Parker GVI Series - 8.8 Open Drain Output

I/O interface description
GVI Product Manual: Frames C, D & E
34 192-300300N1 GVI Frames C, D & E 2019-9
8.8 Open Drain Output
8.8.1. Function
Open Drain outputs can be used for operating services such as the main contactor, relay, hydraulic valves,
parking brake, etc.
The Open Drain outputs may work in different modes depending on the expected behavior of the connected
load. The operating modes are:
• On/Off
• Voltage control (Pull/Hold)
• Current control
• Open-loop PWM control
In order to utilize the built-in free-wheeling diodes, open drain 4, 5 and 6 loads must be supplied from the
HIGH_SIDE_IN, while the open drain 1, 2 and 3 loads can be supplied from either HIGH_SIDE_IN or
HIGH_SIDE_OUT. Recommended wiring of loads, utilizing redundant shut-off capability of the high side
switch, is shown in Figure 22.
In case the vehicle design does not allow usage of the built-in free-wheeling diodes, i.e. if the return path
integrity cannot be guaranteed in all situations, external free-wheeling diodes must be applied over the
inductive loads controlled by the open drain outputs.
Open drain output #
ON/OFF control
PWM control
Closed loop
current control
1,2
Yes
Yes
Yes
3,4
Yes
Yes
No
5,6
Yes
No
No
Table 8. Open drain functionality
PWM frequencies are settable. The setting will apply to all PWM outputs. PWM shall only be used for
inductive loads such as relays, contactors, motor brakes or hydraulic valves.
Each “open loop PWM” output can be voltage controlled with separate pull and hold voltage software
parameters.
The current measurement can be used as open-load and overload detection. Each output has individual
hardware for short circuit detection and rapid shut off to prevent damage to the circuit.
Refer to chapter 13.4.5 for current measurement range. The current is only measured when the Open drain
MOSFET is ON, see circuit in Figure 21. Current measurement offset error is compensated in software.
When using current control it is possible to add dithering by giving the current a low frequency, low amplitude
oscillating waveform.
Dithering is typically used when controlling proportional valves to create microscopic movements in the valve
to prevent it from “sticking”. Successful dithering improves the valve response for small changes.
Set value Hz
250
125
83
62
50
41
Table 9. Dithering frequency in fixed steps
The dithering frequency and current amplitude are adjustable. Actual dithering amplitude is dependent on
load inductance, dithering frequency and current control regulator parameters i.e. P-gain and I-gain.