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TPS65132B - Output capacitor

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: TPS65132

Hello,

Our customer would like to use the output capacitors as following.

CoutP, CoutN, CREG :  LMK107BJ475KA-T (4.7uF, 10Vdc)
CFLY :   LMK107BJ225KA-T (2.2uF 10Vdc)
Vpos=5.5V/10mA, Vneg=-5.5V/10mA

Can we use these capacitors?
Could you please let me know the concerning of this capcitors?

Since the DC Bias characteristics of these capacitors are worse than capacitors of datasheet recommendations, the output noise and load transient response will be worse.

Best Regards,
Ryuji Asaka 

  • 0
    TI__Expert 8010 points
    Hi Ryuji,

    The effective output capacitance of the TPS65132 shall be bigger than 4.7uF., the fly- capacitance higher than 2.2uF.
    Yes your conclusion is right, that due to dc-bias will effect the performance. I can see in the d/s that with VOUT=6V the effective capacitance is less then 30% 4.7uF < 1.5uF, which is undoubtedly too low. If you dont want to use the capacitors recommended in d/s you will need at least 4x 4.7uF of these types to achieve the minimum output capacitance.

    Best Regards,
    Ilona
  • 0 in reply to Ilona
    Guru 20090 points
    Hello Ilona san,

    Thank you for the reply.
    Is the effective output capacitance of the TPS65132 required bigger than 4.7uF?
    In the datasheet , there are the recommendation capacitaors as GRM188R61C475KAAJ for Cin,Cneg, Cpos,Creg and GRM188R61C225KAAD for Cfly.

    Since these capacitor have DC bias characteristics of 40% at 6V , effective capacitance is smaller than 4.7uF and 2.2uF.
    So, the effective output capacitance is about 2.9uF for Cin,Cneg,Cpos,Creg and 1.4uF for Cfly.
    Thus, if we can achieve above effective capacitance by other capacitors, we can use it.
    Is my understanding correct?

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Expert 8010 points

    Hello Ryuji-san,

    I have to correct myself as for this converter there are two different requirements regarding output capacitance:
    1) in smartphone- mode the minimum effective capacitance would be 2.35uF

    2) in tablet-mode the minimum effective capacitance shall be higher than 5uF 

    If you plan to implement the smartphone-mode the chosen capacitance would not be enough, you would need two of them. The recommended capacitor from d/s achieves a capacitance of 2.82uF and yours 1.88uF.

    Best Regards,

    Ilona

  • 0 in reply to Ilona
    Guru 20090 points
    Hello Ilona san,

    Thank you for the reply.
    I understood that there are two different effective capacitance.

    Best Regards,
    Ryuji Asaka