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TPS65133: Efficiency

Yasushi Fujiwara
Genius 12175 points
Part Number: TPS65133

Hello Experts,

Customer has question as follows. Would you please answer them?
1. What are the conditions for completing the efficiency curve on the spec sheet? EVM may vary, but it's around 63%@10mA.
2. Why do you recommend metal alloy inductors?
3. Is there a way to get better efficiency at low current (10 mA)? (Vin=3.3V, Vout=-5.0V, Imax=120mA)
4. Customer measured the quiescent current of EVM, the result was 9mA(Vin=3.3V). Then he changed the inductor to NRS3015T4R7(TAIYO YUDEN) and measured the quiescent current again. The result was 14mA. Also, he measured the quiescent current by changing the inductor to NRS4018T4R7, the result was 12mA. So it seems that the inductor affect the quiescent current at low load current. Do you think that the core material difference is one of the reason? Or does it have another factors?

Best Regards,
Fujiwara

  • 0
    TI__Mastermind 18550 points

    Hello Fujiwara-san,

    Thank you for your post. I am currently occupied with some other urgent support issues but should be able to look into this and provide feedback by Tuesday, June 6th my time. Thank you for your patience.

    Kind Regards,

    Liaqat

  • 0
    TI__Mastermind 18550 points

    Hello Fujiwara-san,

    Than you for your patience. 

    1. Conditions for efficiency figure 10 in the datasheet are Vin=3.7V or 3.3V, Vout=+/-5.0V, 25C. Measurement of 63% @10mA seems about right per the datasheet

    graph.   

    2. Primary consideration for choosing inductor is lower DCR to achieve better efficiency. Customer can choose other inductors if they prefer.

    3.  Efficiency can not be improved drastically and will be similar to what is shown in figure 10 but it can be improved slightly with lower DCR inductors.

    4. As mentioned above, primary factor in inductor affecting the efficiency (and hence input current) is the DCR of the inductor. Lowest DCR inductor should be chosen for best efficiency.

    Kind Regards,

    Liaqat