connected to a 3.3 V supply, V
DD
powers up
to approximately 3.1 V through VP1. If VP2 is then connected
to another 3.3 V supply, VP1 still powers the device, unless VP2
goes 100 mV higher than VP1.
SUPPLY
COMPARATOR
IN
EN
OUT
4.75V
LDO
IN
EN
OUT
4.75V
LDO
IN
EN
OUT
4.75V
LDO
IN
EN
OUT
4.75V
LDO
IN
EN
OUT
4.75V
LDO
VH
VP4
VP3
VP2
VP1
VDDCAP
INTERNAL
DEVICE
SUPPLY
0
4632-022
Figure 18. V
DD
Arbitrator Operation