TC35680FSG datasheet(63/91 Pages) TOSHIBA

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TC35680FSG-002/TC35681FSG-002

2019-04-04

4.13. Sleep Clock Interface

Feature

The sleep clock interface has the following features;



Selection source clock of sleep clock from among the following three clocks



Crystal resonator



External oscillator



Built-in silicon oscillator (SiOSC)



Frequency: 32.768 kHz



Frequency accuracy: ±500 ppm or less (in operating environment)



Built-in 32-step variable capacitor (0 to 15.56 pF)



Load capacitance and equivalent series resistance of the crystal resonator



Load capacitance: 4 pF



Equivalent series resistance: 80

kΩ (recommended)

The SiOSC oscillates at start-up. After the start-up, the clock source can be changed to the crystal resonator or an external oscillator.

The jitter of the oscillation of the SiOSC is too large to comply with the Bluetooth® specification. So it is necessary that the clock

source is changed to the crystal resonator or an external oscillator for the Bluetooth® communication.

Selection of Sleep Clock Source

The sleep clock source of TC35680/TC35681 can be selected from among the three clocks. The command and the API to change

the source are shown in Table 4-15.

After start-up, the selection of the sleep clock source is done only once.

Table 4-15 Command and API to change a clock source

Operating mode

Command and API

HCI mode

HCI_M2_BTL_SET_LOW_POWER_CLOCK

User-App mode

SYS_API_SetBlesglSleepClock

Use of Crystal Resonator

An external feedback resistor and external capacitors are unnecessary for the crystal oscillation circuit in TC35680/TC35681,

because the devices integrate the feedback resistor and a variable capacitor (0 to 15.56 pF) on the input and output pins of the crystal

resonator. A crystal resonator which has a load capacitance of 4 pF should be connected between the SLPXOIN and SLPXOOUT

pins, and the capacitance of the variable capacitor should be adjusted so that the frequency deviation does not exceed ±500 ppm

under the use environment.

The recommended equivalent series resistance of the crystal resonator is 80

kΩ. The oscillation margin should be evaluated

sufficiently when a crystal resonator with a larger equivalent series resistance is used.

For the details of the adjustment of the variable capacitor, refer to the “Hardware Application Note”.

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