TPS25751A: TPS25751A liquid detection question

Hello MarcS,

Thank you for reaching out on E2E. 

I understand that you are wanting to utilize the liquid detection feature for the TPS25751AD. Please see my feedback below for the liquid detection application questions.

1. Execution of LD sampling behavior in regard to an attached and unattached state does depend on if you are using the SBU or CC lines as the monitoring pins for liquid detection. 
   1. When the CC lines are configured to do liquid detection monitoring, the registers field 'Monitor During Attached [74]' must be set to 0. This is because the CC lines are used to send the PD negotiation messages between the PD controller and the port partner.
   2. When the SBU pins or any unused pins are used for LD, the monitoring pins are only configured for LD feature and not meant to be used for other interfaces such as the debug accessory mode. 
2. As I mentioned in Q1, apart from the CC lines, the monitoring pins typically are only used for one application. We recommend using unused pins for liquid detection to minimize interference and to ensure the efficiency of the liquid detection algorithm. and not seen being used for a debug accessory more and liquid detection at the same time.
3. When you configure the TPS25751AD to support liquid detection, this is done in the USBCPD Application Customization Tool. Once the configuration is created in the GUI tool, the configuration bundle can then be flashed to the external EEPROM. During runtime, if the configuration must be modified in any way, an MCU may be required.
4. When the CC pins are used for monitoring of liquid, they are limited to only monitoring during an unattached state. I would like to also note that once a port partner is connected to the PD controller, there is a final liquid detection sampling sequence that occurs prior to moving to an attached state. This is where the Pulldown Threshold ADC [87:80] comes into play. This threshold is used to negate the Ra that may be presented by an E-marked cable.

Please see my follow up questions below:

1. What is you end equipment?
2. Can you please share a block diagram for your design?
3. I am not too familiar with the TPS25751A interfacing with an SWD interface. Can you elaborate more on what the SWD debug interface will be used for?

4. Are the TX/RX pins of the USB-C connector being utilized? My thought is they can be used for the debug accessory mode, so the SBU pins can be used for liquid detection?

Thank you,

Katilynn

Hello Katilynn,

Thanks for the explanations and answers.

Regarding your questions:

1) The end equipment is a micro drone system. The USB-C will allow to connect to the central system (SoC) to collect stored data

2) For some reason I can't embed an image in this post (I get a File embedding is not allowed message). Consider the reference design for the TPS25751A, a GPIO with the event Debug_Accessory_Mode_Event used to drive a USB2 switch (redirecting D+ and D- to SWDIO and SWDCLK, SBU1 and SBU2 to SWO and NRST. CC lines will be used for liquid detection. In Debug mode, standard USB exchanges are not made.

3) The idea is to use the TPS25751A ability to generate an event when an debug accessory is detected (thanks to the CC lines). Once this situation happens, the D+/D- and SBU lines are repurposed for debugging the MCU on the system (SWDIO, SWCLK, NRST and SWO). The idea is to use a simple switch for that. Note that SBU lines are unused otherwise

4) In normal operation, we want to have USB3.2 Gen1 data transfer capability. D+/D- are used for fallback mode.

Hello MarcS,

Thank you for your reply. I understand you are having issues uploading the block diagram image on E2E.

When it comes to uploading a file or image, I typically drag and drop a file from file explore directly into the response box. Another option is to screenshot an image and copy it to my clipboard. Then I paste it into the response box. 

Please let me know if one of these upload option still gives you the same error.

Thank you,

Katilynn

I tried all methods mentioned and more before, didn't work.
Today it does. 

Anyway, here is a block diagram of the principle we try to achieve for the debugging interface. The block PD manager is the TPS25751A.

The same principle applies for the SBU lines with one difference. The output of the switch is always SWO and NRST, simply mirrored in one case as the SBU lines are not symmetrical on the USB-C connector.

Hello MarcS,

Thank you for providing the block diagram and your reply.

A few follow up questions and feedback for the TPS25751A can be found below:

1. The block diagram does not highlight the power rails, nor does it indicate if the PD controller will need to support a sink only or dual role power application.The block diagram below is taken from the TPS25751A data sheet. Note that the PP5V  and PPHV voltages are noted in the example below.

1. 1. Can you please elaborate more on the power path behavior in regards to the PD controller in the block diagram?
   2. If the PD controller needs to be able to provide power to the type-C connector, the PP5V must be powered by an external supply. 
2. I not confident as to what the arrow from the PD manager to the digital switch is indicating. Is this for enabling the digital switch upon entering debug mode? 

MarcS said:

3) The idea is to use the TPS25751A ability to generate an event when an debug accessory is detected (thanks to the CC lines). Once this situation happens, the D+/D- and SBU lines are repurposed for debugging the MCU on the system (SWDIO, SWCLK, NRST and SWO). The idea is to use a simple switch for that. Note that SBU lines are unused otherwise

3. When the SBU lines are repurposed for the MCU debugging, are you expecting the PD controller to continue to do liquid detection on the type-C connector?

A GPIO event can be configured on the TPS25751A to assert high when a debug accessory mode is detected on the CC lines. See screenshot from theTRM below:

Thank you,

Katilynn

Hello Katilynn,

Thanks for the follow up.

Sorry for the diagram lack of details, I will answer your questions below:

1) TPS25751A will work in a dual role mode (DRP). 5V is provided by a regulator on our system.

 a) Normal operation (no debug mode). In source mode, PPHV and PP5V provided by our system. In sink mode, power comes from the USB port and launch the system in dead battery mode, enables PPHV in sink. 

In debug mode, power comes from the USB port (dead battery mode). Same principle as sink mode.

b) See the answer above. In source mode (provider), we generate a 5V used on PP5V

2) The arrow is the DEBUG_EVENT signal from the TPS25751A when a debug accessory is detected. Note that we added another switch to allow the USB-C connector to be connected in both direction to get a correct SBU - SW signal mapping. This one is controlled by the CC_ORIENTATION signal from the TPS25751A

3) No, we know it may disturb the communication at that point and debugging should only be carried in "clean" conditions so we do not expect problems here.