TPS65987D: Internal Switch Turning off during dead battery mode power up

Hi Aaron,

You may want to check the ADCIN1 values again and see that they match the configurations.

However, I see that you're using BP_NoWait, in this configuration though, the PD controller will start up and attempt to load the configuration settings while being powered from VBUS. But, since you don't have SPI Flash or I2C programming available, the configurations won't be loaded and therefore, you won't receive the function you are expecting. I would recommend looking into using a different configuration such as the internal wait configurations perhaps. You may look at the different configurations on Tables 5, 6 and 7 in the datasheet here: https://www.ti.com/lit/ds/symlink/tps65987d.pdf

From my understanding, you are attempting to power the PD controller in dead battery mode from the USB cable. Once it's powered you want to power the microcontroller from the PD controller so you can program it via I2C, is this correct? Another thing to note would be to see if the microcontroller is attempting to pull more current than possible from the PD controller and the USB cable. I would recommend measuring VBUS to ensure it's what you expect it to be as well.

Thank you,

Hari

Hi Hari,

Thanks for the reply.  It was not clear to me from the datasheet and the pre-configuration options in the boot section that you needed the I2C or the SPI flash to enter those preconfiguration states.  I thought that was the point having some ROM encoded configurations in the first place.  

Are you telling me that all the preconfigurations will not actually load into the application until there is a I2C link ready to go?  

For the most part, I am just hoping that I can get the internal sink path switches to automatically turn on so that I can run my external regulator to power my system from Vbus (not your internal 3.3V LDO).  In this way, I desire to power my system from the Vbus supply, not your PD controller supply which I understand is current limited.  My system should only be drawing 10's of milliamps, I will take a measurement to confirm.

Regards,

-Aaron

Hi Hari,

I have determined that my load current draw is about 30mA when my regulator switches on.  My cycling of the internal switch behavior was the result of my microcontroller coming up with the reset line asserting active high.  I have corrected that problem and now my internal power switch path is behaving on a standard 5V USB charger.  

I am still having difficulty getting a smart laptop USB-C charger to come alive with 5V, I see about 3V appear on the CC1 line when I plug in my cord but the adapter never turns its 5V source on.  When I plug the same adapter into the eval board operating in configuration mode 3 just as my circuit is, the 5V does come out of the laptop charger.

I would love additional clarification on the configuration mode 3 and what happens when I have no SPI flash or I2C link active from the micro during the boot process.

Regards,

-Aaron

Hi Hari,

I have a theory as to why my smart adapter might not be cooperating in the sense that the 5V rail is never coming up - I am using the same protection circuit as the Eval board, the TPS6S300A.  Unlike the Eval board however, in my circuit, I did not connect the RPD pins to the CC pins on that protection IC.  My thinking at the time was that my main PD controller, the TPS65987D already was taking care of the RPD pull down resistors in the dead battery mode and I didn't want two sets of these resistors in parallel.

What I now believe is happening is that since the TPS6S300A has internal switches that prevent the CC lines from reaching the PD controller chip until the part is powered.  Since this protection chip derives its power only after the Vbus turns on (and it never does), these CC lines never get the benefit of the Rpd resistors that are built into the TPS65987D.  

Therefore, it appears the Rpd resistors must come from the TPS6S300 since it is the only impedance presented to the connector before power is applied.

I will try connecting that path to see if that gets my smart adapter back up and running.

I am still interested in finding out if configuration mode 3 should be negotiating 15V (the maximum input) or if I'll only ever get 5V out of my smart adapter and it will require me sending I2C commands with my micro to ask for the 15V.

Hope to close out this issue once I complete my test.  Thanks for the support.

-Aaron

Hi Aaron,

I will get back to you with feedback on Wednesday. am traveling at the moment and will be back into the office by then.

Thank you,

Hari

Hi Aaron,

To get back to you, no I am saying that the preconfigurations will load into the application, however, I see on the datasheet that since you are also using the BP_NoWait dead battery mode configuration, then it will depend. I will include a screenshot below of the part I am referencing in the datasheet, it is in the last paragraph.

As far as receiving the 15V contract, I will continue to look into your setup to understand the functionality and get back to you on that.

For the TPD6S300A however, yes I think you should be connecting the RPD pins to CC pins on that as well. In a dead battery condition, the OVP FETs on the TPD6S300A are turned off for protection, so with the PD controller also in dead battery, they should be connected. Below is a paragraph from the datasheet explaining a little better and in detail the functionality.

Were you able to test this and see the results?

Thank you,

Hari