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ADM1069ASTZ Datasheet(PDF) 20 Page - Analog Devices

Part No. ADM1069ASTZ
Description  Super Sequencer with Margining Control
Download  32 Pages
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADM1069ASTZ Datasheet(HTML) 20 Page - Analog Devices

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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
1
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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