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BQ25601: VSYS output voltage while VBAT<VSYSMIN

Krzysztof Kondratowicz
Prodigy 50 points
Part Number: BQ25601


Dear Team,

I'm experiencing an issue with VSYS regulation to be above programmed level. According to the datasheet Figure 15, when VBAT<VSYSMIN, VSYS should be stepped up to the value stored in 0x01 register. However, I can't get this feature to work (VSYS follows VBAT regardless of battery voltage), either with input adapter present or not. Below there's a fragment of the schematic of our board with the charger. The registers values during the test are 04 1E A2 22 58 9F 66 4C 00 80 00 11.  I also found this topic, where VSYS is only said to follow VBAT with a BATFET voltage drop: https://e2e.ti.com/support/power-management/f/196/t/729655 . Does the VSYS regulation need to be enabled somehow? Is this due to some design mistake or am I misunderstanding the datasheet?

Regards,

Krzysztof Kondratowicz

Firmwave

  • 0
    TI__Genius 11850 points

    Hi Krzysztof,

    The minimum system voltage regulation's functionality is as follows. If a good input source/adapter is connected, then VSYS will be maintained above the SYS_MIN register setting even if the battery is deeply discharged. According to the register values you sent, your SYS_MIN setting is 3.7 V. Therefore, even if VBAT is zero, VSYS should still be maintained above 3.7 V as long as a good input source is connected. You do not need to take any extra steps in order to enable SYS_MIN regulation.

    In the waveform below, VBUS = 5 V is connected, and VSYS is maintained above my 3.7 V SYS_MIN setting even when VBAT < 3.7 V. After VBAT rises above SYS_MIN, VSYS and VBAT are roughly equal (ignoring the voltage drop across the BATFET).

    On the other hand, in the waveform below, I had no VBUS connected, so VSYS followed VBAT instead of being maintained above 3.7 V.

    Based on your description, it sounds like VSYS tracks VBAT regardless of the battery voltage and regardless of whether or not the adapter is connected. Please capture a waveform similar to the 1st waveform I sent (with VBUS = 5 V). Sweep VBAT and see how VSYS responds.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 50 points

    Thanks Angelo. The reason for me not getting the regulation while VIN connected was probably it being too low (around 4V1, what made me confused was low /PG pin). Applying proper 5V makes VSYS regulation available. A little pity it's not available while running on battery only.

    Regards,

    Krzysztof Kondratowicz