• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 144 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2124: unexpected behavior

Alen Barisic
Intellectual 1300 points
Part Number: TPS2124
Other Parts Discussed in Thread: TPS2121

Hi Team,

we use the TPS2124YFPR to supply our device with either 5V from the buck converter itself (12V car battery supply to 5V) or from a USB 5V supply.

The switching between the supplies works, but if s supplied by both supplies at the same time, and then turning off the 12V car supply, the device resets.

As shown on the attached scope image the VOUT of the TPS2124  drops to 3.3V for around 100ms. The 4.0V RESET Monitor resets the whole system.

Please find the schematic below.

We use the TPS2124 in VCOMP mode. The 5V from the buck converter has priority as it can supply higher current (2A) then the 5V USB supply (700mA)

5V_Buck = from car batt 12V –> 5V Converter

5VD_USB3 = 5V USB supply

measurement in scope_2.png attached.

CH1 (yellow) = 5V_Buck

CH2 (green) = 5VD_USB3

CH3 (blue) = 5VD

We expected that shortly before the X1 cursor, the output switches to VIN_B, but this seems to happens much later at Cursor X2-

Could the reason be Hysteresis/Prio on VIN_B? Would it then be better to have 5V_Buck on VIN_B and 5V_USB on VIN_A?

Thanks,

Alen

  • +1
    TI__Genius 13260 points

    Hello Alen,

    When operating in vcomp mode PR1 must be below 1.06V so it's usually just tied to ground. In your schematic it is below 1.06V; however, you have a resistor divider on PR1 setting it at 270mV which is unnecessary. In vcomp mode the device will prioritize IN2 over IN1 in the case where IN1 ≈ IN2. Application example below and in section 9.3 in the datasheet:

    The switchover time with this device is 100uS. During this time the output can fall, but should be held up using output capacitance. It looks like your switchover time is ~68uS according to your scope shot which is within specifications. If this switch-over timing isn't fast enough you could use TPS2121 which offers fast switchover ~5uS. 

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    TI__Intellectual 1300 points

    Hi Kalin,

    Thanks a lot for your answer.

    We use PR1 because the device should never switch to 5V_USB as long as the 5V_Buck voltage is applied (>4.5V).

    The 5V_Buck  has always priority as long as it is above 4.5V.

    You mention "In your schematic it is below 1.06V; however, you have a resistor divider on PR1 setting it at 270mV which is unnecessary" - Why is it 270mV in this schematic? If 5V_BUCK = 4.45V then with the resistor divider R638 R639 R640 PR1 is 1.06V if I am not wrong? With that 4.45V should be the limit for the priority?

    Regards,

    Alen

  • 0 in reply to Alen Barisic
    TI__Genius 13260 points

    Hello Alen,

    Apologies- I'm not sure how but I missed the resistance & connection to the OV pin from PR1. You're correct. 

    Regards,

    Kalin Burnside