Transformer Driver Isolated RS-485 Interface MAX253 monolithic os

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Transformer Driver Isolated RS-485 Interface MAX253 monolithic os

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19-0226; 8/09
Transformer Driver Isolated RS-485 Interface
MAX253 monolithic oscillator/power-driver, specifically designed provide isolated power isolated RS-485 RS-232 data interface. drives center-tapped transformer primary from 3.3V power supply. secondary wound provide isolated voltage needed power levels MAX253 consists CMOS oscillator driving pair N-channel power switches. oscillator runs double output frequency, driving toggle flip-flop ensure duty cycle each switches. Internal delays arranged ensure break-beforemake action between switches. puts entire device into low-power shutdown state, disabling both power switches oscillator.
_Features
Power-Supply Transformer Driver Isolated RS-485/RS-232 Data-Interface Applications Single +3.3V Supply Low-Current Shutdown Mode: 0.4µA Pin-Selectable Frequency: 350kHz 200kHz 8-Pin DIP, µMAX® Packages
MAX253
_Ordering Information
PART MAX253CPA MAX253CSA MAX253CUA MAX253C/D MAX253EPA MAX253ESA MAX253MJA TEMP RANGE +70°C +70°C +70°C +70°C -40°C +85°C -40°C +85°C -55°C +125°C PIN-PACKAGE Plastic Dice* Plastic CERDIP**
_Applications
Isolated RS-485/RS-232 Power-Supply Transformer Driver High Noise-Immunity Communications Interface Isolated and/or High-Voltage Power Supplies Bridge Ground Differentials Medical Equipment Process Control
*Contact factory dice specifications. **Contact factory availability processing MIL-STD-883.
_Typical Operating Circuit
OUTPUT 200mA
_Pin Configuration
VIEW
GND1
MAX253
FREQUENCY SWITCH GND1 GND2
GND2 N.C.
MAX253
DIP/SO/MAX
µMAX registered trademark Maxim Integrated Products, Inc.
Maxim Integrated Products
pricing, delivery, ordering information, please contact Maxim Direct 1-888-629-4642, visit Maxim's website www.maxim-ic.com.
Transformer Driver Isolated RS-485 Interface MAX253
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC) .-0.3V Control Input Voltages (SD, .-0.3V (VCC 0.3V) Output Switch Voltage (D1, .12V Peak Output Switch Current (D1, Average Output Switch Current (D1, .200mA Continuous Power Dissipation +70°C) Plastic (derate 9.09mW/°C above +70°C) .727mW (derate 5.88mW/°C above +70°C) .471mW µMAX (derate 4.10mW/°C above +70°C) .330mW CERDIP (derate 8.00mW/°C above +70°C) .640mW Operating Temperature Ranges MAX253C_ .0°C +70°C MAX253E_ .-40°C +85°C MAX253MJA .-55°C +125°C Junction Temperatures MAX253C_ _/E_ _.+150°C MAX253MJA .+175°C Storage Temperature Range .-65°C +160°C Lead Temperature (soldering, 10sec) .+300°C
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC ±10%, TMIN TMAX, unless otherwise noted. Typical values +25°C.) PARAMETER Switch Resistance Switch Frequency Operating Supply Current (Note Shutdown Supply Current (Note Shutdown Input Threshold Shutdown Input Leakage Current Input Threshold Input Leakage Current Start-Up Voltage High 100mA open load, High CONDITIONS 0.45 UNITS
Note Operating supply current current used MAX253 only, including load current. Note Shutdown supply current includes output switch-leakage currents.
Transformer Driver Isolated RS-485 Interface
_Typical Operating Characteristics
(Circuit Figure ±10%, +25°C, unless otherwise noted.)
