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EVAL-ADM1067LFEB View Datasheet(PDF) - Analog Devices

Part Name
Description
MFG CO.
EVAL-ADM1067LFEB
ADI
Analog Devices ADI
'EVAL-ADM1067LFEB' PDF : 32 Pages View PDF
POWERING THE ADM1067
The ADM1067 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 Supply Supervision section). A
VDD arbitrator on the device chooses which supply to use. The
arbitrator can be considered an OR’ing of five 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
ADM1067 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 18. The capacitor has
another use during brownouts (momentary loss of power).
Under these conditions, when the input supply (VPn or VH)
dips transiently below VDD, the synchronous rectifier switch
immediately turns off so that it does not pull VDD down. The
VDD 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.
ADM1067
Note that when two or more supplies are within 100 mV of each
other, the supply that first takes control of VDD keeps control.
For example, if VP1 is connected to a 3.3 V supply, VDD 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.
VDDCAP
VP1
IN
OUT
4.75V
LDO
EN
VP2
IN
OUT
4.75V
LDO
EN
VP3
IN
OUT
4.75V
LDO
EN
VP4
IN
OUT
4.75V
LDO
EN
INTERNAL
VH
IN
OUT
DEVICE
4.75V
SUPPLY
LDO
EN
SUPPLY
COMPARATOR
Figure 18. VDD Arbitrator Operation
Rev. B | Page 13 of 32
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