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19-2443; Rev 1; 2/03
50V Isolated, 3.0V to 5.5V, 250kbps, 2 Tx/2 Rx, RS-232 Transceiver
General Description
The MAX3250 is a 3.0V to 5.5V powered, 50V isolated EIA/TIA-232 and V.28/V.24 communications interface with high data-rate capabilities. The MAX3250 is a dual die part that operates with up to 50V difference between the RS-232 side and the logic side (ISOCOM to GND). This makes the device ideal for operation in noisy conditions with high common-mode voltages. This feature prevents damage to the device if RS-232 lines are inadvertently short-circuited to a +24V or 48V power bus. The MAX3250 is powered by a single 3V to 5.5V supply on the logic side. Power is transferred from the logic side to the isolated side by 100V external capacitors. The MAX3250 has two receivers (Rx) and two drivers (Tx) and is guaranteed to run at data rates of 250kbps while maintaining RS-232 output levels. The transceivers have a proprietary low-dropout transmitter output stage, delivering true RS-232 performance from a 3V to 5.5V supply with a dual charge pump. The device features a FAULT open-drain output to signal an excessive isolated-side voltage condition on any of the RS232 inputs. This output can drive an alarm LED or can be monitored by the processor to prevent operation under these conditions. The receiver outputs are high impedance in shutdown, allowing multiple interfaces (IrDA, RS-232, RS-485) to be connected to the same UART. The MAX3250 is available in a space-saving 28-pin SSOP package. o 50V Isolation o 20A Supply Current in Shutdown o 250kbps Guaranteed Data Rate o FAULT Output o High-Impedance Transmitter and Receiver Outputs in Shutdown o Space-Saving SSOP Package o Inductorless/Transformerless Design Simplifies EMI Compliance o Low-Cost Replacement for Opto-Isolated Transceivers o Meets EIA/TIA-232 Specifications Down to 3.0V
Features
MAX3250
Ordering Information
PART MAX3250CAI MAX3250EAI TEMP RANGE 0C to +70C -40C to +85C PIN-PACKAGE 28 SSOP 28 SSOP
Pin Configuration
TOP VIEW
C1- 1 R1OUT 2 R2OUT 3 T1IN 4 T2IN 5 N.C. 6 N.C. 7 C1+ 8 C3+ 9 V+ 10 C3- 11 C4+ 12 C4- 13 28 VCC 27 C226 GND 25 FAULT 24 SHDN
Applications
Industrial Control Programmable Logic Controller Point-of-Sale Equipment PC-to-Router Connections Diagnostic Ports Telecom Equipment
MAX3250
23 N.C. 22 N.C. 21 C2+ 20 ISOVCC 19 R1IN 18 R2IN 17 T1OUT 16 T2OUT 15 ISOCOM
Typical Operating Circuit appears at end of data sheet.
V- 14
SSOP
________________________________________________________________ Maxim Integrated Products
1
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver MAX3250
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced to GND, Unless Otherwise Noted. VCC ...........................................................................-0.3V to +6V ISOCOM...............................................................................80V ISOVCC to ISOCOM..................................................-0.3V to +6V V+ to ISOCOM (Note 1)............................................-0.3V to +7V V- to ISOCOM (Note 1)............................................+0.3V to -7V V+ + |V-| (Note 1) ...................................................................13V Input Voltages T_IN, SHDN ...........................................................-0.3V to +6V R_IN to ISOCOM...............................................................25V Output Voltages T_OUT to ISOCOM ........................................................13.2V R_OUT .....................................................-0.3V to (VCC + 0.3V) FAULT....................................................................-0.3V to +6V C1-, C2- ......................................................-0.3V to (VCC + 0.3V) C1+, C2+, C3+, C3-, C4+, C4to ISOCOM ......................................-0.3V to (ISOVCC + 0.3V) T_OUT Current ..............30mA (continuous), 50mA (peak, 10s) R_IN Current..................30mA (continuous), 50mA (peak, 10s) ISOCOM Current ...........30mA (continuous), 50mA (peak, 10s) Short-Circuit Duration T_OUT to ISOCOM .................Continuous Continuous Power Dissipation (TA = +70C) 28-Pin SSOP (derate 9.5mW/C above +70C) ...........762mW Operating Temperature Ranges MAX3250CAI .....................................................0C to +70C MAX3250EAI...................................................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: V+ and V- can have a maximum magnitude of 7V, but their absolute difference cannot exceed 13V.
