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How to reduce Turn on time of TPS54620 buck regulator

Mahesh Hooli
Intellectual 740 points
Other Parts Discussed in Thread: TPS54620, TPS65950

Hi All,

 

I am seeing  10mSec of turn on time [input to output]on TPS54620 buck regulator. Input is 5V and it the regulated output is 4.1V. Could you please suggest how to reduce the turn on time of the regulator?

The slow start is designed for 1.7mS.

Please refer the below circuit diagram of the regulator.

Thanks and regards,

Mahesh Hooli

  • 0
    TI__Guru**** 191445 points

    How fast is your input voltage coming up?  How much output capacitance are you trying to charge?  Can you show some waveforms?  ( I would look at your input voltage first...)

  • 0 in reply to JohnTucker
    Intellectual 740 points

    Dear John,

    Thank you for the reply.

    I found that, it is not regulator some other (FETs) which were causing the delay.

    Please find the input /output waveform below,[Channel 1 is 5V input ;; Channel 2 is 4.1V output]

    Actually the 4.1V Li-Ion battery & Output of Buck regulator is connected (OR function) to the load.

    I am seeing a voltage dip of 0.4V / 200 micro sec) when I disconnect the Regulator input.Please refer the below capture.This is supposed to go from 4.1V to 3.2V. This is connected to TPS65950 PMIC. This causes the system to reboot. The load current is 200mA.

    The out put cap for the rgulator is 47uF. There is another cap of 100uF after the OR function.

     

     

  • 0 in reply to Mahesh Hooli
    TI__Guru**** 191445 points

    Ok, it looks like the TPS54620 is powering up properly, but you are having some other difficulty with wired OR on your output.  I am not clear about it.  Can you provide the full schematic?

  • 0 in reply to JohnTucker
    Intellectual 740 points

    Please find the schematics of the power section below,

    I have removed the U17 to avoid the delay.

    Here is the modifications done,

    R125 118K
    R117 200K
    R171 2.15K
    R170  4.7K , 

    1nF on C193 & C194. and  0.1uF cap parallel to R170,R161. U17 is removed. Charger is directly connected to U48.5

     

  • 0 in reply to Mahesh Hooli
    Intellectual 740 points

    Please let me know if  you are finding difficulty in reading this.I can send yo the pdf file by e-mail. In that case could you please provide me your e-mail id?

     

  • 0 in reply to Mahesh Hooli
    Intellectual 740 points

    As mentioned in above post, The power to he system is ORed between Battery and the regulator,

    There is no issue when Battery is present and regulator is turned ON.

    In this case if I turn off the regulator , I am seeing a voltage dip of 0.4V on the VBAT line. This is causing a reboot when battery voltage is 3.25V.

    Please find the capture of voltage dip when regulator is turned off below.