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TPS65987D: whether TPS65987D can operation without Vin_3V3

GW
Intellectual 2370 points
Part Number: TPS65987D
Other Parts Discussed in Thread: TPS65987

Hi, Team

Our customer using TPS65987D as the smart speaker, and the Vin_3V3 is power by the external LDO, the LDO have EN pin can be power down by their MCU.

In one of the special design requirement,  when the product in standby mode, the prefer to disable the LDO in order to improve the system IQ performance. In that case, the 3.3V and 1.8V will power from TPS65987D internal LDO, and the TPS65987 will act hard reset. We know that is normal since the device will act as the dead battery mode.  but customer prefer to check it's that is OK for their design(using internal LDO to power TPS65987D)? any risk for that?

Also, customer have two test to see what's is impact for this application.

Test 1: normal operation, with external LDO for Vin_3V3, they found that the PD will negotiated to 15V. and the CC line is continue to communication. pls check the waveform below.

Test 2: disable the external LDO, the 3.3V/1.8V will power from internal LDO, in that case, when negotiated to 15V, the found that the CC line have no any communication, it's that normal? pls check the waveform below.

Pls help to check with us the below questions from customer:

1, It's that OK to only using internal LDO? Any risk or any special consideration?

2, In test 1, the CC is continue communication, what's the communication content?

3, In test 2, why their are no any CC communication while 15V PD negotiated?

Thanks your help.

G.W

test 1 waveform: 

Test 2 waveform:

  • 0
    TI__Mastermind 30000 points

    Hello,

    For the CC communication, it depends on the messages being sent between test 1 and test 2. You would need to use a PD analyzer such as the Total Phase PD analyzer to read the messages being sent back and forth and if it makes sense that the PD controller is not responding. 

    Here are the answers to your customers questions: 

    Question 1. It's that OK to only using internal LDO? Any risk or any special consideration?

    • If the system will always act as a power sink, then there is no problem being powered from VBUS and the internal LDO. Just know that in such a condition, if the dead battery flag has not been cleared, the PD controller will reject and data role swaps or power role swaps since it cannot provide power over VBUS or VCONN

    Question 2 and 3: Test 1 and Test 2 CC communication

    • I need the actual PD logs to determine what the communication is during this time. Cannot tell the difference in CC communication looking only at the voltage toggling