Good news! It works!

Bad news! It gets really hot!

At the suggestion of tech support, I connected the oscillator pin to the gate to select a "constant off time" mode as referenced in app note AN-50. This allows duty cycles >50% without subharmonic frequencies appearing.

Now, it's putting out the rated 1.4A, but everything is getting really hot! The inductor and diode gets warm (to be expected), the FET gets hot, and the HV9910 gets hot! When I say hot, I mean 150+F. I put the fet on a heatsink, but not sure what to do with the 9910 - or even why it's getting hot.

 

any idea what frequency it's running at? that's the only thing I can think that would make everything heat up.

high freqs increase switching losses in the transistor and diode

only reason I can think the chip should get hot is that it's somehow not wired correctly, or maybe you're taxing the internal regulator too much?

do you have any load connected to the regulator output (Vdd pin 6)

how about voltage on the feedback pin, is it within spec?

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Wow, that's strange....... According to my $50 meter, it's output is 300+khz? It's supposed to be running at 100khz. I'll have to put it on a scope to confirm that though, it might be picking up something. Very strange.

Internal regulator is not used. (it's tied to LD and PWM_D)

The voltage at the current sense resistor is what it should be.

 

Nevermind, 72khz @39% DC, which is within spec.