ADM1065ACPZ(RevD) Просмотр технического описания (PDF) - Analog Devices
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ADM1065ACPZ Datasheet PDF : 28 Pages
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POWERING THE ADM1065
The ADM1065 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 VDD 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
ADM1065 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 15. The capacitor has another
use during brownouts (momentary loss of power). Under these
conditions, when the input supply (VPx 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.
The VH input pin can accommodate supplies up to 14.4 V, which
allows the ADM1065 to be powered using a 12 V backplane supply.
In cases where this 12 V supply is hot swapped, it is recommended
that the ADM1065 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.
ADM1065
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 15. VDD Arbitrator Operation
Rev. D | Page 11 of 28
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