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19-3061; Rev 0; 10/03
12-Output, 76V, Serial-Interfaced VFD Tube Driver
General Description
The MAX6920 is a 12-output, 76V, vacuum fluorescent display (VFD) tube driver that interfaces a multiplexed VFD tube to a VFD controller such as the MAX6850-MAX6853 or to a microcontroller. The MAX6920 is also ideal for driving either static VFD tubes or telecom relays. Data is inputted using an industry-standard 4-wire serial interface (CLOCK, DATA, LOAD, BLANK) for compatibility with both industry-standard drivers and Maxim's VFD controllers. For easy display control, the active-high BLANK input forces all driver outputs low, turning the display off, and automatically puts the MAX6920 into shutdown mode. Display intensity may also be controlled by pulse-width modulating the BLANK input. The MAX6920 has a serial interface data output pin, DOUT, allowing any number of devices to be cascaded on the same serial interface. The MAX6920 is available in a 20-pin SO package. Maxim also offers VFD drivers with either 20 (MAX6921/MAX6931) or 32 outputs (MAX6922 and MAX6932). o 3V to 5.5V Logic Supply Range o 8V to 76V Grid/Anode Supply Range o Push-Pull CMOS High-Voltage Outputs o Outputs can Source 40mA, Sink 4mA Continuously o Outputs can Source 75mA Repetitive Pulses o Outputs can be Paralleled for Higher Current Drive o Any Output can be Used as a Grid or an Anode Driver o Blank Input Simplifies PWM Intensity Control o Small 20-Pin SO Package o -40C to +125C Temperature Range
Features
o 5MHz Industry-Standard 4-Wire Serial Interface
MAX6920
Applications
White Goods Gaming Machines Automotive Avionics Industrial Weighing Security Telecom
PART MAX6920AWP
Ordering Information
TEMP RANGE -40C to +125C PIN-PACKAGE 20 Wide SO
Pin Configuration
TOP VIEW
Typical Operating Circuit
+5V +60V C2 100nF 1 VBB
VBB 1 DOUT 2 OUT11 3 OUT10 4 OUT9 5 OUT8 6 OUT7 7 OUT6 8 BLANK 9 GND 10
20 VCC 19 DIN 18 OUT0 17 OUT1 16 OUT2 C
C1 100nF 20 VCC
MAX6920AWP
14 OUT4 13 OUT5 12 LOAD 11 CLK
VFCLK VFLOAD VFBLANK
11 12 9
CLK LOAD BLANK GND 10
________________________________________________________________ Maxim Integrated Products
VFD TUBE
15 OUT3
VFDOUT
19
MAX6920
DIN OUT0 - OUT11
12
1
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12-Output, 76V, Serial-Interfaced VFD Tube Driver MAX6920
ABSOLUTE MAXIMUM RATINGS
Voltage (with respect to GND) VBB .................................................................................-0.3V to +80V VCC .......................................................................-0.3V to +6V OUT_.......................................................-0.3V to (VBB + 0.3V) All Other Pins..........................................-0.3V to (VCC + 0.3V) OUT_ Continuous Source Current ....................................-45mA OUT_ Pulsed (1ms max, 1/4 max duty) Source Current ...-80mA Total OUT_ Continuous Source Current .........................-540mA Total OUT_ Continuous Sink Current .................................60mA Total OUT_ Pulsed (1ms max, 1/4 max duty) Source Current ............................................................-960mA OUT_ Sink Current ..............................................................15mA CLK, DIN, LOAD, BLANK, DOUT Current .......................10mA Continuous Power Dissipation 20-Pin Wide SO (derate 10mW/C over TA = +70C) ..800mW Operating Temperature Range (TMIN to TMAX) .-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+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
