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LH2426 Dataheets PDF



Part Number LH2426
Manufacturers National Semiconductor
Logo National Semiconductor
Description Triple 80 MHz CRT Driver
Datasheet LH2426 DatasheetLH2426 Datasheet (PDF)

LH2426 Triple 80 MHz CRT Driver June 1992 LH2426 Triple 80 MHz CRT Driver General Description The LH2426 contains three wide bandwidth large signal amplifiers designed for large voltage swings at high frequencies The amplifiers work on a transimpedance principal i e an input current swing of g 4 38 mA results in an output voltage swing of g 25V The device is intended for use in color CRT monitors and is a low cost solution to designs www.DataSheet4U.com conforming to the IBM 8514 graphics stan.

  LH2426   LH2426


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LH2426 Triple 80 MHz CRT Driver June 1992 LH2426 Triple 80 MHz CRT Driver General Description The LH2426 contains three wide bandwidth large signal amplifiers designed for large voltage swings at high frequencies The amplifiers work on a transimpedance principal i e an input current swing of g 4 38 mA results in an output voltage swing of g 25V The device is intended for use in color CRT monitors and is a low cost solution to designs www.DataSheet4U.com conforming to the IBM 8514 graphics standard Features Y Y Y Y Y Operation from 80V power supply 80 MHz bandwidth at 50 VPP swings Rise fall time less than 4 ns Output signal can swing 70V Drives CRT directly Applications Y Y CRT driver for RGB monitors High voltage transimpedance amplifiers Schematic and Connection Diagrams (One Section) TL H 10739 – 2 Top View Order Number LH2426S See NS Package Number HY12B TL H 10739 – 1 IBM is a registered trademark of International Business Machines Corporation C1995 National Semiconductor Corporation TL H 10739 RRD-B30M115 Printed in U S A Absolute Maximum Ratings If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Supply Voltage V a Power Dissipation PD a 85V Storage Temperature Range TSTG Operating Temperature Range TCASE Lead Temperature (Soldering 10 sec ) ESD Tolerance b 25 C to a 100 C b 20 C to a 90 C 10W 300 C TBD DC Electrical Characteristics V a e 80V R1 e 430X C1 e 82 pF CL e 8 pF 50 VPP output swing with 40V DC offset See Figure 1 TCASE e 25 C unless otherwise noted Symbol Va V Parameter Supply Current (per Amplifier) Input Offset Voltage Output Offset Voltage Rise Time Fall Time Bandwidth Voltage Gain Overshoot Linearity Error Gain Matching VOUT from a 10V to a 70V Note 1 Note 2 10% to 90% 90% to 10% b 3 dB Conditions Min No Input or Output Load 14 34 LH2426 Typical 24 16 40 35 35 100 11 13 10 5 02 14 Max 30 18 46 5 5 Units mA V V ns ns MHz V V % % dB INDC www.DataSheet4U.com VOUTDC tR tF BW Av OS LE D Av Note 1 Linearity error is defined as The variation in small signal gain from a 10V to a 70V output with a 100 mVAC 1 MHz input signal Note 2 Calculated value from voltage gain test on each channel Typical Performance Characteristics Typical Test Circuit (One Section) TL H 10739 – 3 FIGURE 1 Test Circuit (One Section) Note 8 pF is total load capacitance It includes all parasitic capacitances Figure 1 shows a typical test circuit for evaluation of the LH2426 This circuit is designed to allow testing of the LH2426 in a 50 X environment such as a pulse generator oscillosope or network analyzer To calibrate pulse generator set to 2 4 VPP into 50 X THEORY OF OPERATION The LH2426 is a two stage amplifier (see schematic on front page) Both stages are in push pull configuration Q2 is biased with two resistors Q1 gets its bias through the 5700X feedback resistor and the input biasing current The bases of Q1 and Q2 are capacitively coupled and therefore Q2 is also actively driven The LH2426 is a transimpedance amplifier an input current is translated into an output voltage An input current of about g 4 5 mA will provide full output swing of g 25V A resistor in series with the input converts the LH2426 into a voltage amplifier with 430X the voltage gain becomes b 13 Application Hints The LH2426 is designed as a triple power amplifier for delivering red blue and green video signals to a cathode ray tube (CRT) It can provide 50V output swing and energize a 12 ns pixel The input capacitance of a CRT grid is typically 8 pF 2 Application Hints (Continued) The emitter resistors of Q1 and Q2 are bypassed with small capacitors This increases the gain to the stage for high frequencies and increases the bandwidth of the amplifier The power supply is internally bypassed If low frequencies are present in the power supply line an electrolytic capacitor is recommended INPUT NETWORKS The voltage gain and the response of the amplifiers can be set by adding an R–C to the input A 430X resistor in series will set the voltage gain to 13 This will increase the rise and fall times of the system (See Figure 2a ) Bypassing the resistor with a capacitor of about 50 pF will restore the rise fall times but will result in some overshoot (Figure 2b) Adding a resistor in series with the capacitor will reduce the overshoot but also increase the rise and fall times (Figure 2c) The addition of a second capacitor will restore the rise and fall times without significant overshoot (Figure 2d) Suggested values for the resistors and capacitors are shown however optimum values may differ depending upon the stray inductances and capacitances present in different board layouts dissipation in the input transistors If this causes a problem it can be compensated with R-C feedback Figure 3 illustrates the circuit and recommended component values PROTECTING AMPLIFIER OUTPUT FROM TUBE ARCING During normal CRT operation intern.


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