Comparator for 4S Li-ion battery

Hello Vindhyachal,

Please see my comments added to your original comments and questions.

2. Checked for push-pull comparator, but all have limited voltage max of 16V. But in my case voltage can go upto 16.8V. I was looking at TLV3701. Although datasheet says absolute max of 17V. Can I use it here? Since this comparator only drive a mosfet fds6690A, so there will not be much load on its output.

Yes, you should be able to apply the TLV3701 in the application providing the supply voltage doesn't ever exceed the absolute maximum of 17 V.

3. If I cannot use this. I have to select open drain comparator like TLV1701. Problem is in case of open drain, circuit will keep on drawing the current from supply everytime. Moreover it has high current consumption compared to TLV3701. I have attached a circuit using TLV1701. Can I use 1M & 10M resistor to drive FDS6690A. 10M resistor is put so that gate & sorce never gets open circuit. 1M is to drive the gate.

The TLV1701 will require the pull-up resistor that you have shown in your schematic and has been set to 1 Megohm. A problem with using such a high value pull-up is the time constant when the TLV1701 output goes high. The 1 Megohm resistor must supply the charge current for the large gate capacitance of the MOSFET. I didn't have a simulation model for the FDS6690A, but did for the FDS6680, which has very similar electrical characteristics and capacitances to the FDS6690A. Modeling the circuit shows that the frequency that the circuit can switch becomes limited by the pull-up resistor resistance. At 1 kHZ the TLV1701 circuit is not producing the desired output characteristic.

When the comparator is changed to the TLV3701, which has the push-pull output, there is more current available to charge the MOSFET gate capacitance and the results are closer to expected. But do note in either case that the comparator output switching speed is limited by the current available to charge the gate capacitance. I would not expect either circuit to be useful beyond a switching speed of several hundred hertz.

The TLV3704 does appear to be a better choice for this application.

Regards, Thomas

PA - Linear Applications Engineering

1. You said "The TLV3704 does appear to be a better choice for this application." i think you mean TLV3701 , since I need only one comparator.

2. battery voltage will never go above 16.8V. I will also put one diode (www.digikey.com/.../789335) in series which has 0.2V drop at 10uA. Since i have additional load of around 30uA, I guess I can go with TLV3701. Speed is not an issue. It is very low speed application