[time-nuts] schematics of frequency counter

Li Ang lllaaa at gmail.com
Thu Jan 8 10:00:59 EST 2015


Hi Neil
   Just now, I disconnected TPS79333 from board and used  LR6 battery for
the analog part of TDC. The result does not show improvement. So I think
LDO might not be the primary noise contributor.


Thanks for the suggestion.

2015-01-03 22:01 GMT+08:00 Neil Schroeder <gigneil at gmail.com>:

> I would reconsider the LDOs while you have some time to play with them.
> The TPS79333DBVR is not even remotely "ultralow noise" at most offsets,
> despite what TI may say.
>
> For 5V5 and under up to about 600ma, I would suggest you take a look at the
> ADM7155 (adjustable) or ADM7154 (fixed). If you need 800ma, the 7150 is
> here for you.
>
>
> http://www.analog.com/en/power-management/linear-regulators/adm7155/products/product.html
>
> http://www.analog.com/en/power-management/linear-regulators/adm7150/products/product.html
>
> The TI part has nearly 35 uVRMS of noise  at just 2.8a with not very good
> PSRR.  The 7155 will produce less than  1.0 ╬╝VRMS Total Integrated Noise
> from 100 Hz to 100 KHz and 1.6 from 10 to 100 KHz,and that's without an RC
> noise compensation network.  Its a fabulous part for a sensitive
> application like yours.
>
> I'm hoping I am right in assuming that the noise performance of the LDOs is
> a concern, and don't mean to even dare suggest that you've done anything
> but a great job! :-)
>
> NS


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