ADM1069ACPZ datasheet(20/32 Pages) AD

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ADM1069

Rev. C | Page 20 of 32

VOLTAGE READBACK

The ADM1069 has an on-board, 12-bit, accurate ADC for voltage

readback over the SMBus. The ADC has an 8-channel analog

mux on the front end. The eight channels consist of the eight

SFD inputs (VH, VPx, and VXx). Any or all of these inputs can be

selected to be read, in turn, by the ADC. The circuit controlling

this operation is called the round-robin circuit. This circuit can be

selected to run through its loop of conversions once or conti-

nuously. Averaging is also provided for each channel. In this case,

the round-robin circuit runs through its loop of conversions

16 times before returning a result for each channel. At the end

of this cycle, the results are written to the output registers.

The ADC samples single-sided inputs with respect to the AGND

pin. A 0 V input gives out Code 0, and an input equal to the

voltage on REFIN gives out full code (4095 decimal).

The inputs to the ADC come directly from the VXx pins and from

the back of the input attenuators on the VPx and VH pins,

as shown in Figure 30 and Figure 31.

VXx

2.048V VREF

NO ATTENUATION

12-BIT

ADC

DIGITIZED

VOLTAGE

READING

Figure 30. ADC Reading on VXx Pins

2.048V VREF

ATTENUATION NETWORK

(DEPENDS ON RANGE SELECTED)

12-BIT

ADC

DIGITIZED

VOLTAGE

READING

VPx/VH

Figure 31. ADC Reading on VPx/VH Pins

The voltage at the input pin can be derived from the following

equation:

V =

4095

Code

ADC

× Attenuation Factor × VREFIN

where VREFIN = 2.048 V when the internal reference is used (that is,

the REFIN pin is connected to the REFOUT pin).

The ADC input voltage ranges for the SFD input ranges are

listed in Table 9.

Table 9. ADC Input Voltage Ranges

SFD Input

Range (V)

Attenuation

Factor

ADC Input Voltage

Range (V)

0.573 to 1.375

0 to 2.048

1.25 to 3.00

2.181

0 to 4.46

2.5 to 6.0

4.363

0 to 6.01

6.0 to 14.4

10.472

0 to 14.41

1 The upper limit is the absolute maximum allowed voltage on the VPx and

VH pins.

The typical way to supply the reference to the ADC on the

REFIN pin is to connect the REFOUT pin to the REFIN pin.

REFOUT provides a 2.048 V reference. As such, the supervising

range covers less than half the normal ADC range. It is possible,

however, to provide the ADC with a more accurate external

reference for improved readback accuracy.

Supplies can also be connected to the input pins purely for ADC

readback, even though these pins may go above the expected

supervisory range limits (but not above the absolute maximum

ratings on these pins). For example, a 1.5 V supply connected to

the VX1 pin can be correctly read out as an ADC code of approxi-

mately 3/4 full scale, but it always sits above any supervisory limits

that can be set on that pin. The maximum setting for the REFIN

pin is 2.048 V.

SUPPLY SUPERVISION WITH THE ADC

In addition to the readback capability, another level of supervision

is provided by the on-chip 12-bit ADC. The ADM1069 has limit

registers with which the user can program a maximum or mini-

mum allowable threshold. Exceeding the threshold generates a

warning that can either be read back from the status registers

or input into the SE to determine what sequencing action the

ADM1069 should take. Only one register is provided for each

input channel. Therefore, either an undervoltage threshold or

overvoltage threshold (but not both) can be set for a given channel.

The round-robin circuit can be enabled via an SMBus write, or

it can be programmed to turn on in any state in the SE program.

For example, it can be set to start after a power-up sequence is

complete, and all supplies are known to be within expected

tolerance limits.

Note that a latency is built into this supervision, dictated by the

conversion time of the ADC. With all 12 channels selected, the

total time for the round-robin operation (averaging off) is approx-

imately 6 ms (500 μs per channel selected). Supervision using

the ADC, therefore, does not provide the same real-time response

as the SFDs.

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