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ML13176 View Datasheet(PDF) - LANSDALE Semiconductor Inc.

Part Name
Description
Manufacturer
ML13176
LANSDALE
LANSDALE Semiconductor Inc. LANSDALE
ML13176 Datasheet PDF : 16 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
ML13175/ML13176
LANSDALE Semiconductor, Inc.
Legacy Applications Information
For C = 0.47 µ:
then
thus,
R1
R2
=
=
t1/C
t2/C
= 33.8 X 10
= 0.283 X 10
–3/0.47 X
– 3/0.47 X
10
10
–6
–6
=
=
72 k
0.60k
In the above example, the following standard value components
are used,
C = 0.47 µf; R2 = 620 and R’1 = 72 k– 53 k~ 18 k
(R’1 is defined as R1 – 53 k, the output impedance of the phase
detector.)
Since the output of the phase detector is high impedance (~50 k)
and serves as a current source, and the input to the frequency con-
trol, Pin 6 is low impedance (impedance of the two diode to
ground is approximately 500 ), it is imperative that the second
order low pass filter design above be modified. In order to mini-
mize loading of the R2C shunt network, a higher impedance must
be established to Pin 6. A simple solution is achieved by adding a
low pass network between the passive second order network and
the input to Pin 6. This helps to minimize the loading effects on
the second order low pass while further suppressing the sideband
spurs of the crystal oscillator. A low pass filter with R3 = 1.0 k
and C2 - 1500 p has a corner frequency (fc) of 106 kHz; the ref-
erence sideband spurs are down greater than – 60 dBc.
Figure 14. Modified Low Pass Loop Filter
Pin 7 18k
1.0k
Pin 6
R' 1
620 R2
0.47 C
µf
R3
C3
1500pf
VCC
HOLD–IN RANGE
The hold–in range, also called the lock range, tracking range and
synchronization range, is the ability of the CCO frequency, fo to
track the input reference signal, fref • N as it gradually shifted
away from the free running frequency, ff. Assuming that the CCO
is capable of sufficient frequency deviation and that the internal
loop amplifier and filter are not overdriven, the CCO will track
until the phase error, θe approaches ±π/2 radians. Figures 5
through 8 are a direct measurement of the hold–in range (i.e.
fref x N = ±fH x 2π). Since sin θe cannot exceed ±1.0, as θe
approaches ±π/2 the hold–in range is equal to the DC loop gain
Kv X N.
±∆ωH = ± Kv x N
where, Kv = KpKoKn.
In the above example,
±∆ωH = ±27.3 Mrad/sec
±fH = ±4.35 MHz
EXTENDED HOLD–IN RANGE
The hold–in range of about 3.4% could cause problems over tem-
perature in cases where the free–running oscillator drifts more
than 2 to 3% because of relatively high temperature coefficients
of the ferrite tuned CCO inductor. This problem might worsen for
lower frequency applications where the external tuning coil is
large compared to internal capacitance at Pins 1 and 4. To
improve hold–in range performance, it is apparent that the gain
factors involved must be carefully considered.
Kn = is either 1/8 in the ML13175 or 1/32 in the ML13176
Kp = is fixed internally and cannot be altered.
Ko = Figures 9 and 10 suggest that there is capability of
greater control range with more current swing. However,
this swing must be symmetrical about the center of the
dynamic response. The suggested zero current operating
point for ±100 µA swing of the CCO is at about + 70
µA offset point.
Ka = External loop amplification will be necessary since the
phase detector only supplies ±30 µA.
In the design example in Figure 15, an external resistor (R5) of
15 kto VCC (3.0 Vdc) provides approximately 100 µA of cur-
rent boost to supplement the existing 50 µA internal source cur-
rent. R4 (1.0 k) is selected for approximately 0.1 Vdc across it
with 100 µA. R1, R2 and R3 are selected to set the potential at
Pin 7 and the base of 2N4402 at approximately 0.9 Vdc and the
emitter at 1.55 Vdc when error current to Pin 6 is approximately
zero µA. C1 is chosen to reduce the level of the crystal sidebands.
Figure 15. External Loop Amplifier
30µA
Phase
Detector
Output
30µA
VCC = 3.0Vdc
12
C1
1000p
R1
R3
68k
4.7k
R4
1.0k
R5 15k
1.6V
6
2N4402
7
R2 33k
5, 10, 15
50µA
Oscillator
Control
Circuitry
Page 8 of 16
www.lansdale.com
Issue cC
 

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