MAX253
OUTPUT RESISTANCE TEMPERATURE LOW)
plot01
OUTPUT RESISTANCE TEMPERATURE HIGH)
MEASURED OUTPUT RESISTANCE
plot02
SHUTDOWN SUPPLY CURRENT TEMPERATURE
INCLUDES SWITCH LEAKAGE CURRENTS SHUTDOWN CURRENT
plot03
10.5 MEASURED 10.0 OUTPUT RESISTANCE 5.0V 4.5V
4.5V 5.0V
TEMPERATURE (°C) TEMPERATURE (°C)
TEMPERATURE (°C)
FREQUENCY TEMPERATURE LOW)
plot04
FREQUENCY TEMPERATURE HIGH)
plot05
SUPPLY CURRENT TEMPERATURE LOW)
6.0V
plot06
FREQUENCY (kHz)
6.0V FREQUENCY (kHz)
6.0V SUPPLY CURRENT 5.5V 4.5V 4.5V TEMPERATURE (°C) TEMPERATURE (°C) 5.0V
5.5V
5.5V 5.0V
5.0V 4.5V
TEMPERATURE (°C)
SUPPLY CURRENT TEMPERATURE HIGH)
plot07
EFFICIENCY LOAD CURRENT LOW)
plot08
SUPPLY CURRENT 5.5V 6.0V
5.5V 4.5V
EFFICIENCY
5.0V
4.5V
LOAD CURRENT (mA)
TEMPERATURE (°C)
Transformer Driver Isolated RS-485 Interface MAX253
_Typical Operating Characteristics (continued)
(Circuit Figure ±10%, +25°C, unless otherwise noted.)
EFFICIENCY LOAD CURRENT HIGH)
plot09
OUTPUT VOLTAGE LOAD CURRENT LOW)
plot10
OUTPUT VOLTAGE LOAD CURRENT HIGH)
OUTPUT VOLTAGE
CIRCUIT FIGURE 3.3V TURNS RATIO 1:2.1 CIRCUIT FIGURE 5.0V TURNS RATIO 1:1.3
plot11
EFFICIENCY 4.5V 5.5V
OUTPUT VOLTAGE
CIRCUIT FIGURE 5.0V TURNS RATIO CIRCUIT FIGURE 3.3V TURNS RATIO 1:2.1 CIRCUIT FIGURE 5.0V TURNS RATIO 1:1.3
CIRCUIT FIGURE 5.0V TURNS RATIO
MEASURED LOAD CURRENT (mA)
MEASURED LOAD CURRENT (mA)
LOAD CURRENT (mA)
SWITCHING WAVEFORMS (TWO CYCLES)
SWITCHING WAVEFORMS (BREAK BEFORE MAKE)
CIRCUIT FIGURE
CIRCUIT FIGURE
TIME FROM SHUTDOWN POWER-UP
(OUTPUT VOLTAGE)
CIRCUIT FIGURE
Transformer Driver Isolated RS-485 Interface
_Pin Description
NAME GND1 N.C. GND2 FUNCTION Open drain N-channel transformer drive Ground. Connect both GND1 GND2 ground. Frequency switch. open, switch frequency 350kHz; switch frequency 200kHz. Shutdown. Ground normal operation, high shutdown. internally connected. supply voltage. Ground. Connect both GND1 GND2 ground. Open drain N-channel transformer drive
MAX253
0.1µF
MAX253
FREQUENCY SWITCH GND1 GND2
Figure Test Circuit
FREQUENCY SWITCH 400kHz/ 700kHz
200mA OUTPUT
MAX253
GND2 GND1
Figure Block Diagram
_Detailed Description
MAX253 isolated power-supply transformer driver specifically designed form heart fully isolated RS-485 data interface. Completely isolated communications obtained combining MAX253 with linear regulator, center-tapped transformer, optocouplers, appropriate Maxim interface product described Isolated RS-485/RS232 Data Interface section). MAX253 consists oscillator followed toggle flip-flop, which generates duty-cycle square waves, out-of-phase half oscillator fre-
quency (see Figure These signals drive ground-referenced output switches. Internal delays ensure break-before-make action between switches. Ground normal operation. When high, disables internal circuitry, including oscillator both power switches. Pulling reduces oscillator frequency lowers supply current (see Supply Current Temperature Typical Operating Characteristics). includes weak pull-up, will float high-frequency state connected.
