Pulse width modulation fault mode for illuminating device drivers
A PWM architecture of a microcontroller is disclosed that includes a fault module for regulating and detecting faults in current sensing or illuminating devices (e.g., LED strings). The fault module is part of a hardware regulation loop of LED voltage and LED current that allows the CPU to be placed in idle mode (“IDLE”) while an LED string is regulated in illumination. The microcontroller includes a PWM generator having a double channels PWM timer with a specific fault mode and an amplified comparator with a voltage reference. The architecture allows tuning of various parameters, including LED peak current, LED voltage supply, LED voltage regulation step and LED dimming value. In IDLE mode, the hardware regulation loop can regulate LED peak current and LED voltage supply without any CPU resource (microcontroller in IDLE mode). The fault module part of the hardware regulation loop can also detect and inform the CPU of: 1) an open LED; 2) a weak battery; and 3) an LED voltage that is under a target value.
1. A system, comprising:
one or more current sensing devices; and
a microcontroller coupled to the one or more current sensing devices and including:
detection circuitry coupled to the one or more current sensing devices;
a central processing unit; and
a pulse width modulation generator including a fault mode module coupled to the detection circuitry and the central processing unit, the fault mode module and detection circuitry configured to regulate the one or more current sensing deviceswhile the central processing unit is idle, to detect a fault of the one or more current sensing devices and, upon detecting the fault, to awaken the idle central processing unit to respond to the fault.
2. The system of claim 1 , where the one or more current sensing devices include Light Emitting Diodes (LEDs).
3. The system of claim 1 , where the fault mode module is configured to regulate voltage across or current through the one or more current sensing devices.
4. The system of claim 1 , where the detection circuitry is configured to compare a measurement of one or more regulated parameters with a reference value and to generate a signal based on results of the comparing.
5. The system of claim 4 , where the reference value is based on a value defined by the central processing unit.
6. The system of claim 1 , further comprising:
circuitry for adding quantums of energy to the one or more current sensing devices, the circuitry configured for receiving output from the microcontroller.
7. The system of claim 6 , where the circuitry is a DC/DC converter.
8. The system of claim 1 , where the fault mode module is configured to manage at least two pulse width modulation (PWM) outputs for performing the regulating and fault detecting.
9. The system of claim 8 , where the fault mode module is configured to force a first PWM output to an inactive value starting from a fault event to an end of a PWM cycle.
10. The system of claim 9 , where the fault mode module is configured to cancel a subsequent active pulse on a second PWM output when the fault event occurs during an active period of the first PWM output.
11. The system of claim 10 , where the fault mode module is configured to send an error signal when an active pulse on the second PWM output is not followed by an error detection during the subsequent active pulse on the first PWM output.
12. The system of claim 1 , where the fault mode module is configured to maintain fault state information, and uses the fault state information in the fault detecting.
13. The system of claim 12 , where the fault state information is reinitialized at each PWM cycle.
14. A method comprising:
receiving, by a microcontroller of an illuminating device driver, a signal indicative of a state of one or more regulated parameters of one or more current sensing devices;
regulating at least one of the one or more regulated parameters based on the signal while a central processing unit in the microcontroller is idle;
monitoring, by a fault mode module included in a Pulse Width Modulation (PWM) generator in the microcontroller, for a fault in the one or more current sensing devices based on the signal,
where the regulating and monitoring is at least partially implemented by two PWM signals that are generated by the PWM generator based at least partially on the signal; and
upon fault detection by the fault mode module,
awakening the idle central processing unit to respond to the fault.
15. The method of claim 14 , where the fault mode module is configured to force a first PWM signal to an inactive value starting from a fault event to an end of a PWM cycle.
16. The method of claim 15 , where the fault mode module is configured to cancel a subsequent active pulse on a second PWM signal when the fault event occurs during an active period of the first PWM signal.
17. The method of claim 16 , where the fault mode module is configured to send an error signal when an active pulse on the second PWM signal is not followed by an error detection during the subsequent active pulse on the first PWM signal.
18. The method of claim 14 , where the fault mode module is configured to maintain fault state information, and the method further comprises using the fault state information in the fault detecting.
19. The method of claim 18 , where the fault state information is reinitialized at each PWM cycle.
20. The method of claim 14 , where monitoring for a fault further comprises:
monitoring for at least one of an open current sensing device, a weak battery, or an current sensing device voltage that is under a target value.