1. I need to select a small form factor MCU with below features:

1. Debug/program on chip
2. 6 I/o
3. Uart
4. One channel 16 or 24 bit adc.
5. IDAC (optional, if not I will use external)

I had searched on internet but I am not getting any MCU with small form factor.
Like for Silabs , the mcu matching thses specs is in TQFP-32 , but I need SSOP-20 or smaller.
TI's does not have mcu in small form factor also

QFN package I am avoiding as they are hard to solder by hand.

 

I'm not sure you'll ever find a small processor with the A/D precision you want. And with a home-built circuit, you'd have a hard time keeping the signal quiet enough to make any use of that kind of conversion anyway.

 

I agree on the lack of 16 bit A2D converters inside micros. Either there is no (market) need for such, or the noise floor inside a micro will not support the extra bits. Microchip does have five devices (dsPIC33's), the smallest in a QFN-S, SOIC, SPDIP (28) package.

As far as getting extra bits, I breadborded a separate 4 channel A2D, forget offhand if it was 16 or 18 bits, in a PIC project, no ground layer. It may have occasionally changed the least sig bit from time to time.

I've soldered small (8 pin) QFN's by hand using a hot air tip. That should work for larger packages too.

 

I'd re-evaluate the need for a 16-24bit ADC, or think about how accurately you expect it to read.

From what I've seen most people posting questions here who want a 16-24bit ADC simply don't need it, or don't understand that it's not going to give them the real world accuracy that they imagined.

 

@THE_RB I want to learn who to calculate ENOB & accurate measurement mathematically.

For example I have selected ADS1247 with 24 bit adc, I need to measure minium step of 75uV & reference = 2.048V & other parameters are also defined.

Can you guide me right literature from where I can learn how accurately I will read, ENOB & other related parameters?

 

If you selected a precision ADC chip already (ADS1247) then you no longer need to have a "16 to 24bit ADC" inside your microcontroller.

Now your micro just needs these;
"1. Debug/program on chip
2. 6 I/o
3. Uart"
which should be very easy to find.