Using LM3489 as a basic lead acid battery float charger.
Specs required:
+V_MAIN is 13.6V-13.8V
Max 300mA constant current limit to charge battery.
13.6V battery float voltage.
Battery automatically supplies system if main input power fails, max 2A required for system.
Low power dissipation.
Low dropout.
Question:
When the main power input fails, current will initially flow through the P-FET body diode and supply the system. In this state will the LM3489 turn in the P-FET? Based on the datasheet I think it will. This is good for me as it gives a low drop out connection from the battery to the system.
Can I have a secondary system, in parallel to the LM3489, pull the P-FET gate low? Or what is the best way to force the LM3489 to turn on the P-FET, e.g. pull the FB pin low.
Schematics available via email
