This integration level adds additional digital control to the standard analog design. In addition to the Level 1 control features, it is possible to control the output voltage, voltage limits, current limits and thermal limits. At this level, most of the operating parameters of the analog power supply can be digitally controlled and monitored. Different soft-start profiles and current limits can be programmed to suit the application. The output voltage can be fine-tuned to provide coordination between multiple power supplies in a system. Depending on the system I/O requirements, 8-bit solutions in the PIC12, PIC16 or PIC18 device families can provide the ideal solution. In larger systems, the 16-bit PIC24 device family can provide more communication peripherals.
A Level 2 control system has much greater integration with the power supply and allows greater power supply environment monitoring. An ADC is used to monitor the power supply inputs and outputs. On-chip comparators can also be employed to ensure fast response to system events or faults. A PWM peripheral provides direct control of the analog PWM circuitry of the power unit. The PWM control can be used to gate the analog power supply under power-up conditions to provide soft-start. The MCU can monitor the power supply input current during the soft-start to ensure that components are not over-stressed.
Serial communication peripherals allow coordination from a host device, control and monitoring of cooling fans, and monitoring of temperature sensors.
Level 2 Integration Example
In this example, the PIC MCU controls reference signals for the PWM Controller chip. In addition to Level 1 control, the PIC MCU will:
- Indirectly Set Voltage, Current and Thermal Limits
- Determine PWM Period and Duty Cycle
- Perform Self calibration
Additional features of the Level 2 Intelligent Power Integration: Proportional Control are listed below:
- On-Off only, typically via a SHUTDN input to a traditional analog
- Switch Mode Power Supply (SMPS) controller
- Proportional control of the SMPS performance, such as output voltage and current
- Current in/out
- Voltage in/out
- Level 1 features
- Soft-start and voltage slew rate control
- Digital temperature compensation
- Sample and hold calibration to an external standard
- Single or multiple preprogrammed output voltages
- Remote monitoring and control
Analog Access Requirements:
- Shutdown and startup control through a SHUTDN input
- Control of reference inputs such as PWM clock, VREF, and ILIMIT
- Analog, digital and frequency based signals for monitoring
- The bulk of the reliability of the system is still determined by the traditional analog SMPS design. However, absolute performance specifications are regulated by the microcontroller and can lead to performance failures in the event of a software failure of the system.