High to low line impedance conversion

Hello Chris,

Welcome to the Forum!

I reckon that this is not the most effective solution.  The first thing that comes to mind is the charging of the batteries.  The second would be thermal protection of your batter pack.  Finally, the TPS63000 is a single cell Li-ion device.

Visit the battery management forum http://e2e.ti.com/support/power_management/battery_management/default.aspx and search it for a aolution to you battery pack and charging requirements.  This is unless the batteries are removed and charged external to the circuit you described.  You can look at some of the battery management devices if your circuit does require charging. http://www.ti.com/lsds/ti/power-management/battery-management-products-products.page

Did you use WeBench for your design?

Thanks,

Thanks for the warm welcome!

The batteries I use are non-rechargeable. I am not worried about charging it at all. They will be replaced with new ones once used up. I am dealing with a legacy circuit here. So, I'm not sure if WeBench was used. The fuses and diodes were not in place earlier. They were placed for certification purposes and this stopped the circuit from working. I am trying to get around the impedance problem. If i short circuit the 80mA fuse with a wire, all works great!

The diodes prevent the batteries from leaking into each other and fuses are current limiting. From the datasheets, the high side switch on resistance of TPS63000 is 100 mOhm. The 80mA fuse has a resistance of 8 Ohms as I mentioned earlier. This is preventing the TPS from starting up from what I can infer. I've looked through the battery management community but didn't find clear solution.

Since it works great when the 80mA fuse is removed, I don't suppose Li cells are causing the problem as such. Also, the datasheets says 1.9V is sufficient to turn it on. The current limiting by the 8 Ohm fuse seems to be the key issue and I cannot get rid of it due to the certification requirements.

Are each of the 250mA fuses required for certification?  Does the circuit work without those fuses?   Can you"bundle" the batteries creating a single pack so that you would only need the single fuse?

I don't think adding an Op Amp to the circuit will help.  If the voltage level is already low, adding another component will only make it lower.  The 8 ohms will always be in series no  matter what you do.  Is there no other option for the 80 mA fuse?  Would a breaker pass certification?

You could put an additional boost circuit in to keep the voltage level consistent in range of 2 to 3.7 volts.  This would of course decrease the overall efficiency of your circuit though. 

Perhaps a diagram of what you are doing would be helpful.

Yes, the fuses and diodes are absolutely necessary. The position of the fuses are also dictated by the certification body. There is not much I can do there. Hence, bundling won't work. Also, the 250mA fuses have very low resistance. It is the 80mA fuse that is causing trouble.

I agree to what you said about Op Amp. Cannot be a breaker. A fast acting non resettable fuse with a minimum of 4 Ohm resistance is required.

Any particular boost converter that I can try? How much efficiency will be dropped?

I am thinking that it might be better to spec out a new part instead of adding another one.  What requirement made you select the TPS63000 in the first place?

You could try plugging in your requirements into Webench to generate a circuit.  Then check the Power Management forum for additional help.

It was selected by an engineer before me. The requirements are pretty basic. 6 Li cells connected in parallel through a diode and a 250mA fuse, which is in series with an 8 Ohm 80mA fuse. This should go through an efficient regulator that can provide 3.3V at the output with minimum ripple. The peak current drawn by the load is around 65 mA. Load transients of about 30mA frequently occur (every second). So, the regulator must be able to handle that. The battery is non-rechargeable. The regular should be able to boost the voltage from 2V in order to make the most out of the battery.

Definitely post that to the Power management forum.  I'm sure someone over there can provide you with some helpful information .