Hi,
I am currently designing a product that uses a LM5001 boost converter to charge a hold-up capacitor bank. The specs are quite tough to meet as the input voltage range can be anywhere between 16v – 70v and the boost circuitry must output 70v. I have current limiting circuitry after the boost converter, which limits the charge current (and therefore the required output current of the LM5001) to about 30mA.
I used webbench to give me a recommended LM5001 design based on my specifications and have built a prototype. The circuit is performing very well, however the LM5001 runs quite hot (case is about 30-40degC above ambient), even when the capacitor bank is charged and the load is effectively zero. For this reason, I added circuitry that detects when the capacitor bank is fully charged and puts the boost circuitry into what I am calling “charge maintenance” mode (pulsing on and off with a duty cycle of about 10% and a period of 2 seconds). This does what I hoped – the case is now only about 5 deg above ambient when in charge maintenance mode.
My question is which LM5001 package should I use? SOIC (and use the LM5001Q1 part) or WSON (and benefit from the lower thermal resistance)?
The cap bank charging period lasts about 7.5 seconds. As the circuit will have to operate at high temperature (up to 105degC), I am worried about burning out the LM5001 during this initial charging period, even though it is only for a short time. I am thinking the WSON part (tightly thermally coupled to the ground plane on the PCB) might stand more of a chance than the SOIC, even though it is not a Q1 part?
Thanks,
David