TIC12400-Q1: application question of 12400

Hi Sherry,

Sherry Liang said:

1. Under what circumstances will cause our chip to fail? Under what circumstances will cause a single channel to fail? If one channel fails, will other channels be affected?

Can you better define what you mean by fail?  Are we talking about physical damage to the device, or the failure to detect a switch changing state?  I'm interpreting this as failing from physical damage and therefore the device should be used according to the datasheet and the absolute voltage levels on the pins should not be exceeded.  Appropriate protections to prevent a power supply reverse polarity and proper RC Filter and or TVS diodes are also recommended to protect the device from potentially harmful over-voltage stress events.  It could also be possible for multiple channels, or the entire device, to be affected by damage to a single input, but this would depend on the type of damage.  Portions of the inputs are independent of each other, and other parts are shared such as the ADC, Comparator and MUX, etc.

Sherry Liang said:

2. In continuous mode, if the wetting current of every channel is 10mA, then our device will always consume 240mA current(24 channels). Then the total consumption of our device is 240mA+7mA, right?

The amount of current consumed will depend on the switch state for every input that is enabled.  A closed switch will consume more current than an open switch.  For example, if all channels were set to source 10mA of current continuously, and all 24 inputs had a switch connected to ground, then yes, all 24 channels would be sourcing 10mA of current continuously.  However, if the switches were open, then there would be no path to ground for the current to be sourced, and therefore the current consumption would be less. 

The Is_cont spec (7mA max) is what the device will consume when all channels are configured for 10mA continuous wetting current, but with all channels having Open Switches.  An additional 10mA of current should be added for each switch that is closed.

Sherry Liang said:

3. In the datasheet, there are two switches, analog switches and digital switches. For our device, the only difference between these two switches is that analog switch may have several states while digital switch only have two states, right?

Yes, this is really just terminology and the datasheet trying to distinguish between different types of input switches.  Really this is all about whether you will want to use the ADC or the Comparator for sampling the input switch state.  Either the Comparator, or ADC can be used on any or all input channels, and each channel can be configured individually, so some can use the Comparator, and others use the ADC.

"Digital" switches are more simple and therefore have an Open or Closed status (effectively a binary choice).

"Analog" switches are more of a resistor coded switch that may have multiple different resistance values that would result in a different voltage level for each switch state.  An example of this might be a widshield wiper speed control switch where each setting had a different resistor associated with it.  To detect this type of switch, the ADC would be needed so that the different voltage thresholds could be determined.

Regards,

Jonathan