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
(VCC = 3.0V to 5.5V, see Typical Operating Circuit and Table 1 for capacitor values, ISOCOM = GND, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25C.) (Note 2)
PARAMETER DC CHARACTERISTICS Supply Current Supply Current Shutdown Maximum Ground Differential Isolation Resistance LOGIC INPUTS Input Logic Low Input Logic High Transmitter Input Hysteresis Input Leakage Current RECEIVER OUTPUTS Output Leakage Current Output Voltage Low Output Voltage High FAULT OUTPUT Output Voltage Low (Open Drain) Output Leakage Current FAULT Trip Level SHDN = GND IOUT = 1.6mA IOUT = -1.0mA VCC - 0.6 VCC - 0.1 -10 0.05 +10 0.4 A V V T_IN, SHDN -1 T_IN, SHDN T_IN, SHDN VCC = 3.3V VCC = 5.0V 2.0 2.4 0.5 0.01 +1 0.8 V V V A SHDN = VCC, no load SHDN = GND, VISOCOM = GND SHDN = GND, VISOCOM = 50V |VGND - VISOCOM| Between GND and ISOCOM 60 15 20 35 45 350 50 mA A V k CONDITIONS MIN TYP MAX UNITS
IOUT = 5mA FAULT not asserted |VGND - VISOCOM| 55
0.4 1
V A V
2
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.0V to 5.5V, see Typical Operating Circuit and Table 1 for capacitor values, ISOCOM = GND, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25C.) (Note 2)
PARAMETER RECEIVER INPUTS (relative to ISOCOM) Input Voltage Range Input Threshold Low Input Threshold High Input Hysteresis Input Resistance Output Voltage Swing Output Resistance Output Short-Circuit Current Output Leakage Current VCC = 0 or 3V to 5.5V, T_OUT = 12V, SHDN = GND TA = +25C All transmitter outputs loaded with 3k to ISOCOM ISOVCC = V+ = V- = 0V, T_OUT = 2V 3 5.0 300 -60 -25 TRANSMITTER OUTPUTS (relative to ISOCOM) 5.4 10M +60 +25 V mA A TA = +25C TA = +25C VCC = 3.3V VCC = 5.0V VCC = 3.3V VCC = 5.0V 2.4 2.4 -25 1.2 1.3 1.6 1.7 0.5 5 7 +25 0.6 0.8 V V V V k CONDITIONS MIN TYP MAX UNITS
MAX3250
TIMING CHARACTERISTICS
(VCC = 3.0V to 5.5V, see Typical Operating Circuit and Table 1 for capacitor values, ISOCOM = GND, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25C.)
PARAMETER Maximum Data Rate Receiver Propagation Delay Receiver Skew Transmitter Skew CONDITIONS RL = 3k, CL = 1000pF to ISOCOM, one transmitter R_IN to R_OUT, CL = 150pF to GND |tPHL - tPLH| |tPHL - tPLH| (Note 3) VCC = 3.3V, TA = +25C, RL = 3k to 7k to ISOCOM, measured from +3V to -3V or -3V to +3V CL = 150pF to 1000pF to ISOCOM CL = 150pF to 2500pF to ISOCOM 6 4 0.3 0.5 VISOCOM = GND VISOCOM = 50V 300 350 MIN 250 0.4 100 120 30 V/s 30 s s s TYP MAX UNITS kbps s ns ns
Transition-Region Slew Rate
FAULT Propagation Delay Time to Shutdown Time to Exit Shutdown
Note 2: All currents into the device are positive; all currents out of the device are negative. All voltages are referenced to device ground, unless otherwise noted. Note 3: Transmitter skew is measured at the transmitter zero crosspoints.
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver MAX3250
Typical Operating Characteristics
(VCC = 3.3V, 250kbps data rate, see Typical Operating Circuit and Table 1 for capacitor values, all transmitters loaded with 3k and CL to ISOCOM, TA = +25C, unless otherwise noted.)
TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE
MAX3250 toc01
SLEW RATE vs. LOAD CAPACITANCE
MAX3250 toc02
OPERATING SUPPLY CURRENT vs. LOAD CAPACITANCE
80 SUPPLY CURRENT (mA) 70 60 50 40 30 20 120kbps 20kbps 250kbps T1 TRANSMITTING AT 250kbps T2 TRANSMITTING AT 20kbps
MAX3250 toc03
8 TRANSMITTER OUTPUT VOLTAGE (V) 6 VOUT+ 4 2 0 -2 -4 -6 0 1000 2000 3000 4000 VOUTT1 TRANSMITTING AT 250kbps T2 TRANSMITTING AT 20kbps
30 25 SLEW RATE (V/s) 20 15 10 5 FOR DATA RATES UP TO 250kbps 0 +SLEW -SLEW
90
10 0 4000 5000 0 1000 2000 3000 4000 5000
5000
0
1000
2000
3000
LOAD CAPACITANCE (pF)
LOAD CAPACITANCE (pF)
LOAD CAPACITANCE (pF)
TIME TO EXIT SHUTDOWN VISOCOM = 0V
SHUTDOWN CURRENT vs. TEMPERATURE
SHDN 5V/div SUPPLY CURRENT (A) ISOCOM = -50V
MAX3250 toc05
MAX3250 toc04
400 300 200 100 0 -100 -200 -300 ISOCOM = +50V
TOUT 5V/div
ISOCOM = 0V
100s/div
-40
-15
10
35
60
85
TEMPERATURE (C)
PEAK GROUND OFFSET VOLTAGE vs. FREQUENCY
VCC = 5V 50 PEAK GROUND OFFSET (V) 40 30 20 10 0 0 100 200 300 400 500 600 VCC = 3.3V
MAX3250 toc06
COMMON-MODE FAULT RESPONSE
MAX3250 toc07
60
ISOCOM 50V/div
FAULT 5V/div
4ms/div
FREQUENCY (Hz)
4
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver
Pin Description
PIN 1 2 3 4 5 6, 22, 23 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 24 25 26 27 28 NAME C1R1OUT R2OUT T1IN T2IN N.C. N.C. C1+ C3+ V+ C3C4+ C4VISOCOM T2OUT T1OUT R2IN R1IN ISOVCC C2+ SHDN FAULT GND C2VCC FUNCTION Negative Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C1- to C1+. See Table 1 for values. TTL/CMOS Receiver Output TTL/CMOS Receiver Output TTL/CMOS Transmitter Input TTL/CMOS Transmitter Input No Connection. Not internally connected. No Connection. Leave unconnected or connect to ISOCOM. Positive Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C1+ to C1-. See Table 1 for values. Positive Terminal of the Voltage-Doubler Charge-Pump Capacitor. Connect a 0.1F capacitor from C3+ to C3-. +5.5V Generated by the Charge Pump, Referenced to ISOCOM. Bypass V+ to ISOCOM with a 0.47F capacitor. Negative Terminal of the Voltage-Doubler Charge-Pump Capacitor. Connect a 0.1F capacitor from C3- to C3+. Positive Terminal of the Inverting Charge-Pump Capacitor. Connect a 0.47F capacitor from C4+ to C4-. Negative Terminal of the Inverting Charge-Pump Capacitor. Connect a 0.47F capacitor from C4- to C4+. -5.5V Generated by the Charge Pump, Referenced to ISOCOM. Bypass V- to ISOCOM with a 0.47F capacitor. Isolated Ground RS-232 Transmitter Output RS-232 Transmitter Output RS-232 Receiver Input RS-232 Receiver Input Internally Generated Isolated Power-Supply Voltage, Referenced to ISOCOM. Bypass ISOVCC to ISOCOM with a 1F capacitor. Positive Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C2+ to C2-. See Table 1 for values. Shutdown Control. Drive SHDN low to enter low-power shutdown mode. Drive SHDN high or connect to VCC for normal operation. Overvoltage Indicator. Active low, open drain. Ground Negative Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C2- to C2+. See Table 1 for values. 3.0V to 5.5V Supply Voltage. Bypass VCC to GND with a 1F capacitor.
