19-0302; Rev 0; 9/94 Low-Cost, High-Resolution, 200MHz Video CRT Driver ________________________Applications CRT Driver for High-Resolution Monochrome and Color Displays High-Voltage, Variable-Gain Transconductance Amplifier ________________Functional Diagram RL VOUT BLANK IOUT MAX445 ♦ 2.5ns Rise/Fall Time into an 8pF Load ♦ 200MHz Small-Signal Bandwidth ♦ 50Vp-p Output ♦ Ground Referenced Differential Inputs ♦ Linear Variable Gain for Contrast Control ♦ Offset Adjustment for Black Level ♦ 5.5V Bandgap Reference ♦ Drives 1280 x 1024 and 1530 x 1280 Displays ______________Ordering Information TEMP. RANGE PIN-PACKAGE MAX445CPG PART 0°C to +70°C* 24 Power-Tab DIP MAX445C/D 0°C to +70°C** Dice * Case temperature range, TCASE = 0°C to +90°C. See Absolute Maximum Ratings and Applications Information for thermal/heat sink considerations. **Dice are specified at TJ = +25°C, DC parameters only. __________________Pin Configuration TOP VIEW VAA CONTRAST ____________________________Features VCB GND 1 24 GND VREF 2 23 GND OFFSET 3 22 GND CONTRAST 4 21 VEEO GNDA 5 20 N.C. VIN- 6 19 IOUT VIN+ 7 18 N.C. VEE 8 17 VCB VEE 9 16 VCB VCC 10 15 GND BLANK 11 14 GND GND 12 13 GND VIN+ CURRENT AMP PRE-AMP VINBAND GAP GNDA OFFSET VREF GND MAX445 Power-Tab DIP ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX445 _______________General Description The MAX445 is a high-performance, monolithic, variablegain transconductance amplifier with a high-voltage open-collector output capable of directly driving a video display (CRT cathode). A 2.5ns rise time is achieved using a peaking network with a 200Ω load resistor and an 8pF total load (CRT and parasitic capacitance). Differential inputs and a linear adjustable gain stage with an output offset adjustment make the versatile MAX445 well suited for many video display applications. A buffered bandgap reference voltage is available for the gain (contrast) and offset adjustments along with a TTL BLANK input to turn off the output current, independent of signal input. The MAX445 is available in a 24-pin power-tab DIP package. A suitable heatsink must be attached to maintain the junction temperature within the recommended operating range. MAX445 Low-Cost, High-Resolution, 200MHz Video CRT Driver ABSOLUTE MAXIMUM RATINGS VAA Output Supply.................................................................80V VAA Output Supply with Respect to VCB...............................70V VCB Common-Base Supply ...................................................20V VCC Positive Supply ............................................................12.5V VEE Negative Supply..........................................................-12.5V Differential Input Voltage..........................................................2V Common-Mode Input Voltage................................................±2V Contrast Input Voltage.................................................-1V to +6V Offset Input Voltage.....................................................-1V to +6V Blank Input Voltage .....................................................-1V to +6V Bandgap-Reference Output Current ...................................-5mA Continuous Power Dissipation derate at 170mW/°C above TCASE = +90°C.......................10W Operating Junction Temperature ......................-55°C to +150°C Storage Temperature.........................................-55°C to +150°C Lead Temperature (soldering, 10sec) .............................