TIC12400: TIC12400 or TIC12400-Q1 for our customized PLC?

Hi Luca,

Yes, the TIC12400-Q1 meets the automotive AEC-Q100 requirements, while the TIC12400 does not. They are functionally very similar, but the TIC12400-Q1 has slightly different specifications such as safe operating temperature and voltage ranges as well a few additional parameters that must be met for the AEC-Q100 requirements.

Over voltage condition for Vs (Vov_r) will be set with voltages above 35V and the current sources/sinks will be de-activated and switch monitor stops to prevent damage to the internal structures of the device. This is outlined in section 8.3.7 of the TIC12400 datasheet.

If your 24V supply increases to 28V, the Over Voltage condition should be avoided. However, there are several internal LDOs inside the device and operating at a higher supply voltage will result in an increased junction temperature inside the device. You will notice that the maximum ambient temperature is 105 degrees C for a supply voltage of 18V, but only 85 degrees C for a supply voltage of 24V. Operating above 24V will reduce this even more and also limit the maximum wetting current and prevent the use of continuous mode due to additional device heating. Prolonged usage with high junction temperatures can also shorten the overall lifespan of the device and it is always recommended to operate within the datasheet limits.

I’m not sure I fully understand your LED configuration and idea. The TIC12400 should be capable of sourcing or sinking enough current to illuminate an LED, but I’m not how this works with your switches and inputs. Perhaps you could make a simple diagram to help me understand so that I can offer a better answer. But I’ll offer some general thoughts on the topic that might be helpful to you.

There are two types of wetting current modes, Continuous, and Polling. In Continuous mode, the current to all the input pins is always on. In Polling mode, the current is only on the input pin that is actively sampled. The device will disable the current for all pins not being actively sampled as a way to lower the overall power and thermal heating. Because of your high supply voltage I would recommend not using continuous current mode with the higher levels of current such as the 5mA or 10mA that would be needed to illuminate an LED. And in Polling mode, the sampling window is very short which will make it difficult to see LED.

However, if the current for your inputs and LEDs comes from a different source, then you could use the ADC as the input threshold without wetting current (0mA setting) and it will simply sample the voltage level of the input pin to determine the switch state. This is also how you can read the value of your analog sensor output voltage which is your final question.

Regards,

Jonathan

HI Jonathan,
thanks for the quick reply.
In other words, for my application I cannot use the TIC-12400 and neither the TIC-12400-Q unless I accept a maximum operating temperature <85 ° C, which I cannot accept.

This is the list of required features:
- Read the status of 8 NPN inputs 24Vcc + -10% on SPI 3.3Vcc. Total digital inputs to read 24;
- Possibility of daisy chain. It is not needed if a single component manages 24 inputs like the TIC-12400;
- Insulation not required;
- Have LEDs to monitor the status of the inputs;

What Texas products do you recommend?
Thanks

Hi Luca,

The higher voltage + higher temperature conditions you require are a little out of the datasheet specifications of the TIC12400 device.  This does not necessarily mean the device would not function, just that the performance outlined in the datasheet may not be met for all parameters for the lifetime of the device.

If you do not need to source a current to measure the value of your inputs, then I know of a device that may be a better fit for your application.  The SN65HVS88x family of devices are 34V 8-channel High Voltage Digital Input Serializers that can be daisy chained on a single SPI interface to return the status of the inputs. They also will directly drive a status LED for each input.

The SN65HVS882 and SN65HVS885 look like they might meet your temperature and voltage requirements but I don't know how high of a temperature you will need to support.

These are designed for a 5V digital IO system, but the input threshold for a high bit on the SPI is 2V which will allow it to detect a 3.3V SPI signal.  However, you may need a level shifter on the output signal if your MCU is not 5V tolerant.

Regards,

Jonathan

Hi Jonathan, thanks for the reply.
A couple more questions:
-Do SN65HVS88X models also work in NPN?
-If for our PLC we choose the TIC-12400, constantly powered at 24Vdc, we should choose the TIC-12400 not the TIC-12400-Q, right?

Thanks.

Hi Luca,

On a closer look, the SN65HVS88x devices can only sink current on their inputs, therefore they would not be useful with an NPN sensor that is also sinking current.

Generally speaking the TIC12400-Q1 will have better specified performance and the TIC12400-Q1 has a higher specified operating junction temperature of 150 degrees C compared with the 125 degrees C rating of the TIC12400.  Therefore between the two, I would think that the TIC12400-Q1 would be preferred for your application.  But they are functionally very similar and you will need to verify that the differences between the two meet your requirements.

Regards,

Jonathan

Hi Jonathan, thanks for the reply,
I also thought I would try the TIC12400-Q, but after reading this:

e2e.ti.com/.../896262

I don't know if this "automotive" component can be constantly powered at 24Vdc, it seems that constant 16Vdc cannot be exceeded. Correct? Can I use the TIC12400-Q at 24 / 26Vdc or not?
Thank you

Hi Luca,

The available information does seem a bit misleading, or at least incomplete in terms of an explanation for the supply voltage recommendations and limitations.  So I have spoken with the lead designer for these devices in order to give you a reliable answer.

The TIC12400-Q1 was first designed to operate in a 12V automotive application and meet the stringent requirements for the transient voltages up to 35V.  The device components are rated to survive and support voltages up to 35V.  However, a 24V system has even larger transient voltages than a 12V system, and therefore there is a risk of exceeding the limitations of the device and incurring some damage.

The datasheet specifications take into account Voltage, Temperature, and Semiconductor Processing variations when setting the performance limits based on statistical extrapolation. 

The recommended 16V operating limitation for a 12V system is due to the possibility that an imperfection that is common across the semiconductor industry may occur in some devices that affects the voltage tolerance of some of the internal components and make them more susceptible to damage from larger voltage transients.

A lot of effort was given by our design team to ensure the design used components large enough to ensure proper operation even if a device contained one of these rare imperfections.  The datasheet limits and supply recommendations were set for these reasons and for automotive applications.

The TIC12400 is a variation of the TIC2400-Q1 that is not rated for the automotive safety requirements but it is still susceptible to the same manufacturing process where transient voltages may exist.

The device will operate at voltages of 24V, but large transient voltage spikes may exceed the capabilities of the device and cause a failure. The question becomes what is the tolerance for failure in your end application if a device suffers damage to a transient voltage?  In an automotive application, this could lead to a crash and human injury.  In an industrial application, it may only lead to a equipment failure that requires servicing.

This is a parts per million (PPM) situation where there is a very small statistical possibility that a defect could exist that causes a device to be less tolerant of a transient voltage and suffer damage.  Because 24V systems have larger transients than 12V systems, if the device is operated with a supply voltage towards the higher end of the device ratings, the risk of damage from a large transient spike is greater.  By lowering the system voltage, these transient voltages are reduced and risk is reduced.

The risk is well understood for a 12V system and the datasheet accounts for this and guarantees safe operation which is why the Vs = 12V language exists in the Q1 datasheet and was also carried over to the non-Q1 datasheet.

Regards,

Jonathan

Hi Luca,

I wanted to add that it is possible to implement transient protection to the input pins allowing the TIC12400 device to safely operate in a 24V system as shown in this application brief.

If you can add some transient suppression to the system, then the TIC12400 will work well in a 24V system.

Regards,

Jonathan