I'm looking to use a buck controller to achieve current regulation for a battery charger. My input supply is already voltage regulated and will be suitable to directly connect to the battery. However I must ensure I have current limiting. Having seen the interesting article on the LM5117 as a precision current regulator (snva609.pdf), this seemed like a possible solution.
However I am limited by the max duty cycle of the IC, having a minimum off time of 320nS to recharge the bootstrap. Even at lower switching frequencies I can not achieve better than 97% max duty cycle and I don't think it is possible to circumvent the min off-time even if I opted for an external charge pump.
I have also considered using the COT non-sync PFET buck switch to get 100% duty cycle, but this causes huge variation in output currents, due to the cycle by cycle current control.
I would like to have the predictable freq operation of a sync buck controller but use current sensing in the primary feedback loop. However I can not find any IC that seems to allow operation very close to or better still 100% duty cycle. I would also like to avoid using a buck-boost topology for simpilicity's sake.
Could TI make any recommendation.
Thanks
Aidan
