BQ2002C and NCP3065 battery charging questions

[fishy12]

Hey folks - first - thanks for your help.

I'm trying to charge a NiMH battery (2Ah) from a USB supply (mains, not a low powered computer one)

I'm thinking to charge it using the BQ2002C, configured at 1/2C charge rate.  I'm a bit puzzled by the 'open drain output' of the chip though, and how I can use this to trigger a current source.  I realise that when the gate output is high, it's tied to ground, but I'm confused how to get this to control a current source.

That brings me to my second question.  I'm aware a linear regulator would just ditch a fair bit of heat which is less than ideal as my board is inside a narrow tube, and thus won't get much airflow.  Thus, I was wondering if the NCP3065 might be appropriate - and if so, the best way to control it/turn it on and off with the BQ2002C (which pulses the current source to allow trickle charging once the battery is full)?  I've used the manufacturer's design spreadsheet for the chip, which suggests that it is possible to configure it to limit current to 1A max at 2V, with a 5V supply, with only 1.6W lost to the chip/resistors etc.  Does this seem like a reasonable way forward/what might be better/simpler/easier/cheaper?

Thanks very much
Claire