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MAX253CPA+MAXIMN/a5000avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253CSA+ |MAX253CSAMAXIMN/a300avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253CSA+T |MAX253CSATMAXIMN/a5995avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253CUA+ |MAX253CUAMAXIMN/a455avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253CUA+TMAXICN/a2500avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253EPA+ |MAX253EPAMAXIMN/a109avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253ESA+ |MAX253ESAMAXIMN/a355avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253ESA+TMAXIMN/a20000avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253ESA-T |MAX253ESATMAXIMN/a643avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253EUA+ |MAX253EUAMAXIMN/a300avai1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies


MAX253ESA+T ,1W Primary-Side Transformer H-Bridge Driver for Isolated SuppliesTransformer Driver forMAX253Isolated RS-485 Interface
MAX253ESA-T ,1W Primary-Side Transformer H-Bridge Driver for Isolated SuppliesTransformer Driver forMAX253Isolated RS-485 Interface
MAX253EUA+ ,1W Primary-Side Transformer H-Bridge Driver for Isolated SuppliesGeneral Description Benefits and
MAX253MJA ,Transformer Driver for Isolated RS-485 InterfaceMAX25319-0226; Rev 0; 1/94Transformer Driver forIsolated RS-485 Interface_______________
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MAX253CPA+-MAX253CSA+-MAX253CSA+T-MAX253CUA+-MAX253CUA+T-MAX253EPA+-MAX253ESA+-MAX253ESA+T-MAX253ESA-T-MAX253EUA+
1W Primary-Side Transformer H-Bridge Driver for Isolated Supplies
MAX253Transformer Driver for
Isolated RS-485 Interface
General Description

The MAX253 monolithic oscillator/power-driver is
specifically designed to provide isolated power for an
isolated RS-485 or RS-232 data interface. The device
drives a center-tapped transformer primary from a 5V
or 3.3V DC power supply. The secondary can be
wound to provide any isolated voltage needed at power
levels up to 1W.
The MAX253 consists of a CMOS oscillator driving a
pair of N-channel power switches. The oscillator runs
at double the output frequency, driving a toggle flip-
flop to ensure 50% duty cycle to each of the switches.
Internal delays are arranged to ensure break-before-
make action between the two switches.
The SD pin puts the entire device into a low-power
shutdown state, disabling both the power switches and
oscillator.
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
Benefits and Features
Simple Power-Supply Transformer Driver Design for
Isolated RS-485/RS-232 Data-Interface ApplicationsSingle 5V or 3.3V SupplyLow-Current Shutdown Mode: 0.4µAPin-Selectable Frequency: 350kHz or 200kHz8-Pin DIP, SO, and µMAX®Packages Take Minimal
Board Space
Ordering Information

MAX253FS
GND1GND2
VCC1
VIN
FREQUENCY
SWITCH
5V @ 200mA
OUTPUTON / OFF
Typical Operating Circuit
PART TEMP RANGE PIN-PACKAGE

MAX253CPA0°C to +70°C8 Plastic DIP
MAX253CSA0°C to +70°C8 SO
MAX253CUA0°C to +70°C8 µMAX
MAX253C/D0°C to +70°CDice*
MAX253EPA-40°C to +85°C8 Plastic DIP
MAX253ESA-40°C to +85°C8 SO
MAX253ESA/V-40°C to +85°C8 SO
MAX253MJA-55°C to +125°C8 CERDIP**
*Contact factory for dice specifications.
**Contact factory for availability and processing to MIL-STD-883.
Devices are also available in a lead(Pb)-free/RoHS-compliant
package. Specify lead-free by adding a (+) to the part number
when ordering.
/V Denotes an automotive qualified part.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX253Transformer Driver for
Isolated RS-485 Interface
Absolute Maximum Ratings
Electrical Characteristics

(VCC= 5V ±10%, TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°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.
Note 1:
Operating supply current is the current used by the MAX253 only, not including load current.
Note 2:
Shutdown supply current includes output switch-leakage currents.
PARAMETERMINTYPMAXUNITS

Shutdown Input Threshold0.8µA
2.4V
Shutdown Supply Current (Note 2)0.4µA
Operating Supply Current (Note 1)0.455.0mA
Shutdown Input Leakage Current10pA
2.4VFS Input Threshold0.8µA
Switch On-Resistance1.54.0Ω
250350500kHzSwitch Frequency150200300
FS Input Leakage Current10pA
Start-Up Voltage2.52.2V
CONDITIONS

