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LM5085 battery charger application

Yash Rajwade
Prodigy 80 points
Other Parts Discussed in Thread: LM5085, LM5007, LM5017, LM5008

Hello,

I am planning to use LM5085 in a NiCd battery charger application. Specs are-> 48 to 62Vdc input, 12V, 0.25A output. I have a some questions before I begin the design-

1. The interactive webench tool gave me a efficiency of only around 65% for these specs. Is this part not recommended for low current design? As I understand, losses will be mainly in PMOS and diode.

2. How accurate is the current limit on this device? I need +/- 5% accuracy in charging current and my ambient temperature is from 0 to 55C

3. What will happen if I use a 6V battery in place of the 12V battery for which the circuit is designed? Will it still stay in CC mode?

Thanks,

Yash.

  • 0
    TI__Genius 11490 points
    Hi Raj,
    LM5085 is a PFET controller that is useful for low drop out. I think for a high conversion ratio (48V to 12VOUT) the efficiency is usually lower. The tools only provide a rough estimate at lower power levels when the converter can be in DCM. Testing an EVM with your conditions can provide a more accurate value. Again at this low IOUT, it is very dependent on FET selection and frequency of operation.
    If your load requires only 250mA of load I think a regulator can also be used (please see LM5007, LM5008, LM5017 etc).
    For a 6VOUT, the part should still be current limit protected as long as the current limit is set properly and an inductor of appropriate current rating has been selected.
  • 0 in reply to Vijay86929
    Prodigy 80 points

    Hi Vijay,

    Thanks for your reply! Could you please elaborate on your point that efficiency will be lower for a higher conversion ratio?

    Thanks,

    Yash.