NXP Semiconductors MPC5566, Reference Manual

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Voltage Regulator Controller (VRC) and POR Module
MPC5566 Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 23-3
The voltage regulator controller keeps the 1.5 V supply in regulation as long as V
RC33
is in regulation. If
more protection is desired, you can also supply an external 1.5 V low voltage reset circuit.
• If the on-chip voltage regulator controller is not used, an external 1.5 V supply is required. To avoid
a power sequencing requirement when an external power supply is used, external 3.3 V must power
V
RC33
while the V
RCCTL
pad is unconnected. In this case, the internal 1.5 V POR remains enabled.
• If V
RC33
is not powered, the device is subject to the power sequencing requirements for the 1.5 V
and 3.3 V, or RESET supplies. This ensures that the 1.5 V supply is high enough for internal logic
to operate correctly during power-up.
Refer to Section 23.5.3, “Power Sequencing Requirements ” for more information.
23.4.2 POR Circuits
The individual POR circuits asserts whenever the supply being monitored drops below the specified
threshold. The entire device is in power-on reset if any of these supplies are below the values specified in
the
MPC5566 Microcontroller Data Sheet .
Power-on reset asserts as soon as possible after the voltage level of the POR supplies begin to rise. Each
POR circuit negates before its supply rises to its specified range. Power-on reset remains asserted until all
POR supplies rise above the maximum POR threshold. Each POR asserts after its supply drops below its
specified range. The behavior for each POR during power sequencing is shown in
Figure 23-2 .
Before the 3.3 V POR circuit asserts when ramping up, or after it negates when ramping down, the device
can exit POR but remain in system reset. In this case, MDO[0] is driving high and no clocks are toggling.
If the 3.3 V POR circuit is asserted, the device behaves as if in POR even if the 1.5 V and RESET power
POR circuits have not yet asserted when ramping up or have negated when ramping down.
NOTE
The PORs for each supply are not intended to indicate that the voltage has
dropped below the specified voltage range. You must monitor the supplies
externally and assert RESET to achieve precise monitoring.