SPRSP52C December 2019 – September 2023 AM6526 , AM6528 , AM6546 , AM6548
PRODUCTION DATA
Refer to the PDF data sheet for device specific package drawings
WKUP_LFOSC_XO/WKUP_LFOSC_XI - External main crystal interface pins connected to internal oscillator which sources reference clock provides a clock for low power operation in deeper sleep modes. For a list of supported low power modes for this device, please refer to Overview of Device Low-Power Modes section in the device TRM.
Figure 6-24 shows the recommended crystal circuit. It is recommended that preproduction printed-circuit board (PCB) designs include the two optional resistors Rbias and Rd in case they are required for proper oscillator operation when combined with production crystal circuit components. In most cases, Rbias is not required and Rd is a 0 ohm resistor. These resistors may be removed from production PCB designs after evaluating oscillator performance with production crystal circuit components installed on preproduction PCBs.
The load capacitors, Cf1 and Cf2 in Figure 6-25, should be chosen such that the below equation is satisfied. CL in the equation is the load specified by the crystal manufacturer. All discrete components used to implement the oscillator circuit should be placed as close as possible to the associated oscillator WKUP_LFOSC0_XI, WKUP_LFOSC0_XO, and VSS pins.
The crystal must be in the fundamental mode of operation and parallel resonant. Table 6-22 summarizes the required electrical constraints
NAME | DESCRIPTION | MIN | TYP | MAX | UNIT | ||
---|---|---|---|---|---|---|---|
fp | Parallel resonance crystal frequency | 32768 | Hz | ||||
Cf1 | Cf1 load capacitance for crystal parallel resonance with Cf1 = Cf2 | 12 | 24 | pF | |||
Cf2 | Cf2 load capacitance for crystal parallel resonance with Cf1 = Cf2 | 12 | 24 | pF | |||
Cshunt | Shunt capacitance | 1.35 | pF | ||||
ESR | Crystal effective series resistance | 65 | kΩ |
When selecting a crystal, the system design must consider the temperature and aging characteristics of a based on the worst case environment and expected life expectancy of the system.
Table 6-23 details the switching characteristics of the oscillator and the requirements of the input clock.
NAME | DESCRIPTION | MIN | TYP | MAX | UNIT |
---|---|---|---|---|---|
fxtal | Oscillation frequency | 32768 | Hz | ||
tSX | Start-up time | (1) | s |