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LM34927: LM34927 24V to 12V output current ability and output inductance value

Brian Chou
Prodigy 60 points
Part Number: LM34927
Other Parts Discussed in Thread: LM5161

I want to use LM34927 to converter Input voltage 24V to output voltage 12V. The output just to drive the 16pcs relays. Every relay core resistance has 270Ω . So I calculate output current about 711mA . I want so make sure the LM34927 can drive it. I see in the datasheet page 6 showed the current limit threshold minimum is 0.7A when the Vin equally 48V . Can help me make sure below 2 questional.

1. What output current maximum current value when Use the LM34927 to make 24V converter to 12V?

2. If the output current maximum current value can satisfied my design how to decide the output inductance value?

Best regard,

Brian

  • 0
    TI__Expert 6245 points
    I am refering this request to our LM34927 expert, Tim
  • 0
    TI__Guru 73522 points
    Hi Brian,

    The LM34927 is rated for 600mA of DC output current. The inductor is generally chosen to provide a peak-to-peak ripple current of 30-50% of the rated full-load current. With the minimum current limit setting of 700mA (corresponding to peak inductor current), there is no margin.

    Depending on the maximum input voltage, one option to consider for your application is the LM5161 100V, 1A converter (there are other options if 100V input rating is not required). The LM5161 includes configurable soft-start and FPWM/DEM features. Also, the output voltage of 12V can be connected to VCC via a diode to reduce bias power dissipation (although not a huge benefit if the input is only 24V). Given your load configuration, a Type-3 ripple injection circuit is probably your best choice to provide the required ripple amplitude at FB.

    Regards,
    Tim