(Typical Operating Circuit, VBB = 8V to 76V, VCC = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER Logic Supply Voltage Tube Supply Voltage SYMBOL VCC VBB All outputs OUT_ low, CLK = idle Logic Supply Operating Current ICC All outputs OUT_ high, CLK = idle All outputs OUT_ low Tube Supply Operating Current IBB All outputs OUT_ high VBB 15V, IOUT = -25mA High-Voltage OUT_ VH VBB 15V, IOUT = -40mA 8V < VBB < 15V, IOUT = -25mA VBB 15V, IOUT = 1mA Low-Voltage OUT_ VL 8V < VBB < 15V, IOUT = 1mA TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C 0.8 VBB - 2 VBB - 2.5 VBB - 3.5 VBB - 4.0 VBB - 1.2 VBB - 2.5 VBB - 3.0 0.75 1 1.5 1.9 1.1 1.6 2.0 V V VBB - 1.1 0.53 1 350 CONDITIONS MIN 3 8 72 TYP MAX 5.5 76 170 200 650 700 2 4.2 0.85 0.9 mA A UNITS V V
2
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12-Output, 76V, Serial-Interfaced VFD Tube Driver
ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, VBB = 8V to 76V, VCC = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER Rise Time OUT_ (20% to 80%) Fall Time OUT_ (80% to 20%) LOAD Rising to OUT_ Falling Delay LOAD Rising to OUT_ Rising Delay BLANK Rising to OUT_ Falling Delay BLANK Falling to OUT_ Rising Delay Input Leakage Current CLK, DIN, LOAD, BLANK Logic-High Input Voltage CLK, DIN, LOAD, BLANK Logic-Low Input Voltage CLK, DIN, LOAD, BLANK Hysteresis Voltage DIN, CLK, LOAD, BLANK High-Voltage DOUT Low-Voltage DOUT Rise and Fall Time DOUT CLK Clock Period CLK Pulse-Width High CLK Pulse-Width Low CLK Rise to LOAD Rise Hold DIN Setup Time DIN Hold Time DOUT Propagation Delay LOAD Pulse High tCP tCH tCL tCSH tDS tDH tDO tCSW 3V to 4.5V 4.5V to 5.5V CDOUT = 10pF 3.0V to 4.5V 4.5V to 5.5V (Note 2) IIH, IIL VIH VIL VI VOH VOL ISOURCE = -1.0mA ISINK = 1.0mA CDOUT = 10pF (Note 2) 3V to 4.5V 4.5V to 5.5V 200 90 90 100 5 20 15 25 20 55 120 75 240 150 60 30 VCC 0.5 0.5 100 80 0.6 0.8 x VCC 0.3 x VCC SYMBOL tR tF CONDITIONS VBB = 60V, CL = 50pF, RL = 2.3k VBB = 60V, CL = 50pF, RL = 2.3k MIN TYP 0.9 0.6 MAX 2 1.5 UNITS s s
MAX6920
SERIAL INTERFACE TIMING CHARACTERISTICS (Notes 2, 3) (Notes 2, 3) (Notes 2, 3) (Notes 2, 3) 0.9 1.2 0.9 1.3 0.05 1.8 2.4 1.8 2.5 10 s s s s A V V V V V ns ns ns ns ns ns ns ns ns
Note 1: All parameters are tested at TA = +25C. Specifications over temperature are guaranteed by design. Note 2: Guaranteed by design. Note 3: Delay measured from control edge to when output OUT_ changes by 1V.
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3
12-Output, 76V, Serial-Interfaced VFD Tube Driver MAX6920
Typical Operating Characteristics
(VCC = 5.0V, VBB = 76V, and TA = +25C, unless otherwise noted.)
TUBE SUPPLY CURRENT (IBB) vs. TEMPERATURE (OUTPUTS LOW)
MAX6920 toc01
TUBE SUPPLY CURRENT (IBB) vs. TEMPERATURE (OUTPUTS HIGH)
1.8 1.6 SUPPLY CURRENT (mA) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 VBB = 40V -40 -20 0 20 40 60 VBB = 8V 80 100 120 VBB = 76V
MAX6920 toc02
LOGIC SUPPLY CURRENT (ICC) vs. TEMPERATURE (OUTPUTS LOW)
350 SUPPLY CURRENT (A) 300 250 200 150 100 50 0 -40 -20 0 20 40 60 80 100 120 VCC = 5V, CLK = IDLE VCC = 3.3V, CLK = IDLE VCC = 3.3V, CLK = 5MHz VCC = 5V, CLK = 5MHz
MAX6920 toc03 MAX6920 toc05
2.0 1.8 1.6 SUPPLY CURRENT (mA) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -15 10 35 60 85 110 TEMPERATURE (C) VBB = 40V VBB = 8V VBB = 76V
2.0
400
TEMPERATURE (C)
TEMPERATURE (C)
SUPPLY CURRENT (ICC) vs. TEMPERATURE (OUTPUTS HIGH)
VCC = 5V, CLK = 5MHz 550 SUPPLY CURRENT (A) 500 450 400 350 300 250 -40 10 60 110 TEMPERATURE (C) VCC = 5V, CLK = IDLE VCC = 3.3V, CLK = IDLE VCC = 3.3V, CLK = 5MHz
MAX6920 toc04
OUTPUT VOLTAGE (VBB - VH) vs. TEMPERATURE (OUTPUT HIGH)
3.5 IOUT = -40mA 3.0 VBB = 8V OUTPUT VOLTAGE (V) 2.5 2.0 VBB = 40V 1.5 1.0 0.5 0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C) VBB = 76V
600
OUTPUT VOLTAGE vs. TEMPERATURE (OUTPUT LOW)
IOUT = 4mA 12 OUTPUT VOLTAGE (V) 10 8 6 4 2 0 -40 -20 0 20 40 60 80 100 120 VBB = 8V VBB = 76V VBB = 40V
