Datasheet

ADM1062
Rev. C | Page 14 of 36
POWERING THE ADM1062
The ADM1062 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
arbitrator 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 ADM1062 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 21. 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 ADM1062 to be powered using a 12 V backplane supply.
In cases where this 12 V supply is hot swapped, it is recommended
that the ADM1062 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 approxi-
mately 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
4433-022
Figure 21. V
DD
Arbitrator Operation