AFE8220TPZPQ1 datasheet(27/49 Pages) TI1

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Master Clock Oscillator

AFE8220

MCLKI

MCLKO

1nF

Crystal

DVS 2

Real-Time Clock Oscillator

AFE8220-Q1

www.ti.com....................................................................................................................................................... SBAS455A – JANUARY 2009 – REVISED JULY 2009

The master clock oscillator supports third-overtone designs from 55 MHz to 75 MHz. It can also support

fundamental operations in the 20-MHz to 30-MHz range. The recommended third-overtone circuit for

third-overtone operation is shown in Figure 17 and Table 11.

Figure 17. Third-Overtone Operation

Table 11. Third-Overtone Operation Recommendations

FREQUENCY (MHz)

C1 (pF)

C2 (pF)

L1 (

µH)

L2 (

µH)

R1 (kΩ)

0.1

4.7

6.8

0.82

3.3

4.7

0.68

2.7

3.3

0.56

2.7

3.3

0.56

2.2

3.3

The master clock oscillator may be optionally divided down to provide a reference clock on the REFCLK pin.

Control variable refclk_en enables the generation of the reference clock when high. Two variables, refclk_hi and

refclk_lo, define the high and low periods of REFCLK in terms of MCLK cycles. REFCLK is high for refclk_hi

cycles of MCLK, then low for refclk_lo periods of MCLK. REFCLK frequency is limited to integer submultiples of

MCLK. Table 12 shows the refclk operation control settings.

Table 12. REFCLK Control Register Settings

PARAMETER

ADDRESS

BITS

refclk_en

refclk_hi

15:0

refclk_lo

15:0

The real-time clock oscillator supports crystals in the frequency range of 32.768 kHz through 150 kHz. The

real-time clock module can be programmed to operate accurately with crystals in this frequency range.

The real-time clock oscillator output may be optionally output on the RTC_OUT pin when rtc_oe is set high. This

option allows the real-time clock oscillator to be used as an alternate reference clock in the event that an

acceptable frequency cannot be derived from MCLK. Table 13 shows the rtc_oe control setting.

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