MAX6920 toc06
OUTPUT RISE AND FALL WAVEFORM
MAX6920 toc11
14
BLANK 2V/div
OUT_ 20V/div
1s/div
TEMPERATURE (C)
4
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12-Output, 76V, Serial-Interfaced VFD Tube Driver
Pin Description
PIN 1 2 3-8, 13-18 9 10 11 12 19 20 NAME VBB DOUT OUT0 to OUT11 BLANK GND CLK LOAD DIN VCC VFD Tube Supply Voltage Serial-Clock Output. Data is clocked out of the internal shift register to DOUT on CLK's rising edge. VFD Anode and Grid Drivers. OUT0 to OUT11 are push-pull outputs swinging from VBB to GND. Blanking Input. High forces outputs OUT0 to OUT11 low, without altering the contents of the output latches. Low enables outputs OUT0 to OUT11 to follow the state of the output latches. Ground Serial-Clock Input. Data is loaded into the internal shift register on CLK's rising edge. Load Input. Data is loaded transparently from the internal shift register to the output latch while LOAD is high. Data is latched into the output latch on LOAD's rising edge, and retained while LOAD is low. Serial-Data Input. Data is loaded into the internal shift register on CLK's rising edge. Logic Supply Voltage FUNCTION
MAX6920
CLK
DIN
SERIAL-TO-PARALLEL SHIFT REGISTER
DOUT
LOAD
LATCHES
BLANK
MAX6920
OUT0 OUT1 OUT2
OUT11
Figure 1. MAX6920 Functional Diagram
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5
12-Output, 76V, Serial-Interfaced VFD Tube Driver
VBB
40 TYPICAL SLEW- RATE CONTROL 750 TYPICAL OUT_
the shift register outputs when LOAD is high, and latches the current state on the falling edge of LOAD. Each driver output is a slew-rated controlled CMOS push-pull switch driving between VBB and GND. The output rise time is always slower than the output fall time to avoid shoot-through currents during output transitions. The output slew rates are slow enough to minimize EMI, yet are fast enough so as not to impact the typical 100s digit multiplex period and affect the display intensity.
MAX6920
Initial Power-Up and Operation
Figure 2. MAX6920 CMOS Output Driver Structure
Detailed Description
The MAX6920 is a VFD tube driver comprising a 4-wire serial interface driving 12 high-voltage Rail-to-Rail(R) output ports. The driver is suitable for both static and multiplexed displays. The output ports feature high current-sourcing capability to drive current into grids and anodes of static or multiplex VFDs. The ports also have active current sinking for fast discharge of capacitive display electrodes in multiplexing applications. The 4-wire serial interface comprises a 12-bit shift register and a 12-bit transparent latch. The shift register is written through a clock input CLK and a data input DIN and the data propagates to a data output DOUT. The data output allows multiple drivers to be cascaded and operated together. The output latch is transparent to
An internal reset circuit clears the internal registers of the MAX6920 on power-up. All outputs OUT0 to OUT11 and the interface output DOUT initialize low regardless of the initial logic levels of the CLK, DIN, BLANK, and LOAD inputs.
4-Wire Serial Interface
The MAX6920 uses a 4-wire serial interface with three inputs (DIN, CLK, LOAD) and a data output (DOUT). This interface is used to write output data to the MAX6920 (Figure 3) (Table 1). The serial interface data word length is 12 bits, D0-D11. The functions of the four serial interface pins are: * CLK input is the interface clock, which shifts data into the MAX6920's 12-bit shift register on its rising edge. * LOAD input passes data from the MAX6920's 12bit shift register to the 12-bit output latch when LOAD is high (transparent latch), and latches the data on LOAD's falling edge.