FS = VCC
Low
High
SD = VCC
No load, VSD= 0V, FS low
High
Low
VFS= 0V
D1, D2; 100mA
FS = VCCor open
VFS= 0V
Supply Voltage (VCC)...............................................-0.3V to +7V
Control Input Voltages (SD, FS).................-0.3V to (VCC+ 0.3V)
Output Switch Voltage (D1, D2).............................................12V
Peak Output Switch Current (D1, D2)......................................1A
Average Output Switch Current (D1, D2).........................200mA
Continuous Power Dissipation (TA= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C).............727mW
SO (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 to +70°C
MAX253E_ _.....................................................-40°C to +85°C
MAX253MJA...................................................-55°C to +125°C
Junction Temperatures
MAX253C_ _/E_ _..........................................................+150°C
MAX253MJA.................................................................+175°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10s).................................+300°C
Soldering Temperature (reflow)
PDIP, SO, µMAX lead(Pb)-free.....................................+260°C
PDIP, SO, µMAX, CERDIP containing lead(Pb)............+240°C
MAX253Transformer Driver for
Isolated RS-485 Interface
OUTPUT RESISTANCE vs. TEMPERATURE
(FS = LOW)
plot01
TEMPERATURE (°C)
OUTPUT RESISTANCE (100
VIN = 4.5V
VIN = 5.0V
MEASURED AT TP1
OUTPUT RESISTANCE vs. TEMPERATURE
(FS = HIGH)
plot02
TEMPERATURE (°C)
OUTPUT RESISTANCE (100
VIN = 4.5V
VIN = 5.0V
MEASURED AT TP1
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
plot03
TEMPERATURE (°C)
SHUTDOWN CURRENT (100
INCLUDES SWITCH LEAKAGE CURRENTS
D1, D2 FREQUENCY vs. TEMPERATURE
(FS = LOW)
plot04
TEMPERATURE (°C)
FREQUENCY (kHz)100
VIN = 5.5V
VIN = 4.5V
VIN = 5.0V
VIN = 6.0V
SUPPLY CURRENT vs. TEMPERATURE
(FS = HIGH)
plot07
TEMPERATURE (°C)
SUPPLY CURRENT (100
VIN = 5.5V
VIN = 6.0V
VIN = 4.5V
VIN = 5.0V
D1, D2 FREQUENCY vs. TEMPERATURE
(FS = HIGH)
plot05
TEMPERATURE (°C)
FREQUENCY (kHz)100
VIN = 4.5V
VIN = 5.0V
VIN = 6.0V
VIN = 5.5V
SUPPLY CURRENT vs. TEMPERATURE
(FS = LOW)
plot06
TEMPERATURE (°C)
SUPPLY CURRENT (100
VIN = 4.5V
VIN = 5.0V
VIN = 5.5V
VIN = 6.0V
EFFICIENCY vs. LOAD CURRENT
(FS = LOW)
plot08
LOAD CURRENT (mA)
EFFICIENCY (%)16060140100180
VIN = 5.5V
VIN = 4.5V
Typical Operating Characteristics

(Circuit of Figure 6, VIN= 5V ±10%, TA = +25°C, unless otherwise noted.)
MAX253Transformer Driver for
Isolated RS-485 Interface40220
OUTPUT VOLTAGE vs. LOAD CURRENT
(FS = LOW)

plot10
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)60140120100160180200
CIRCUIT OF FIGURE 6
VIN = 5.0V
TURNS RATIO = 1:1
CIRCUIT OF FIGURE 6
VIN = 5.0V
TURNS RATIO = 1:1.3
CIRCUIT OF FIGURE 7
VIN = 3.3V
TURNS RATIO = 1:2.1
MEASURED AT TP1
OUTPUT VOLTAGE vs. LOAD CURRENT
(FS = HIGH)
plot11
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)60140120100160180200
CIRCUIT OF FIGURE 6
VIN = 5.0V
TURNS RATIO = 1:1
CIRCUIT OF FIGURE 6
VIN = 5.0V
TURNS RATIO = 1:1.3
CIRCUIT OF FIGURE 7
VIN = 3.3V
TURNS RATIO = 1:2.1
MEASURED AT TP1
CIRCUIT OF FIGURE 1
SWITCHING WAVEFORMS
(TWO CYCLES)

CIRCUIT OF FIGURE 1
SWITCHING WAVEFORMS
(BREAK BEFORE MAKE)

TIME FROM SHUTDOWN TO POWER-UP

TP1 (OUTPUT VOLTAGE)
Typical Operating Characteristics (continued)

Circuit of Figure 6, VIN= 5V ±10%, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(FS = HIGH)
plot09
LOAD CURRENT (mA)
EFFICIENCY (%)16060140100180
VIN = 5.5V
VIN = 4.5V
MAX253Transformer Driver for
Isolated RS-485 Interface
GND2
VCC
N.C.SD
GND1
DIP/SO/µMAX

TOP VIEW
MAX253
Pin ConfigurationPin Description

Not internally connected.N.C.5
5V supply voltage.VCC6
GND27
Open drain of N-channel transformer drive 2.D2843
PIN

