DS90UB953-Q1: 100nf capacitors on IDX and MODE pin

Hello,

To answer your question these capacitors were removed because they are not necessary.  We recommend LDOs in designs so the voltage at the pin should be pretty stable.  With that being said I still see them used regularly and should be fine to use in your design.  

Is there any specific reason you want to replace the capacitor?  I do not believe it would be a problem.

If you are using CLK_OUT you should not use a capacitor on the output as it will interfere with the signal.  

Regards,

Nick

Hello Nick,

I looked at ref designs eg.TIDA-02003 and i will also use the same PMIC and 1.8V then comes form SMPS, and there are no capacitors on IDX or MODE pin.

The design i do is relay small and i want to remove all components that are not needed.

1) i want to use CLK_OUT so the capacitor in IDX will be No mount, in general i can remove it

2) the cap on MODE i want to make smaller footprint, so i see better fit the 10nf then 100nf, is also 10nf ok?

What do you think?

3) i also now see that where some changes in resistors for MODE and IDX in recent documentation , also all the ref designs have different configuration for same mode.

SO i want to use for MODE only 10k Rlow and not place a spare footprint for Rhigh, and for IDX only 40k2 Rlow and not place a spare footprint for Rhigh

is that OK?

Mode-> synchronous

IDX -> I2c -> 0x30 , mode coax cable

Best Regards,

David.

Hi David,

1) You should be fine here.

2) I think it should be okay.  The only thing that I think might be a problem is that the mode strap is set very quickly after power-up and the charging cap may interfere but I think a 10nF cap should be fine.

3) Are you asking if its okay to not waste the space and just pull the pin low? If so yes you can do this and it will work fine.  The only thing would be you could not change the strap value later on, you would have to overwrite the registers.

Regards,

Nick

Hi Nick,

i will have only pull-down on MODE and IDX because of space, and i don't need to change the mode nor I2C address later. ( and we still have the option to  overwrite the registers)

the CLK-OUT can be set when MODE in Synchronous ( 10k pull-down) ?

My configuration

4) IDX -> 40.2k pull-down  if use clk_out then no capacitor here, please confirm.

5) MODE-> 10k pull-down synchronous mode , and your suggestion is not to use capacitor here also, please confirm.

Regarding schematic and layout review, can i contact you via e-mail or through our FAE?

Best Regards.

David.

Hi David,

The CLK_OUT functionality is disabled when in non-synchronous mode so you must be in sync mode.  

4.) 40.2k pull-down sets i2c address 0x30 and correct do not use a cap if using the CLK_OUT

5.) 10k pull-down does set synchronous mode

You can either go through the FAE and they can forward to us or we can do private messages on this forum where we can share files or we can move to email.  It is up to you.

Regards,

Nick

Hi Nicholas,

please can you provide the e-mail in PM so we can move to e-mail and i can loop in our FAE.

Best Regards,

David.