Electronics > Microcontrollers

Problems with internal temperature sensor - MCP3561

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MasterT:
I think microchip failed with MCP356X (& MCP3918 ).
What are you designing?
I

Dave_PT:
Sorry for the delay mate.

I'm designing a nanoAmp meter... but now I've lost all desire to continue.
I will have to reproject using another ADC...

MasterT:
 I was busy with TI ads8691 for a couple of weeks, had similar issue with noise.  I'm debugging everything on a breadboard and was using TSSOP-20 to DIP-20 adapter board.
Making 1 MSPS SAR adc to work is very tricky w/o 4-layers properly designed layout, and even worse - on a breadboard w/o good contacts.
But I made it. After I soldered 3x 10uF MLCC just right to the adapter - so contacts quality and 1 cm leads has no effect.  SINAD is only 2 dB off compare to DS, -90dB vs -92.
This makes me re-think again my strategy for mcp3561R (there is common part - tssop-20 to dip adapter). Today I did same thing - solder 10uF MLCC to AVDD & AGND, another to DVDD & DGND and third one to REF+ and REF-. Reference most important, cap should reside as close to IC as possible.
 And miracle happened - noise is flashed away.
Linearity is also fixed replacing 100 Ohms resistors at the inputs to 10 Ohms. Microchip erroneously recommends high R values, it's may works only below 10 MHz.
I have 2.2k in series with clock (17.2 MHz for now) and 470 Ohms in each SPI lines.   

Dave_PT:
I'll try to apply some more filtering as a feature and see if there are any improvements in the conversion.

At this point neither speed nor noise level nor resolution seem to be consistent with the datasheet. Microchip support says there is nothing to do...

Perhaps these reasons explain why an ADC with similar characteristics costs twice or more than the MCP3561.

MasterT:
Can't agree on price vs quality comment.
I have tested 3 adc in almost the same conditions, microchip mcp3561R vs industry leaders AD & TI. It's not quite correct tests - since 3561R is SD adc, but 2 competitors SAR. It would make sense to compare mcp33131D-10 - just not have time for now.
Sampling rate for AD & TI about 500ksps - 1 MSPS. Microchip - 31.25ksps, OSR = 128, clock 14-16 MHz.
Approximate SINAD 90dB - means 15 noise-free bits.
 Linearity talks for itself.

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