Hi ! I'm currently designing a battery charger using UC2909. I have some problems with the current sense amplifier.
The charger is a 72V / 24V forward power supply. I use the UC2909 to control the battery current and voltage and a UC2897 to drive the primary semi-conductors. UC2909's CAO pin is connected to UC2897's FB pin (U-155 application note).
The experiment : I make the input voltage rise slowly. The output current rise so CSO pin's voltage decrease. It's OK. But when output current is arround 1A (200mV between CS+ and CS-), CSA pin's voltage become instable and there is finally a saturation to 5V. I added a 100nF capacitor between CS+ and CS- but it's ineffective.
I realised the same function with an external current sense amplier instead of UC2909's internal one. It's working.
If somebody have an idea, I would be grateful...
Thierry