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LM5107 / recommended value of capacitors

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Hi Team,

I looked Layout Guidelines and have following questions.


question 1)
Could you tell me the recommended value of the capacitor that should be connected between VDD and VSS?
I would also like to know the value of bootstrap capacitor that should be connected between HB and HS.

question 2)
Could you tell me the recommended value of the capacitor that should be connected between the drain of the top MOSFET and VSS?
I would also like to know if it is possible to put ceramic capacitor although electrolytic capacitor is recommended.


Best Regards,
Yaita / Japan disty

  • Thank you for your interest in LM5107. Regarding your please questions, see below:

    1) The capacitor between VDD and VSS placed as close as possible to the IC can be a small value. Typical values are 0.1uF or 0.22uF. This will depend on the magnitude of transient currents when the driver switches. Note that one or two larger capacitors (e.g. 1uF, 10uF) should be connected in parallel with this small cap, although these can be placed slightly further away from the IC.

    The bootstrap cap between HB and HS can also be a 0.1uF. The goal is to ensure that the voltage from HB to HS remains at the desired voltage range to turn the high-side FET ON during normal operation, so this value could be made smaller (or larger) depending on how the system is performing.

    2) The selection of the capacitor for the DC main depends on the system requirements, but 10uF would be a typical value. Ceramic capacitors can be used here, but note that ceramics are best for high frequency and large-value electrolytic capacitors are good for low frequency.

    The following app notes from TI provide some good insight on input/output cap selection:

    SLTA055 -- Input and Output Capacitor Selection

    Ceramic or electrolytic output capacitors in DC/DC converters

    Regards,

    - Daniel

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