Transformer Driver Isolated RS-485 Interface MAX253
0.1µF
ISOLATION BARRIER
ICT:1.3CT** 1N5817 0.1µF 22µF
22µF
MAX253
1N5817
MAX667
GND1
GND2
SHDN
PC410
3.3k
*74HC04
3.3k PC357T
*74HC04
3.3k PC410
MAX481 MAX483 MAX485 MAX487
*74HC04
*74HC04 EQUIVALENT TABLE
Figure Typical RS-485 Application Circuit, Configuration
Transformer Driver Isolated RS-485 Interface MAX253
3.3V 0.1µF
ISOLATION BARRIER
ICT:2.1CT** 1N5817 0.1µF 22µF
N.C. GND1 GND2
22µF
MAX253
1N5817
MAX667
SHDN
1N5817
1N5817
0.1µF PC410
*74HC04
3.3k
3.3k
PC357T
*74HC04
3.3k PC410
MAX481 MAX483 MAX485 MAX487
*74HC04
*74HC04 EQUIVALENT TABLE
Figure Typical RS-485 Application Circuit, 3.3V Configuration
Transformer Driver Isolated RS-485 Interface MAX253
0.1µF N.C. ISOLATION BARRIER ICT:1.3CT**1N5817 0.1µF 22µF MAX667 22µF
MAX253
GND1 GND2
1N5817 3.3k PC417
SHDN
*74HC04 T1IN 74HC04 T2IN 74HC04 T3IN 74HC04 T4IN 74HC04 T5IN 3.3k 74HC04 R1OUT 74HC04 R2OUT 74HC04 R3OUT 74HC04 R4OUT 74HC04
T1IN
T1OUT
T2IN
T2OUT
T3IN
T3OUT
T4IN
T4OUT
T5IN
T5OUT
MAX205
R2OUT R2IN R1OUT R1IN
R3OUT
R3IN
R4OUT
R4IN
R5OUT *74HC04 EQUIVALENT
R5OUT
R5IN
TABLE
4N25 LOWER SPEED, LOWER COST ALTERNATE OPTOCOUPLER CONFIGURATIONS (FOR DATA RATES BELOW 9.6kbps) 1N5711 4N25 1N5711 4N25 3.3k 3.3k ROUT 74HCO4 *74HC04
ROUT
Figure Typical RS-232 Application Circuit
Transformer Driver Isolated RS-485 Interface
_Applications Information
Figures typical isolated RS-485/RS-232 data-interface circuits. These circuits withstand 1800VRMS (1sec) intended industrial communications control applications where very high voltage transients, differential ground potentials, high noise encountered. Table lists transformer characteristics applications Figures 3-10. Some suggested manufacturers transformers, transformer cores, optocouplers listed Table along with their respective phone numbers. Important layout considerations include: maximum isolation, "isolation barrier" should breached. Connections components from side should located near those other side. Since optocoupler outputs relatively highimpedance nodes, they should located close possible Maxim interface This minimizes stray capacitance maximizes data rate. Refer µMAX package information spacing physical dimensions. appropriate Maxim interface device data-transfer rates 2.5Mbps. Refer MAX1480 data sheet complete isolated RS-485 solution package.
MAX253
Isolated RS-232 Data Interface
MAX253 ideal isolated RS-232 data-interface applications requiring more than four transceivers. power output capability MAX253 enables drive more than transceivers simultaneously. Figure shows typical application circuit complete 120kbps isolated RS-232 data interface. figure also shows Sharp PC417 optocouplers replaced lower-cost 4N25 devices achieve data-transfer rates 9.6kbps. 3.3V operation, substitute primary portion Figure with circuit Figure applications requiring transceivers fewer, refer MAX250/MAX251 MAX252 data sheet.
