What would cause the IHold current to constantly drift up? The hold current increases approximately 5 mA per minute. The output shuts off when VSense reaches 110mV and that doesn't change.
IPeak is set at 1 A
IHold is set at 0.55 A
RSense is 0.2 ohm
f(PWM) is 25kHz
Thanks,
RJJ
Hi,
Based on your description the maximum hold current doesn't change over time, it is the expected Ihold_set*Rsense=110mV
Rhold sets with this current for the PWM comparator, when Vsense reaches 110mV Vout turns off.
The Ihold current will vary between:
-Ihod max =110mV/Rsense at the end of PWM on pulse.
-Imin is the lowest current at the end of the PWM off pulse
The duty cycle and Imin depend on the solenoid inductance and resistance, the solenoid supply voltage PWM frequency and the freewheeling diode forward voltage
If the average current changes over time you should see duty cycle variation and/or Imin change. It is possible solenoid Inductance and resistance changes due to heat.
Another possibility( very unlikely) is Rsense variation due to heat. In this case you'll see the max current drift.
Regards,
Costin
