PHD User Guide
15
DC-coupled frequency inputs are more susceptible to system noise than digital inputs.
To reduce system noise:
•
Connect DC-coupled frequency inputs to sensors that produce signals with no DC offset.
•
Use the shortest possible wires when connecting DC-coupled frequency inputs to sensors to prevent
noise pickup on the sensors.
Ground Level Shift
Ground level shift affects the accuracy of DC-coupled frequency inputs. Ground level shift refers to the
difference between the system ground input (GND) voltage, and the sensor ground voltage.
To reduce ground level shift:
•
If there are more than 1 GND pins in the system, dedicate one of them to sensors that have ground
wires, and connect all sensor grounds to that system ground pin.
•
Splice the other system ground inputs together in the vehicle harness (close to the connector), to
provide a better ground for the noisier low-side outputs and digital circuits.
•
Ensure the sensor’s ground connection is close to the system ground connections. This will help
ensure the signal remains within the digital activation range of the input.
Note:
The PHD system ground inputs are rated for low-current signals, which ensures the
sensor’s ground is very close in voltage potential to the system ground.
Note:
Sensors that don’t have a dedicated ground wire are typically grounded to the vehicle
chassis through the sensor’s body.
The following shows a typical DC-coupled frequency input connection:
Internal to product
Sensor Voltage
Sensor Ground
Hall Effect Sensor
DC Coupled
Frequency Input
Figure 3.6. DC-coupled frequency input installation connections
3.4. Using inputs as low power outputs
Certain input pins, (
GPIO1
through
GPIO7
) of the PHD28 and (
GPIO2
through
GPIO6
) of the PHD50,
may be used as high side, low voltage / low current outputs. All of the inputs (
GPIO1
through
GPIO10
) of
the PHD70 may be used this way.
A software configurable internal pull-up to 5V provides the drive for this flexible usage of the pins. These