Isolated Power Supplies
MAX253 versatile isolated power driver, capable driving center-tapped transformer primary from 3.3V power supply (see Figures secondary wound provide isolated voltage needed power levels with supply, 600mW with 3.3V supply. Figure shows typical isolated application circuit that delivers 200mA isolated power. Figure MAX253 configured operate from 3.3V supply, deriving "boost" MAX253 connecting diodes both ends transformer primary. This produces nearly double input supply, useful other applications, shown Figure average current each MAX253 switch must still limited less than 200mA, total power available approximately 600mW.
Isolated RS-485 Data Interface
MAX253 power-supply transformer driver designed specifically isolated RS-485 data-interface applications. application circuits Figures combine MAX253 with low-dropout linear regulator, transformer, several high-speed optocouplers, Maxim RS-485 interface device. With modifications these circuits, full-duplex communications implemented substituting MAX481/MAX485 with MAX490/MAX491 (for data rates 2.5Mbps) substituting MAX483/MAX487 with MAX488/MAX489 (for data rates 250kbps). data transfer rates application circuits Figures critically limited optocouplers. Table lists suggested optocouplers
Table Optocouplers RS-485 Interface Various Data Rates
DATA RATE 250kbps 2.5Mbps FULL DUPLEX RS-485 MAX488/MAX489 MAX490/MAX491 HALF DUPLEX RS-485 MAX483/MAX487 MAX481/MAX485 OPTOCOUPLER PC417* PC410* OPTOCOUPLER PC357T* PC357T
PC-Series Optocouplers, Sharp Electronics Phone: (206) 834-2500 FAX: (206) 834-8903 Sharp Electronics, Europe GmbH Germany Phone: (040) 2376-0 FAX: (040) 230764
Transformer Driver Isolated RS-485 Interface MAX253
0.1µF
ICT:1.3CT*1N5817 0.1µF 22µF 200mA OUTPUT
MAX253
FREQUENCY SWITCH GND1 GND2
OUTPUT
1N5817
OPTIONAL 21kHz LOWPASS OUTPUT FILTER 25µH FILTER OUTPUT 2.2µF
*SEE TABLE
Figure Isolated Application Circuit
3.3V 0.1µF ICT:2.1CT* 1N5817 0.1µF 100mA OUTPUT 22µF
MAX253
FREQUENCY SWITCH GND1 GND2 1N5817 1N5817
OUTPUT
1N5817
OPTIONAL 21kHz LOWPASS OUTPUT FILTER 25µH FILTER OUTPUT 2.2µF
*SEE TABLE
0.1µF
Figure 3.3V Isolated Application Circuit
Transformer Driver Isolated RS-485 Interface MAX253
ISOLATION BARRIER 1CT:5CT* 1N5817 UNREGULATED 10µF
MAX253
GND1 GND2 1N5817 78L05
0.1V 0.5V
IL300
MAX480
49.9k
49.9k
MAX480
2N3904 2N3904
*SEE TABLE
24.9
Figure Typical 20mA Application Circuit
Output-Ripple Filtering simple lowpass pi-filter (Figures added output reduce output ripple noise about 10mVp-p. cutoff frequency shown 21kHz. Since filter inductor series with circuit output, minimize resistance voltage drop across excessive.
Isolated 20mA Analog Interface
20mA current loop standard analog signal range that widely used process-control industry transducer actuator control signals. These signals commonly referred distant ground that considerably higher voltage with respect local ground. analog signal range 0.1V 0.5V applied first MAX480 generate signal current range 20µA 100µA. This low-level signal transferred across barrier Siemens IL300 linear optocoupler. This device unique that corrects dominant nonlinearity present most optocou-
plers-the efficiency variation. IL300 really optocouplers same package sharing same LED; detector across isolation barrier, other same side (Figure latter detector used generate feedback signal identical signal isolated side barrier. current signal transferred across barrier converted back voltage that matches input 100mV 500mV range. This voltage then transformed final 20mA current signal range second MAX480, Darlington stage, resistor.
