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LP38852: About stability

Yuto Sakai
Mastermind 6100 points
Part Number: LP38852

Hi,

When LP38852 rises, it oscillates for 30 to 80ms.
(Vout = 1.2V, Iout = 1A, Cout = 10μF (GRM188B30J106)
The feedback resistors and feedforward capacitors use constants as shown in Table1 in the datasheet.

A filter (1.0μF, NFM18PS105) is connected between the output and load.
Do you think that is the cause of oscillation?
I could not think it oscillates because of its large capacitance.

Could you give me some advice?

Best regards,
Yuto Sakai

  • 0
    TI__Intellectual 825 points

    Hi Yuto,

       Based from your statement, I assume that the oscillation is gone after ~80mS? Maybe adding a capacitor on Css (soft start) pin could help by slowing down the rise of Vout (section 7.3.4 of datasheet) during startup.

    Would you be able to send a scope shot with at least the Vout and Vin plots in it? This will help us better understand more what is going on.  Also, could you please send the schematic showing the LDO circuit/connections? What's the Vin,Vbias, Ven voltages etc. We'll try to replicate your setup.

    Regards,

    Chito

  • 0 in reply to Chito Tapia
    Mastermind 6100 points

    Hi Chito-san,

    Thank you for your reply.

    Your assumption is correct.

    Since it is a customer's measurement waveform, I want to send it by e-mail or E2E private message.
    The customer's schematic is also sent at this time.

    Also,the others measurement conditions are as follows.
    VIN = 1.4, VBIAS = 4V, VEN = floating, Css = 10nF, CIN = 10μF, CBIAS = 1μF

    Best regards,
    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Intellectual 825 points

    Hi Yuto,

     Please send the files to my work email at ctapia@ti.com.

    Thanks.

    Regards,

    Chito