Maxim Integrated MAX32660 - Table 4-1: Operating Voltage Range Selection and the Effect on V; System Clocks, Reset, and Power Management

MAX32660 User Guide
Maxim Integrated Page 21 of 195
4 System Clocks, Reset, and Power Management
The MAX32660 includes a High-Frequency Internal Oscillator (HFIO), an 8kHz nano-ring oscillator and support for an
external 32kHz crystal or external clock. Support for selectable core operating voltage is provided and the HFIO frequency is
scaled based on the specific core operating voltage range selected.
4.1 Core Operating Voltage Range Selection
The MAX32660 supports three selections for the core Operating Voltage Range (OVR). In single supply operation, changing
the OVR sets the output of the internal LDO regulator to the voltage shown in Table 4-1. For dual supply designs, setting the
OVR allows the MAX32660 to use an external PMIC to provide the required V
CORE
voltage dynamically. Changing the OVR
also reduces the output frequency of the High-frequency Internal Oscillator (HFIO), further reducing power consumption.
Changes to the OVR affect the access time of the internal flash memory and the application firmware must set the flash
wait states for each OVR setting as outlined in section 4.1.2 Flash Wait States for details on minimum flash wait states for
the internal flash memory.
Changing the core operating voltage immediately reduces the output frequency of the High Frequency Internal Oscillator as
shown in Table 4-1, below. When operating the MAX32660 using dual external supplies requires special considerations and
must be handled carefully in the application firmware.
Table 4-1: Operating Voltage Range Selection and the Effect on V
CORE
and f
HFIO
PWRSEQ_LP_CTRL
ovr
FLC_CTRL
lve
V
CORE
Typical
f
HFIO
0
1
0.9
24
1
1
1.0
48
2
0
1.1
96
4.1.1 Setting the Operating Voltage Range
The Operating Voltage Range (OVR) selection is controlled using the Power Sequencer Low Power Control Register
PWRSEQ_LP_CTRL.ovr which is only reset by a Power-On Reset (POR) and these bits should be checked after every reset to
determine the correct clock speed and flash wait states. Adjusting the OVR setting effects the frequency of the HFIO. Prior
to changing the OVR settings, it is required to set the system clock to either the 8kHz Low-Frequency Internal Oscillator or
the 32.768kHz External Oscillator. The MAX32660 coordinates OVR change between the internal LDO and the HFIO set
frequency. When changing the OVR setting, the MAX32660 must be operating from the internal LDO. In a system using an
external supply for V
CORE
, firmware must transition to the internal LDO prior to changing the OVR setting.