i'm trying to design a battery charger for 5Ah li-ion battery. Due to cost management problems, i am not able to use advanced 5A charger controller ICs; instead, i am going to use a 1A controller with an amplification stage. Power FET configured as common drain seems a good solution; however, the problem is that, as you know, voltage tolerance of li-ion battery is quite low, about 30mV for my case. Vgs voltage of mosfet leads to voltage loss at the output more than that value. Is there a way to amplify DC current of controller IC by keeping output voltage in specified limits?
ps: it is my first question in the site, please let me know if anything is wrong:)
the output of the controller is directly connected to the input of Nmos. Common drain amplifier is said to be voltage buffer and the DC current amplifier. Assuming 5A will be drawn by the battery during the constant current period and 4.2V will be supplied during constant voltage period, what modifications do I need if the controller supplies 0.5A during CC and 4.2V during CV?
the controller will be something like this: http://www.ti.com/lit/ds/symlink/bq24090.pdf DC current amplifier should be directly connected between Vout and the positive terminal of the battery pack.