Designing in this way requires updating the design concept and transferring the control logic of the system from hardware to firmware or software. What's more, these advantages reduce the number of components required, reduce the cost of the system, and have greater flexibility in meeting the unpredictable needs. When the circuit board is inserted into the backplane, the hot plug controller must perform the following actions perfectly:
First, the power supply voltage, current and the status signal of the subsystem on the circuit board are monitored to determine whether everything is working properly. If this is the case, then the controller can make the HEALTHY signal on the cPCI bus valid. In the event of a failure, the controller needs to respond in a way that minimized potential damage.
Second 、 test the cPCI bus power supply in a stable state, and use /BRD_SEL signal to make the circuit board in place. When these conditions are met, the controller can connect the circuit board power system to the bus power supply. For circuit boards that absorb large current power lines, power management may also need to control the rate of voltage rise to prevent transient damage in the system to the operation of other circuit boards.
Third 、 monitor the control signal of cPCI bus, especially /PCI_RST. The power manager must make the local reset signal /LOCAL_PCI_RST valid and maintain a certain amount of time after all board level voltages have been stabilized to ensure that the system on the circuit board is properly initialized.
Conversely, when the hot plug controller detects that the circuit board is pulling out of the system, it must ensure that the power on the edge of the circuit board is disengaged before disconnecting the power connector. Failure to do so will cause arcing and transients on the backplane's power supply, potentially interfering with other circuit boards that are operating.
With the continuous improvement of board level integration, the function and complexity of power management are becoming more and more demanding. Multiple devices may need to follow special power up and power down timings. Even single chip that uses multiple voltages to support cores and I/O circuitry may require specialized timing. Through the use of DC-DC converters and load point regulators, it is often possible to provide multiple power supplies on the local board and may require separate monitoring and control functions.
The power management system can be implemented by combining standard power management ICs with top level control functions. Although simple design is possible, this approach quickly becomes uncontrollable when people try to provide the various functions and interface requirements of an independent controller.
Instead of implementing power management systems from one or more pre-defined Controller ICs, a more efficient approach is to first consider the need for those basic functions to support power management systems. These functions can be divided into resources that support hardware measurement and control, and logical operations that support timing and combination processing. Table 1 lists the most common part functions that need to be implemented for power management.