Scope issue or GND bounce or other?

[travulous]

I'm experiencing an unusual phenomenon when testing a hardware design. The design has 5 high current Low-side PMOS drive circuits which are designed to actuate 1 ohm solenoids with a short (<100ms) pulse. Each drive circuit is individually controlled via an MCU port. The supply voltage to each of the drive circuits is the same and all of the grounds return to the same analog ground. Each drive circuit has an active current limit which limits the drive current to 8A for each solenoid. What I notice during testing is that it appears that the adjacent channels are being affected when other drive circuits are turned on. For example, if I monitor channels 1-4 with a scope and turn on channels 1-3, the channels 1-3 turn on perfectly (~8V) but channel 4 (which should be off) also turns on slightly (<1V). The scope is grounded to the same system ground as the drive circuits.

Could this be ground bounce?

Thanks for your help.

Travis

 

[chuckey]

If you are actuating 3 outputs (3 X 8 = 24A), there is a lot of current flowing! I can't quite make out you measurements, because with a low side switch, when the switch is on Vo ~ .2V and when off ~ 8V(power supply volts), so are you measuring from your power supply +?, could it be that your power supply is sagging?
Frank