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19-0302; Rev 0; 9/94
Low-Cost, High-Resolution, 200MHz Video CRT Driver
_______________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 200 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.
____________________________Features
o 2.5ns Rise/Fall Time into an 8pF Load o 200MHz Small-Signal Bandwidth o 50Vp-p Output o Ground Referenced Differential Inputs o Linear Variable Gain for Contrast Control o Offset Adjustment for Black Level o 5.5V Bandgap Reference o Drives 1280 x 1024 and 1530 x 1280 Displays
MAX445
______________Ordering Information
PART MAX445CPG MAX445C/D TEMP. RANGE 0C to +70C* 0C to +70C** PIN-PACKAGE 24 Power-Tab DIP Dice
________________________Applications
CRT Driver for High-Resolution Monochrome and Color Displays High-Voltage, Variable-Gain Transconductance Amplifier
* Case temperature range, TCASE = 0C to +90C. See Absolute Maximum Ratings and Applications Information for thermal/heat sink considerations. **Dice are specified at TJ = +25C, DC parameters only.
________________Functional Diagram
VAA
__________________Pin Configuration
TOP VIEW
RL VOUT IOUT
GND VREF OFFSET CONTRAST
1 2 3 4 5 6 7 8 9 10 11 12
24 23 22 21
GND GND GND VEEO N.C. IOUT N.C. VCB VCB GND GND GND
CONTRAST
BLANK
MAX445
VIN+ PRE-AMP VINBAND GAP CURRENT AMP
VCB
GNDA VINVIN+ VEE VEE
MAX445
20 19 18 17 16 15 14 13
GNDA
VCC BLANK GND
OFFSET
VREF
GND
Power-Tab DIP
________________________________________________________________ Maxim Integrated Products
1
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Low-Cost, High-Resolution, 200MHz Video CRT Driver MAX445
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 = +90C.......................10W Operating Junction Temperature ......................-55C to +150C Storage Temperature.........................................-55C to +150C Lead Temperature (soldering, 10sec) .............................+300C
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 = 0, BLANK = 0.4V, TCASE = +25C, unless otherwise noted.) PARAMETER Output-Common-Base Supply Current Positive Supply Current Negative Supply Current Power-Supply Rejection Ratio Low Blank Input Bias Current High Blank Input Bias Current Contrast Input Bias Current Offset Input Bias Current VIN+ or VIN- Signal Input Current Input Common-Mode Rejection Ratio VIN+ or VIN- DC Input Impedance VIN+ or VIN- Input Capacitance Reference Output Voltage Output Current (Blanked) Output Current Output Current Change vs. Temperature Output Current Change vs. Contrast ADJ Output Current Change vs. VIN, Blanked SYMBOL ICB ICC IEE PSRR IIL IIH IIC IIB IIS CMRR RVIN CIN VREF IOUT IOUT IOUT IOUT IOUT ILOAD = 2mA BLANK = 2.4V, OFFSET = 1V, VAA = 75V BLANK = 2.4V, OFFSET = 3V OFFSET = 0V, CONTRAST = 4.0V OFFSET = 5.0V, CONTRAST = 1V TC = +25C to +90C CONTRAST = 0V to 5V BLANK = 2.4V, CONTRAST = 5.0V, VIN- = 0.3V CONTRAST = 5.0V Transconductance, IOUT to VIN Amplifier Linearity Error (Gm/VIN) Contrast Linearity Error (Gm/Contrast) Bandwidth, 3dB BW Gm CONTRAST = 1.0V CONTRAST = 0V CONTRAST = 4.0V, OFFSET = 1.0V VIN = 0.2V, OFFSET = 0V OFFSET = 0V, RLOAD = 100 200 400 70 -25 -0.1 80 3 10 1 600 120 25 2 3 % % MHz mA/V 5.25 VCM = 0.5V, CONTRAST = 5.0V IVEE + IVEEO VCC, VEE = 5%, VIN = +250mV, CONTRAST = 5.0V, referred to input BLANK = 0.4V BLANK = 2.4V CONTRAST = 5.0V OFFSET = 1.0V -100 25 -0.6 -0.4 0 0 -50 36 10 2 5.75 1 1 25 140 0 0 10 10 50 CONDITIONS MIN TYP MAX 40 70 UNITS mA mA mA dB mA mA A A A dB k pF V mA mA mA mA mA
2
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Low-Cost, High-Resolution, 200MHz Video CRT Driver
ELECTRICAL CHARACTERISTICS (continued)
(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 = 0, BLANK = 0.4V, TCASE = +25C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS RL = 200, CL = 8pF, VAA = 75V, tr(VIN) < 1ns, No peaking, OUTp-p = 50V With peaking, OUTp-p = 45V MIN TYP 3.6 ns 2.5 8 2 ns % MAX UNITS
MAX445
Rise/Fall Time (10% to 90%)
tr, tf
Settling Time (90% to 100% 2%) Thermal Distortion
ts
CL = 8pF, no peaking
______________________________________________________________Pin Description
PIN 1, 12, 13, 14, 15, 22, 23, 24 2 3 4 5 6 7 8, 9 10 11 16, 17 18, 20 19 21 NAME GND VREF OFFSET CONTRAST GNDA VINVIN+ VEE VCC BLANK VCB N.C. IOUT VEEO FUNCTION High-Current Ground. Connect all pins to ground plane. Reference Output (+5.5V) Output Voltage Offset-Adjustment Input Output Gain-Adjustment Input Pre-Amp Ground Inverting Signal Input Noninverting Signal Input Negative Supply (-10.5V) Positive Supply (+10V) Blanking Input, TTL Output Common-Base Supply (+10V) No Connection--leave open Open-Collector Current Output Negative Supply for Output Stage (-10.5V)
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Low-Cost, High-Resolution, 200MHz Video CRT Driver MAX445
