TIC12400-Q1: TIC12400-Q1 INx pins external pull up or pull down requirement

Hi Jonathan, 

Thanks for the clarification.

Now can you confirm one more point

Can we configure INx channels wetting current individually ?

I mean for few channels with internal wetting current and few channels with external resistors by disabling wetting 0mA. Please confirm. 

Thanks & Regards,

Murali Penta.

Hi Murali,

Some INx channels can have there own wetting current settings, and others are grouped to a common setting with another INx channel.  Similarly the Comparator and ADC thresholds settings have some independent and shared settings for different combinations of INx pins.  You can find the wetting current and threshold setting details in section 8.3.8 of the datasheet in table 8-1. 

I've highlighted IN0 and IN1 to show they have a common wetting current setting.  They also share a common Comparator threshold setting but could have different ADC thresholds.  IN1 and IN2 can have different wetting current settings, but would still have to have the same Comparator threshold.

You will have to verify your pin assignment and configuration settings will be compatible based on this table.

I will also note that there is some leakage current when the wetting current is set to 0mA.  If the voltage supplied to the INx pin is not a driven voltage that will hold it steady, but derived from a weak source such as a resistor voltage divider, then this leakage current could have an impact on the voltage level that is measured.  Therefore, it is recommended to have a capacitor on the INx pin to absorb this leakage current and stabilize the voltage level. 

Regards,

Jonathan

Hi Jonathan, 

Thanks a lot for the inputs. 

These are useful for our design implementation.

We would like to review our schematic with you and it will help us to design more robust circuit.
Since this forum is common for every one, We cant share our schematic here.
can you share your mail ID, so that we will share our schematic for your review. 

Thanks & Regards, 

Murali Penta 

Hi Murali,

Yes, I will contact you through email so that you can share the schematics directly with me to review.

Regards,

Jonathan

Hi Jonathan, 

Thanks for connecting through mail.
Further to our discussion. can you please address following our query 

In the process of diagnostics/automotive safety considerations,  whether Inx pins of TIC12400-Q1 are designed for detecting of short to BAT or short to GND scenarios/conditions also??

Please confirm whether TIC12400-Q1 have above feature ?

Thanks & regards, 

Murali Penta

Hi Murali,

There are no dedicated fault diagnostics specific for short to BAT or short to GND outside of the normal operation of the device.  These types of conditions are essentially normal for the device when using switches designed to provide a low impedance connection with either BAT or GND when closed.

Once the device has been configured and trigger, it will simply monitor the INx pins and use the Comp or ADC to determine the voltage state of the INx pin as either above or below the threshold, and or return the ADC code if using the ADC.

Depending on the configuration, it is possible to perform some diagnostic fault testing by reconfiguring the device with different settings and then polling the INx pins again with these new settings (current source vs current sink, ADC vs Comp, different wetting current levels, etc.).  The two points of data would allow the MCU to use some logic to determine if a fault condition exists.  However, this requires a configuration change and the normal polling for the primary configuration would be disrupted while the MCU would be running this special diagnostic test routine.

Regards,

Jonathan

HI Jonathan, 

Understood the limitation with TIC12400-Q1  regarding short to BAT & GND. I am not sure how much easy to reconfigure/re initialize the device for software team. while running overall/entire system

Hi Murali,

I'm not sure this is a limitation with the device because the device can detect these types of conditions.  For example, a pin that is used to detect whether a switch is closed and making a connection to GND, or there is a short to GND on the pin, are effectively the same condition from the perspective of the TIC12400-Q1. 

Fault detection is important, but it is difficult to achieve with a single configuration. 

Regards,

Jonathan

HI Jonathan, 

Understood, But  we want to detect both the conditions like switch close condition and INx pin short to GND/BAT conditions
Based on the current features of TIC12400-Q1, for our requirement  as you said we may need to reconfigure the device to detect the short condition on the INx pin.

Thanks & Regards, 

Murali Penta 

Hi Murali,

Yes I understand.  Unfortunately there are no direct fault detection features that can determine the difference between a short and a closed switch at the same time.

Regards,

Jonathan