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TPS53515: Pins 27 and 28

Yale Friend
Prodigy 40 points
Part Number: TPS53515
Other Parts Discussed in Thread: TPS53915,

Hello,

We have previously been using the TPS53915 and we are now looking at using the TPS53515 as a potential replacement. Do pins 27 and 28 (previously the SDA/SCL pins) actually have to be grounded? Will they bring down the i2c bus if we leave it connected?

Thanks!

  • 0
    TI__Genius 16760 points

     The pins will not bring down the i2c bus.   I will check my team on other consequences. 

  • 0
    TI__Genius 16760 points

    The pins will not bring down the i2c.   The devices are trimmed differently during production.   The TPS53915 has a default switching frequency of 400kHz and  pin 1 sets the ADDR.   The pin 1 sets the switching frequency for TPS53515.   If the TPS53515 is placed into a TPS53915 application, the device will ACK pmbus commands but the device will not make the requested adjustments in the device.    The addr is determine by the pin 1 resistors

  • 0 in reply to David_Daniels
    Prodigy 40 points

    Interesting...easy enough to swap the addr resistors to set the 53515 to 400k. does it have a default internal address that it will ACK or are you saying it will ACK at the equivalent address of the 53915 given the fsw resistor strapping at pin 1?

  • 0 in reply to Yale Friend
    TI__Genius 16760 points

    The ACK response will be at the address set by the pin 1 resistors.

  • 0 in reply to David_Daniels
    Prodigy 40 points

    So just as an example. To set the FSW on the 53515 to 400k, you could use 249k and 47.5k. On the 53915, that would set the pmbus address to 0010101 = 0x15. So with the 53515 at 400k, it will ACK at 0x15?

  • +1 in reply to Yale Friend
    TI__Genius 16760 points

    Yes, that is correct. 

  • 0 in reply to David_Daniels
    Prodigy 100 points

    Hi David,

    Regarding to the question pin 27 and 28 when TPS53915 replaced by TPS53515 then I have some concerns as below:

    1. Is there a connection between pin 27 & 28 to any elements inside the TPS53515?
    2. As my current design, I have pulled up pin 27 & 28 to 3V3 power rail via 2k2 resistor then it can effect to these pins or TPS53515's functions.
    3. Currenly I'm setting TPS53915's pin 1 address with PMBus address 0011101 and switching frequency 400Khz. But when I change to TPS53515 then the switching frequency is 850Khz because the resistor divider is set  R_rf_h = 180K and R_rf_l=154K at TPS53515's pin 1 RF. So are there any potential issues at here? (note: I can't change the current design)

    Thanks

    Tuan Le

  • 0 in reply to Tuan Le
    TI__Genius 16760 points

    1.  Yes,  The TPS53915 and TPS53515 are built will same controller and fets.   The devices are trimmed differently. 

    2.  see the post in the thread above. 

    3.   Switching at 850kHz will increase power dissipation and lower the efficiency.    The  output ripple will be lower.   The converter will probably be stable but i would recommended to review or test the stability..   

  • 0 in reply to David_Daniels
    Prodigy 100 points

    Hi David,

    Thank you for your explanation. I have fully cleared about my concern

    Tuan Le