Part Number: TPS65982
Hello, I am using the TPS65982 in a Display port application. For the aux channel, I wanted to know if any external components were required to bias the differential pair. I have include the DP AUX channel for the
source. Specifically are the 100kohm pullup/pulldown included in the TPS 65982. If they are how are they invoked.
In reply to Eric Beljaars:
can you clarify how these pullups get enabled in the TI part. I am a bit worried that you recommend having an external pullup/pulldown on the AUX_P AND AUX_N lines. This indicates that there might be a problem with the TPS controller in how these resistors are configured?
I assume that once we configure the TPS65982 in DP Alt mode the pullup/pulldowns on AUX_CH_P and AUX_CH_N are automatically set.
AUX_CH_P should be a 100k pulldown to GND and AUX_CH_N should be a 100k pullup to 3V3. This resistor is RPU100 in the datasheet I believe.
Q. Is there any register that I can check to configure these pullup/down resistors are getting set correctly, or to over-ride these values, so that I can check the pullup/down status?
When we measure the voltage on the AUX_P/AUX_N (SBU1/2) we are seeing an incorrect voltage. It appears that the pullup/pulldown are not set correctly in the TPS controller.
I attached the project file I am using.
In reply to guy lemire:
we do not have issue going into display port mode, but it appears the DC bias point on the AUX_P and AUX_N are incorrect.
Can you clarify what the TPS65982 is doing between the AUX_P/AUX_N IOs and the SBU1/SBU2 IOs. My understanding is that it should simply apply a 100k pulldown resistor for AUX_P and a 100k pull-up resistor to 3.3V for AUX_N.
When dealing with a cable swap is there also a mux in this circuit? Is there any other control or setting needed to correctly configure this pullup/pulldown?
we are measuring after the device is configured. If you look in the DP Alt specification, AUX_P should be less than 400mV and AUX_N should be > 2.4 V when biased. We are measuring AUX_P to be 2.4V and AUX_N to be 400mV. So it appears the pullup/pulldowns are reversed in the TPS. This is why I am asking what configuration registers will effect this pullup/down.
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