MAX3250
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver MAX3250
TIN1
TOUT1
ROUT1
RIN1
TIN2
TOUT2
ROUT2
RIN2
SHDN
FAULT OSC
ISOVCC V+
MAX3250
VCC RS-232 CHARGE PUMP
C3+ C3C4+ C4V-
FAULT DETECTOR
POWER CONTROLLER
GND
C1-
C2-
C1+ C2+
ISOCOM
Figure 1. Functional Diagram
Detailed Description
The MAX3250 is a 3.0V to 5.5V powered, 50V isolated EIA/TIA-232 and V.28/V.24 communications interface with high data-rate capabilities. The MAX3250 is a dual die part that operates with up to 50V difference between the RS-232 side and the logic side (ISOCOM to GND). This makes the device ideal for operation in noisy conditions with high common-mode voltages. This feature prevents damage to the device if RS-232 lines are inadvertently short-circuited to a +24V or 48V power bus. The MAX3250 typically draws 15mA of supply current when unloaded. Supply current drops to 20A when the device is placed in shutdown mode.
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The MAX3250 has two receivers and two drivers and is guaranteed to operate at data rates up to 250kbps. The device features a FAULT open-drain output to signal an excessive isolated-side voltage condition on any of the RS-232 inputs. This output can drive an alarm LED or can be monitored by the processor to prevent operation under these conditions. The receiver outputs are high impedance in shutdown, allowing multiple interfaces (IrDA, RS-232, RS-485) to be connected to the same UART (Figure 1). The MAX3250 is a low-cost replacement for opto-isolated transceivers.
Isolated Power Supply
The MAX3250 drives a high-frequency square wave into C1 and a complementary square wave into C2. These
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver
AC waveforms are rectified on the isolated side of the dual die to power its internal circuitry (ISOV CC ). Capacitor C6 filters the output of the rectifier. See the Typical Operating Circuit. The power controller works in a dual power mode. Power is maximum when the isolated power supply is below its regulation point. Power is reduced when the isolated power supply is above its regulation point.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic output levels. The receivers' outputs are forced into a high-impedance state when the device is in shutdown. This allows a single UART to multiplex between different protocols.
MAX3250
Low-Power Shutdown Mode
Shutdown mode is obtained by driving SHDN low. In shutdown, the devices typically draw only 20A of supply current and no power is transferred across the isolation capacitors. The charge pumps are disabled, and the receiver outputs and transmitter outputs are high impedance. When exiting shutdown the charge pumps and transmitter outputs are fully operational in typically 500s (Figure 3). Connect SHDN to VCC if the shutdown mode is not used.
Dual Charge-Pump Voltage Converter
The RS-232 drivers are powered from a regulated dual charge pump that provides output voltages of +5.5V (doubling charge pump) and -5.5V (inverting charge pump) relative to ISOCOM over the 3.0V to 5.5V VCC range. The charge pumps are powered from ISOV CC and operate in a discontinuous mode. If the output voltages are less than 5.5V, the charge pumps are enabled. If the output voltages exceed 5.5V, the charge pumps are disabled. Each charge pump requires a flying capacitor (C3, C4) and a reservoir capacitor (C7, C8) to generate the V+ and V- supplies.
Applications Information
Power Isolation Capacitors
The values for capacitors C1 and C2 are important for proper operation of the device. These capacitors should be 0.047F for 4.5V to 5.5V operation, and 0.47F for 3.0V to 3.6V operation. Smaller values result in insufficient supply voltage on the isolated side. Larger values are not allowed. Capacitor C9 provides an AC feedback path for proper controller operation. Connect C9 from ISOCOM to GND. The values for C1, C2, and C9 determine the maximum frequency and amplitude of the voltage difference between the local and isolated ground. Table 1 shows proper capacitance values.
RS-232 Transmitters
The transmitters are inverting level translators that convert TTL/CMOS-logic levels to 5.0V EIA/TIA-232-compliant levels. They guarantee a 250kbps data rate with worstcase loads of 3k in parallel with 1000pF to ISOCOM. In shutdown, the transmitters are disabled and the outputs are forced into a high-impedance state. When powered off or shut down, the outputs can be driven up to 12V relative to ISOCOM. The transmitter inputs do not have pullup resistors. All unused inputs should be connected to VCC or GND.
