I am using the TPS40210 as a 81V boost circuit. I have used Webench Buck / Boost circuits many time with no problems. But this one is giving me trouble.
The MOSFET is running hot, even with no load. At 100ma load it heats up enough to melt the solder joint. I started with a TI CSD19533Q5A MOSFET Rds ~ 8mohm, then switched to a Toshiba TPW4R50ANH Rds <4mohm.
Toshiba is running noticeably cooler but still way to hot.
The gate drive looks good at just over 8V (internal 8V LDO), but the drain (while switched on) is still hovering at around 2V. I expect this to be much closer to 0. The source is at zero. I must be missing something. Why am I not slamming the FET on all the way to gnd?