tCSW LOAD tCL tCH tCSH tCP
CLK tDH tDS DIN D11 D10 D1 D0
tDO DOUT D11
Figure 3. 4-Wire Serial Interface Timing Diagram Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd. 6 _______________________________________________________________________________________
12-Output, 76V, Serial-Interfaced VFD Tube Driver MAX6920
Table 1. 4-Wire Serial Interface Truth Table
BLANKING SERIAL CLOCK SHIFT REGISTER CONTENTS LOAD LATCH CONTENTS OUTPUT CONTENTS INPUT INPUT INPUT DATA INPUT CLK D0 D1 D2 ... Dn-1 Dn LOAD D0 D1 D2 ... Dn-1 Dn BLANK D0 D1 D2 ... Dn-1 Dn DIN H L X H L R0 X P0 R0 R1 ... Rn-2 Rn-1 R0 R1 ... Rn-2 Rn-1 R1 R2 ... Rn-1 X P1 X ... X P2 ... Pn-1 Rn X Pn L H R0 R1 R2 P0 X P1 X P2 X ... Rn-1 Rn ... Pn-1 Pn ... X X L H P0 L P1 P2 L L ... ... Pn-1 L Pn L
L = Low logic level. H = High logic level. X = Don't care. P = Present state (shift register). R = Previous state (latched).
* *
DIN is the interface data input, and must be stable when it is sampled on the rising edge of CLK.
DOUT is the interface data output, which shifts data out from the MAX6920's 12-bit shift register on the falling edge of CLK. Data at DIN is propagated through the shift register and appears at DOUT (20 CLK cycles + tDO) later. A fifth input pin, BLANK, can be taken high to force outputs OUT0 to OUT11 low, without altering the contents of the output latches. When the BLANK input is low, outputs OUT0 to OUT11 follow the state of the output latches. A common use of the BLANK input is PWM intensity control. The BLANK input's function is independent of the operation of the serial interface. Data can be shifted into the serial interface shift register and latched regardless of the state of BLANK.
LOAD may be high or low during a transmission. If LOAD is high, then the data shifted into the shift register at DIN appears at the OUT0 to OUT11 outputs. CLK and DIN may be used to transmit data to other peripherals. Activity on CLK always shifts data into the MAX6920's shift register. However, the MAX6920 only updates its output latch on the rising edge of LOAD, and the last 12 bits of data are loaded. Therefore, multiple devices can share CLK and DIN as long as they have unique LOAD controls.
Determining Driver Output Voltage Drop
The outputs are CMOS drivers, and have a resistive characteristic. The typical and maximum sink and source output resistances can be calculated from the VH and VL electrical characteristics. Use this calculated resistance to determine the output voltage drop at different output currents.
Writing Device Registers Using the 4-Wire Serial Interface
The MAX6920 is written using the following sequence: 1) Take CLK low. 2) 3) Clock 12 bits of data in order D11 first to D0 last into DIN, observing the data setup and hold times. Load the 12 output latches with a falling edge on LOAD.
Output Current Ratings
The continuous current source capability is 40mA per output. Outputs may drive up to 75mA as a repetitive peak current, subject to the on time (output high) being no longer than 1ms, and the duty cycle being such that the output power dissipation is no more than the dissipation for the continuous case. The repetitive peak rating allows outputs to drive a higher current in multiplex grid driver applications, where only one grid is on at a time, and the multiplex time per grid is no more than 1ms.
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7
12-Output, 76V, Serial-Interfaced VFD Tube Driver MAX6920
Since dissipation is proportional to current squared, the maximum current that can be delivered for a given multiplex ratio is given by: IPEAK = (grids x 1600)1/2mA where grids is the number of grids in a multiplexed display. This means that a duplex application (two grids) can use a repetitive peak current of 56.5mA, a triplex application (three grids) can use a repetitive peak current of 69.2mA, and higher multiplex ratios are limited to 75mA. higher for multiplexed tubes. When using multiple driver devices, try to share the average dissipation evenly between the drivers. Determine the power dissipation (PD) for the MAX6920 for static tube drivers with the following equation: PD = (VCC x ICC) + (VBB x IBB) + ((VBB - VH) x IANODE x A)) where: A = number of anodes driven (a MAX6920 can drive a maximum of 12). IANODE = maximum anode current. (VBB - VH) is the output voltage drop at the given maximum anode current IOUT. A static tube dissipation example follows: VCC = 5V 5%, VBB = 10V to 18V, A = 12, IOUT = 2mA PD = (5.25V x 0.7mA) + (18V x 0.9mA) + ((2.5V x 2mA/25mA) x 2mA x 12) = 24.7mW Determine the power dissipation (PD) for the MAX6920 for multiplex tube drivers with the following equation: PD = (VCC x ICC) + (VBB x IBB) + ((VBB - VH) x IANODE x A) + ((VBB - VH) x IGRID)) where: A = number of anodes driven G = number of grids driven IANODE = maximum anode current IGRID = maximum grid current The calculation presumes all anodes are on but only one grid is on. The calculated PD is the worst case, presuming one digit is always being driven with all its anodes lit. Actual PD can be estimated by multiplying this PD figure by the actual tube drive duty cycle, taking into account interdigit blanking and any PWM intensity control. A multiplexed tube dissipation example follows: V CC = 5V 5%, V BB = 36V to 42V, A = 6, G = 6, IANODE = 0.4mA, IGRID = 24mA PD = (5.25V X 0.7mA)+ (42V x 0.9mA) + ((2.5V x 0.4mA/25mA) x 0.4mA x 6) + ((2.5V x 24mA/25mA) x 24mA) = 99mW Thus, for a 20-pin wide SO package (TJA = 1 / 0.01 = +100C/W from Absolute Maximum Ratings), the maximum allowed ambient temperature TA is given by: TJ(MAX) = TA + (PD x TJA) = +150C = TA + (0.099 x +100C/W) So TA = +140C.
