AUX 3 Output - M800

[LOLA-Christian]

Hi all,
I was thinking of using the AUX output (I selected AUX3) to PWM-drive the cooling fan.
Selected a low RDsON Mosfet for the task (STH320N4F6-6), but it didn't worked as expected.
When I added a pullup (680 ohm) to AUX3 to PWR Supply, the signal looked much better, as long as it not was connected to the Mosfet.
Has anyone a schematic of how the HW for AUX3 looks like (inside the golden box)?
How should these outputs be connected?
Some scilloscope screenshots:

AUX3 Capture.JPG (129.82 KiB) Viewed 10059 times

[Scott@FP]

In the aux3 setup, how are you switching it? Aux3 and Aux4 cannot PWM high side. Also Aux3-4 are limited to 5K Hz, the manual is incorrect.

Info from F1 Help-

"Low Side" mode switches the output to ground (Battery Negative). The load
is normally connected to Battery Positive. All outputs including the Fuel
and Ignition Outputs can be used in "Low Side" mode.

"High Side" mode switches the output to Battery Positive. The load is
normally connected to ground.

NOTE : The following limitations apply to the "High Side" mode.

1. Only Aux 1 & 2 and Aux 5,6,7 & 8 are capable of High Side mode.

2. Only Aux 5,6,7 & 8 can Pulse Width Modulate (PWM) in "High Side" mode.
If High Side mode is required for a function that uses PWM then one of
these outputs must be used. (Functions that use PWM have a Function
Number less than 100).

"Both" Mode is used when the output needs to switch to both Battery+ and
Ground. This mode is normally used for devices with high impedance inputs.

[LOLA-Christian]

In the aux3 setup, how are you switching it? Aux3 and Aux4 cannot PWM high side. Also Aux3-4 are limited to 5K Hz, the manual is incorrect.

Thanks Scott,
these are my AUX3 settings:
Function: 3
PWM/Switched: 0
Output Mode: 0
Polarity: 1
Frequency: 5000
Min Duty Cycle: 0
Max Duty Cycle: 100
Hysteresis: 0

I realize now (with your screen dump from F1 Help) that I was just confused by the signal shape when I didn't had any pull-up to the output (but still had a nice signal wave-form (althoug low amplitude)) when it was not connected to the gate of the Mosfet.
Although I can't understand why it differ so much (at rising edge) between connected to gate and and not connected?
I will continue my work, and will add a gate-driver between AUX3 and the gate of the Mosfet.

[Scott@FP]

Even though it won't high side drive, have you tried Output Mode = 2?

A PNP style transistor would be better for aux3-4.

Racegrade SSD-P (4 channel, 10A per channel) will work for you on low side drive with no other electronics and possibly 2 channels left over for other items. You can gang inputs/outputs together for high current devices. Not as much fun as doing it yourself but an easy solution.

http://racegrade.com/downloads/RG_SPEC- ... Driver.pdf