7.6 Snooze Mode
Snooze mode is entered by setting the SNOOZE bit while operating from the internal 24.5 MHz oscillator (HFOSC0). Upon entry into
snooze mode, the hardware halts both of the high-frequency internal oscillators and goes into a low power state as soon as the instruc-
tion that sets the bit completes execution. The internal LDO is then placed into a low-current standby mode. All internal registers and
memory maintain their original data.
Snooze mode is terminated by any enabled wake or reset source. When snooze mode is terminated, the LDO is returned to normal
operating conditions and the device will continue execution on the instruction following the one that set the SNOOZE bit. If the wake
event was configured to generate an interrupt, the interrupt will be serviced upon waking the device. If snooze mode is terminated by an
internal or external reset, the CIP-51 performs a normal reset sequence and begins program execution at address 0x0000.
7.7 Shutdown Mode
In shutdown mode, the CPU is halted and the internal LDO is powered down. External I/O will retain their configured states.
To enter Shutdown mode, firmware should set the STOPCF bit in the regulator control register to 1, and then set the STOP bit in
PCON0. In Shutdown, the RSTb pin and a full power cycle of the device are the only methods of generating a reset and waking the
device.
Note:
In Shutdown mode, all internal device circuitry is powered down, and no RAM nor registers are retained. The debug circuitry will
not be able to connect to a device while it is in Shutdown. Coming out of Shutdown mode, whether by POR or pin reset, will appear as
a power-on reset of the device.
7.8 5V-to-3.3V Regulator
The 5-to-3.3 V regulator is powered from the VREGIN pin on the device. When active, it regulates the input voltage to 3.3 V at the VDD
pin, providing up to 100 mA for the device and system. In addition to the normal mode of operation, the regulator has two low power
modes which may be used to reduce the supply current, and may be disabled when not in use.
Table 7.2. Voltage Regulator Operational Modes
Regulator Condition
SUSEN Bit
BIASENB Bit
REG1ENB Bit
Relative Power Consumption
Normal
0
0
0
highest
Suspend
1
0
0
low
Bias Disabled
x
1
0
extremely low
Disabled
x
1
1
off
The voltage regulator is enabled in normal mode by default. Normal mode offers the fastest response times, for systems with dynami-
cally-changing loads.
For applications which can tolerate a lower regulator bandwidth but still require a tightly regulated output voltage, the regulator may be
placed in suspend mode. Suspend mode is activated when firmware sets the SUSEN bit. Suspend mode reduces the regulator bias
current at the expense of bandwidth.
For low power applications that can tolerate reduced output voltage accuracy and load regulation, the internal bias current may be disa-
bled completely using the BIASENB bit. If firmware sets the BIASENB bit, the regulator will regulate the voltage using a method that is
more susceptible to process and temperature variations. In addition, the actual output voltage may drop substantially under heavy
loads. The bias should only be disabled for light loads (5 mA or less) or when the voltage regulator is disabled.
If the regulator is not used in a system, the VREGIN and VDD pins should be connected together. Firmware may disable the regulator
by writing both the REG1ENB and BIASENB bits in REG1CN to turn off the regulator and all associated bias currents.
EFM8UB3 Reference Manual
Power Management and Internal Regulators
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