ADM1063ACPZ datasheet(12/36 Pages) AD

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ADM1063

Rev. 0 | Page 12 of 36

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 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 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 VDD, the synchronous rectifier switch immediately turns

off so that it does not pull VDD down. The VDDCAP can then

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 VDD first keeps control.

For example, if VP1 is connected to a 3.3 V supply, then 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.

SUPPLY

COMPARATOR

OUT

4.75V

LDO

OUT

4.75V

LDO

OUT

4.75V

LDO

OUT

4.75V

LDO

OUT

4.75V

LDO

VP4

VP3

VP2

VP1

VDDCAP

INTERNAL

DEVICE

SUPPLY

Figure 21. VDD Arbitrator Operation

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