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SLAS826F – MARCH 2015 – REVISED MARCH 2017
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Detailed Description
Copyright © 2015–2017, Texas Instruments Incorporated
6.8.4
Clock System (CS)
The CS contains the sources of the various clocks in the device. It also controls the mapping between the
sources and the different clocks in the device.
6.8.4.1
LFXT
The LFXT supports 32.768 kHz low-frequency crystals.
6.8.4.2
HFXT
The HFXT supports high-frequency crystals up to 48 MHz.
6.8.4.3
DCO
The DCO is a power-efficient tunable internal oscillator that generates up to 48 MHz. The DCO also
supports a high-precision mode when using an external precision resistor.
6.8.4.4
Very Low-Power Low-Frequency Oscillator (VLO)
The VLO is an ultra-low-power internal oscillator that generates a low-accuracy clock at typical frequency
of 9.4 kHz.
6.8.4.5
Low-Frequency Reference Oscillator (REFO)
The REFO can be used as an alternate low-power lower-accuracy source of a 32.768 kHz clock instead of
the LFXT. The REFO can also be programmed to generate a 128 kHz clock.
6.8.4.6
Module Oscillator (MODOSC)
The MODOSC is an internal clock source that has a very low latency wake-up time. It is factory-calibrated
to a frequency of 25 MHz. The MODOSC is typically used to supply a 'clock on request' to different
modules. It can be used as a clock source for ADC operation at 1 Msps sampling rate.
6.8.4.7
System Oscillator (SYSOSC)
The SYSOSC is an internal clock source that is factory calibrated to a frequency of 5 MHz. It can be used
as a clock source for ADC operation at 200 ksps sampling rate. In addition, the SYSOSC is also used for
timing of various system-level control and management operations.
6.8.4.8
Fail-Safe Mechanisms
All clock sources that operate with external components have a built-in fail-safe mechanism that
automatically switches to the relevant backup source, thereby ensuring that spurious or unstable clocks
never impact the device operation.
shows the different types of clock source faults and the
corresponding fail-safe clocks.
Table 6-43. Fail-Safe Clocks
Fault Type
Fail-Safe Clock
LFXT oscillator fault
REFO clock
HFXT oscillator fault
SYSOSC clock
DCO external resistor open circuit fault
DCO clock in internal resistor mode