Paralleling Outputs
Any number of outputs within the same package may be paralleled in order to raise the current drive or reduce the output resistance. Only parallel outputs directly (by shorting outputs together) if the interface control can be guaranteed to set the outputs to the same level. Although the sink output is relatively weak (typically 750), that resistance is low enough to dissipate 530mW when shorted to an opposite level output at a VBB voltage of only 20V. A safe way to parallel outputs is to use diodes to prevent the outputs from sinking current (Figure 4). Because the outputs cannot sink current from the VFD tube, an external discharge resistor, R, is required. For static tubes, R can be a large value such as 100k. For multiplexed tubes, the value of the resistor can be determined by the load capacitance and timing characteristics required. Resistor Rl discharges tube capacitance C to 10% of the initial voltage in 2.3 x RC seconds. So, for example, a 15k value for R discharges 100pF tube grid or anode from 40V to 4V in 3.5s, but draws an additional 2.7mA from the driver when either output is high.
Power Dissipation
Take care to ensure that the maximum package dissipation ratings for the chosen package are not exceeded. Over dissipation is unlikely to be an issue when driving static tubes, but the peak currents are usually
MAX6920
OUT0
D1 OUTPUT D2
OUT1 R
Figure 4. Paralleling Outputs 8
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12-Output, 76V, Serial-Interfaced VFD Tube Driver
This means that the driver can be operated in this application up to the MAX6920's +125C maximum operating temperature.
Typical Application Circuit
MAX6920
Power-Supply Considerations
The MAX6920 operates with multiple power-supply voltages. Bypass the VCC and VBB power-supply pins to GND with a 0.1F capacitor close to the device. For multiplex applications, it may be necessary to add an additional 1F bulk electrolytic capacitor, or greater, to the VBB supply.
MAX685x
VFDOUT VFCLK VFLOAD VFBLANK DIN CLK
MAX6920
LOAD BLANK DOUT
Power-Supply Sequencing
The order of the power-supply sequencing is not important. The MAX6920 will not be damaged if either VCC or VBB is grounded (or maintained at any other voltage below the data sheet minimum), while the other supply is maintained up to its maximum rating. However, as with any CMOS device, do not drive the MAX6920's logic inputs if the logic supply VCC is not operational because the input protection diodes clamp the signals.
MAX6920
VFD TUBE DOUT DOUT DIN CLK LOAD BLANK
Chip Information
TRANSISTOR COUNT: 2743 PROCESS: BiCMOS
DIN CLK LOAD BLANK
MAX6920
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9
12-Output, 76V, Serial-Interfaced VFD Tube Driver MAX6920
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
SOICW.EPS
INCHES
N
MILLIMETERS MIN 2.35 0.10 0.35 0.23 MAX 2.65 0.30 0.49 0.32
E
H
DIM A A1 B C e E H L
MAX MIN 0.104 0.093 0.012 0.004 0.019 0.014 0.013 0.009 0.050 0.299 0.291 0.394 0.419 0.050 0.016
1.27 7.40 7.60 10.00 10.65 0.40 1.27
VARIATIONS:
1
INCHES
MILLIMETERS MIN 10.10 11.35 12.60 15.20 17.70 MAX 10.50 11.75 13.00 15.60 18.10 N MS013 16 AA 18 AB 20 AC 24 AD 28 AE
TOP VIEW
D
DIM D D D D D
MIN 0.398 0.447 0.496 0.598 0.697
MAX 0.413 0.463 0.512 0.614 0.713
A e B
C 0 -8 L
A1
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, .300" SOIC
APPROVAL DOCUMENT CONTROL NO. REV.
21-0042
B
1 1
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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