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Original question:

LM66200: Question about switching between VIN1 and VIN2

LM66200: High Temperature with VIN1 similar to VIN2

Artur Vieira
Prodigy 30 points
Part Number: LM66200
Other Parts Discussed in Thread: LMR51430, TPS2116, TPS2117

Tool/software:

Hello

I have a design where I am using the LM66200 to control whether the System Voltage is 5V from an USB Connector or 5V (output of LMR51430X). It seems to work for some time (minutes) when booth inputs are valid, but after a while the chip starts heating up (+80ºC) and the device power consumption increases by around (40mA on the 12V Input that powers LMR51430X).

The circuit is very "basic":

The (+5V) then pass on another LMR66200 that control the system power either from +5V or from a SuperCap.

The second chip (U23) seems to be working normally.

Is this a problem from VIN1 and VIN2 are too close?

On the first attempt the output of LMR51430 was set to 5.04V which is very close to the USB (5.02~5.11) value, I have increased the output of LMR51430X to 5.19V but the same situation happens after a couple of minutes with booth inputs valid the chips start heating and some extra current consumption.

Is this some issue with having booth voltages very close to one another? Should I use another approach for this function (particularly U24).

Thank You

  • 0
    TI__Guru* 79181 points

    Hi ,

    Please let me check and get back. 

    Regards 

    Kunal Goel 

  • 0 in reply to Kunal Goel
    Prodigy 30 points

    Hi

    Any feedback regarding this issue?

    I have made some more tests, and it seems to be more stable with the following modifications around U24:

    - Added a 1K PullDown resistor on signal "+5V_DCDC"

    - Increased the voltage of "+5V_DCDC" to 5.24V

    - Added an 22uF capacitor on line "+5V_USB" (Originally only have around 2uF)

    - Added an extra 22uF capacitor on the output "+5V" (originally have 1uF "close" + 10uF "far") 

    It seems to be more stable, at the moment the prototype with these modifications seems to be working fine, but not quite confident on the circuit at this moment.

    Would a TPS2116 or TPS2117 in priority mode be something more advisable for this purpose? In this case I want the "+5V_DCDC" to always have priority over "+5V_USB" even if "+5V_USB" is slighter higher than the internal "+5V_DCDC" voltage.

  • 0 in reply to Artur Vieira
    TI__Guru* 79181 points

    Hi Artur,

    Really sorry for delay.

    I think earlier device was switching between supplies .

    I feel since you want priority you should consider using TPS2116 or TPS2117.

    Regards

    Kunal Goel