Document
19-0226; Rev 0; 1/94
Transformer Driver for Isolated RS-485 Interface
_______________General Description
The MAX253 is a monolithic oscillator/power-driver, specifically designed to provide isolated power for an isolated RS-485 or RS-232 data interface. It 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-beforemake 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.
____________________________Features
o Power-Supply Transformer Driver for Isolated RS-485/RS-232 Data-Interface Applications o Single +5V or +3.3V Supply o Low-Current Shutdown Mode: 0.4µA o Pin-Selectable Frequency: 350kHz or 200kHz o 8-Pin DIP, SO, and µMAX Packages
MAX253
______________Ordering Information
PART MAX253CPA MAX253CSA MAX253CUA MAX253C/D MAX253EPA MAX253ESA MAX253EUA MAX253MJA TEMP. RANGE 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -55°C to +125°C PIN-PACKAGE 8 Plastic DIP 8 SO 8 µMAX Dice* 8 Plastic DIP 8 SO 8 µMAX 8 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 for dice specifications. **Contact factory for availability and processing to MIL-STD-883.
__________Typical Operating Circuit
ON / OFF 4 SD 6 VCC D1 1 C3 C2 VIN 5V C1 OUTPUT 5V @ 200mA
__________________Pin Configuration
TOP VIEW
D1 GND1
1 2
8 7
D2 GND2 VCC N.C.
MAX253
3 FREQUENCY SWITCH FS GND1 2 D2 GND2 7 8
FS 3 SD 4
MAX253
6 5
DIP/SO/µMAX
________________________________________________________________ Maxim Integrated Products
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Transformer Driver for Isolated RS-485 Interface MAX253
ABSOLUTE MAXIMUM RATINGS
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, 10sec) .............................+300°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.
ELECTRICAL CHARACTERISTICS
(VCC = 5V ±10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Switch On Resistance Switch Frequency Operating Supply Current (Note 1) Shutdown Supply Current (Note 2) Shutdown Input Threshold Shutdown Input Leakage Current FS Input Threshold FS Input Leakage Current Start-Up Voltage High Low FS = 0V FS = VCC 2.5 10 2.2 2.4 0.8 50 D1, D2; 100mA FS = VCC or open FS = 0V No load, SD = 0V, FS low SD = VCC High Low 10 2.4 0.8 250 150 CONDITIONS MIN TYP 1.5 350 200 0.45 0.4 MAX 4.0 500 300 5.0 UNITS Ω kHz mA µA V µA pA V µA pA V
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.
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Transformer Driver for Isolated RS-485 Interface
__________________________________________Typical Operating Characteristics
(Circuit of Figure 6, VIN = 5V ±1.