TLC3702-Q1: TLC3702-Q1

Siddharth Sangam

Intellectual 640 points

Part Number: TLC3702-Q1
Other Parts Discussed in Thread: TLC3702

Hi,

As per datasheet it is recommended that the input voltage should be in range from -0.3V to VDD.

and pin current should be limited to +/-5mA.

I have to apply Automotive standard pulse 0f -600V with Ri = 20Ohm for 1ms duration.

which is clamped using TVS clamped diode to 78V.

Now this voltage is passed through series resistor and clamped diode as shown.

which would result as maximum of 300uA input current for pin but voltage at pin is around -450mV for 1ms duration.

Then will the opamp pin get damage??.

I think as long as we are controlling the current within range the pin will not get damaged.

Need your suggestion on this.

with regards

Siddharth Sangam

over 5 years ago

0 Paul Grohe over 5 years ago

TI__Guru 52196 points

Hello Siddharth,

I would recommend that you limit the current to less than abs-max, say 1mA or less.

Your circuit should work. I would recommend breaking R3 into two or more series resistors to distribute the voltage and reduce the resistor series capacitance.

ESD transients are an high frequency AC event, and can "bypass" the 120k resistance by passing through the <1pF series capacitance of the resistor.

C2 will shunt any transients to GND, so make sure "DGND" can handle these transients and their return currents. If DGND cannot handle it, then a separate (smaller) capacitor to "GND" may be needed immediately after R3 to GND.

0 Siddharth Sangam over 5 years ago in reply to Paul Grohe

Intellectual 640 points

Hi Paul,

Yes I agree to you , prior to TVS diode we have added ESD capacitor to take care of ESD pulse.
So,we now we are on same page that as long as I am controlling my input pin current the pin will not get damage.
But I am also interested to know that if I am controlling pin current how voltage can it will be sustained.

with regards,
Siddharth Sangam

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Siddharth,

what is the purpose of this circuit? What is the input signal? What is the comparator used for?

Kai

0 Siddharth Sangam over 5 years ago in reply to kai klaas69

Intellectual 640 points

Input for comparator will be battery supply ranging from 0-36V in normal condition.

0 kai klaas69 over 5 years ago in reply to Siddharth Sangam

Guru 140200 points

Hi Siddharth.

I would insert a voltage divider between D3 and pin 3 of U1. Increase the turn-on voltage of D1 and modify the voltage divider R3/R4, if necessary.

Kai

0 Siddharth Sangam over 5 years ago in reply to kai klaas69

Intellectual 640 points

Sorry Kai,
Not convinced with the solution.

Siddharth Sangam

0 kai klaas69 over 5 years ago in reply to Siddharth Sangam

Guru 140200 points

Hi Siddharth,

first, the simulation of your circuit is shown:

siddharth.TSC

The comparator trips at 10.5V and 11.9V input voltage. The voltage at the +input of TLC3702 goes down to -0.29V. And the maximum voltage at the +input of TLC3702 leaves with 3.82V the allowed common mode input voltage range of 0...3.5V of TLC3702.

My circuit with the added voltage divider show this result in the simulation:

siddharth1.TSC

The comparator again trips at 10.5V and 11.9V input voltage. The voltage at the +input of TLC3702 only goes down to -0.1V. And the maximum voltage at the +input of TLC3702 is only 3.56V.

C1 across R2 was omitted for clarity. But never put a cap from the +input of a comparator to ground when using a positive feedback for introducing a hysteresis! This would be the same as if the driver of a car accelerates and brakes at the same time.

Kai

0 Jonathan Nguyen over 5 years ago in reply to kai klaas69

TI__Expert 4555 points

Kai,

Thanks for your help and input.

Kai's solution will help your original design stay within the operational conditions of the device as defined in the datasheet and provide enough guard band to prevent damage to the input pins of the device.

Regards,
Jonny

0 Siddharth Sangam over 5 years ago in reply to kai klaas69

Intellectual 640 points

Hi Kai,

Thanks for the simulation I appreciate it.
But the threshold values you are mentioning are not correct.
The upper thresold is VTH = 7.5V and lower threshold is VTL = 5.5V.
Hysteresis of 2V has been set.

Output will be toggled between these values.

As per my design calculations and Pspice simulation they are showing similar results.

with regards
Siddharth Sangam

0 kai klaas69 over 5 years ago in reply to Siddharth Sangam

Guru 140200 points

Hi Siddharth,

the correct simulation results also depend on the actually used TVS and D1. What components do you use? And where exactly are VTH and VTL measured?

Kai

0 Siddharth Sangam over 5 years ago in reply to kai klaas69

Intellectual 640 points

Hi Kai,
Zener diode of 5.1V is used and Bat54 54 is used.
But my interest is in how much max voltage the pin of opamp can sustain
if we are controlling the current.

with regards
Siddharth Sangam

0 kai klaas69 over 5 years ago in reply to Siddharth Sangam

Guru 140200 points

Hi Siddharth,

read section 9.1 of datasheet to see why I limited the input voltage to -0.1V...+3.56V.

Kai

0 Jonathan Nguyen over 5 years ago in reply to Siddharth Sangam

TI__Expert 4555 points

Siddharth,

Do you have any more questions regarding the topic of this thread?

Regards,
Jonny

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TLC3702-Q1: TLC3702-Q1