MC44818 データシートの表示（PDF） - Motorola => Freescale
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MC44818 Datasheet PDF : 8 Pages
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MC44818
Bit T14: Controls the Charge Pump Current of the
Bit T14: Phase Comparator
T14 = 0
T13 = 1
Pump Current 15 µA Typical
Pump Current 50 µA Typical
The Programmable Divider
The programmable divider is a presettable down counter.
When it has counted to zero it takes its required division ratio
out of the latches B. Latches B are loaded from latches A by
means of signal TDI which is synchronous to the
programmable divider output signal.
Since latches A receive the data asynchronously with the
programmable divider; this double latch scheme is needed to
assure correct data transfer to the counter.
The division ratio definition is given by:
N = 16384 x N14 + 8192 x N13 + … + 4 x N2 + 2 x N1 + N0
Maximum Ratio 32767
Minimum Ratio 17
N0 … N14 are the different bits for frequency information.
At power “on” the whole bus receiver is reset and the
programmable divider is set to a counting ratio of N = 256 or
higher.
The Prescaler
The prescaler has a preamplifier which guarantees high
input sensitivity.
The Phase Comparator
The phase comparator is phase and frequency sensitive
and has very low output leakage current in the high
impedance state.
Lock Detector
The lock detector output is low in lock. The output goes
immediately high when an unlock condition is detected. The
output goes low again when the loop is in lock during a
complete period of the reference frequency.
Figure 4. Equivalent Circuit of the Lock Output
VCC1 5.0 V
200 µA Typical
2.0 k
Lock
100 k 25 V Protection
The Operational Amplifier
The operational amplifier is designed for very low noise,
low input bias current and high power supply rejection. The
positive input is biased internally. The operational amplifier
needs 28.5 V supply (VCC2) as minimum voltage for a
guaranteed maximum tuning voltage of 28 V.
Figure NO TAG shows a possible filter arrangement. The
component values depend very much on the application
(tuner characteristic, reference frequency, etc.).
The Oscillator
The oscillator uses a 3.2 to 4.0 MHz crystal tied to ground in
series with a capacitor. The crystal operates in the series
resonance mode.
The voltage at Pin 3 has low amplitude and low harmonic
distortion.
Figure 5. Typical Tuner Application
IF
UHF
External Switching
VHF B III
13 12 11 10
14 12 V
Antenna
Filter
B. P. Filter
Mixer
5.0 V 7
1.0 nF 8
Fosc
B3 B2 B1 B0
MC44818
Bus
Rec
÷8
Program
Pres
Divider
Oscillator
VTUN
AGC
NOTES: 1. On some layouts the 100 Ω resistor will not be required.
2. C2 = 330 pF minimum is required for stability.
Gnd
9
65
2.7 V
4
(Note 1)
47 k
330 p
(Note 2)
33 V
47 nF
22 nF
VCC3
2
1
16
Osc & 3
Ref Div
Phase
Comp
15
Lock
SCL
SDA
AS
12 pF
3.2/4.0 MHz
MOTOROLA ANALOG IC DEVICE DATA
5
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