Hi there!
I am utilizing the boost converter to charge a battery so I need to step-up the connector input voltage of 5V to the voltage level of the cells which have a nominal value of 16.8V. Depending on the power source, I want the current limit to be different, hence I want to dynamically adjust this current. In the datasheet, the only option is to set a constant current limit which is proportonal to the resistor value connected in the ILIMIT pin. I have checked the functional block diagram to find out how this limiting works and I have seen that there is a constant current source (that I have highlighted in orange with Is) powered by the intrenally generated voltage supply Vcc of 6V. This current flows through the external resistor connected to ILIMIT which generates a voltage drop that is taken to the inverting input of an op amp that compares it to the measured current to perform current limitation.
As a result, I thought that if I can adjust the voltage that is seen in the ILIMIT pin, I could adjust the current limit. For that I need to know what is the current of the current source (Is on the picture) and I have made some simple calculation connecting different resistors to the ILIMIT pin and measuring the voltage. In all cases the current is the same: 190uA. I am confused about this since the datasheet provides a graph stating that resistors can go up to 220k ohms but if this value was connected the resulting voltage would be well over the absolute maximum voltage of ILIMIT whih is 7V.
It is true that the resistors I have connected have much lower values that the graph presented below, I used 1k6, 2k8 abnd 4k4 but I am guessing the current source works the same for all imits. I would appreciate if you could shed some light on my problem and if you think it is possible to dynamically adjust this limit with a DAC output of a processor for example.
Thank a lot beforehand!
