TEC Driver REF pin loading and capacitance

[nkrackow]

The TEC Driver IC has a Reference pin that outputs the internal reference voltage. This pin should have a 1uF capacitor according to the datasheet, Thermostat curretly has a 10nF. The pin can sink 1mA but only source 10uA. With the current loading the pin is pulled from nominal 1.5V to ~1.05V.

[jordens]

This was a bug from https://github.com/sinara-hw/Thermostat_EEM/issues/46 I meant adding an 10k R 10n C filter to VREF, after the 1u C and not replacing the 1u with a 10n C 10k R combo. That doesn't work.

[jordens]

Still, there seems to be something loading it. @SingularitySurfer sure you measured the 1.05V on the pin 4 side or R224? In any case the voltage divider at IC14 is broken due to the non-zero impedance of R224.

[nkrackow]

Still, there seems to be something loading it. @SingularitySurfer sure you measured the 1.05V on the pin 4 side or R224? In any case the voltage divider at IC14 is broken due to the non-zero impedance of R224.

Actually I measured on the wrong side of the resistor, sorry! The highlighted net on the pin has 1.5V. Behind R224 there is 1.05V left.

[jordens]

Ok. Then it's just the divider. And the RC. Should fix both.

[gkasprow]

R224=0R, C168=1uF

[jordens]

@gkasprow I think that's too much load. VREF can do +10µA to -1mA. We are loading it with 25k from 4.3V worst case (see IC14).

[gkasprow]

Right. So let's add another opamp to buffer it. It can be one for all four channels

[gkasprow]

Or, let's replace IC14 with LMV358

[gkasprow]

[jordens]

The buffer should also drive the other vref users, e.g. to the CPU.

[gkasprow]

good idea.

[gkasprow]

Fixed in v1.1rc2