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Original question:

TPS53688: How to adjust the TPS53688 output voltage

TPS53688: Pin-strap detection question

Will Wang47
Expert 6930 points
Part Number: TPS53688

Hi team,

I'm working with my customer on the TPS53688 + CSD95410 project. And now they get some questions about the detection logic of the Pin-strap detection. 

It sail in datasheet, I will short the upper resistor and then measure the low-side resistor. Could you let us know how the internal circuit work? We did some test with customer, waveform as follow. 

The figure 1 up side / low side resistor are 43.2k / 20k. Figure 2 up side / low side resistor are 26.1k/20k. The time from rise up to lower side value detect is ~8msHowever, figure 1 show the detect waveform value get 60mV difference. 

Figure 3 is another TPS53688 on another project, up side/ low side resistor are 1.2k / 20k. It's detect value is ~1.3V, and the time from rise up to lower side value detect is ~4ms

Since all the low side resistor is 20k, why there will be different value? And why the time from rise up to low side resistor value detect time is difference?

Could you help explain the internal working logic to help understand more abou the detect level difference and time difference?

Figure 1

Figure 2

Figure 3

Best Regards,

Will

  • 0
    TI__Genius 11095 points

    The datasheet description (which I wrote...) is out of date here. Shorting the high-side resistor was done for the VR13 generation controllers. For TPS53688 it is slightly different. 

    There are 8 bits total decoded from the ADDR pin. 5 bits from the pin voltage and 3 bits from the low-side resistor. 

    At power-on, the ADDR pin will come up to Vref * (divider ratio on ADDR pin). The PMBus address is determined from an A-to-D conversion of the raw pin voltage. Call this V1. 

    Then, based on the pin voltage, the controller will either pull ADDR up to VREF, or down to Gnd through a 15k resistor. This is why you see the pin voltage going up sometimes, and down other times. With the internal resistor switched in, it will make another A-to-D conversion, call this V2. 

    Then 5-bits address come from a direct mapping of V1 voltage to Address. And the low-side resistor value is calculated based on the delta between (V2-V1) and whether the pin was pulled-up or pulled-down. 

  • 0 in reply to Matt Schurmann
    Prodigy 40 points

    Hi Matt, Thank you for your detailed reply. I have one more question, " based on the pin voltage, the controller will either pull ADDR up to VREF, or down to Gnd through a 15k resistor" , then what is the range of this pin voltage? Regards!

  • 0 in reply to Tianyi Yuan
    TI__Genius 11095 points

    Since ADDR is pulled up to VREF, the full scale is 1.5V.

    When the V1 measurement (Vref * external divider ratio, no internal resistors) is greater than 750mV, the internal resistor to GND is activated before measuring V2. So, you would expect to see: 

    V2 ~= Vref * [Rbot||15k] / ( [Rbot||15k] + Rtop )

    When the V1 measurement is less than 750mV, the internal resistor to VREF is activated before measuring V2. 

    V2 ~= Vref * Rbot / ( Rbot + [Rtop || 15k] )