Introduction:
Processing requirements for automotive ECUs has been on the rise. This has resulted in automotive microprocessors demanding more power while also going to smaller manufacturing nodes.
This trend presents a two-fold challenge for a power supply designer:
Board space and budgets are constrained so the power supply designer needs to solve the above 2 challenges while staying below the space and cost budgets.
On top of this, there is a trend to meeting functional safety requirements for the system of which the power supply is a critical part of. This blog presents considerations a designer needs to take while designing such a power supply and how the PF53 core supply regulator from NXP Semiconductors offers a convenient solution.
Power Supply Focus Points:
Figure 1. PF53 High Level Block Diagram
Figure 2. Benefit of AVP
Figure 3. PF5300 AVP Characteristics
Using AVP and the high bandwidth loop, the PF53 can regulate within a 3% tolerance window that includes DC and AC tolerances with just 150 uF of capacitance. Figure 5 shows the transient response of the PF53 with only 150 uF of capacitance. This complies with the requirements for a leading vision processor.
Figure 4. Transient Response with and without AVP; Cout = 150 uF
With advances is MOSFET and switching design, the PF53 provides high efficiency across load currents in a low thermal resistance package. Figure 5 shows efficiency of the PF53 for loads up to 15 A. Refer to the PF53 datasheet for more performance curves.
Figure 5. PF53 efficiency at 3.3V input and 1.0 V output
The PF53 features the XFAILB pin which is used in other PMICs from NXP. This single pin is used to co-ordinate power up and power down timing among different ICs in the system during normal as well as during fault operation. In addition, it has programming power up timing, power down timing and delay before power good (PGOOD) release which come in handy when designing a complex power management system.
Functional Safety Needs:
Power management ICs are responsible for managing and distributing power throughout the vehicle's electronic systems, including critical components such as airbags, anti-lock brakes, and electronic stability control and ADAS. In case of a malfunction, a faulty power management IC could potentially cause these systems to fail, which could have catastrophic consequences. To prevent such scenarios, power management ICs must be designed and evaluated to ensure they meet rigorous functional safety standards, such as ISO 26262, which specifies requirements for the functional safety of road vehicles.
The PF53 is designed per ISO 26262 to meet the stringent needs of an ASIL D system. The output voltage is monitored for over and undervoltage faults with programmable fault thresholds and fault reaction.
The monitoring functions in the IC are independent and provide a high level of diagnostic coverage. Not only are the monitors independent, but the analog core of the IC is also independently monitored for faults. The PGOOD output has 2 input buffers to ensure that the output is not ‘stuck-at’ the system level. The PF53 also integrates a window watchdog timer for monitoring the processor in the system. Complete documentation such as FTA, DFA, FMEDA, detailed Safety Manual are available for customers.
In summary, the PF53 offers a high efficiency, low bill of material (BOM) solution for demanding automotive applications. The functional safety architecture and features of the PF53 exceed the ASIL D levels as prescribed in the ISO 26262 with complete documentation. For more details, head to nxp.com/pf53.
For inquiries/questions open a thread conversation on the forum Power Management.
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