__________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. 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).
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 5k 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 200 load resistor). An internal reference supply pin, VREF, provides the nominal 5.5V needed to drive the contrast input. Normally, a 5k 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):
+10V VEE (-10.5V) D1 1N4152 50V D2 1N4152 50V D3 1N486A 100V
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.
BEAD*
24
VAA (+75V) 0.1F 2 0.1F 3 5k D4 0.1F 4 5k ANALOG INPUT 6 25 7 VINVIN+ NOTES: CL COMBINES CRT CATHODE, AND PARASITIC C. BLANK GNDA GND 5 24* VEE 8 VEE 9 VEEO 21 D4 (PHILIPS BAV20 OR HITACHI 1SS91) IS ARC PROTECTION DIODE. SEE APPLICATIONS INFORMATION SECTION. IOUT 19 L3 L1 LS CONTRAST OFFSET 10 VCC VREF 16 VCB 17 VCB 22F 100V RL 200 10W CR CB L2
1 2
10pF 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. RS 100 W (CARBON) CL
MAX445
50 BLANK
11
BEAD* * STACK POLE 57-0180 OR INDIANA GENERAL F-1650-H 0.1F -10.5V 0.1F
Figure 1. Typical Connection Diagram
4 _______________________________________________________________________________________
Low-Cost, High-Resolution, 200MHz Video CRT Driver
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.
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 = 200 (and RS = 100). 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.
MAX445
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 24 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 0.1F 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.
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Low-Cost, High-Resolution, 200MHz Video CRT Driver MAX445
Table 1. Peaking Networks (RL = 200, RS = 100)
CL (pF) 2 4 6 8 10 12 L3 (nH) 0 0 20 50 75 100 L1 (nH) 20 40 60 80 100 120 L2 (nH) 60 120 180 240 300 360 CB (pF) 0.4 0.8 1.1 1.5 2.0 2.2 tR (ns) 1.7 1.9 2.1 2.3 2.7 3.0
not cause component damage. Junction-to-case thermal resistance is rated at 6C/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 = 200
Output Level Duty Cycle Relative to (%) Black (V) 0 35 35 50 0 100 80 80 IC Power Load Power Total (W) (W) (W) 1.6 7.8 6.5 5.6 0 6.1 4.9 10.0 1.6 13.9 11.4 15.6
Inductors L1, L2, and L3 should be air or ferrite-core coils with self-resonant frequencies higher than 500MHz.
Thermal Environment
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 0.01F capacitor with no tab insulator. Inadvertently shorting the package tab to ground for less than 10 seconds will
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 (0.01F 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.
3.0
MAX445 FG2
BANDWIDTH (MHz)
175
RISE OR FALL TIME (ns)
2.5
150
2.0
125
1.5
100 2 4 6 8 10 12 LOAD CAPACITANCE (pF)
1.0 2 4 6 8 10 12 LOAD CAPACITANCE (pF)
Figure 2. Typical Rise/Fall Time vs. Loading, with Peaking Network Optimized for Load Capacitance
6 _______________________________________________________________________________________
MAX445 FG2
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
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Low-Cost, High-Resolution, 200MHz Video CRT Driver MAX445
___________________Chip Topography
VCB** VCB** IOUT GND* GND* GND* GND* V EEO V EEO GND* GND* GND* GND* 0.133" (3.378mm) BLANK VREF OFFSET CONTRAST V CC
V EE
V EE VIN+
VIN- GNDA GNDA
0.118" (2.997mm)
* All high-current ground pads must be bonded and connected to a low-inductance ground plane. **Connect both VCB pads.
________________________________________________________Package Information
D D1 D2
DIM A A1 A2 B B1 C D D1 D2 E E1 e1 L S K K1 K2 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
K1
B1
K
O.140.005 E E1 A1
K2
HEAT SPREADER
A2
A
L C e1 S B SEATING PLANE
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 (c) 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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