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CHAPTER 9 STANDBY MODE AND VOLTAGE REGULATOR CONTROL CIRCUIT
9.7.1
Changing the Voltage Regulator operation mode
The voltage regulator operation modes are automatically controlled by hardware
depending on the selected CPU operation mode. However in some modes and under
certain conditions, it is permitted to manually change the regulator from High Power
mode to Low Power mode for further current saving.
■ Overview
The current consumption of the MCU core depends on the operation mode of the MCU (Run, Sleep, Timer
or Stop mode), the activated oscillators and PLL and the selected frequencies (CLKS1, CLKS2, CLKB,
CLKP1/2).
The automatic voltage regulator control logic sets the regulator to the High Power mode whenever the Main
or the RC oscillator is activated. In this High Power mode, the regulator is able to drive any current
consumed by the core. This guarantees a safe MCU operation independent of the selected CPU operation
mode and the RC or Main clock frequency.
Certain applications however require a very small MCU current consumption in dedicated Low Power CPU
operation modes. This can be achieved by manually setting the voltage regulator to the Low Power mode
even if the Main or RC oscillator is active. This reduces the MCU current consumption by several 100µA.
Using this feature is permitted only for CPU operation modes with a small dynamic current consumption.
In the automatic voltage regulator control, the stabilization time of the regulator takes place during the
stabilization of the oscillators. Hence there is no additional delay for stabilization of the voltage regulator.
■ Setting Voltage regulator to Low Power mode by user program
The voltage regulator can be set to the Low Power mode by controlling the SMCR:LPMS and
SMCR:LPMSS bits, depending on the CPU operation mode where power consumption should be reduced.
●
Switching to the Low Power mode with the SMCR:LPMS bit
Setting the SMCR:LPMS bit to "1" immediately switches the voltage regulator to the Low Power mode. This
is permitted only in RC Run mode (100kHz) with disabled PLL and a maximum Main clock frequency of
4MHz. The regulator stays in Low Power mode until this bit is cleared, independent of the MCU operation
mode (Run or Standby mode).
The MCU must be set to the RC Run mode and also CLKS2 must be set to RC or Sub clock by setting the
SC1S/SC2S bits and confirming the transition by reading the SC1M/SC2M bits. Then the SMCR:LPMS bit
can be set to "1" and the voltage regulator switches to the Low Power mode.
The regulator must be switched back to the High Power mode before changing the CPU operation mode to a
setting with a higher current consumption. This must be done in the following sequence:
- Clear the SMCR:LPMS bit.
- Apply a wait time of 40µs for stabilization of the voltage regulator.
- Switch to the new operation mode (change SC1S/SC2S bits, enable PLL, etc.).
256
MB96300 Super Series
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