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (V AA = 20V, VCB = 10V ±0.5V, V CC = 10V ±0.5V, V EE = -10.5V ±0.5V, VIN = (VIN+) - (VIN-) = 0V, CONTRAST = 1.0V, OFFSET = 1.0V, RL = 0Ω, BLANK = 0.4V, TCASE = +25°C, unless otherwise noted.) MAX UNITS Output-Common-Base Supply Current PARAMETER SYMBOL ICB CONDITIONS 40 mA Positive Supply Current ICC 70 mA Negative Supply Current IEE Power-Supply Rejection Ratio PSRR Low Blank Input Bias Current IIL IVEE + IVEEO VCC, VEE = ±5%, VIN = +250mV, CONTRAST = 5.0V, referred to input BLANK = 0.4V High Blank Input Bias Current IIH BLANK = 2.4V Contrast Input Bias Current IIC CONTRAST = 5.0V Offset Input Bias Current IIB OFFSET = 1.0V VIN+ or VIN- Signal Input Current IIS Input Common-Mode Rejection Ratio CMRR VIN+ or VIN- DC Input Impedance RVIN VIN+ or VIN- Input Capacitance CIN Reference Output Voltage VREF Output Current (Blanked) IOUT Output Current IOUT VCM = ±0.5V, CONTRAST = 5.0V mA 25 dB -0.6 0 mA -0.4 0 mA 0 10 µA 0 10 µA -50 50 36 ILOAD = 2mA kΩ 5.25 pF 5.75 BLANK = 2.4V, OFFSET = 1V, VAA = 75V ±1 BLANK = 2.4V, OFFSET = 3V ±1 OFFSET = 0V, CONTRAST = 4.0V -0.1 25 OFFSET = 5.0V, CONTRAST = 1V 80 140 ∆IOUT TC = +25°C to +90°C ∆IOUT Output Current Change vs. VIN, Blanked ∆IOUT CONTRAST = 0V to 5V BLANK = 2.4V, CONTRAST = 5.0V, ∆VIN- = 0.3V CONTRAST = 5.0V ±3 ±1 mA 600 CONTRAST = 1.0V 70 120 CONTRAST = 0V -25 25 CONTRAST = 4.0V, OFFSET = 1.0V ±2 VIN = 0.2V, OFFSET = 0V ±3 2 200 _______________________________________________________________________________________ mA mA 400 OFFSET = 0V, RLOAD = 100Ω mA mA Contrast Linearity Error (∆Gm/∆Contrast) BW V ±10 Amplifier Linearity Error (∆Gm/∆VIN) Bandwidth, 3dB µA dB 2 Output Current Change vs. Contrast ADJ Gm -100 TYP 10 Output Current Change vs. Temperature Transconductance, IOUT to VIN MIN mA/V % % MHz Low-Cost, High-Resolution, 200MHz Video CRT Driver (V AA = 20V, VCB = 10V ±0.5V, V CC = 10V ±0.5V, V EE = -10.5V ±0.5V, VIN = (VIN+) - (VIN-) = 0V, CONTRAST = 1.0V, OFFSET = 1.0V, RL = 0Ω, BLANK = 0.4V, TCASE = +25°C, unless otherwise noted.) PARAMETER Rise/Fall Time (10% to 90%) Settling Time (90% to 100% ±2%) SYMBOL tr, tf ts CONDITIONS RL = 200Ω, CL = 8pF, VAA = 75V, tr(VIN) < 1ns, MIN TYP No peaking, OUTp-p = 50V 3.6 With peaking, OUTp-p = 45V 2.5 MAX UNITS ns CL = 8pF, no peaking Thermal Distortion 8 ns ±2 % ______________________________________________________________Pin Description PIN NAME FUNCTION 1, 12, 13, 14, 15, 22, 23, 24 GND High-Current Ground. Connect all pins to ground plane. 2 VREF Reference Output (+5.5V) 3 OFFSET 4 CONTRAST 5 GNDA Output Voltage Offset-Adjustment Input Output Gain-Adjustment Input Pre-Amp Ground 6 VIN- Inverting Signal Input 7 VIN+ Noninverting Signal Input 8, 9 VEE Negative Supply (-10.5V) 10 VCC Positive Supply (+10V) 11 BLANK 16, 17 VCB Output Common-Base Supply (+10V) 18, 20 N.C. No Connection—leave open 19 IOUT Open-Collector Current Output 21 VEEO Negative Supply for Output Stage (-10.5V) Blanking Input, TTL _______________________________________________________________________________________ 3 MAX445 ELECTRICAL CHARACTERISTICS (continued) MAX445 Low-Cost, High-Resolution, 200MHz Video CRT Driver VAA - VO = [VIN (Gm) + VOFFSET (0.02)] (RL) VAA - VO = [VIN (VCONTRAST) (0.09) + VOFFSET (0.02)] (RL) The MAX445’s overall gain can vary by ±20% due to normal process variations of internal components. Also, if multiple devices are used in a system, all devices must track thermally (i.e., a common heatsink). __________Applications Information Differential Inputs VIN+ and VIN- are differential video input pins designed to allow DC coupling of a 0V to +1V signal into VIN+, with respect to VIN-. For correct operation, it is recommended that the signals applied to these inputs be kept within ±1V, with respect to ground. Although large signals and offsets can be handled safely without damage, exceeding