DRV8803: Output voltage not correspond to input PWM duty cycle

Tool/software:

Hello,

I'm using the DRV8803 to control 4 proportional solenoid valves like in this application:

• VCLAMP is connected directly to VM without the Option Zener. VM = +12V
• IN1-4: 25kHz, adjustable Duty Cycle

Behavior: when I try to measure the voltage between the valve with a multimeter: at red and brown arrows (respectively), the voltage drop is not the same as it supposed to be corresponding to %duty cycle*VM:

The following is the actual measured voltage at corresponding duty cycle of input signal

1. 10%: 0.5V
2. 15%: 1V
3. 20%: 1,6V
4. 25%: 2,3V
5. 30%: 2.9V
6. 35%: 3.5
7. 40%: 4,1V
8. 45%: 4.7V
9. 50%: 5.4V
10. 60%: 6.6V
11. 70%: 7.8V
12. 80%: 9.1V
13. 90%: 10.39V

Is this behaviour normal? Am I missing something?

My solenoid valve is rated at 12V@150mA each.

Thanks very much for your help.

Best,