Powering The Adm1168 - Analog Devices Super Sequencer ADM1168 Manual

ADM1168

POWERING THE ADM1168

The ADM1168 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
device chooses which supply to use. The arbitrator can be
considered an OR'ing of four 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 ADM1168 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 14. 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
, the synchronous rectifier switch immediately turns off
DD
so that it does not pull V down. The V
DD
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 value of the VDDCAP capacitor may be increased if it is
necessary to guarantee a complete fault record is written into
EEPROM should all supplies fail. The value of the capacitor to
use is discussed in the Black Box Writes with No External
Supply section.
The VH input pin can accommodate supplies up to 14.4 V, which
allows the ADM1168 to be powered using a 12 V backplane supply.
In cases where this 12 V supply is hot swapped, it is recommended
that the ADM1168 not be connected directly to the supply. Suitable
precautions, such as the use of a hot swap controller or RC filter
network, should be taken to protect the device from transients
that may cause damage during hot swap events.
arbitrator on the
DD
capacitor can then
DD
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When two or more supplies are within 100 mV of each other, the
supply that first takes control of V
VP1 is connected to a 3.3 V supply, V
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.
VP1
VP2
VP3
VH
SUPPLY
COMPARATOR
Figure 14. V
DD
keeps control. For example, if
DD
powers up to approximately
DD
VDDCAP
IN OUT
4.75V
LDO
EN
IN OUT
4.75V
LDO
EN
IN OUT
4.75V
LDO
EN
INTERNAL
IN OUT
DEVICE
SUPPLY
4.75V
LDO
EN
Arbitrator Operation