MC1391P View Datasheet(PDF) - Motorola => Freescale
Part Name
Description
Manufacturer
MC1391P Datasheet PDF : 6 Pages
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MC1391
CIRCUIT OPERATION
The MC1391P contains the oscillator, phase detector and
predriver sections needed for a television horizontal APC loop.
The oscillator is an RC type with one pin (Pin 7) used to
control the timing. The basic operation can be explained
The phase detector is isolated from the remainder of the
circuit by R14 and Z2. The phase detector consists of the
comparator Q15, Q16 and the gated current source Q17.
Negative going sync pulses at Pin 3 turn off Q12 and the
easily. If it is assumed that Q7 is initially off, then the capacitor
connected from Pin 7 to ground will be charged by an
external resistor (RC) connected to Pin 6. As soon as the
voltage at Pin 7 exceeds the potential set at the base of Q8
by resistors R8 and R10, Q7 will turn on and Q6 will supply
base current to Q5 and Q10. Transistor Q10 will set a new,
lower potential at the base of Q8 determined by R8, R9 and
R10. At the same time, transistor Q5 will discharge the
capacitor through R4 until the base bias of Q7 falls below that
of Q8, at which time Q7 will turn off and the cycle repeats.
current division between Q15 and Q16 will be determined by
the phase relationship of the sync and the sawtooth
waveform at Pin 4, which is derived from the horizontal
flyback pulse. If there is no phase difference between the
sync and sawtooth, equal currents will flow in the collectors of
Q15 and Q16 each of half the sync pulse period. The current
in Q15 is turned around by Q18 so that there is no net output
current at Pin 5 for balanced conditions. When a phase offset
occurs, current will flow either in or out of Pin 5. This pin is
connected via an external low–pass filter to Pin 7, thus
The sawtooth generated at the base of Q4 will appear
across R3 and turn off Q3 whenever it exceeds the bias
set on Pin 8. By adjusting the potential at Pin 8, the duty
cycle (MSR) at the predriver output pin (Pin 1) can be
changed to accommodate either tube or transistor horizontal
controlling the oscillator.
Shunt regulation for the circuit is obtained with a zero
temperature coefficient from the series combination of D1,
D2 and Z1.
output stages.
APPLICATION INFORMATION
Although it is an integrated circuit, the MC1391P has all
the flexibility of a conventional discrete component horizontal
APC loop. The internal temperature compensated voltage
regulator allows a wide supply voltage variation to be
tolerated, enabling operation from nonregulated power
supplies. A minimum value for supply current into Pin 6 to
maintain zener regulation is about 18 mA. Allowing 2.0 mA for
the external dividers
RA + RB =
Vnonreg(min)–8.8
20 x 10–3
Components RA, RB and CA are used for ripple rejection. If
the supply voltage ripple is expected to be less than 100 mV
(for a 30 V supply) then RA and RB can be combined and
CA omitted.
The output pulse width can be varied from 6.0 µs to 48 µs
by changing the voltage at Pin 8 (see Figure 5). However,
care should be taken to keep the lead lengths to Pin 8 as
short as possible at Pin 1. The parallel impedance of RD and
RE should be close to 1.0 kΩ to ensure stable pulse widths.
For 15 mA drive at saturation
RF
=
Vnonreg –0.3
15 x 10–3
The oscillator free–running frequency is set by RC and CB
connected to Pin 7. For values of RC ≥ Rdischarge (R4 in
Figure 6), a useful approximation for the free–running
frequency is
fO
=
0.6
1
RCCB
Proper choice of RC and CB will give a wide range of
oscillator frequencies – operation at 31.5 kHz for countdown
circuits is possible for example. As long as the product RCCB
≈ 10–4 many combinations of values of RC and CB will satisfy
the free–running frequency requirement of 15.734 kHz.
However, the sensitivity of the oscillator (β) to control–current
from the phase detector is directly dependent on the
magnitude of RC, and this provides a convenient method of
adjusting the dc loop gain (fc).
For a given phase detector sensitivity (µ) = 1.60 x 10–4 A/rad
fc = µβ and β = 3.15 x RC Hz/mA
Increasing RC will raise the dc loop gain and reduce the static
phase error (S.P.E.) for a given frequency offset. Secondary
effects are to increase the natural resonant frequency of the
loop (ωn) and give a wider pull–in range from an out–of–lock
condition. The loop will also tend to be underdamped with fast
pull–in times, producing good airplane flutter performance.
However, as the loop becomes more underdamped impulse
noise can cause shock excitation of the loop. Unlimited
increase in the dc loop gain will also raise the noise bandwidth
excessively causing horizontal jitter with thermal noise. Once
the dc loop gain has been selected for adequate SPE
performance, the loop filter can be used to produce the balance
between other desirable characteristics. Damping of the loop is
achieved most directly by changing the resistor RX with respect
to RY which modifies the ac/dc gain ration (m) of the loop.
Lowering this ratio will reduce the pull–in range and noise
bandwidth (fnn). (Note: very large values of RY will limit the
control capability of the phase detector with a corresponding
reduction in hold–in range.)
Static phasing can be adjusted simply by adding a small
resistor between the flyback pulse integrating capacitor and
ground. The sync coupling capacitor should not be too small
or it can charge during the vertical pulse and this may result in
picture bends at the top of the CRT.
Note: In adjusting the loop parameters, the following
equations may prove useful:
fnn =
1 x χ2 TωC
4χT
χ = RX
RY
wn
=
√
ωC
(1 + c )T
ωC = 2 π fc
T = Ry CC
K
=
χ 2TωC
4
where: K = loop damping coeffecient
4
MOTOROLA ANALOG IC DEVICE DATA
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