Datasheet

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AVAILABLE

Functional Diagrams

Pin Configurations appear at end of data sheet.

Functional Diagrams continued at end of data sheet.

UCSP is a trademark of Maxim Integrated Products, Inc.

For pricing, delivery, and

ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

_______________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

____________________________Features

♦♦

Power-Supply Transformer Driver for Isolated

RS-485/RS-232 Data-Interface Applications

♦♦

Single 5V or 3.3V Supply

♦♦

Low-Current Shutdown Mode: 0.4µA

♦♦

Pin-Selectable Frequency: 350kHz or 200kHz

♦♦

8-Pin DIP, SO, and µMAX

Packages

______________Ordering Information

MAX253

Transformer Driver for

Isolated RS-485 Interface

MAX253

D2FS

GND1 GND2

FREQUENCY

SWITCH

5V @ 200mA

OUTPUT

ON / OFF

__________Typical Operating Circuit

PART TEMP RANGE PIN-PACKAGE

MAX253CPA 0°C to +70°C 8 Plastic DIP

MAX253CSA 0°C to +70°C 8 SO

MAX253CUA 0°C to +70°C 8 μMAX

MAX253C/D 0°C to +70°C Dice*

MAX253EPA -40°C to +85°C 8 Plastic DIP

MAX253ESA -40°C to +85°C 8 SO

MAX253ESA/V -40°C to +85°C 8 SO

MAX253MJA -55°C to +125°C 8 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.

__________Typical Operating Circuit

19-0226; Rev 2; 4/10

MAX253

Summary of content (18 pages)

