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DRV8301 Internal Buck Converter, bad Start behaviour

Markus Hoffet
Prodigy 220 points
Other Parts Discussed in Thread: DRV8301, TPS54160

Hello Ti,

I am using a DRV8301 Motor gate driver. 

The internal Buck converter (tps54160) does not start at the 2.5V as described by the data sheet. The EN_BUCK PIN is floating (not connected to anything).

I slowly rise the voltage on the PVDD2 PIN and measure the voltage on the EN_BUCK PIN. At apprx. 2.5V the voltage on the EN_BUCK PIN jumps to 1.7V which is a logical high (internally pulled up). I expect that the buck converter will start as soon as I measure a ligical high on this EN_BUCK PIN.

On my 3.3V output I measure 0V. When I increase the voltage to 5.8V the buck converter starts- up and I measrue clean 3.3V on my output.

The reason why we selected this device for the design is, that i can start the buck converter at 2.5V!

Thank for a quick reply

Markus Hoffet

  • 0
    TI__Guru**** 191445 points
    Well you most definitely cannot get 3.3 V output with 2.5 V input as the TPS54160 is strictly a step down converter. It should start to switch and output some lower voltage until the input is well above 3.3V.
  • 0 in reply to JohnTucker
    Prodigy 220 points

    Hi John,

    Thanks for you reply.

    It is clear that it can not generate 3.3V out of 2.5V But out of the Data sheet description, we assumed, that this Buck regulator will start at 2,5V and then run with its maximum duty- cycle until the input voltage is higher than the desired output voltage.

    Why does it need a voltage of much more than 5.5V to generate a 3.3V Output?

    A short moment after start- up my input voltage will rise to above 14V This problem only happens in the very first moment. But the microcontroller should start as quick as possible.

    What is the minimum output voltage I can achive with this device? Other if I ask the other way around, what is the maximum output voltage I can achieve with a 2.5V input?

    Regards

    Markus Hoffet

  • 0 in reply to JohnTucker
    Intellectual 565 points

    Hi John 

    I have to agree with Markus on this point from the Datasheet the description is quite clear as it mentions with no resistor divider the device will switch ON at 2.5V 

    Ti should rephrase the section and clearly mention that this is the Low drop-out voltage once the device is running it will drop-out at 2.5V and not switch ON or I am totally mistaken here however the datasheet is not very clear and that should be corrected .

  • 0 in reply to Peter Erasmus
    TI__Guru**** 191445 points
    I think it should start switching at 2.5 V also. Let me see if I have a circuit to check in the lab.
  • 0 in reply to JohnTucker
    Prodigy 220 points

    Hello John,

    Thank you for yous investigations. I am looking forward to the results you will submit to us.

    Best Regards

    Markus Hoffet

  • 0 in reply to Markus Hoffet
    TI__Guru**** 191445 points
    I checked this in the lab. Actually, the TPS54160 starts up at around 3.1 V. Remember the U VLO spec is "typ " 2.5V. For lower voltages, it may have better start up, but with that low input, there is not much gate drive. Since Vin is lower than Vout, the circuit cannot regulate. This causes COMP to rail out and that causes SS to discharge.. Basically it will not regulate well until Vin is somewhat above Vout. If the load is light, you may still operate in low head room drop out. In that case Vin will need to be above Vout plus 2.1V. I confirmed this is normal operation with the IC designer. Let me know if you have further questions.
  • 0 in reply to JohnTucker
    Intellectual 565 points

    Hi John

    Thank you for your investigation and report .This helps to understand things better