Other Parts Discussed in Thread: BQ25792, TPS25751
Tool/software:
Hi Team,
Our customer “Cadstar” is using the TPS25750 in combination with our BQ25792 for their new battery powered system and they had some questions:
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In addition to the TPS25 we are using your BQ25792 IC as our battery charger. The overall block diagram for our battery pack is the following:
We want to use full USBC protocol to charge/discharge our battery pack, min 5V3A and max 20V3A. We are using a single cell battery with maximum voltage of 4.2V and minimum 2.5V (nominal voltage is 3.7V), maximum battery charge current is 3A.
- We are supplying TPS25 with 5V from TPS630, but this buck-boost converter is capable of providing MAX 1A, which breaks USBC PD protocol to provide 3A and when PDO1 is negotiated, the IC heats up to 110C and delivers around 1.2A of current.
Is it possible to control TPS25 that it would not supply VBUS from PP5V pins but only source the required voltage from PPHV pins? According to 0x32 TX_SOURCE_CAPS Register we can set PDO1 source as PP_EXT1 which is a default source for PDO2/3/4. After generating new bin file to source the PDO1 from PP_EXT1 (PP3) and when a PDO is negotiated the device is not functioning (VBUS=0V, Vsys=4V,Vbat=4V, PP_5V=5V ,TS-disabled).
My assumption is that when PDO1 is sourced from PP_EXT1 there is no I2C command to set BQ25 as power source. How should we alter the TPS25 bin file to send a I2C command and set BQ25 VBUS voltage to 5V 3A?
Also, after PDO1 has been negotiated TPS25 0x34 ACTIVE_CONTRACT_PDO Register value is 0x060000000000 – It does not look right to us.
If we can fix the correct errors and source 5V3A from BQ25 then whole battery pack would be USBC-PD compliant.
Another option is to break USBC compliance and only source 5V0.5A TPS630 but this is the last resort.
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When source PDOX is negotiated (as long as it is not 5V) we have a massive voltage drop on PPHV and VBUS line, please see the image below.
In this case 9V PDO was negotiated and my phone was charging with 0.4A current. PPHV amplitude is 18V, VBUS is 10V and the harmonics are 3kHz frequency – easily audible.
The TPS25750 cannot establish a higher than 5V source PDO with the USB-C-PD-DUO-EVM board. TPS25 can negotiate with my and colleague phones a 5V and 9V PDO but not with EVM board. (sinking works fine)
Conclusion:
We have significant issues when battery pack is discharging (USBC PD source).
Maybe we should switch from TPS25 to another PD chip? (I am not sure if TPS25751 will fix the issue)
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Suggested already was if they can switch to the TPS25751.
I would appreciate your swift response to this issue.
Best regards,
Ahmad
