CVA1405T データシートの表示（PDF） - Calogic, LLC

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CVA1405T

Triple CRT Driver

Calogic, LLC 

CORPORATION

CVA1405T

FIGURE 2.

+80V

VBIAS

VIDEO

CVA1405T

L

R

919

339

SPARK

GAP

1T-39

FIGURE 3.

+80V

VBIAS

VIDEO

1K

CVA1405T

L

339

R

C

CVA4502

Vcc

SPARK

GAP

DC BIAS

I.C.

1T-46

BIAS

APPLICATION INFORMATION

The CVA1405T is a high voltage triple CRT driver suitiable to

drive 69kHz, 1024 x 768 CRT displays. It features a high

impedance input to match any pre-amplifier. The CVA1405T

has a true class AB output stage that results in excellent gray

scale linearity and consistent EMI performance.

As with any high speed amplifier used in CRT display

applications, specific precaution should be taken to get the

required performance. Power supply should be by pass as

close to the device pin as possible. Use 0.01µf very near to

the device and a large capacitor of 10µf or more (preferable

100µf) near the device. A 0.1µf and 10µf should be connected

near the Vbias pin (#10). Arc protection is very essential. Fast

diodes together with the spark gap will achieve sufficient

protection. However, in certain applications depends on the

tubes a high value of resistor is required to reduce the current

into the CVA1405T during arcing. This will result in less than

desireable performance some of which can be restored by

using a peaking inductor at the output pin, Figure 2. Another

way to achieve this is by using a RC network at the output of

the device and use a peaking inductor at the tube, Figure 3.

The rise and fall time of the CVA1405T may suffer due to

stray capacitances associated with the PC Board and other

components. It can be improved by carefully designing the

PC Board where the output stage and input stage ground path

are seperated. Calogic will assist customers in the layout of

the PC Board that will result in quick EMI passage and better

performance. The output peaking should be used only to

restore the performance loss due to stray capacitances. Over

peaking will cause excessive ringing that will have better

results but poor EMI. The DC restore circuit is also important

when considering the high frequency performance. Using

CVA4502, DC Bias IC, better results can be obtained and

high frequency performance can be maximixed.

THERMAL CONSIDERATIONS

Power supply current increases as the input signal increases

and consequently power dissipation also increases.

The CVA1405T cannot be used without heat sinking. The

calculations below shows the power dissipated in each

channel over the operating voltage range of the device.

Under white screen conditions, i.e.: 25V output, dissipation

increases to 8.1W total. The CVA1405T case temperature

must be maintained below +100oC. If the maximum expected

ambient temperature is +50oC, then a heat sink is needed

with thermal resistance equal to or less than:

Rth

=

(100 − 50oC)

8.1W

=

6.2oC/W

The output of CVA2405T is not short circuit proof.

CALOGIC CORPORATION, 237 Whitney Place, Fremont, California 94539, Telephone: 510-656-2900, FAX: 510-651-3025

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