PAGE 1
MAX253 LE AVAILAB Transformer Driver for Isolated RS-485 Interface ____________________________Features 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.
PAGE 2
MAX253 Transformer Driver for Isolated RS-485 Interface 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) .........................
PAGE 3
MAX253 Transformer Driver for Isolated RS-485 Interface __________________________________________Typical Operating Characteristics (Circuit of Figure 6, VIN = 5V ±10%, TA = +25°C, unless otherwise noted.) MEASURED AT TP1 1.0 plot02 15 plot01 10.5 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE OUTPUT RESISTANCE vs. TEMPERATURE (FS = HIGH) MEASURED AT TP1 INCLUDES SWITCH LEAKAGE CURRENTS VIN = 4.5V 9.0 8.5 8.0 VIN = 5.0V 7.5 SHUTDOWN CURRENT (μA) OUTPUT RESISTANCE (Ω) OUTPUT RESISTANCE (Ω) 10.0 9.
PAGE 4
MAX253 Transformer Driver for Isolated RS-485 Interface ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 6, VIN = 5V ±10%, TA = +25°C, unless otherwise noted.) OUTPUT VOLTAGE vs. LOAD CURRENT (FS = LOW) 90 9 VIN = 5.5V 70 VIN = 4.5V 60 50 40 30 8 OUTPUT VOLTAGE (V) EFFICIENCY (%) 80 8 5 4 3 2 10 1 0 0 20 40 60 80 100 120 140 160 180 200 9 CIRCUIT OF FIGURE 6 VIN = 5.0V TURNS RATIO = 1:1.3 6 20 0 CIRCUIT OF FIGURE 6 VIN = 5.
PAGE 5
MAX253 Transformer Driver for Isolated RS-485 Interface __________________Pin Configuration TOP VIEW + D1 1 GND1 2 FS 3 MAX253 SD 4 DIP/SO/μMAX Maxim Integrated 8 D2 7 GND2 6 VCC 5 N.C. _____________________Pin Description PIN NAME FUNCTION 1 D1 Open drain of N-channel transformer drive 1. 2 GND1 3 FS 4 SD 5 N.C. Not internally connected. 6 VCC 5V supply voltage. 7 GND2 8 D2 Ground. Connect both GND1 and GND2 to ground. Frequency switch.
PAGE 6
MAX253 Transformer Driver for Isolated RS-485 Interface VIN 5V C1 0.1µF R1 50Ω 6 VCC 4 SD D1 1 ON / OFF R2 50Ω MAX253 3 FS FREQUENCY SWITCH D2 GND1 GND2 2 7 8 Figure 1. Test Circuit VIN 5V C1 VCC F/F MAX253 Q C3 N C2 T FS OSC FREQUENCY SWITCH 5V @ 200mA ISO OUTPUT D1 400kHz/ 700kHz D2 Q N SD GND2 ISO GND GND1 ON / OFF Figure 2.
PAGE 7
MAX253 Transformer Driver for Isolated RS-485 Interface ISOLATION BARRIER VIN 5V C1 0.1μF 6 VCC D1 ON / OFF 4 SD 2 8 C3 0.1μF MAX253 D2 GND1 1CT:1.3CT** 1N5817 1 GND2 FS IN OUT C2 22μF ISO 5V 2 C4 22μF MAX667 8 1N5817 3 SET GND 6 SHDN 4 5 7 3.3kΩ PC410 / 417 6 *74HC04 390Ω DI 1 5 3.3kΩ 3 8 4 PC357T *74HC04 390Ω DE 4 1 4 A 3 *74HC04 3.
PAGE 8
MAX253 Transformer Driver for Isolated RS-485 Interface ISOLATION BARRIER VIN 3.3V C1 0.1µF 5 ON / OFF 4 6 D1 N.C. SD 1CT:2.1CT** 1N5817 1 8 C3 0.1µF MAX253 D2 VCC FS GND1 2 IN OUT C2 22µF C4 22µF MAX667 8 3 1N5817 SET GND2 7 ISO 5V 2 GND 6 1N5817 SHDN 4 5 1N5817 C5 0.1µF PC410 / 417 3.3kΩ 6 *74HC04 390Ω DI 1 5 3.3kΩ 3 8 4 PC357T *74HC04 390Ω DE 4 1 A 3 *74HC04 3.
PAGE 9
MAX253 Transformer Driver for Isolated RS-485 Interface VIN 5V C1 0.1µF 5 ON / OFF 4 ISOLATION BARRIER 1CT:1.3CT** 1N5817 6 VCC N.C. SD D1 1 MAX253 D2 FS GND1 GND2 2 7 8 2 IN OUT C2 22µF MAX667 C3 0.1µF ISO 5V C4 22µF 8 3 SET GND SHDN 6 4 5 1N5817 5 x 3.
PAGE 10
MAX253 Transformer Driver for Isolated RS-485 Interface __________Applications Information Figures 3–5 are typical isolated RS-485/RS-232 data-interface circuits. These circuits withstand 1800VRMS (1sec) and are intended for industrial communications and control applications where very high voltage transients, differential ground potentials, or high noise may be encountered. Table 2 lists transformer characteristics for the applications of Figures 3–10.
PAGE 11
MAX253 Transformer Driver for Isolated RS-485 Interface VIN 5V C1 0.1µF 6 VCC 4 D1 SD ON / OFF 1 1CT:1.3CT* 1N5817 5V @ 200mA ISO OUTPUT TP1 C3 0.1µF C2 22µF MAX253 3 FS FREQUENCY SWITCH D2 8 1N5817 GND1 GND2 2 7 OPTIONAL 21kHz LOWPASS OUTPUT FILTER L2 25µH FILTER OUTPUT OUTPUT C7 2.2µF *SEE TABLE 2 Figure 6. 5V to Isolated 5V Application Circuit VIN 3.3V C1 0.1µF 4 ON / OFF D1 SD 1 5V @ 100mA TP1 ISO OUTPUT 1CT:2.1CT* 1N5817 C3 0.
PAGE 12
MAX253 Transformer Driver for Isolated RS-485 Interface VIN ISOLATION BARRIER 6 5V VCC D1 24V UNREGULATED 1CT:5CT* 1 1N5817 10µF MAX253 4 SD D2 GND1 78L05 1N5817 GND2 2 5V 8 7 1 3 7 0.1V to 0.5V MAX480 2 RL 0kΩ to 1kΩ IL300 6 4 2 3 6 4 5 49.9kΩ ISO 5V 3 49.9kΩ 6 MAX480 2 7 2N3904 4 2N3904 *SEE TABLE 2 10kΩ 24.9Ω Figure 8.
PAGE 13
MAX253 Transformer Driver for Isolated RS-485 Interface VIN INPUT 6 VCC D1 1 1CT:1CT* 1N5817 +VOUT ≈ 2V IN OUTPUT RL+ MAX253 D2 GND2 GND1 2 8 RL+ ≅ RLRL- 7 *SEE TABLE 2 -VOUT ≈ -2V IN OUTPUT 1N5817 Figure 9a. Half-Wave Rectifier—Bipolar VIN INPUT 6 VCC D1 1 1CT:1CT* 4 x 1N5817 VOUT ≈ +VIN OUTPUT MAX253 D2 GND1 8 GND2 2 7 VOUT ≈ -VIN OUTPUT *SEE TABLE 2 Figure 9b.
PAGE 14
MAX253 Transformer Driver for Isolated RS-485 Interface VIN 5V ISOLATION BARRIER 1CT : 1.5CT : 3CT* 1 78L05 4 x 1N5817 10μF ISO 5V 6 8 79 L12 ISO -12V D1 MAX253 VCC D2 SD GND1 10μF 2 4 ON/OFF GND2 7 5V 74HC04 START 8 6N136 7 INPUT CLOCK 1 2 200Ω QH 3kΩ 10μF MAX176 0.1μF ANALOG INPUT 1 2 3 0.1μF 10μF VDD AIN VREF VSS CONVST CLOCK 4 GND DATA 14 6 3 5 4 11 1 12 8 8 7 3kΩ 6 5 0.
PAGE 15
MAX253 Transformer Driver for Isolated RS-485 Interface sensor, an extra several hundred milliwatts could easily be supplied by the circuit, as shown. A 12V supply could be generated by adding two more diodes to the ends of the secondary, and a -5V supply could be generated by connecting additional diodes to the 1/4 and 3/4 tap points on the secondary. For 5V only applications, the MAX187 is recommended.
PAGE 16
MAX253 Transformer Driver for Isolated RS-485 Interface age. In addition, include in the calculations an allowance for worst-case losses in the rectifiers. Since the turns ratio determined in this manner will ordinarily produce a much higher voltage at the secondary under conditions of high input voltage and/or light loading, be careful to prevent an overvoltage condition from occurring (see Output Voltage vs. Load Current in the Typical Operating Characteristics).
PAGE 17
MAX253 Transformer Driver for Isolated RS-485 Interface ___________________Chip Information PROCESS: CMOS Maxim Integrated Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
PAGE 18
MAX253 Transformer Driver for Isolated RS-485 Interface Revision History REVISION NUMBER REVISION DATE 0 1/94 Initial release — 1 8/09 Deleted the MAX253EUA part number from the Ordering Information table 1 2 4/10 Added automotive qualified part number to the Ordering Information table 1 DESCRIPTION PAGES CHANGED Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.