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ADM1063
POWERING THE ADM1063
The ADM1063 is powered from the highest voltage input on
either the positive-only supply inputs (VPn) 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 (discussed in the Programming the Supply Fault
Detectors section). A V
arbitrator on the device chooses
DD
which supply to use. The arbitrator can be considered an OR'ing
of five LDOs together. A supply comparator determines which
of the inputs is highest and selects it 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 VXn 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 (VPn or VH) dips transiently
below V
, the synchronous rectifier switch immediately turns
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off so that it does not pull V
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act as a reservoir to keep the device active until the next highest
supply takes over the powering of the device. For this
reservoir/decoupling function, 10 µF is recommended.
Note that when two or more supplies are within 100 mV of each
other, the supply that takes control of V
For example, if VP1 is connected to a 3.3 V supply, then V
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.
down. The VDDCAP can then
first keeps control.
DD
DD
VP1
VP2
VP3
VP4
VH
Rev. 0 | Page 12 of 36
IN
OUT
4.75V
LDO
EN
IN
OUT
4.75V
LDO
EN
IN
OUT
4.75V
LDO
EN
IN
OUT
4.75V
LDO
EN
IN
OUT
4.75V
LDO
EN
SUPPLY
COMPARATOR
Figure 21. V
Arbitrator Operation
DD
VDDCAP
INTERNAL
DEVICE
SUPPLY
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