these limits may cause output linearity to suffer. Offset Control The offset control is used to set the output quiescent current from 5mA to 110mA (typ) when the control input is adjusted from 0V to 5V. Normally, offset is adjusted using a 5kΩ potentiometer between VREF and ground. Contrast Control The contrast control is the overall DC-gain control that will vary the voltage gain from 0V/V to -90V/V (with a 200Ω load resistor). An internal reference supply pin, VREF, provides the nominal 5.5V needed to drive the contrast input. Normally, a 5kΩ potentiometer between VREF and ground is used to vary the contrast, but an external source can be used instead of VREF, with some degradation of gain stability with temperature. The contrast control is a linear relationship. Vary the input from 0V to 5V to achieve a voltage-gain range of 0V/V to -90V/V. This yields the following relationship for overall voltage gain of this device (for IOUT < 250mA): Blank Control When asserted (BLANK = TTL high), this input will disable the video signal and allow the output to rise to the VAA supply independent of offset control. Bandgap Reference VREF is a bandgap bias reference for easy adjustment of the offset and contrast inputs. This reference has a nominal output voltage of 5.5V ±5% that can source up to 4mA. +10V VEE (-10.5V) D1 D2 1N4152 50V 1N4152 50V D3 24Ω BEAD* 1N486A 100V VAA (+75V) 0.1µF 10 2 16 VCC VREF 10pF 17 VCB VCB 22µF 100V 0.1µF 3 L1, L2, L3, AND CB ARE ELEMENTS OF THE PEAKING COIL. LS IS THE TOTAL INDUCTANCE TO THE CATHODE. RS IS A SERIES ARC PROTECTION ELEMENT. RL 200Ω 10W OFFSET 5k D4 0.1µF 4 CR MAX445 L2 CB CONTRAST 1 2 5k ANALOG INPUT 6 25Ω 50Ω BLANK 7 11 VIN- IOUT 19 L3 L1 RS 100Ω W (CARBON) LS NOTES: CL COMBINES CRT CATHODE, AND PARASITIC C. BLANK GNDA GND 5 24* VEE 8 D4 (PHILIPS BAV20 OR HITACHI 1SS91) IS ARC PROTECTION DIODE. SEE APPLICATIONS INFORMATION SECTION. VEEO 21 VEE 9 BEAD* * STACK POLE 57-0180 OR INDIANA GENERAL F-1650-H 0.1µF 0.1µF -10.5V Figure 1. Typical Connection Diagram 4 CL VIN+ _______________________________________________________________________________________ Low-Cost, High-Resolution, 200MHz Video CRT Driver Impedance Matching Network For maximum speed from the MAX445, be sure to “match” the output to the CRT. Figure 1’s typical connection diagram shows a network (including parasitic reactances) associated with arc protection devices, CRT wiring and grid structure, and load resistors. These parasitic reactances are all detrimental to good transient response and should be minimized as much as possible. CL is the grid-to-cathode capacitance of the CRT, plus any parasitic capacitance to ground associated with the cathode structure. This capacitance varies from tubetype to tube-type over the 4pF to 12pF range. In Figure 1, LS is the inductance of the lead from the amplifier board to the CRT cathode and the return path from the grid to circuit ground. A wire in free space has an inductance of 20nH/inch to 25nH/inch. With care, the total path through the CRT gun can be kept at 1.5 to 2 inches, such that L S ranges from 30nH to 50nH. Excessive lead length will cause undesirable overshoot and ringing in the transient response. The peaking networks assume that 2pF of parasitic capacitance is associated with the CRT arc protection diode connected at the junction of L3 and L1. Lr is the parasitic inductance of the load resistor, RL. In some cases, C R may be needed to improve step response. RS is a damping resistor in series with the CRT grid. It also provides current limiting in the event of CRT arcing. The equations for determining optimum peaking network values are as follows: L1 = (RL)2 (CL) / 4 L2 = 3(RL)2 (CL) / 4 CB = CL / 5 RS = RL / 2 L3 = k3 (RL)2 [2.5 x 10-12] CR (optional) = Lr / (2RL2) k3 is an empirically determined factor increasing with CL and varying from 0 for CL ~ 2pF to 1 for CL ~ 12pF. However, L3 >100nH will compromise large-signal performance. Table 1 shows peaking networks for the nominal load, RL = 200Ω (and RS = 100Ω). Optimum peaking depends on board layout and CRT construction. The values given by these equations should be used as starting points for empirically determining optimum values. VCB The output stage consists of a common-base, high-voltage stage and a high-speed, low-voltage current amplifier in a cascode arrangement. The VCB input is the base connection to the common-base device of this stage. Be sure to provide a stable DC voltage at this pin of nominally +10V. High-frequency compensation at this input is required to avoid output oscillations. Use a series 24Ω resistor to supply, shunted with a 10pF capacitor to ground (Figure 1). Smaller values of this RC combination will improve output rise/fall times, but can cause output oscillations. Power Supplies +10V and -10.5V supplies are required for proper operation. These supplies can be set to ±12V for convenience, however this will add additional component power dissipation. The high-voltage supply, VAA, can be any voltage between VCB + 10V and VCB + 65V. VEEO (pin 21) is the negative supply to the output stage and must be DC connected to VEE (pins 8 and 9), the most negative voltage applied to the device. However, VEEO must be decoupled from VEE to prevent output oscillations. A ferrite bead and separate 0.1µF decoupling capacitors, as shown in Figure 1, will provide appropriate decoupling. Power-Supply Sequencing Power-supply sequencing is important to avoid internal device latchup. To avoid sequencing problems, external diodes should be placed from V EE to ground, from ground to VCC, and from VCC to the output supply (VAA), as shown in Figure 1. With diodes used as shown, special power-supply sequencing is not required. CRT Arc Protection The MAX445 must be protected from electrostatic discharge (“arcs”) from the CRT. It is recommended that the output be clamped with a low-capacitance (less than 2pF) diode to the VAA supply. The peak current-handling capability required of the diode is a function of the CRT arc characteristics, but typically should be 1A or more, such as Philips BAV20 or Hitachi 1SS91. For additional information regarding arc protection, contact Maxim’s applications department. _______________________________________________________________________________________ 5 MAX445 IOUT The MAX445’s output is an open collector of a cascode amplifier. This output is designed to work with nominal output supplies of VAA = +75V. The high-voltage supply must be greater than any applied VCB voltage for proper operation. The MAX445 sinks up to 250mA. Optimum performance into a capacitive load can be achieved when an impedance-matching network is used. Table 1. Peaking Networks (RL = 200Ω, RS = 100Ω) CL (pF) L3 (nH) L1 (nH) L2 (nH) CB (pF) tR (ns) 2 0 20 60 0.4 1.7 4 0 40 120 0.8 1.9 6 20 60 180 1.1 2.1 8 50 80 240 1.5 2.3 10 75 100 300 2.0 2.7 12 100 120 360 2.2 3.0 not cause component damage. Junction-to-case thermal resistance is rated at 6°C/W for the power-tab DIP package. Table 2 shows the relationship of output voltage and duty cycle to total power. Table 2. Power Dissipation at VAA = 70V and Load Resistor = 200Ω Output Level Duty Cycle Relative to (%) Black (V) IC Power Load Power Total (W) (W) (W) Inductors L1, L2, and L3 should be air or ferrite-core coils with self-resonant frequencies higher than 500MHz. 0 0 1.6 0 1.6 35 100 7.8 6.1 13.9 35 80 6.5 4.9 11.4 Thermal Environment 50 80 5.6 10.0 15.6 3.0 RISE OR FALL TIME (ns) MAX445 FG2 200 Circuit Layout and Bypassing Due to the extremely high-speed performance of the MAX445, layout design precautions are required to realize the display driver’s full high-speed capability. The precautions are as follows: 1) A printed circuit board with a good, unbroken, lowinductance ground plane is required. 