ADM1168ASTZ datasheet(13/28 Pages) AD

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ADM1168

Rev. 0 | Page 13 of 28

SUPPLY SUPERVISION WITH VXx INPUTS

The VXx inputs have two functions. They can be used as either

supply fault detectors or as digital logic inputs. When selected as

analog (SFD) inputs, the VXx pins have functionality that is very

similar to the VH and VPx pins. The primary difference is that the

VXx pins have only one input range: 0.573 V to 1.375 V. Therefore,

these inputs can directly supervise only the very low supplies.

However, the input impedance of the VXx pins is high, allowing

an external resistor divide network to be connected to the pin.

Thus, potentially any supply can be divided down into the input

range of the VXx pin and supervised. This enables the ADM1168

to monitor other supplies, such as +24 V, +48 V, and −5 V.

An additional supply supervision function is available when the

VXx pins are selected as digital inputs. In this case, the analog

function is available as a second detector on each of the dedicated

analog inputs, VPx and VH. The analog function of VX1 is mapped

to VP1, VX2 is mapped to VP2, and so on. VX4 is mapped to

VH. In this case, these SFDs can be viewed as secondary or

warning SFDs.

The secondary SFDs are fixed to the same input range as the

primary SFDs. They are used to indicate warning levels rather

than failure levels. This allows faults and warnings to be generated

on a single supply using only one pin. For example, if VP1 is set

to output a fault when a 3.3 V supply drops to 3.0 V, VX1 can be

set to output a warning at 3.1 V. Warning outputs are available

for readback from the status registers. They are also OR’ed together

and fed into the SE, allowing warnings to generate interrupts on

the PDOs. Therefore, in this example, if the supply drops to 3.1 V, a

warning is generated, and remedial action can be taken before

the supply drops out of tolerance.

VXx PINS AS DIGITAL INPUTS

As described in the Supply Supervision with VXX Inputs section,

the VXx input pins on the ADM1168 have dual functionality.

The second function is as a digital logic input to the device.

Therefore, the ADM1168 can be configured for up to four digital

inputs. These inputs are TTL-/CMOS-compatible inputs. Standard

logic signals can be applied to the pins: RESET from reset generators,

PWRGD signals, fault flags, manual resets, and more. These

signals are available as inputs to the SE and, therefore, can be used

to control the status of the PDOs. The inputs can be configured

to detect either a change in level or an edge.

When configured for level detection, the output of the digital

block is a buffered version of the input. When configured for

edge detection, a pulse of programmable width is output from

the digital block, when the logic transition is detected. The

width is programmable from 0 μs to 100 μs.

The digital blocks feature the same glitch filter function that is

available on the SFDs. This function enables the user to ignore

spurious transitions on the inputs. For example, the filter can be

used to debounce a manual reset switch.

When configured as digital inputs, each VXx pin has a weak

(10 μA) pull-down current source available for placing the input

into a known condition, even if left floating. The current source,

if selected, weakly pulls the input to GND.

DETECTOR

VXx

(DIGITAL INPUT)

GLITCH

FILTER

DIGITIAL THRESHOLD = 1.4V

SEQUENCING

ENGINE

–

Figure 17. VXx Digital Input Function

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