NXP Semiconductors MPC5746R - DC Electrical Specifications

Power Supply
MPC5746R Hardware Design Guide, Rev. 1
NXP Semiconductors 11
3.5 Decoupling capacitor layout priorities
When trade offs must be made in the layout, it is important to ensure that the highest priority decoupling
capacitors are placed as close as possible to the MCU. The list below orders the power supply domains
from highest to lowest priority in terms of decoupling capacitor placement.
• Highest priority is given to the analog-to-digital converters reference and power supply
decoupling: VDD_HV_ADR_SAR, VDD_HV_ADR_SD, VDD_HV_ADV_SAR, and
VDD_HV_ADV_SD. Clean supplies are vital to ensure that the highest accuracy is achieved with
the ADCs. In addition, linear supplies must be used as analog references. The supply for the
oscillator (VDD_HV_IO_JTAG) is also prioritized as this helps to ensure reliable and stable
operation from the external oscillator.
• Medium priority is given to VDD_LV, VDD_HV_PMC, and VDD_HV_FLA. VDD_LV is the
main supply for the on-chip digital logic, including the cores, and this is prioritized because it
affects the largest amount of logic on the device. VDD_HV_PMC powers the flash regulator and
VDD_HV_FLA is the output of this regulator. A good supply to the flash memory ensures reliable
flash programming and erasing.
• VDD_HV_IO_MAIN, VDD_IO_MSC, and VDDSTBY are given lower priority. Although it is
still important that these supplies have a clean power signal, the hardware they power is less
affected by noise.
3.6 Supply monitoring
MPC5746R monitors the voltage supplies internally. The function of the power-on reset (POR),
low-voltage detect (LVD) and high-voltage detect (HVD) circuits is to hold the device in reset until critical
1.See the MPC5746R Reference Manual for complete information on the power segmentation, input multiplexing and
other pin characteristics.
Table 9. Decoupling Capacitor Layout Priorities
Priority Domain Description
1
VDD_HV_ADR_SAR
VDD_HV_ADR_SD
ADC references
2
VDD_HV_ADV_SAR
VDD_HV_ADV_SD
ADC supplies
3 VDD_HV_IO_JTAG JTAG debug and XOSC supply
4 VDD_LV Core(s) supply
5
VDD_HV_PMC Power Management Controller
supply
6 VDD_HV_FLA Flash memory supply/decouple
7 VDD_HV_IO_MAIN GPIO supply
8 VDD_HV_IO_MSC Microsecond channel supply
9 VDDSTBY SRAM standby voltage