Post Go back to editing

Inductor calculation for LT8709

Hi

I'm a DFAE in Japan.

I design LT8709 Negative Inverting Converter for my customer following Table 2 in datasheet. I'd like to know how the three voltage values as 12.5mV, 40mV and 3mV in Step 6 L calculation are derived.

I make the calculation sheet by Excel. When I finish making it, I'll submit it to the customer to adopt LT8709 instead of COSEL power module.

I've already design the schematic. But the simulation result of efficiency by LTspice is about 85%. My target value is over 90%. I recognize the ripple current of the inductor is over 5Ap-p. I think it is too large. So I'll try to reduce the current below 4Ap-p.

The spec of power supply is as follows.

Vin_min = -50.4V, Vin_typ = -48V, Vin_max = -45.6V

Vout = +12V, Iout = 2.5A

Regards,

Hiroyuki