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| Triple 140MHz CRT Driver CORPORATION CVA6627S FEATURES DESCRIPTION The CVA6627S contains three wideband amplifiers designed specifically to drive high resolution CRTs. It features excellent gray scale linearity and high load capacitance driving capability. This device can drive monitors with resolution of 1600 x 1280 (non-interlaced) with pixel frequency of 300MHz. The part is housed in 12L Ceramic package with heat sink grounded. ORDERING INFORMATION Part CVA6627S Package CY12B Temperature -20oC to +100oC * * * * * Rise/Fall Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3ns Swing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70VP-P Symmetrical Rise and Fall Time Excellent Gray Scale Linearity APPLICATION CRT Driver for up to 90khz Monitors with Resolution upto 1600 x 1280 (Non-Interlaced). CONNECTION DIAGRAM AND SIMPLIFIED SCHEMATIC Q1 Q2 5.7K 1 1 2 3 4 5 6 7 8 9 10 11 GND B 12 OUT B IN R GND R OUT R V+ R GND G OUT G V+ G V+ B IN G IN B Q4 Q3 250 1j-40 CALOGIC CORPORATION, 237 Whitney Place, Fremont, California 94539, Telephone: 510-656-2900, FAX: 510-651-3025 CVA6627S CORPORATION ABSOLUTE MAXIMUM RATINGS Supply Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85V Storage Temperature . . . . . . . . . . . . . . . . . . -25oC to +125oC Operating Temperature . . . . . . . . . . . . . . . . -20oC to +100oC Lead Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . +300oC DC ELECTRICAL CHARACTERISTICS VS = 80V, CL = 10pF, VOUT = 50VP-P, TCASE = +25oC. See Figure 1. SYMBOL ICC VIN DC VOUT DC AV CHARACTERISTICS Supply Current Input DC Level Output DC Level Voltage Gain Gain Matching 1.4 34 11 MIN TYP 26 1.6 38 13 0.2 MAX 32 1.8 42 15 UNITS mA V V V dB AC ELECTRICAL CHARACTERISTICS VS = 80V, CL = 10pF, VOUT = 50VP-P, TCASE = +25oC. See Figure 1. SYMBOL tr tf BW Le OS CHARACTERISTICS Rise Time Fall Time Bandwidth Linearity Overshoot MIN TYP 3.1 3.1 140 5 4 MAX 4.0 4.0 UNITS ns ns MHz % % FIGURE 1. TEST CIRCUIT VCC C3 C2 R2 INPUT R1 3,7,11 GND R1 = 15 R2 = 430 R4 = 200k R5 = 22 R6 = 22 C1 = VARIABLE 20 TO 150pF TYPICAL 68pF C2 = VARIABLE 4 to 20pF TYPICAL 17pF C3 = 75pF C4 = 10 f/160V C6 = 0.01 f/160V C L = 10pF D1 = DS464 D2 = DS464 L1 = 150nH 1J-32 R4 1,5,9 VCC 4,8,12 VOUT D1 R5 C4 C6 2,6,10 1/3 CVA6627S VIN R6 L1 OUTPUT CL D2 C1 CALOGIC CORPORATION, 237 Whitney Place, Fremont, California 94539, Telephone: 510-656-2900, FAX: 510-651-3025 CVA6627S CORPORATION APPLICATION INFORMATION The CVA6627S is a transimpedance amplifier with two stage feedback configurations. Any change in input current will be reflected as change in output voltage swing. A resistor in series with the input will change the CVA6627S into a voltage amplifier. The output is emitter follower with load(capacitive) driven capability. With a true Class AB output stage, the rise and fall time is symmetric. CVA6627S has an internal feedback resistor of 5.7K. In the absence of any input signal, the VOUT DC is set by VOUT (DC) = (1 + RF 3) Streaks and overshoot: For a cross-hatch pattern with white background, a whitish line will appear just after the black line, this is called streak. Looking at the waveform it is due to undershoot of the waveform. For a Box pattern with white background, a dark black area just after white is a sign of overshoot. It is due to overshoot of the waveform. Adjusting the value of C2, R1, C1 will get the optimum result. The value of C2 should be kept at minimum for less overshoot, typical is <20pF. Value of R1 should be less than 47 ohms otherwise rise and fall time will suffer. First adjust the overshoot to minimum, keeping value of C1 and R2 to minimum, then adjust the undershoot (Streak) by adjusting C3 again. Since both need to be adjusted together, this may need a few iteration to get to the optimum result. It should be noted here that the output peaking with L1 and R3 is only to overcome the affect of stray capacitance. Keep the value of L1 to minimum, typ 150nH and R, to be 820. The value of L1 depends on the associated capacitance with the board and the cable(if any). CVA6627S is specifically designed to handle extra capacitance associated with the cable(typ. 10pF) assuming the driver is not part of the neck board. The value of R3 should be less than 1K to damped the resonant ringing. The output of CVA6627S is not short circuit proof. Precaution is required. Thermal Characteristics Under normal operating conditions the CVA6627S will dissipate up to 11W. The maximum allowed case temperature is +100oC. To calculate maximum heatsink thermal resistance use the following equation: (100 - 50) = 4.5C/W 11W The Thermalloy #11699 is one example of a heatsink that meets this requirement. Rth = RB ) VIN (DC); RB = 250. An input resistor RG will set the gain as RF VOUT = ( ) VIN ; RG = gain resistor. RG Input and Transfer Characteristics An input current swing of 4.4mA causes the output to change by 25V. A resistor of 430 will set the gain to -13. Input pins are internal DC feedback nodes and thus have low impedance. These pins must be fed from a series RC network for high frequency emphasis. The following section will explain how to overcome some of the problems that are typical. 1) Input drive: CVA6627S gives best results when the amplifier is driven by a fast pulse with proper voltage level. Since all pre-amplifiers have output from 0 to 8V, a level shifter is required. Also, most pre-amplifiers cannot drive a large capacitive load. 2) Smear: For a box pattern with white background, a shadow after the black is called smear. It is due to the tilt of the white level. It can easily be adjusted by adding an RC feedback network (R4, C3). The value of R4 will affect the gain, for CVA6627S, the typical value is 200K. CALOGIC CORPORATION, 237 Whitney Place, Fremont, California 94539, Telephone: 510-656-2900, FAX: 510-651-3025 CVA6627S CORPORATION FIGURE 2. APLICATION CIRCUIT 12V .01F PRE AMP 10pF Q1 D1 R1 R3 C1 2,6,10 1,5,9 CVA6627S 4,8,12 D2 C4 L1 R5 R3 CRT R6 C2 10pF .01F -5V R4 3,7,11 D3 VMIN = -0.5V C3 DC RESTORE R1 = 15 R2 = 430 R3 = 820 R4 = 200K R5 = 39 R6 = 120 D1 = DS464 D2 = DS464 L1 = 150nH C1 = VARIABLE 20 TO 150pF TYPICAL 68pF C2 = VARIABLE 4 to 20pF TYPICAL 17pF C3 = 75pF C4 = 1 F 1J-37 ELECTRICAL CHARACTERISTICS BOX PATTERN -- 50VP-P BOX PATTERN -- 50VP-P 10V/DIV 20ns/DIV 1J-33 10V/DIV 20ns/DIV 1J-34 CROSS HATCH PATTERN -- BLACK BACKGROUND CROSS HATCH PATTERN -- WHITE BACKGROUND 10V/DIV 10ns/DIV 1J-35 10V/DIV 10ns/DIV 1J-36 CALOGIC CORPORATION, 237 Whitney Place, Fremont, California 94539, Telephone: 510-656-2900, FAX: 510-651-3025 |
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