TLC393 vs. TLC7302

Hi Dirk,

Closely studying the TLC393 data sheet and the mention on page 14 about the possibility of forward biasing the input ESD diodes when the input is driven higher than Vcc, tells me that it uses a different input ESD cell structure than the TLC3702. The TLC393 appears to use what are referred to as ESD steering diodes to the supply rails. The TLC3702, in data sheet Figure 1, shows a complex ESD clamping circuit. The latter would allow the input voltage to exceed the supply rail as mentioned on data sheet page 8. Because of those ESD cell differences the input behavior beyond the supply rail can be quite different and the data sheets reflect those differences.

Regarding you questions: 

In the datasheet of the TLC7302 it is written, that the input voltage may exeed Vcc without damage and without corrupting the output signal as long as the current is limited. In my application one input is connected to a 3V reverence, wheras the other monitors the voltage across a resistor. The resistor current is limited with a current limiting diode to less than 0.5mA. In this configuration the input voltage should be handeled correctly and without any damage to the device up to the voltage limit of the CRD. Is that correct?

From the TLC3702 data sheet, page 8, "Normal operation and correct output state can be expected even when the input voltage exceeds the positive supply voltage. Again, the input current should be externally limited even though internal positive current limiting is achieved in the input protection circuit by the action of Q1." So indeed it does appear that your application meets the criteria.

If TLC7302 and TLC393 are mainly identical this should also be correct for the TLC393. Is this assumption also correct or is there any difference in the input stage of the devices?

The cited ESD cell differences may result in different input behaviors.

In the datasheet of the TLC393 on page 14 you can find "To maintain the expected output state, the inputs must remain within the common-mode range". Does this mean both inputs have to remain within the common-mode range or only one as for the TLC3702? The datasheet of this devices states on page 8: "Normal operation and correct output state can be expected even when the input voltage exceeds the positive supply voltage."

We must observe what each data sheet states.

Regards, Thomas

PA - Linear Applications Engineering 

Hi Thomas,

from your answer it is quite clear that you have read the datasheets carefully. However, the datasheet of the TLC393 doesn't state anything about the used ESD protection of the input stage. So your answer is only guessing what the author of the datasheet had in mind when it was written. I would be very glad, if you could have a look at the schematic of the device. I would be very surprised if there is a difference in the input stage of the devices since even the spice model is identical.

Best regards,

Dirk

Hi Dirk,

I am very familiar with the different ESD protection circuits used in our Precision Analog circuits. The following is from the TLC393 data sheet, page 14. It discusses the TLC393 input ESD protection:

"APPLICATION INFORMATION The input should always remain within the supply rails in order to avoid forward biasing the diodes in the electrostatic discharge (ESD) protection structure. If either input exceeds this range, the device will not be damaged as long as the input current is limited to less than 5 mA. To maintain the expected output state, the inputs must remain within the common-mode range. For example, at 25°C with VDD = 5 V, both inputs must remain between −0.2 V and 4 V to assure proper device operation. To assure reliable operation, the supply should be decoupled with a capacitor (0.1-µF) positioned as close to the device as possible. The TLC393 has internal ESD-protection circuits that prevent functional failures at voltages up to 2000 V as tested under MIL-STD-883C, Method 3015.2; however, care should be exercised in handling these devices, as exposure to ESD may result in the degradation of the device parametric performance."

The simulation models for the TLC393 and TLC3702 are nearly identical with the primary exception being the output stage differences. These two models were developed in 1990 and are simplistic by today's standards. A quick view of the syntax listing isn't revealing any ESD cells in the model. 

I would gladly take a look at the TLC393 and TLC3702 internal schematics if I had them. Since the products were developed in 1986 and at a distant location I do not have direct access to them. I will attempt to have a search done for the schematics, but likely if anything is found it won't be until sometime after the first of the year. Many of the US businesses essentially close down for the holidays.

Regards, Thomas

PA - Linear Applications Engineering