2) Place a decoupling capacitor (0.01µF ceramic) as close to VCC as possible. 3) Pay close attention to the decoupling capacitors’ resonant frequency and keep leads short. 4) On the inputs and outputs, keep lead lengths short to avoid unwanted parasitic feedback around the display driver. 5) Solder the MAX445 directly to the printed circuit board. Do not use sockets. 175 150 125 MAX445 FG2 The MAX445 can dissipate a large amount of power depending on speed and load-driving requirements. The power-tab package provides a low thermal resistance path from the chip to an external heatsink. Be sure the board design provides sufficient heatsinking capacity for the intended operating range. When mounting to a chassis, it should be noted that the device tab is attached to VEE (-10.5V). This tab should be electrically isolated from ground through a thermally conductive insulator. It is highly recommended that the external heatsink be connected to ground, since an arc or electrostatic discharge entering the heatsink may break down or bypass the tab insulator and damage the device. Also, the grounded heatsink to package tab capacitance will help to bypass the VEE supply. Another option would be to bypass the heatsink to ground with a 0.01µF capacitor with no tab insulator. Inadvertently shorting the package tab to ground for less than 10 seconds will BANDWIDTH (MHz) MAX445 Low-Cost, High-Resolution, 200MHz Video CRT Driver 2.5 2.0 1.5 1.0 100 2 4 6 8 10 LOAD CAPACITANCE (pF) 12 2 4 6 8 10 LOAD CAPACITANCE (pF) Figure 2. Typical Rise/Fall Time vs. Loading, with Peaking Network Optimized for Load Capacitance 6 _______________________________________________________________________________________ 12 Low-Cost, High-Resolution, 200MHz Video CRT Driver MAX445 70V VOUT (10V/div) 0V TIME (10ns/div) Figure 3. Step Response Showing Typical Rise/Fall Times from MAX445 EV Kit Using a Tektronix 11401 Oscilloscope _______________________________________________________________________________________ 7 MAX445 Low-Cost, High-Resolution, 200MHz Video CRT Driver ___________________Chip Topography VCB** VCB** IOUT V EEO V EEO GND* GND* GND* GND* GND* GND* GND* GND* 0.133" (3.378mm) VREF BLANK OFFSET CONTRAST V CC V EE V EE VIN+ VIN- GNDA GNDA * All high-current ground pads must be bonded and connected to a low-inductance ground plane. **Connect both VCB pads. 0.118" (2.997mm) ________________________________________________________Package Information DIM D D1 D2 K1 B1 K Ø.140±.005 E HEAT SPREADER K2 A1 A2 E1 A α L A A1 A2 B B1 C D D1 D2 E E1 e1 L S K K1 K2 α INCHES MAX MIN 0.200 0.170 0.052 0.048 0.155 0.145 0.020 0.016 0.155 0.145 0.011 0.009 1.610 1.590 1.345 1.330 0.145 0.135 0.600 BSC 0.555 0.545 0.100 BSC 0.130 0.120 0.120 0.110 0.402 0.398 0.205 0.195 0.102 0.098 15˚ 0˚ MILLIMETERS MIN MAX 4.318 5.080 1.219 1.321 3.683 3.937 0.406 0.508 3.683 3.937 0.229 0.279 40.386 40.894 33.782 33.163 3.429 3.683 15.240 BSC 13.843 14.097 2.540 BSC 3.048 3.302 2.794 3.048 10.109 10.211 4.953 5.207 2.489 2.591 0˚ 15˚ 21-7000A C B e1 SEATING PLANE S 24-PIN POWER-TAB PLASTIC DUAL-IN-LINE PACKAGE WITHOUT HEAT SINK Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 8 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.