Isolated
Almost serial-interface device candidate operation across isolation barrier; Figure illustrates example. MAX176 analog-to-digital converter (ADC) operates from -12V supplies, provided multiple-tapped secondary linear regulators. some additional isolated power needed signal conditioning, multiplexing, possibly
Transformer Driver Isolated RS-485 Interface MAX253
INPUT 1CT:1CT* 1N5817 +VOUT OUTPUT RLRL-VOUT OUTPUT
MAX253
GND2
GND1
*SEE TABLE
1N5817
Figure Half-Wave Rectifier-Bipolar
INPUT
1CT:1CT* 1N5817
MAX253
GND1 *SEE TABLE GND2
VOUT +VIN OUTPUT
VOUT -VIN OUTPUT
Figure Full-Wave Rectifier-Bipolar
INPUT
1CT:1CT* 1N5817
MAX253
GND1 GND2
VOUT OUTPUT
*SEE TABLE
Figure Full-Wave Rectifier-Unipolar
Transformer Driver Isolated RS-485 Interface MAX253
ISOLATION BARRIER 1.5CT 3CT* 78L05 10µF 1N5817
-12V 10µF
GND1 GND2
MAX253
ON/OFF
74HC04
START INPUT CLOCK
10µF CONVST CLOCK DATA SIGNAL GROUND
6N136
SCLR
74HC595
MAX176
0.1µF ANALOG INPUT VREF
6N136
D11(MSB) 0.1µF
0.1µF 10µF
74HC04
6N136
0.1µF 10µF
8.2k SCLR
D0(LSB) 0.1µF
74HC595
*SEE TABLE
Figure Typical Isolated Application
Transformer Driver Isolated RS-485 Interface MAX253
sensor, extra several hundred milliwatts could easily supplied circuit, shown. +12V supply could generated adding more diodes ends secondary, supply could generated connecting additional diodes points secondary. only applications, MAX187 recommended. half primary simply product maximum supply voltage half maximum period. With tied high, guaranteed minimum frequency 250kHz, giving maximum period 4µs. secondary winding center tapped, depending rectifier topology used. phasing secondary winding critical. some applications, multiple secondaries might required. Half-wave rectification could used, discouraged because normally adds imbalance magnetic flux core, reducing product. load imbalanced, full-wave rectification recommended, shown Figure transformer turns ratio must provide minimum required output voltage maximum anticipated load with minimum expected input volt-
_Component Selection
Transformer Selection
transformer primary used with MAX253 must center-tapped winding with sufficient product prevent saturation worst-case lowest selected frequency. MAX253's guaranteed minimum frequency with held 150kHz, equating maximum period 6.67µs. required product
Table Typical Transformer Characteristics
CHARACTERISTIC Figure Turns Ratio Typical Windings Primary Product Primary Secondary High ±10V 1CT*:1 44CT 18.3V-µs 11V-µs 1CT:1.3CT 44CT 56CT 18.3V-µs 11V-µs +3.3V 1CT:2.1CT 28CT 56CT 12V-µs 7.2V-µs 1CT:5CT 44CT 220CT 18.3V-µs 11V-µs +24V ±5V; ±12V 1CT:1.5CT:3CT 44CT 66CT, 132CT 18.3V-µs 11V-µs
Center Tapped
Table Transformer, Transformer Core, Optocoupler Suppliers
TRANSFORMERS Electronics Phone: (507) 532-3211 FAX: (507) 532-3705 Coilcraft Phone: (708) 639-6400 FAX: (708) 639-1469 Coiltronics Phone: (516) 241-7876 FAX: (516) 241-9339 TRANSFORMER CORES Philips Components Phone: (407) 881-3200 FAX: (407) 881-3300 Magnetics Inc. Phone: (412) 282-8282 FAX: (412) 282-6955 Fair-Rite Products Phone: (914) 895-2055 FAX: (914) 895-2629 OPTOCOUPLERS Quality Technology Phone: (408) 720-1440 FAX: (408) 720-0848 Sharp Electronics Phone: (206) 834-2500 FAX: (206) 834-8903 Siemens Components Phone: (408) 777-4500 FAX: (408) 777-4983
Transformer Driver Isolated RS-485 Interface
age. addition, include calculations allowance worst-case losses rectifiers. Since turns ratio determined this manner will ordinarily produce much higher voltage secondary under conditions high input voltage and/or light loading, careful prevent overvoltage condition from occurring (see Output Voltage Load Current Typical Operating Characteristics). Transformers used with MAX253 will ordinarily wound high-permeability magnetic material. minimize radiated noise, common closed-magneticpath physical shapes (e.g., cores, toroids, E/I/U cores). typical core Philips 213CT050-3B7, which toroid 0.190" diameter 0.05" thick. operation with this core 5.5V maximum supply voltage, primary should have about turns each side center tap, turns total. This will result nominal primary inductance about 832µH. secondary scaled produce required output. good choice through-hole applications, NIEC* SB05W05C dual SOT-23 package recommended surface-mount applications. higher frequency setting reduce ripple.
