Need help in trimming Bandgap

[rajanarender_suram]

When designing bandgap trimming bits(digital switching) are provided.. what are the ways to use these bits to control BG voltage externally.. what are the external components required to do this to 1-2%?

- - - Updated - - -

Actually in the system level i need to understand what needs to be done with these trimming bits.. & what is external looping system to control these bits

 

[dick_freebird]

The bits are for fine tuning tempco and output, you
will not see more than tens of mV of pull-range. The
details of driving them depend on the technology but
would expect CMOS control using the local rails.

 

[nitishn5]

I think you are asking how to implement the trimming bits in in the system level. Correct me if it is otherwise.

You would need some registers to store the values of the trim bits. The design block can take the values(High or Low) from the registers and use them to turn on/off some MOS switches or whatever to achieve the trimming.

Now I am guessing that you do not want to have like 8 individual pins to give values for an 8bit trim right?

So to store the values into this registers from outside, using lets say only 1 or 2 pins, you would need some basic digital. Perhaps some protocol to pass the trim code into the register. You could use some asynchronous logic to pass the trim code into the register.