Frequency-controlled load driver for an electromechanical system

1. A frequency-controlled load driver circuit comprising:

a solenoid load connected with a series sense resistor;

a switching driver coupled to the load, the driver operable to switch a load current at a predetermined switching frequency during a steady-state operational mode;

an analog-to-digital converter (ADC) coupled to the sense resistor for oversampling a voltage thereacross, wherein the ADC oversamples the sense resistor voltage 2 N times, where N is an integer, within each period of the predetermined switching frequency; and

a control circuit coupled to the ADC and driver, the control circuit is operable to set the switching frequency of the driver during the steady-state operational mode by providing predetermined switching times, and the control circuit is also able to disable switching during a transient operational mode.

2. The circuit of claim 1 , wherein the control circuit is operable to apply a dither to the load current during steady-state conditions.

3. The circuit of claim 2 , wherein a frequency of the applied dither is different than the switching frequency and is applied to the load current by varying the switching frequency at a desired dither frequency.

4. The circuit of claim 2 , wherein the dither frequency is the same as the switching frequency.

5. The circuit of claim 1 , wherein the control circuit is operable to adjust a duty cycle of the switching driver to maintain a desired average of the load current.

6. The circuit of claim 1 , wherein the control circuit is operable to maintain the operating phase of the load driver circuit when switching between steady-state and transient modes.

7. A frequency-controlled load driver circuit comprising:

a solenoid load connected with a series sense resistor;

a switching driver coupled to the load, the driver operable to switch a load current at a predetermined switching frequency during a steady-state operational mode;

an analog-to-digital converter (ADC) coupled to the sense resistor for oversampling a voltage thereacross, wherein the ADC oversamples the sense resistor voltage 2 N equally-spaced times, where N is an integer, and sums the samples within each period of the predetermined frequency; and

a control circuit coupled to the ADC and driver, the control circuit is operable to set the switching frequency of the driver during the steady-state operational mode by providing predetermined switching times, and the control circuit is also operable to apply dither to the load current and to disable switching and dither during a transient operational mode.

8. The circuit of claim 7 , wherein the dither frequency is different than the switching frequency and is applied to the load current by varying the switching frequency at a desired dither frequency.

9. The circuit of claim 7 , wherein the control circuit is operable to adjust a duty cycle of the switching driver to maintain a desired average of the load current.

10. The circuit of claim 7 , wherein the control circuit is operable to maintain the operating phase of the load driver circuit when changing from the steady-state mode to the transient mode.

11. The circuit of claim 7 , wherein the control circuit is operable to change the load driver circuit from the steady-state mode to the transient mode by setting at least one new switching setpoint and disabling dither, and the control circuit is operable to switch from transient mode to steady-state mode when the load current is within a predetermined percentage of the new setpoint.

12. The circuit of claim 11 , wherein the control circuit is operable to maintain the operating phase of the load driver circuit when switching between transient and steady-state modes, wherein when the load driver circuit is being switched from transient mode to steady-state mode, the control circuit is operable to reinstate a dither frequency to the load current for resynchronization until a start of a next period, whereupon the switching frequency is also reinstated in phase with the control logic.

13. A method for controlling a frequency-controlled load driver circuit, the method comprising the steps of:

providing a solenoid load with a series switching driver and a series sense resistor and an analog-to-digital converter coupled thereto;

setting the switching driver to operate at a predetermined switching frequency during a steady-state operational mode by determining appropriate switching times;

oversampling a voltage across the sense resistor due to a load current of the solenoid by the analog-to-digital converter 2 N of times, where N is an integer, within each period of the predetermined switching frequency;

applying dither to the load current;

changing to a transient operational mode by disabling switching of the switching driver; and

changing to a steady-state operational mode by enabling switching of the switching driver at predetermined switching times to set the switching frequency of the switching driver.

14. The method of claim 13 , wherein the applying step includes applying a frequency of the dither different than the switching frequency by varying the switching frequency at a desired dither frequency.

15. The method of claim 13 , further comprising the step of adjusting a duty cycle of the switching driver to maintain a desired average of the load current.

16. The method of claim 13 , wherein the changing steps include maintaining the operating phase of the load driver circuit when changing between the steady-state mode and the transient modes.

17. The method of claim 13 , wherein the changing to a transient operational mode includes disabling the dither.

18. The method of claim 13 , wherein the changing to a steady-state operational mode includes reinstating dither to the load current for resynchronization until a start of a next period, whereupon the switching frequency is also reinstated in phase with control logic.

19. The method of claim 13 , wherein the applying step includes applying a frequency of the dither the same as the switching frequency.