MAX253
Output Filter Capacitor applications sensitive output-ripple noise, output filter capacitor should have effective series resistance (ESR), capacitance should remain fairly constant over temperature. Sprague 595D surface-mount solid tantalum capacitors Sanyo OS-CON through-hole capacitors recommended their extremely ESR. Capacitor usually rises temperatures, OS-CON capacitors provide very below 0°C.
applications where output ripple critical, 0.1µF chip ceramic capacitor sufficient. Refer Table suggested capacitor suppliers. higher frequency setting reduce ripple.
Diode Selection
MAX253's high switching frequency demands high-speed rectifiers. Schottky diodes recommended. Ensure that Schottky diode average current rating exceeds load-current level. 1N5817
Input Bypass Capacitor input bypass capacitor critical. Unlike switching regulators, MAX253's supply current fairly constant, therefore less dependent input bypass capacitor. low-cost 0.1µF chip ceramic capacitor normally sufficient input bypassing.
Table Suggested Capacitor Suppliers
PRODUCTION METHOD CAPACITORS Matsuo series (low ESR) Phone: (714) 969-2491, FAX: (714) 960-6492 Sprague Electric 595D/293D series (very ESR) Phone: (603) 224-1961, FAX: (603) 224-1430 Murata Erie Ceramic Phone: (800) 831-9172, FAX: (404) 436-3030 Sanyo OS-CON series (very ESR) Phone: (619) 661-6835, FAX: (619) 661-1055 Japan Phone: 81-7-2070-1005, FAX: 81-7-2070-1174 Nichicon series (low ESR) Phone: (708) 843-7500, FAX: (708) 843-2798 Japan Phone: 81-7-5231-8461, FAX: 81-7-5256-4158
Surface Mount
High-Performance Through Hole
Through Hole
Nihon Inter Electronics Corp. Phone: (805) 867-2555 FAX: (805) 867-2556 Japan Phone: 81-3-3494-7411 FAX: 81-3-3494-7414
Transformer Driver Isolated RS-485 Interface MAX253
_Chip Topography
Package Information
latest package outline information land patterns, www.maxim-ic.com/packages. PACKAGE TYPE µMAX PACKAGE CODE DOCUMENT 21-0036
0.085" (2.159mm) GND1
GND2
0.058" (1.4732mm)
TRANSISTOR COUNT: SUBSTRATE CONNECTED VCC.
Transformer Driver Isolated RS-485 Interface
Revision History
REVISION NUMBER REVISION DATE 1/94 8/09 Initial release. Deleted MAX253EUA part number from Ordering Information table. DESCRIPTION PAGES CHANGED
MAX253
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600
2009 Maxim Integrated Products Maxim registered trademark Maxim Integrated Products, Inc.

Transformer Driver Isolated RS-485 Interface MAX253 monolithic os

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