AD2S80: Maximum power consumption

Document created by analog-archivist Employee on Feb 23, 2016
Version 1Show Document
  • View in full screen mode

could you please advise the

Quiesecnt power consumption
Mean power consumption
Maximum power consumption

values for the above RDC


Maximum power consumption is the simplest so let me start with that:
Assuming maximum power supplies of +12V, -12V and +5V, the data sheet gives
values for the maximum current on each supply.

(24V x 23mA ) + (5V x 1.5mA) = 560mW

For supply voltages higher than +/-12V, you should assume the higher maximum
current of 30mA and recalculate the above equation.

Quiescent power consumption is not really a meaningful term for the AD2S80A
RDC. The converter is tracking converter (it continuously looks at the input
signal and uses feedback to null the error signal) and is therefore always
converting. In a Successive Approximation Register ADC, where the part is
sitting idle for most of the time consuming very little power, and only
consumes power when you request a conversion, quiescent current is meaningful.
In a tracking converter, the part never goes into a low power mode.

It is true that if the input shaft is idle and not turning, the part will
consume less power than when the input shaft is turned sharply to a new angle
and the converter must slew to the new angle consuming more instantaneous power
as it does so. However this is a dynamic effect and has not been characterized,
indeed it would be difficult to do in meaningful way and in any case the
difference in power consumption will be minimal and any effect should be
mitigated by power supply decoupling.

A similar argument will apply to average/mean power consumption. We do include
typical power specs on the datasheet, but these refer instead to differences in
power consumption due to part to part variation rather than power consumption
differences due to different operating conditions.

In short I suggest using the maximum power consumption throughout in your
calculations and assume that the power dissipation is essentially constant.
This will slightly over estimate the power consumption for most applications
but is has the benefit of being guaranteed by production testing. 

One final word. You will also see a maximum power dissipation spec  of 860mW in
the Absolute Maximum Ratings on page 5 of the datasheet. This refers to the max
power dissipation allowed by the package and is not an indication that the
AD2S80A will dissipate this much power under normal operation.