Hi all,
I am using LTC3892 step down converter for my Battery Management System. I need current limit at various steps, For eg, If the maximum current is designed to be 20amps, I need current to be limited at 5A, 10A, 12A, 15A, 18A. For this, I need a idea to implement a circuit. According to the functional block diagram of LTC3892 datasheet, current can be limited by changing the voltage at feed back pin, Vfb pin. Is that correct, If so I need a analog circuit to limit the current changing the Vfb pin. Please give me some suggestion to limit the current.

 

LTC3892 microcircuit has special pins for restriction of the current (Sense1+,Sense1-, Sense2+,Sense2-). Honour Datasheet and change the nominal value a resistor that to get the necessary maximum current. The Defect of this way - fixed a restriction of the current. The Switch to put it is impossible since resistors have small importance of the value of the resistance. The Resistance of the switch will influence upon current.

 

You could, in principle, use a four pole switch to switch the terminals of a selection of 4 wire current shunts. This would keep the switch resistance out of the loop. I don't think the chip would like it if you switched shunts while the chip was running as it would briefly open the feedback loop, but it would be fine if the switch was set before powering up.

 

As the chip has foldback current limiting, I don´t think it is suitable to use the Rsense to limit the average current. A better solution seems to mesasure the current with another differential amplifier, and use the signal from that to influence the voltage feedback to limit the current at your desired value.