Closed loop magnetic boost LED driver system and method

An apparatus for closed-loop control of an output current (IOUT) that is delivered to a load circuit from an inductor, the apparatus comprising:

• a switching means that is arranged to selectively couple a switch node to a power supply node when activated, such that the inductor is charged by an input voltage (VIN) when the switching means is activated, wherein the inductor is arranged to deliver the output current (IOUT) to the load circuit when the switching means is deactivated;
• an output sense means that is arranged to provide a sense signal (VSNS) that is proportional to the output current (IOUT);
• a difference means that is arranged to adjust an error signal (VERR) in response to a difference between the sense signal (VSNS) and a reference signal (VREF);
• a ramp means that is arranged to provide a ramp signal (VRAMP), wherein the ramp means is arranged to initialize the ramp signal (VRAMP) to a predetermined level in response to a reset signal (ENR);
• an adjustment means that is arranged to adjust a slope of the ramp signal (VRAMP) in response to the error signal (VERR);
• a comparison means that is arranged to compare the ramp signal (VRAMP) to the error signal (VERR) to provide a comparison signal (VCOMP), wherein the comparison signal (VCOMP) is asserted when the ramp signal (VRAMP) reaches the reference signal (VERR);
• a discharge sense means that is arranged to activate a pulse signal (VFF) when the voltage (VSW) associated with the switch node is sensed as decreasing by a predetermined amount;
• and
• a latch means that is arranged to:
• assert the reset signal (ENR) when the pulse signal (VFF) is asserted, activate the switching means when the reset signal (ENR) and the comparison signal (VCOMP) are de-asserted, and deactivate the switching means when the comparison signal (VCOMP) is asserted.

A method for providing closed-loop control of an output current (IOUT) to a load circuit from an inductor (L), the method comprising:

• evaluating a switch signal (VSW), wherein the switch signal is associated with the inductor (L);
• resetting a ramp signal (VRAMP) to a reset level when the switch signal (VSW) drops below a predetermined level, wherein the ramp signal (VRAMP) has a characteristic slope;
• generating an error signal (VERR) that is responsive to changes in the output current (IOUT);
• adjusting the characteristic slope of the ramp signal (VRAMP) in response to the error signal (VERR);
• comparing the ramp signal (VRAMP) and the error signal (VERR);
• controlling an on-time interval in response to the ramp signal (VRAMP) and the error signal (VERR), wherein the on-time interval is related to the characteristic slope of the ramp signal (VRAMP);
• charging the inductor with an input voltage (VIN) over the on-time interval (TON);
• and
• coupling current from the inductor to the load circuit when a ramp signal level has reached the error signal level and the switch signal (VSW) is above the predetermined level.