Other Parts Discussed in Thread: TPS735, , TM4C1294KCPDT
Hello,
Have 2 temp sensors monitor 2 heat sinks on 20Khz PWM system. One sensor is very quite direct coupled to ADC channel input no decoupling is required. The other sensor is very unstable no matter what ADC over sample or hold time, adding any amount decoupling cap 12pf<1.1nf makes temp roaming worse. The only way to settle it's output down was to add 2k pull down, sink/source current 1.67mA, far from 50µA. The VDD, GS0, GS1 trace now has 3.3µF>0.1uf ceramic and still required the 2k pull down.
The part that makes no sense is both sensors share VDD (3v3) source a single VIA. Also tried new sensor and concerned 1.67mA sink/source to ground should not be required alters temp results. Can not get stable reading, temp +/-3°C roaming as PWM duty cycle nears 85%. Both sensors are within 1" of each other, 2" from ADC input and both located on top side of PCB.They share same 3v3 rail VIA of star net on opposite sides of PCB, the noisy VDD net is stubbed 10mm next to 3v3 rail bus and source VIA. The other sensor 1" away VDD net runs through analog ground plane, only real difference. Thanks for suggestions.
What is recommended to quiet noisy sensor make it's output more stable?