Datasheet

ADM1166
Rev. 0 | Page 21 of 32
VOLTAGE READBACK
The ADM1166 has an on-board, 12-bit accurate ADC for
voltage readback over the SMBus. The ADC has a 12-channel
analog mux on the front end. The 12 channels consist of the
10 SFD inputs (VH, VPx, and VXx) and two auxiliary (single-
ended) ADC inputs (AUX1 and AUX2). 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 continuously. 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
09332-025
Figure 30. ADC Reading on VXx Pins
2.048V VREF
A
TTENU
A
TION NETWORK
(DEPENDS ON RANGE SELECTED)
12-BIT
ADC
DIGITIZED
VOLTAGE
READING
VPx/VH
09332-026
Figure 31. ADC Reading on VPx/VH Pins
The voltage at the input pin can be derived from the following
equation:
V =
4095
CodeADC
× Attenuation Factor × V
REFIN
where V
REFIN
= 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 6.0
1
6.0 to 14.4 10.472 0 to 14.4
1
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 ADM1166 has limit
registers with which the user can program a maximum or minimum
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 ADM1166
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 a 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 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
approximately 6 ms (500 μs per channel selected). Supervision
using the ADC, therefore, does not provide the same real-time
response as the SFDs.