Today’s car dashboards are often crowded with lots of noise sources and temperature-sensitive sources such as radios, Bluetooth, GPS and cell phone-based network connections. Therefore, it is critical that all circuits in this environment, including the power supplies, do not produce excessive heat or EMI. In many cases, there are strict Electromagnetic Compatibility (EMC) requirements, covering radiated and conducted emissions, radiated and conducted immunity or susceptibility and Electrostatic Discharge (ESD). Conforming to all of these requirements affects many performance aspects of a potential PMIC design. Some are straightforward, such as requiring that the DC-DC switching regulators operate at a fixed frequency outside of the AM radio band. However, others are more difficult to address, such as adjusting the slew rate of internal power FETs to minimize radiated emissions due to a DC-DC converter’s switch node transitions.
Furthermore, many of today’s embedded systems and advanced processors require controlled and choreographed sequencing as power supplies are started and applied to various circuits. Allowing for system flexibility and a simple approach to sequencing not only makes the system design easier, but it also ensures system reliability and allows for a single PMIC to handle a broader range of the system than just a specific processor’s requirements.
“Feature creep”, or the changing of product specifications such as input & output voltages, and output currents as the development cycle marches on, can wreak havoc on the selection of ICs and associated discrete components. In a best-case scenario, when a system specification is changed after the board layout is set, perhaps a voltage can be tweaked by swapping a few resistors on an adjustable output converter. In the worst case, perhaps a number of ICs need to be replaced with non-pinout compatible ICs because the new output current level requirements exceed the switch current rating of the incumbent ones.