Low power opamp for battery cutoff, zener operation

Hello Vindhyachal,

Please see my answers after your comments:

Voltage divider of V1 has total 1M of value. V1 varies from 5V-20V. So max current to ground will be 20uA here also. Can I set high voltage divider value to TLC3702 pins?

Yes, you can increase the resistance of the two resistors but maintain the ratio of R3 to R2. The input bias current of the TLC3702 is typically 5 pA at room temperature, but can be as high as 0.6 nA at 70 C. That current will flow through either R3, or R4, depending on polarity, and will add a very small offset to the input voltage. The larger you make the resistors the larger that offset will be, but likely it will still be very small and not have a noticeable effect. You should be able to increase these resistors into the Megohms and reduce the divider current accordingly.

Also now main current path is V1 with zener path. I = (12v-2.7)/100k = 93uA. Can I increase R1(100k) further, so that zener can still maintain 2.7V across it & don't have any affect on TLC also...

The voltage developed by the zener will be a function of the current flowing through it; less current, lower zener voltage. If you increase the R1 resistance the current will decrease and zener voltage will be lower. If V2 is relatively constant why not just set up a resistive divider with R1 for a voltage of 2.7 V? Then, the resistors could be increased and scaled as you were thinking of doing for the other input.

Regards, Thomas

PA - Linear Applications Engineering

Hi,

I have redesigned my circuit. Some of its specs are changed.
Now I am using TLV3701(push-pull comparator) & TPS715-5V.
I have to turn off system at 5V & turn it on at 7V. Circuit is attached

1. Voltage V1, when falls below 5V then cut till it rises above 7V.
V1 vaires from 5V-20V. It may also be removed from circuit.
Rest of circuit is powered by V1 whhich varies from 9V-13V.

2. Now first V1 is stepped down, so that at 5V it gives 1.39V & at 7V it gives 1.95V.

3. U1 which is powered by +5V is used here as inverting schmitt trigger.
R2,R9 & R6 forms a network so that it acts as schmitt at desired levels.
It gives low when voltage is above 7V & high when voltage is below 5V.
(as it is inverting)

3. Since I need to turn on a mosfet at around 9V gate voltage, so U2 is added. Non-inverting pin has arounf 1/10th voltage of V2 i.e 0.9 to 1.3V

When U1 sends high(5V), then U2 output is low. i.e when V1 is below 5V
When U1 sends low(0V), then U2 output is high. i.e when v1 is above 7V

4. So I can turn on/off mosfet as desired where load is connected.

Queries:
1. What I am thinking, will the circuit behave the same way?

2. At page 5 of datasheet of TLV3701, min voh = vcc-0.450 & max vol = 0.3V
Although I am taken care of these values, can these values increase/decrease further for full operating range?

3. This is final circuit. Is there any need more decoupling caps?

4. U1 acts as schmitt whose output is fed to U2.
Can U2 disturb the schmitt action of U1?

5. Circuit is designed for battery powered application. At places current is in acceptable range except R2,R6 & R9 where I want to reduce current by further increasing resistor in 100K ranges.
Current for this circuit I have taken help here:
pcbheaven.com/.../index.php

5228.Design1.pdf

Hi Vindhyachal,

I set your circuit up in our TINA-TI circuit simulator to see how it behaved relative to your explanation. You can see the results below and assess if it is doing what you want. Also, I have included the TINA-TI circuit should you wish to test the circuit yourself (see note at bottom).

Queries:
1. What I am thinking, will the circuit behave the same way?

The simulation shows the MOSFET output stays high up until V1 exceeds 6 V. Then, the MOSFET output goes low.

2. At page 5 of datasheet of TLV3701, min voh = vcc-0.450 & max vol = 0.3V
Although I am taken care of these values, can these values increase/decrease further for full operating range?

The VOH and VOL values do change with supply voltage, temperature and the amount of current that is being supplied by the output. See the data sheet Figures 5 through 8 for the supply ranges that are closest to your application voltage.

3. This is final circuit. Is there any need more decoupling caps?

No, it looks like you have it covered.

4. U1 acts as schmitt whose output is fed to U2.
Can U2 disturb the schmitt action of U1?

It shouldn't, it is a very high impedance load for U1.

5. Circuit is designed for battery powered application. At places current is in acceptable range except R2,R6 & R9 where I want to reduce current by further increasing resistor in 100K ranges.

The TINA-TI simulation circuit should allow you to make changes and evaluate their effect.

Note that the E2E system is not allowing me to insert images or attach files, currently. Please send me your email address and I will send them to you directly. My email address is kuehl_tom@ti.com

Regards, Thomas

PA - Linear Applications Engineering

Hello Vindhyachal,

I am now able to include the TINA circuit diagram and attach the simulation file here to my E2E response. Please see them in relation to my last response.

Regards, Thomas

PA - Linear Applications Engineering

TLV3701_sweep_01.TSC