ADUCM4050BCBZ-R7 datasheet(33/46 Pages) AD

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Data Sheet

ADuCM4050

Rev. A | Page 33 of 46

Clocking

The ADuCM4050 MCU has the following clocking options:

•

High frequency clocks

•

Internal high frequency oscillator (HFOSC) at

26 MHz

•

High frequency external crystal oscillator (HFXTAL)

at 26 MHz or 16 MHz

•

GPIO clock in (SYS_CLKIN)

•

Phase-locked loop (PLL)

•

Low frequency clocks at 32 kHz

•

Internal low frequency oscillator (LFOSC)

•

Low frequency external crystal oscillator (LFXTAL)

The clock options have software configurability with the

following exceptions: the HFOSC cannot be disabled when

using an internal buck regulator, and the LFOSC cannot be

disabled even if using LFXTAL.

Clock sources with a frequency greater than 26 MHz can be

achieved by using a PLL. The maximum frequency sourced

from the PLL is 52 MHz.

When core frequency is greater than 26 MHz, program the flash

wait states to 1.

As PLL is disabled and relock is transparent to user software,

hibernate mode can enter and exit seamlessly when the system

frequency is sourced from PLL.

Clock Fail Detection

The LFOSC clock continuously monitors the LFXTAL in

hibernate, active, and flexi power modes. If the LFXTAL stops

running, there is an option to detect and generate an interrupt

and/or automatically switch to the LFOSC without software

intervention. The HFOSC clock monitors the HFXTAL clock,

GPIO clock, and the PLL clock. If using any of these clocks as

the system clock and it fails to toggle, the clock can be detected

through an interrupt. There is an option to automatically switch

to the HFOSC.

Real-Time Clock (RTC)

The ADuCM4050 MCU has two RTC blocks: RTC0 and RTC1,

also called flexible real-time clock (FLEX_RTC™). The RTC

blocks share a low power crystal oscillation circuit that operates

in conjunction with a 32,768 Hz external crystal.

The RTC has an alarm that interrupts the core when the

programmed alarm value matches the RTC count. The software

enables and configures the RTC.

The RTC also has a digital trim capability to allow a positive or

negative adjustment to the RTC count at fixed intervals.

The FLEX_RTC supports three SensorStrobe outputs:

RTC1_SS1, RTC1_SS2, and RTC1_SS3 (see the ADuCM4050

Ultra Low Power ARM Cortex-M4F MCU with Integrated

Power Management Hardware Reference). Using this

mechanism, the ADuCM4050 MCU can be used as a

programmable clock generator in all power modes except

shutdown mode. In this way, the external sensors can have their

timing domains mastered by the ADuCM4050 MCU, as the

SensorStrobe output is a programmable divider from the

FLEX_RTC, which can operate at 0.5 Hz to 16.384 kHz. The

sensors and MCU are in sync, which removes the need for

additional resampling of data to time align it.

In the absence of the SensorStrobe mechanism, the external

sensor uses an RC oscillator (approximately ±30% typical

variation). The MCU must sample the data and resample it on

the time domain of the MCU before using it.

Alternatively, the MCU remains in a higher power state and

drives each data conversion on the sensor side.

The SensorStrobe mechanism allows the ADuCM4050 MCU to

be in a lower power state for a long duration and avoids

unnecessary data processing, extending the battery life of the

end product. The key differences between RTC0 and RTC1 are

shown in Table 26.

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