LMP90100_16 Datasheet, PDF (63/74 Pages) Texas Instruments – Sensor AFE System: Multichannel, Low-Power, 24-Bit Sensor AFE

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11 Power Supply Recommendations
LMP90100, LMP90099, LMP90098, LMP90097
SNAS510S – JANUARY 2011 – REVISED JANUARY 2016
11.1 VA and VIO
Any ADC architecture is sensitive to spikes on the analog voltage, VA, digital input/output voltage, VIO, and
ground pins. These spikes may originate from switching power supplies, digital logic, high power devices, and
other sources. To diminish these spikes, the LMP90xxx’s VA and VIO pins should be clean and well bypassed. A
0.1 µF ceramic bypass capacitor and a 1 µF tantalum capacitor should be used to bypass the LMP90xxx
supplies, with the 0.1 µF capacitor placed as close to the LMP90xxx as possible.
Because the LMP90xxx has both external VA and VIO pins, the user has two options on how to connect these
pins. The first option is to tie VA and VIO together and power them with the same power supply. This is the most
cost effective way of powering the LMP90xxx but is also the least ideal because noise from VIO can couple into
VA and negatively affect performance. The second option involves powering VA and VIO with separate power
supplies. These supply voltages can have the same amplitude or they can be different.
11.2 VREF
Operation with VREF below VA is also possible with slightly diminished performance. As VREF is reduced, the
range of acceptable analog input voltages is also reduced. Reducing the value of VREF also reduces the size of
the LSB. When the LSB size goes below the noise floor of the LMP90xxx, the noise will span an increasing
number of codes and performance will degrade. For optimal performance, VREF should be the same as VA and
sourced with a clean source that is bypassed with a ceramic capacitor value of 0.1 µF and a tantalum capacitor
of 10 µF.
LMP90xxx also allows ratiometric connection for noise immunity reasons. A ratiometric connection is when the
ADC’s VREFP and VREFN are used to excite the input device’s (i.e. a bridge sensor) voltage references. This
type of connection severely attenuates any VREF ripple seen the ADC output, and is thus strongly
recommended.
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