Part Number: BQ32000
Hi,
I'm looking at the trickle charge circuit of the real time clock BQ32000. We are using a 0.22F supercapacitor as recommended in the data sheet. On the data sheet (section 7.3.3) it says between the Vcc pin and the Vback pin there is a diode, and 940R and 180R resistors (we leave the switch TCFE open, the one that would switch 20k in parallel). To work out the diode drop and check the resistance in the trickle charge circuit I removed the supercapacitor, replaced it with a resistor (between the Vback pin and ground), and measured the voltage drop across it. Vcc is 3.3V. For 100R I got 0.10V, for 1k I got 0.73V, and for 15k I got 2.12V. That gives a diode drop of 0.87V, and a total resistance inside the trickle charge circuit of 2.3k. Why is this different to your data sheet? The reason I'm checking this is the supercapacitor takes a lot longer to charge up than I initially calculated using the information on the data sheet, is there something I'm missing?
Thanks,
Simon
