+

+

KR

To IK interface

circuit or RGB

SURFHVVRU¶V ,.

current input

IK current from

other two LM2432s

OBSOLETE

LM2432

www.ti.com

SNOSAL4E – MARCH 2005 – REVISED APRIL 2013

normal video resumes, a protection element should shunt high video current away from the IK input of the RGB

RGB processor input and LM2432 IK output in this case. Again, it may be necessary for the RGB processor to

have IK leakage compensation for the leakage current attributed to the zener. See a simplified current feedback

interface circuit in Figure 15.

Figure 15. Simplified IK Interface for Current Feedback Systems

LM2432 IK Output and Protection Requirements

The LM2432 IK output sources a copy of the actual cathode current to the interface circuit during the closed-loop

IK measurement interval and during normal video when the IK feedback loop is opened. Because the cathode

current during normal video is much higher than the low current being measured during the measurement

be maintained within the range specified in the Operating Ranges.

the current through the diode when clamping. See the TI Demonstration Board for an example. For current

chosen zener voltage and shunt the high video current away from the RGB processor's IK input. The zener

voltage should be higher than the clamping voltage of the processor's IK pin and lower than the maximum

In a Direct-View TV application with a single neck PCB, it is possible for the three LM2432 IK outputs to share

the one feedback circuit and protection diode by connecting the IK pins together on the neck PCB. This will

reduce component count. In a Rear-Projection TV application with three neck PCBs, the IK pins can be

connected on the central neck PCB or the RGB processor mainboard through cabling. This way, they can share

the interface circuit to feed back the IK voltage or current signal to the RGB processor. However, each LM2432

IK output should have its own protection diode on its PCB.

PC BOARD LAYOUT CONSIDERATIONS

For optimum performance, an adequate ground plane, isolation between channels, good supply bypassing and

minimizing unwanted feedback are necessary. Also, the length of the signal traces from the preamplifier to the

LM2432 and from the LM2432 to the CRT cathode should be as short as possible. The following references are

recommended:

Ott, Henry W., “Noise Reduction Techniques in Electronic Systems”, John Wiley & Sons, New York, 1976.

“Video Amplifier Design for Computer Monitors”, TI Application Note 1013.

Pease, Robert A., “Troubleshooting Analog Circuits”, Butterworth-Heinemann, 1991.

Because of its high small signal bandwidth, the part may oscillate in a TV if feedback occurs around the video

channel through the chassis wiring. To prevent this, leads to the video amplifier input circuit should be shielded,

and input circuit wiring should be spaced as far as possible from output circuit wiring.

Copyright © 2005–2013, Texas Instruments Incorporated

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