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LM5001: 48V maximum output current?

Darren (FAE)
Expert 5483 points
Part Number: LM5001
Other Parts Discussed in Thread: LM3481, LM2586, LM5000

I have a customer wanting to implement a 20-30V input and 48V@450mA with the LM5001.

I followed the SLVA372C document: Basic Calculation of a Boost Converter's Power Stage 

I have also attached an excel file with the math.

The EVM shows 48V 150mA output, and he was wondering if modifications could be done to get 450mA.

But from the math, I think I understand why the EVM was set to 150mA...

Fsw = 250kHz, L = 100uH, Efficiency set to 80%, Vmin set to 16V, and the Ilim min at 0.8A means you have a150mA output before the inductor ripple goes over the 0.8A rating and the device shutsdown.

I couldn't get higher than around 300mA by changing the Vin to 20V, Fsw to 1MHz, and inductor to 1mH.

Is this understanding correct?

Would the LM3481 be a good replacement? (Not P2P)

Customer needs a device with 0.65mm pin-pitch, or as low as 0.5mm if absolutely necessary...and the spacing between a pin and the thermal pad needs to be >0.35mm

Is there any option besides the LM3481 you could recommend?

Thanks,

Darren

BST-設計.xlsx

  • 0
    TI__Guru 58215 points

    Hello Darren,

    For an estimation, we can have a look at the input and output power and currents of an ideal converter (100% efficiency):

    VIN*IIN = VOUT*IOUT in an ideal converter => IIN = VOUT * IOUT / VIN

    In this case, IIN = 48V * 0.45A / 20V = 1.08A.

    This means even if there is no ripple on the input current (in a boost converter, the input current is the inductor current filtered by the input capacitor), the peak current of the switch needs to be 1.08A. LM5001 has minimum 0.8A, so 450mA will not be possible with this part.

    Maybe before you have a look on the controllers with external switches, please have a look at LM5000 or LM2586.

  • 0 in reply to Brigitte
    TI__Guru 58215 points

    Hello Darren,

    As I did not hear back from you, I expect that this problem is solved. I will close this thread. If you still have questions, please post either here again or create a new thread if this one is locked already,