GND12
Open drain of N-channel transformer drive 1.D11
FUNCTIONNAME

Ground. Connect both GND1 and GND2
to ground.
Frequency switch. If FS = VCCor open,
switch frequency = 350kHz; if VFS= 0V,
switch frequency = 200kHz.
Shutdown. Ground for normal operation,
connect high for shutdown.
Ground. Connect both GND1 and GND2
to ground.
MAX253Transformer Driver for
Isolated RS-485 Interface
Detailed Description

The MAX253 is an isolated power-supply transformer
driver specifically designed to form the heart of a fully
isolated RS-485 data interface. Completely isolated
communications are obtained by combining the
MAX253 with a linear regulator, a center-tapped trans-
former, optocouplers, and the appropriate Maxim inter-
face product (as described in the Isolated
RS-485/RS-232 Data Interfacesection).
The MAX253 consists of an RC oscillator followed by a
toggle flip-flop, which generates two 50% duty-cycle
square waves, out-of-phase at half the oscillator fre-
quency (Figure 2). These two signals drive the ground-
referenced output switches. Internal delays ensure
break-before-make action between the two switches.
Ground SD for normal operation. When high, SD dis-
ables all internal circuitry, including the oscillator and
both power switches.
Pulling FS low reduces the oscillator frequency and low-
ers the supply current (see Supply Current vs.
Temperature in the Typical Operating Characteristics).
FS includes a weak pull-up, so it will be set to the high-
frequency state if not connected.
MAX253FS
GND1GND2
VCC
FREQUENCY
SWITCH
ON / OFF
50Ω
50Ω
VINC1
0.1µF
Figure 1. Test Circuit
MAX253
GND2GND1
VCC
FREQUENCY
SWITCH
5V @ 200mA
ISO OUTPUT
OSC
F / F
VIN
ON / OFF
400kHz/
700kHz
ISO
GND
Figure 2. Block Diagram
MAX253Transformer Driver for
Isolated RS-485 Interface
0.1µF
0.1µF
22µF
ISO 5V
ISOLATION
BARRIER
VIN
MAX253
GND1GND2
VCC1N58174ON / OFF
390Ω*74HC04
390Ω*74HC04
3.3kΩ*74HC04
*74HC04 OR EQUIVALENT
** SEE TABLE 2
MAX66764
SHDNSETGND
MAX481
MAX483
MAX485
MAX4872GND
22µFOUT821N5817
390Ω
3.3kΩ
3.3kΩ
PC410 / 417
PC357T
PC410 / 417
1CT:1.3CT**
VCC
I/O
Figure 3. Typical RS-485 Application Circuit, 5V Configuration
MAX253Transformer Driver for
Isolated RS-485 Interface
0.1µF
0.1µF
22µF
ISO 5V
ISOLATION
BARRIER
3.3V
VIN
MAX253
GND1GND2
VCC6
N.C.5
1N5817
1N5817
0.1µF4ON / OFF
390Ω*74HC04
390Ω*74HC04
3.3kΩ*74HC04
*74HC04 OR EQUIVALENT
** SEE TABLE 2
MAX66764
SHDNSETGND
MAX481
MAX483
MAX485
MAX4872GND
22µFOUT821N5817
390Ω
PC410 / 417
PC357T
PC410 / 417
1N58173
1CT:2.1CT**
VCC
3.3kΩ
3.3kΩ
I/O
Figure 4. Typical RS-485 Application Circuit, 3.3V Configuration
MAX253Transformer Driver for
Isolated RS-485 Interface
0.1µF
22µF
ISO 5V
ISOLATION
BARRIER5V
VIN
0.1µF
1N5817
MAX253
GND1GND2
VCC
N.C.4ON / OFF
10 x PC417
*74HC04 OR EQUIVALENT
** SEE TABLE 2
MAX205SD
22µF1N5817
MAX66764
SHDNSETGNDOUT
390ΩT1INT1OUT
390Ω*74HC04
T1IN44
390Ω74HC04
T2IN
390Ω74HC04
T3IN
390Ω74HC04
T4IN
390Ω74HC04
T5IN
74HC04
R1OUT
74HC04
74HC04
74HC04
74HC04
R2OUT
R3OUT
R4OUT
R5OUT
5 X 3.3kΩ
390Ω
390Ω
390Ω
390ΩT2INT2OUT2T3INT3OUT1T4INT4OUT19T5INT5OUT
910R1OUTR1INR2OUTR2IN24R3OUTR3IN18R4OUTR4IN13R5OUTR5IN
VCC21
GND
5 x 3.3kΩ
1N57116
390Ω
3.3kΩ
VCC
ISO
ROUTROUT
1N5711
390Ω3.3kΩ
VCC
ISO
TIN
TIN
*74HC04
4N25 LOWER SPEED, LOWER COST ALTERNATE OPTOCOUPLER CONFIGURATIONS (FOR DATA RATES BELOW 9.6kbps)3
74HCO4
4N25
ISO
GND
4N25
ISO
GND
1CT:1.3CT**
Figure 5. Typical RS-232 Application Circuit
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