Hello,
I am looking at using the LTC4097 in place of a DS2715 from maxim for a 5 AAA cell NiMH battery pack charging solution. I need to charge the batter pack at 100mA. My input voltage is adjustable, but ideally around 7.5V. This battery pack is permanently installed in my product and plugged into a computer for communication, control and lab testing etc...so it will be plugged into a PCs usb port a lot and this is where the boost regulator gets its 5V input power to then boost that up to around 7.5V. The architecture is attached in pdf format below.
When the product is connected to a computer via USB current paths i1 and i2 in the block diagram are active. I added the diode or'ing option so that the device can be powered directly from the boost supply when connected to a USB port. I was worried that if I didn't do that the battery would charge up then the LTC4097 would shut off and my product electronics would then drain the battery and cause the 4097 to start another charging cycle and this would go on as long as the product was plugged into the computer. When the product is unplugged and on battery power current path i3 will be active. I hope this makes sense. Basically I don't want the battery to get drained while the product is plugged into a computer so I've or'd a path from the boost regulator to my buck regulator for logic power.
As a note the orange dashed line/box denotes a basic fuel gauge and battery protection circuit. This really isn't important regarding the LTC4097.
So my questions are as follows:
1. The LTC4097 only allows current to flow from the boost supply block to the battery pack? It doesn't let current flow backwards into the boost supply when fully charged?
2. If the answer to #1 is no - the 4097 doesn't allow current to flow backwards then would I need a protection diode D1?
3. Does this architecture look like the intended use of the LTC4097?
4. I saw in the datasheet that you should set the voltage divider to terminate based on a target voltage on the battery pack, but setting this too high could cause a hysteresis problem. I've noticed that my battery pack voltage is high while charging and when the charger shuts off it drops a bit. I still don't understand how to set the voltage divider so that the 4097 doesn't keep turning on after every charge cycle finishes and the voltage drops. What is a recommended approach for setting the divider - I know what my peak voltage is when charging these cells (1.4V) but I don't know if that really denotes the batteries being at full capacity.
5. Is there a way to get an EVM or dev board? I've looked around and can't find any in stock? Could I get one from ADI as an evaluation board? They are also very expensive - I'm surprised they cost 130 bucks. If possible could I send my information to ADI and possibly have one shipped out to me to do some testing?
