MC145572PB Freescale Semiconductor, MC145572PB Datasheet - Page 240

• Manufacturer Part Number: MC145572PB
• Manufacturer: Freescale Semiconductor

Specifications of MC145572PB

• Number Of Line Interfaces: 1
• Control Interface: HDLC
• Lead Free Status / Rohs Status: Not Compliant

Freescale Semiconductor, Inc.
to its maximum value. Once the frequency of oscillation has stabilized, the negative direction pull-
ability can be measured with a frequency counter at BUFXTAL out . If a board is designed to have a
pull up resistor on FREQREF, then automatic test equipment can be programmed for the low frequen-
cy measurement and to inject a high frequency clock for the high frequency measurement.
To measure the pullability towards the high frequency direction, FREQREF is driven with a square
wave signal that can be between 8001 Hz and 20 MHz. Note that 8001 Hz is + 1000 ppm, which
exceeds the pull range of the on–chip PLL. This causes the on–chip capacitance array to go to its
minimum value and thereby increases the frequency of the 20.48 MHz oscillator. Once the oscillator
has stabilized, the frequency of oscillation is measured at BUFXTAL out .
It is also possible to use the 4.096 CLKOUT pin to do these measurement, but it is necessary to relate
the pullability in ppm to 4096 kHz instead of 20.48 MHz.
Example 1: Free Running Frequency of Oscillation Measurement at Room Temperature
Configuration:
MC145572 in NT mode
Crystal specification is 20.48 MHz
15 ppm. See Section B.3.2.
Results:
BUFXTAL out measures as 20,480,307.2 Hz
(( |20,480,307.2 Hz – 20,480,000 Hz| ) *1,000,000 ppm) / 20,248,000 Hz = + 15 ppm
Example 2: Oscillator Pullability Measurement at Room Temperature
Crystal specification is
20.48 MHz with 360 ppm or
180 ppm pull between 15 and 45 pF. See
Section B.3. In this example, 20,480,000 MHz is used as the nominal frequency. In a real life situation
it may be desirable to use the actual measured free run frequency when measuring pullability.
Configuration 1:
MC145572 in LT mode
FREQREF connected to V SS
Results:
BUFXTAL out measures as 20,475,801.6 Hz
(( |20,475,801.6 Hz – 20,480,000 Hz| ) *1,000,000 ppm) / 20,248,000 Hz = – 205 ppm
Configuration 2:
MC145572 in LT mode
FREQREF connected to 4 MHz
Results:
BUFXTAL out measures as 20,483,952.6 Hz
(( |20,483,952.6 Hz – 20,248,000 Hz| )*1,000,000 ppm) / 20,248,000 Hz = + 193 ppm
Conclusion:
Since 20.48 MHz + 193 ppm, – 205 ppm exceeds the
180 ppm minimum crystal pull range specifi-
cation, the oscillator is working correctly.
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