HOLT HI?8470 User Manual - page 11
AN‐8470, Rev. A
HOLT INTEGRATED CIRCUITS
3/2/15
11
3. A similar test can be done with the sensors in Supply/Open mode. In this mode, the
internal thresholds are VTHImin = 15.5V and VTHLOmax = 11V. Set all the ‘Sensor Type
Select’ switches to ‘1’. Put J5 and J11 in the non‐GND position. Connect a 15.5V supply on
the VSense 0:7 and VSense 8:15 terminals. The guaranteed switching threshold of 15.5V is
being applied to the input, with all the sensor input switches ‘ON’, all sensor outputs
should be a ‘0’.
4. Lower the input voltage to 11V, this is the guaranteed low switching threshold, all the
sensors outputs should now have changed to a ‘1’. This can be observed on the ARINC 429
output or on the Sensor Out pins.
5. To change the thresholds, remove the EXTTHSOG and EXTTHVO jumpers. External
thresholds can now be applied using the potentiometers VR1 to VR4. Connect a voltmeter
to the terminal above the potentiometer, adjust the potentiometer to set the threshold
voltage. Note that threshold set is 10x the voltage on the test point. A typical set of
threshold settings is shown in the table below:
TEST POINT
VOLTAGE
THRESHOLD (X10)
THSLOGO
0.45
4.5
THSHIGO
1.05
10.5
THSLOVO
0.6
6.0
THSHIVO
1.2
12.0
6. To test the external thresholds, the sensor input switches should be set to ‘Open’ and the
sensor input voltage applied to the Sensor Input pin (see table in next section).
Connecting an external ARINC 429 driver
The connector ‘EXT ARINC 429 DRIVER’, provides CMOS logic level outputs for connecting an
external ARINC 429 driver. In this case, the VDD supply is still required on the board as this
supplies the Crystal Oscillator and the Clean Switch circuit. However if pin one of the XTAL VDD
link and pin 1 of TXENB link are connected to an external 3.3V, then VDD link can be removed.