(55V − 165V), Test Circuit - Figure 3 unless otherwise specified) (Continued)

TABLE 1. Power Dissipation for Various Video Patterns

Power Dissipation (W)

Pattern

Format

480i

480p

720p

1080i

Raster

2.4

2.4

2.4

2.4

Full White Field

6.1

6.1

6.0

6.5

White Box, 75% Screen Size

4.6

4.6

4.0

4.2

Gray Bars

4.8

4.8

4.7

5.0

Color Bars 75% Amplitude

3.9

4.0

4.0

4.1

Color Bars 100% Amplitude

4.3

4.3

4.3

4.5

SMPTE Color Bars

3.8

3.8

3.8

4.0

SMPTE 133

5.0

5.2

5.4

5.7

Cross Hatch 16x12

2.8

3.0

3.0

2.9

Resolution Chart

5.3

5.5

5.6

5.8

Multiburst

5.4

6.6

10.1

10.9

White Text on Black Background

5.2

7.1

11.1

12.3

Windows Pattern

4.0

4.5

6.4

6.6

Windows Pattern

4.7

5.2

6.7

7.0

Windows Pattern

6.0

6.7

8.6

9.4

Vertical Lines 5 On 5 Off

5.1

5.9

8.7

9.5

Vertical Lines 4 On 4 Off

5.3

6.3

9.8

10.8

Vertical Lines 3 On 3 Off

5.6

7.0

11.7

12.9

Vertical Lines 2 On 2 Off

6.3

8.5

14.4

16.2

Vertical Lines 1 On 1 Off

8.5

12.7

21.8

24.6

Theory of Operation

The LM2426TE is a high voltage monolithic three channel

CRT driver suitable for HDTV applications. The LM2426TE

operates with 180V and 8V power supplies. The part is

housed in the industry standard 11-lead TO-220 molded

plastic power package with thin leads for improved metal-to-

metal spacing.

The circuit diagram of the LM2426TE is shown in Figure 2.

The PNP emitter follower, Q5, provides input buffering. Q1

and Q2 form a fixed gain cascode amplifier with resistors R1

and R2 setting the gain at −53. Emitter followers Q3 and Q4

isolate the high output impedance of the cascode stage from

the capacitance of the CRT cathode which decreases the

sensitivity of the device to load capacitance. Q6 provides

biasing to the output emitter follower stage to reduce cross-

over distortion at low signal levels.

Figure 3 shows a typical test circuit for evaluation of the

LM2426TE. This circuit is designed to allow testing of the

LM2426TE in a 50

Ω environment without the use of an

expensive FET probe. In this test circuit, the two 4.99k

Ω

resistors form a 400:1 wideband, low capacitance probe

when connected to a 50

Ω coaxial cable and a 50Ω load

(such as a 50

Ω oscilloscope input). The input signal from the

generator is ac coupled to the base of Q5.

Application Hints

INTRODUCTION

National Semiconductor (NSC) is committed to provide ap-

plication information that assists our customers in obtaining

the best performance possible from our products. The fol-

lowing information is provided in order to support this com-

mitment. The reader should be aware that the optimization of

performance was done using a specific printed circuit board

designed at NSC. Variations in performance can be realized

due to physical changes in the printed circuit board and the

application. Therefore, the designer should know that com-

ponent value changes may be required in order to optimize

performance in a given application. The values shown in this

document can be used as a starting point for evaluation

purposes. When working with high bandwidth circuits, good

layout practices are also critical to achieving maximum per-

formance.

IMPORTANT INFORMATION

The LM2426TE performance is targeted for the HDTV mar-

ket. The application circuits shown in this document to opti-

mize performance and to protect against damage from CRT

arcover are designed specifically for the LM2426TE. If an-

other member of the LM242X family is used, please refer to

its datasheet.

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