TIC12400-Q1: Questions about Wetting Current Auto-Scaling

Hi Johnny,

Please see the details below:

1. If working in Wetting Current Auto-Scaling and current is 10mA or 15mA, how to calculate IN pin average current when DET_FILTER= 00, 01, 10?

Since the wetting current auto-scaling only applies to 10mA and 15mA settings and is only available in continuous mode, the IN pin current will be 2mA when the  DET_FILTER= 00, 01, 10

2. When working in Wetting Current Auto-Scaling, if INX is set CSI and use comparator to acquire data, how to calculate IN pin threshold voltage?

From your schematic in the 2nd bullet:

For closed switch, the voltage drop at INX will be Vsupply (14V) minus the voltage drop across the resistors (RDIRT and RSW).

For open switch, the path is connected to ground.

You need to set the IN pin threshold voltage between the open and closed switch voltage drop limits.

3. What does below maximum voltage mean? According to CSI current 2mA, IN pin voltage shoule be 2mA*5k=1V<2V, if CSI current is 10mA, it should be 10mA*5k=5V>1.7V.

The maximum voltage drop across the current sink makes sure you configure the threshold above the maximum voltage drop. When the switch is open, the voltage drop will be 1.7V as shown in the in the datasheet table above.

When the switch is closed, the voltage drop will what you calculated in  bullet No.2.

The spec in the datasheet refers to the matrix use case where you have higher current sink setting but actual current flowing in INX pin is limited by the current source.

Thanks

Saminah

Hi, Saminah,

Thanks for reply. For each item I have question listed as below.

1. In Wetting Current Auto-Scaling, I calculate current by 2mA and ignore 10mA or 15mA, is it?

2. IN x`s threshold is same as comparator`s threshold? If comparator`s threshold is set 4V.

3. When the switch is open. Will the IC break, If the voltage of IN x is more than 1.7V?  what is function for VCSI_DROP_OPEN or VCSI_DROP_closed?

Thanks.

Johnny