TPS54561: SS/TR-to-reference crossover

Hi,

Let me consult with a product expert on this one

Thanks

-Arief

Hi,

I believe that this value of 1.16V is just a value of SS/TR pin when the FB voltage is at 0.784V (98% of 0.8V)

Thanks

-Arief

Hi Arief, 

Thanks for prompt feedback. I wonder if this is the case, how do you calculate the equation 5? Do you use 0.8V or 1.18V for the Vref? The 1.18V is deducted using 1.16V / 98%. It also puzzles me with Fig 54. 

Is this modeled in the pspice model? Can you help check this using a model?

Thanks,

Tony

Hi,

It looks like based on the datasheet, you use the value of Vref = 0.8V for equation 5.

Because by the time you are in regulation, the Vref will be at 08V

Thanks

-Arief

Arief,

Thank you for follow up. In this case, how to use the 1.16V threshold? I would assume there is some dependency on the datasheet that may need attention. Is there any planned revision? 

Thanks,

Tony

I am having trouble understanding this post.

Can you please explain?

Hi Marshall,

Thank you for following up. Let me rephrase my question as below. 

I am trying to design using TPS54561, while I have problem understanding the crossover threshold of SS/TR feature. 

Datasheet chapter 7.3.8 looks fine. As I understood from 7.3.8, the SS/TR reference voltage is 0.8V. When SS/TR voltage is above 85% of the internal reference voltage (which I assume is 0.8) with 42mV offset, the device started to transit from external to internal. This all seems perfectly OK for me to design. 

However in the electrical table, there is a SS/TR-to-reference crossover voltage, with comment of "98% nominal" of 1.16V typical. I cannot understand how this 1.16V comes while all reference voltage for SS/TR is 0.8V. Could you please help me here? 

Appreciated in advance. 

Regards,

Tony