REFERENCE BASED CLOCK ENABLE
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-19
For a microcontroller with imbedded EEPROM, a voltage greater than the CMOS VDD is required for read as well as write and erase operations. This voltage is generated by a self contained on chip charge pump. The charge pump includes an oscillator as well as the pumping circuits and the charge storage element. To achieve the lowest current when oper- ating in a low power mode, the charge pump must be turned off along with the chip oscillator and the system clocks. If the microcontroller is required to resume operation with the first system clock upon returning from low power mode and that the first operation afier returning from low power mode may be an EEPROM access, it is necessary to inhibit the system clocks until the charge pump has reached the minimum voltage level required for correct EEPROM operation. In addition it is desired that the chip oscillator be allowed to start up and stabi- lize during this time so as to not impose any addi- tional latency when returning from low power mode.