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TPSM831D31: TPSM831D31

Kerry Tracey
Intellectual 450 points
Part Number: TPSM831D31
Other Parts Discussed in Thread: LM3880,

I am using three TPSM831D31s in my design along with a LM3880MFE-1AE/NOPB.  FLAG1 output from the LM3880 is going to the A_EN/B_EN pins of each of the TPSM831D31s.  I am talking A_EN & B_EN from one PMBus connector (pins 7 & 4) and tying them together along with a couple of other signals through a AND gate (SN74LVC1G08DCKR) which the output goes to the EN pin of the LM3880.  I have the PMBus A_EN/B_EN tied high to +3.3V via a 10K.  When I plug in the PMBus it pulls the EN signal low and if I toggle the control signals in the Fusion Digital Power GUI the enable path does change.  I did verify the enable signal path works by programming the supplies and then removing the PMBus.  My control signal then when high & all TSPM831D31s came up.  I have a couple of questions: 1) Can A_EN & B_EN pins on the PMBus be connected together?  2) Do I need to change the 10k pull-up to a different value?        

  • 0
    TI__Mastermind 24075 points

    Hi Kerry, 

    In PMBus USB adaptor, the two control signals are separate. I'm not sure if there will be problem if they are tied together. You can try. 

    For the A_EN and B_EN pins of TPSM831D31 , they can be shorted together externally. 

    10k pull-up resistor is fine. 

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Intellectual 450 points

    Looking at the USB Interface Adapter it uses the TUSB3210PM and P0.3 (A_EN) and P0.4 (B_EN) appear to be the control pins.  The TUSB3210 datasheet indicates that these are open drain outputs with a 100uA active pullup.  Since I tied the A_EN and B_EN pins together on my PWB I use only one 10k pullup (10k came from the TPSM831D31EV schematic).   I've removed all obstacles from my control pin except for pins 4 (B_EN) and pin 7 (A_EN) connected together.  I've measured the voltage at pin 4 without the PMBus connected and the voltage is 3.297V.  When I plug in the ribbon cable/connector from the USB Interface Adapter, voltage at pin 4 drops to 22mV.   The A_EN/B_EN signal goes into the input of a SN74LVC1G08DCKR.  Do I need to change my 10k to something else?    

  • 0 in reply to Kerry Tracey
    Intellectual 450 points

    Changing the 10k pull-up to a 1k did not fix the issue.  However, lifting pin 4 of the PMBus did allow the GIU to enable the control pin High.