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Original question:

TPS65094: Set TPS650940 buck4/buck5 to Forced PWM mode fail

TPS65094: VTT has no output

Lumina Gui
Genius 3680 points
Part Number: TPS65094

Hi All,

One of our Apollo lake notebook projects uses tps650940 for PMIC design, and the DDR is LDDR3. But we encountered a problem, VTT has no output, and both the input and EN (S0) have signal at present.

From the datasheet we know that TPS650941 is suitable for LDDR3, and we have used TPS650940 for LPDDR4 design before, and it has in MP status. But now we have changed to LPDDR3 due to other reasons, we also tried to increase VDDQ voltage to 1.2V, but VTT still has no output yet.

We have checked other circuit designs, all other signals are normally, and the machine can be turned on now. But the VTT voltage is actually not output (We disconnected all loads of VTT and measured its output and found no signal), the timing and signal of the PMIC are OK.

We want to know whether VTT has no output is affected by I2C and OTP, or tps650940 does not support LDDR3 at all? I added our schematic diagram to the below and hope it can help for the analyse.

P3252_schematic.pdf

Thanks,

Best Regards

  • 0
    TI__Genius 12735 points

    Hi Lumina,

    According to table 3-1 of the TPS65094 datasheet VTT LDO is disabled for the TPS650940 device by default. If you need to use VTT LDO for this device you need to change the VTT_DISABLEB bit in register VR_CTRL3 (offset = 9Fh) from 0 to 1 to enable VTT LDO. However if you are planning on using LPDDR3 then I would recommend using TPS650941 as this OTP has VTT LDO enabled by default.

    Best regards,

    Layne J

  • 0 in reply to Layne J
    Genius 3680 points

    Hi Layne,

    Thanks a lot, but we still have some question about this.

    How do we access the register VR_CTRL3 and how does the BIOS read and write the registers of the power IC? Do I need to contact INTEL for help?

    Thanks,

    Best Regards

  • 0 in reply to Lumina Gui
    TI__Genius 17380 points

    Hello Lumina,

    I am back from paternity leave and will take over from Layne who was covering. The VR_CTRL3 register is I2C accessible, so you can read and write from it with anything that can access the I2C bus. If you want to use the Apollo Lake processor to do this, I would recommend reaching out to Intel. We do not have experience with their software directly.