ADM1260 datasheet(16/71 Pages) AD

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ADM1260

Data Sheet

Rev. 0 | Page 16 of 71

INPUTS

SUPPLY SUPERVISION

The ADM1260 has 10 programmable inputs. Five of these inputs

are dedicated supply fault detectors (SFDs). These dedicated inputs

are VH and VPx (VP1 to VP4) by default. The other five inputs

are VXx (VX1 to VX5) and have dual functionality. These dual

function inputs can be used either as SFDs, with functionality

similar to that of VH and VPx, or as CMOS-/TTL-compatible

logic inputs to the device. Therefore, the ADM1260 can have up

to 10 analog inputs, a minimum of five analog inputs and five

digital inputs, or a combination thereof. If an input is used as an

analog input, it cannot be used as a digital input. Therefore, a

configuration requiring 10 analog inputs has no available digital

inputs. Table 6 shows the details of each input.

PROGRAMMING THE SUPPLY FAULT DETECTORS

The ADM1260 can have up to 10 SFDs on its 10 input channels.

These highly programmable reset generators enable the supervision

of up to 10 supply voltages. The supplies can be as low as 0.573 V

and as high as 14.4 V. The inputs can be configured to detect an

undervoltage fault (the input voltage drops below a preprogram-

med value), an overvoltage fault (the input voltage rises above a

preprogrammed value), or an out of window fault (the input

voltage is outside a preprogrammed range). The thresholds can

be programmed to an 8-bit resolution in registers provided in the

ADM1260. This 8-bit resolution translates to a voltage resolution

that is dependent on the range selected.

The resolution is given by

Step Size = Threshold Range/255

Therefore, if the high range is selected on VH, calculate the step

size as

(14.4 V − 6.0 V)/255 = 32.9 mV

Table 5 lists the upper and lower limits of each available range,

the bottom of each range (VB), and the range itself (VR).

Table 5. Voltage Range Limits

Voltage Range (V)

VB (V)

VR (V)

0.573 to 1.375

0.573

0.802

1.25 to 3.00

1.25

1.75

2.5 to 6.0

2.5

3.5

6.0 to 14.4

6.0

8.4

The threshold value required is given by

VT = (VR × N)/255 + VB

where:

VT is the desired threshold voltage (undervoltage or overvoltage).

VR is the voltage range.

N is the decimal value of the 8-bit code.

VB is the bottom of the range.

Reversing the equation, the code for a desired threshold is given by

N = 255 × (VT − VB)/VR

For example, if the user wants to set a 5 V overvoltage threshold

on VP1, the code to be programmed in the PS1OVTH register

is given by

N = 255 × (5 − 2.5)/3.5

Therefore, N = 182 (1011 0110 or 0xB6).

INPUT COMPARATOR HYSTERESIS

The undervoltage and overvoltage comparators shown in Figure 23

are always monitoring VPx. To avoid chatter (multiple transitions

when the input is very close to the set threshold level), these

comparators have digitally programmable hysteresis. The hysteresis

can be programmed up to the values shown in Table 6.

The hysteresis is added after a supply voltage goes out of

tolerance. Therefore, the user can program the amount above

the undervoltage threshold to which the input must rise before

an undervoltage fault is deasserted. Similarly, the user can program

the amount below the overvoltage threshold to which an input

must fall before an overvoltage fault is deasserted.

–

COMPARATOR

VREF

FAULT TYPE

SELECT

COMPARATOR

FAULT

OUTPUT

GLITCH

FILTER

VPx

MID

LOW

RANGE

SELECT

ULTRA

LOW

Figure 23. Supply Fault Detector Block

ADM1260 Datasheet(PDF) 16 Page - Analog Devices

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