LM1295 National Semiconductor, LM1295 Datasheet - Page 8

• Manufacturer Part Number: LM1295
• Description: DC Controlled Geometry Correction System for Continuous Sync Monitors
• Manufacturer: National Semiconductor

www.national.com
Pin Descriptions
See Figure 4 through Figure 8 for Input and Output schemat-
ics.
GND (Pin 1): This pin should be connected to the power
ground at pin 17.
V Height (Pin 2): Vertical Height. A voltage between 0V and
4V on this pin controls the amplitude of the +V and −V Drive
currents, with increasing voltage giving increasing current.
The control range is approximately 1.8 to 1. The response
time is slow, being limited by the automatic level control loop.
4 V Cap (Pin 3): 4 Volt Cap Capacitor. A 10 µF capacitor,
aluminum electrolytic or tantalum, should be connected be-
tween pin 3 (positive side) and GND (pin 17) to bypass the
internal 4V reference.
V Sync In (Pin 4): Vertical Sync Input. The vertical sync in-
put takes a negative-going TTL level pulse which injection
locks the vertical oscillator to the vertical sync frequency if it
is above the LM1295 minimum frequency. The input thresh-
old level is approximately 2V, so pulses other than TTL level
are satisfactory as long as they cross the 2V threshold with
at least a 400 mV margin either side. The minimum pulse
width is approximately 200 ns. For free-running detection (no
V Sync in), this input should be at logic high.
8 V Cap (Pin 5): 8 Volt Capacitor. A 100 µF capacitor, alumi-
num electrolytic or tantalum, should be connected between
pin 5 (positive side) and GND (pin 17) to bypass the internal
8V reference.
V Dyn Height (Pin 6): Vertical Dynamic Height. A voltage
between 3V and 4V on this pin controls the amplitude of the
+V and −V Drive currents with increasing voltage giving in-
creasing current. The control range is approximately
1.3 to 1. The bandwidth of this input is DC to greater than
125 kHz in contrast to the slow Vertical Height input.
V
to GND (pin 17) with a 10 µF aluminum electrolytic or tanta-
lum capacitor.
Vref Cap (Pin 8): Voltage Reference Cap. A 10 µF capacitor,
aluminum electrolytic or tantalum, should be connected be-
tween pin 8 (positive side) and GND (pin 17).
H Dyn Width (Pin 9): Horizontal Dynamic Width. This output
consists of the sum of the vertical ramp and the parabola de-
rived from the ramp. The amplitude and polarity of the ramp
signal is DC controlled by H Trap Cntl (pin 11) and of the pa-
rabola by E-W Pin Cntl (pin 10). The weighting of the ramp is
4V, the output is 3 parts parabola and 1 part ramp. Horizontal
Dynamic Width is used to correct for trapezoid and east-west
pincushion distortion. The output stage is similar to a stan-
dard op-amp output. The bandwidth from either of the 2 con-
trol pins to the output is DC to greater than 125 kHz.
E-W Pin Cntl (Pin 10): East-West Pincushion Control. A
voltage of 0V to 4V adjusts the polarity and the amount of
parabola in the Horizontal Dynamic Width (pin 9) output. At
approximately 2V, the amount is zero. From 2V to 4V, the
amplitude increases and the parabola is positive-going.
From 2V to 0V, the amplitude increases and the parabola is
negative-going.
H Trap Cntl (Pin 11): Horizontal Trapezoid Control. A volt-
age of 0V to 4V adjusts the polarity and the amount of verti-
cal ramp in the Horizontal Dynamic Width (pin 9) output. At
approximately 2V, the amount is zero. From 2V to 4V, the
amplitude increases and the ramp is positive-going. From 2V
to 0V, the amplitude increases and the ramp is
negative-going.
1
⁄
3
CC
the parabola; i.e., with the H Trap and E-W Pin Cntls at
(Pin 7): Power, 12V nominal. V
CC
should be bypassed
8
H Para Cntl (Pin 12): Horizontal Parallelogram Control. A
voltage of 0V to 4V adjusts the polarity and the amount of
vertical ramp in the Horizontal Dynamic Center (pin 14) out-
put. At approximately 2V, the amount is zero. From 2V to 4V,
the amplitude increases and the ramp is positive-going.
From 2V to 0V, the amplitude increases and the ramp is
negative-going.
H Bow Cntl (Pin 13): Horizontal Bow Control. A voltage of
0V to 4V adjusts the polarity and the amount of parabola in
the Horizontal Dynamic Center (pin 14) output. At approxi-
mately 2V, the amount is zero. From 2V to 4V, the amplitude
increases and the parabola is positive-going. From 2V to 0V,
the amplitude increases and the parabola is negative-going.
H Dyn Cntr (Pin 14): Horizontal Dynamic Center. This out-
put consists of the sum of the vertical ramp and the parabola
derived from the ramp. The amplitude and polarity of the
ramp signal is DC controlled by H Para Cntl (pin 12) and of
the parabola by H Bow Cntl (pin 13). The difference between
this output and the Horizontal Dynamic Width output is in the
weighting of the ramp, which is equal to the parabola; i.e.,
with the H Para and H Bow Cntls at 4V, the output is 1 part
parabola and 1 part ramp. Horizontal Dynamic Center is
used to correct for parallelogram and bow distortion. The
output stage is similar to a standard op-amp output. The
bandwidth from either of the 2 control pins to the output is
DC to greater than 125 kHz.
V Dyn Focus Cntl (Pin 15): Vertical Dynamic Focus Con-
trol. A voltage of 0V to 4V adjusts the polarity and the amount
of parabola in the Vertical Dynamic Focus (pin 16) output. At
approximately 2V, the amount is zero. From 2V to 4V, the
amplitude increases and the parabola is positivegoing. From
2V to 0V, the amplitude increases and the parabola is
negative-going.
V Dyn Focus (Pin 16): Vertical Dynamic Focus. This output
consists of the parabola derived from the vertical ramp. The
amplitude and polarity are controlled by V Dyn Focus Cntl.
The output stage is similar to a standard op-amp output. The
bandwidth from the control pin to the output is DC to greater
than 125 kHz.
GND (Pin 17): Ground. This is the power supply ground for
the 12V supply and the point to which the bypass capacitors
are returned.
ALC Cap (Pin 18): Automatic Level Control Capacitor. This
capacitor is part of the level control circuit that maintains
constant vertical height in spite of vertical sync frequency
changes. The recommended value is 4.7 µF, aluminum elec-
trolytic or tantalum capacitor. If the VCO capacitor value is
changed, this capacitor value should change in the same ra-
tio. A 300k resistor should be connected from this pin to
ground.
2f Cap (Pin 19): Double frequency Capacitor. This capacitor
prevents the vertical oscillator from locking at twice the ver-
tical sync frequency. The recommended value is 0.47 µF. If
the VCO capacitor value is changed, this capacitor value
should change in the same ratio.
Osc Cap (Pin 20): A timing capacitor is connected from this
pin to ground for the internal oscillator. The capacitance de-
termines the lowest lock frequency. See Graph 1.
Rvert (Pin 21): Vertical Resistor. One end of the Vertical Re-
sistor connects to this pin. This resistor determines the gain
of the vertical ramp current generator. The gain is inversely
proportional to the resistance. It is recommended that this be
a standard 5%
1
⁄
4
W carbon film resistor whose negative tem-