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AN-1135
Application Note
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ADC Sampling Information ADM1275/ADM1276/ADM1075
by Paul O’Sullivan
Rev. 0 | Page 1 of 4
INTRODUCTION
The ADM1275, ADM1276, and ADM1075 all share the same
basic analog-to-digital converter (ADC) core and PMBus inter-
face. There are some subtle differences between the devices with
regard to averaging calculations and ADC register updates. There
are also factors and limitations to consider when reading data
quickly from any of the ADM1275, ADM1276, or ADM1075
devices. This document describes the ADC operation for each
of these devices and describes how to maximize the data rate
from each device, if required.
ADC CONVERSIONS
The ADM1275 features current and voltage readback via the
PMBus interface. Figure 1 shows the sampling order. The current
is sampled first, followed by a current register update. Then, the
voltage is sampled followed by a voltage register update. The
register update completes in one clock cycle. On the ADM1275,
the user can select whether to monitor the VIN voltage or the
VOUT voltage but cannot monitor both at the same time.
Figure 1. ADM1275 ADC Updates, Single Sample
Figure 2 shows the current and voltage conversions and updates
in the case where averaging is enabled on the device. The current
register updates after the final current sample; the voltage register
updates after the final voltage sample. Again, the voltage con-
version corresponds to VIN or VOUT.
Figure 2. ADM1275 ADC Updates, Device Averaging
The ADM1276 and ADM1075 both have power metering as
well as voltage and current monitoring. The power is calculated
as VIN × I; therefore, the VIN voltage is always sampled. The
user can opt to sample another ADC voltage input, as well. In
the case of the ADM1276, the VOUT voltage can be measured.
After the power calculation is complete, all of the voltage, current,
power, and energy registers update. See Figure 3 for details.
Figure 3. ADM1276 ADC Updates, Single Sample
As shown in Figure 4, when averaging is enabled, a single power
and energy calculation is completed following the last voltage
and current samples. After these calculations complete, all of
the registers update.
Figure 4. ADM1276 ADC Updates, Device Averaging
The ADM1075 is very similar to the ADM1276. The order of
current and voltage conversions is the same. The main difference
between them is that the VOUT measurement on the ADM1276
is a VAUX measurement on the ADM1075, as shown in Figure 5
and Figure 6
.
Figure 5. ADM1075 ADC Updates, Single Sample
Figure 6. ADM1075 ADC Updates, Device Averaging
I V
UI UV
UI = UPDATE CURRENT
UV = UPDATE VOLTAGE
10384-001
II I I VV V V ....
UI UV
10384-002
VIN I
VIN × IIVIN
VOUT DISABLED
VOUT ENABLED
VIN × IVOUT
UI/UV
UP/UE
UP = UPDATE POWER
UE = UPDATE ENERGY
10384-003
VIN × IIII VINVINVIN ....
VIN × III VOUTVOUT VINVIN ....
VOUT DISABLED
VOUT ENABLED
UI/UV
UP/UE
10384-004
VIN I
VIN × IIVIN
VAUX DISABLED
VAUX ENABLED
VIN × IVAUX
UI/UV
UP/UE
UP = UPDATE POWER
UE = UPDATE ENERGY
10384-005
VIN × IIII VINVIN ....
VIN × II
VIN
I VAUXVAUX VINVIN ....
VAUX DISABLED
VAUX ENABLED
UI/UV
UP/UE
10384-006