TRANSMITTER OUTPUT VOLTAGE (V)
6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 0
VCC = 3.0V
VOUT+
SHDN 5V/div T1OUT
T1
VOUT1+
VCC
T2
VOUT2-
2V/div
VOUTVCC = 3.3V 1 2 3 4 5 6 7 8 100s/div T2OUT
LOAD CURRENT PER TRANSMITTER (mA)
Figure 2. Transmitter Output Voltage vs. Load Current per Transmitter
Figure 3. Transmitter Outputs when Exiting Shutdown or Powering Up 7
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver MAX3250
Table 1. Required Capacitor Values
VCC (V) 3.0 to 3.6 4.5 to 5.5 C1, C2 (F) 0.47 0.047 C3 (F) 0.1 0.1 C4, C7, C8 (F) 0.47 0.47 C5, C6 (F) 1 1 C9 (nF) 10 10
To achieve full isolation capability, C1, C2, and C9 should be rated for 100V or higher operation and be X7R or X5R type or metalized film dielectric. Y5V and Z5U dielectrics should be avoided as their voltage and temperature coefficients make their power-transfer capabilities insufficient.
Maximum Voltage Between ISOCOM and Logic GND
High values of applied isolation voltage and frequency can cause ripple on ISOVCC, V+, V-, and in extreme cases on VCC. Therefore, it is recommended that the isolation-voltage and frequency be limited to the values shown in the Typical Operating Characteristics. Insert a 1k 1/4W resistor in series with any isolation test voltage when testing for maximum values of applied isolation voltage. Exceeding the maximum limits of voltage and frequency (see the Typical Operating Characteristics) could trigger a holding current in the internal ESD-protection device if the 80V isolation limit is exceeded. This resistor should not be used in normal application.
Charge-Pump and Bypass Capacitors
Capacitors C3-C8 should be X7R or X5R type dielectric. Their voltage rating needs to be 10V or higher.
Layout Information
Because the MAX3250 is intended for systems requiring 50V isolation, some consideration in component placement is necessary. A 20mil air gap should isolate the logic side and the isolated RS-232 side, across the N.C. pins (pin numbers 6, 7, 22, and 23) of the MAX3250. The only components that cross this air gap should be C1, C2, and C9, which should all have a minimum 100V rating. All capacitors should be located as close to the MAX3250 as possible.
Transmitter Outputs when Exiting Shutdown
Figure 3 shows two transmitter outputs when exiting shutdown mode. As they become active, the two transmitter outputs are shown going to opposite RS-232 levels (one transmitter input is high, the other is low). Each transmitter is loaded with 3k in parallel with 2500pF. The transmitter outputs display no ringing or undesirable transients as they come out of shutdown. Note that the transmitters are enabled only when the magnitude of V- exceeds approximately -3V.
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver
Typical Operating Circuit
VCC C5 1F VCC RIN1 TOUT1 FAULT SHDN MICRO TIN1 ROUT1 TIN2 ROUT2 C1+ C1C2+ C2GND C9 10nF ISOCOM RIN2 TOUT2 C4+ C4 0.47F C3 0.1F CABLE REMOTE MICRO REMOTE XCVR
MAX3250
MAX3250
C4C3+ C3V+ VISOVCC C6 1F
C1 0.47F C2 0.47F
C8 0.47F
C7 0.47F
50V GND OFFSET REMOTE GROUND
Chip Information
TRANSISTOR COUNT: 2094 PROCESS: BiCMOS
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50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver MAX3250
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.)
SSOP.EPS
2
1
INCHES DIM A A1 B C E H D E e H L MIN 0.068 0.002 0.010 MAX 0.078 0.008 0.015
MILLIMETERS MIN 1.73 0.05 0.25 MAX 1.99 0.21 0.38 D D D D D INCHES MIN 0.239 0.239 0.278 0.317 0.397 MAX 0.249 0.249 0.289 0.328 0.407 MILLIMETERS MIN 6.07 6.07 7.07 8.07 10.07 MAX 6.33 6.33 7.33 8.33 10.33 N 14L 16L 20L 24L 28L
0.20 0.09 0.004 0.008 SEE VARIATIONS 0.205 0.301 0.025 0 0.212 0.311 0.037 8 5.20 7.65 0.63 0 5.38 7.90 0.95 8 0.0256 BSC 0.65 BSC
N
A C B e D A1 L
NOTES: 1. D&E DO NOT INCLUDE MOLD FLASH. 2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006"). 3. CONTROLLING DIMENSION: MILLIMETERS. 4. MEETS JEDEC MO150. 5. LEADS TO BE COPLANAR WITHIN 0.10 MM.
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, SSOP, 5.3 MM
APPROVAL DOCUMENT CONTROL NO. REV.
21-0056
1 1
C
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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