BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 33

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

Rev. 1.00
Standby Current Considerations
Wake-up
As the main reason for entering the Idle/Sleep Mode is to keep the current consumption of the MCU
to as low a value as possible, perhaps only in the order of several micro-amps, there are other
considerations which must also be taken into account by the circuit designer if the power
consumption is to be minimised.
Special attention must be made to the I/O pins on the device. All high-impedance input pins must be
connected to either a fixed high or low level as any floating input pins could create internal
oscillations and result in increased current consumption. Care must also be taken with the loads,
which are connected to I/O pins, which are setup as outputs. These should be placed in a condition in
which minimum current is drawn or connected only to external circuits that do not draw current,
such as other CMOS inputs.
If the configuration options have enabled the Watchdog Timer internal oscillator LIRC then this will
continue to run when in the Idle/Sleep Mode and will thus consume some power. For power
sensitive applications it may be therefore preferable to use the system clock source for the Watchdog
Timer. The LXT, if configured for use, will also consume a limited amount of power, as it continues
to run when the device enters the Idle/Sleep Mode. To keep the LXT power consumption to a
minimum level the LXTLP bit in the CTRL0 register, which controls the low power function, should
be set high.
Note that even though execution of a HALT instruction may have caused the MCU to power down,
the touch key circuits will continue to consume power. The touch key circuits will only power down
when a period of time has elapsed after no touch detections have been made.
After the microcontroller enters the Idle/Sleep Mode, it can be woken up from one of various
sources listed as follows:
An external reset
An external falling edge on PA0 to PA7
A system interrupt
A WDT overflow
Interrupt Pin Wake-up
Timer Pin Wake-up
33
BS2824/BS2854/BS2868
Touch Key MCU
January 27, 2010