TPS22959 VBIAS

Hi Franc,

Can you please clarify which pin of the load switch you want to put into a high-Z state?  Are you referring to turning the part off (and disconnecting VIN from VOUT)?

Are you looking to do this to the output?  If so, then pulling VBIAS high and ON low would enable the quick output discharge circuitry, and this connects the output of the load switch to ground through an internal resistance (not high-Z).

Another thing to note is that the ON pin for the device should not be left floating (high-Z) since there is no internal pulldown which keeps the part off.  With a floating ON pin, the state of the output cannot be determined.

If VBIAS and ON are controlled by the GPIO, and the load switch is to be disabled. would the GPIO pull the pins down or would it leave them floating (high-Z)?

Thanks,

Alek Kaknevicius

Hi Alek.

Yes, high-Z between VIN and VOUT. I have no problems with VOUT pulling low when the TPS22959 is shut down.

The GPIO pins will become tri-stated (high-z) when the microprocessor goes into deep sleep, hence my question regarding the operation of the device with floating VBIAS and ON pins. Am I correct in assuming the state of the path (high-z or low-z) from VIN to VOUT is unable to be determined if VBIAS or ON are floating?

To ensure ON is not floating it seems I need to tie the ON pin low and pull it high when the TPS22959 needs to be turned on. Is this correct? If so, what range of resistor values would be recommended to pull ON low?

With regard to VBIAS I plan to tie it directly to VIN and the output of a lithium iron phosphate cell (expect 2.5 to 3.6V). Are there any problems with this approach?

Cheers,

Franc

Hi Franc,

Apologies for the delayed response here.

You are correct, if VBIAS or the ON pin are floating then the state of the output cannot be determined.  If you need to tie the ON pin low with a resistance and pull it high to turn it on, then that is a good solution.  While we don't have any specific recommended resistance, a 100kΩ resistance will do the trick.  Also, VIN and VBIAS can be tied together with no penalty to the function or performance of the device.

Thanks,

Alek Kaknevicius

Hi Alek.

Thanks for responding.

Sorry, your last statement confused me, doesn't VBIAS need to be high and EN low to ensure high-z between VIN and VOUT?

Or will pulling VBIAS and EN low via a resistor ensure high-z between VIN and VOUT?

Cheers,

Franc

Hi Franc,

If VBIAS is high and ON is low, then the part will be turned off (high Z) and the output will be discharged through quick output discharge.  If VBIAS and ON are both low, then the part will be turned off (high Z) and the output will be left floating.

Let me know if that clears things up.

Thanks,

Alek Kaknevicius