MAXIM MAX253 Technical data

_______________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-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.

________________________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

________________________________________________________________

Maxim Integrated Products

1

__________Typical Operating Circuit

19-0226; Rev 2; 4/10

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

*

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.

PART TEMP RANGE PIN-PACKAGE

MAX253CP A 0°C to +70°C 8 Plastic DIP

MAX253CS A 0°C to +70°C 8 SO

MAX253CU A 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**

V

5V

ON / OFF

46

SD

MAX253

3

FREQUENCY

SWITCH

GND1 GND2

27

IN

C1

OUTPUT

C3

5V @ 200mA

C2

V

CC

1

D1

8

D2FS

MAX253

Transformer Driver for
Isolated RS-485 Interface

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= 5V ±10%, TA= T

MIN

to T

MAX

, 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.

PARAMETER

MIN TYP MAX UNITS

Shutdown Input Threshold

0.8 µA

2.4 V

Shutdown Supply Current (Note 2) 0.4 µA

Operating Supply Current (Note 1) 0.45 5.0 mA

Shutdown Input Leakage Current 10 pA

2.4
VFS Input Threshold

0.8

50 µA

Switch On-Resistance 1.5 4.0 Ω

250 350 500

kHzSwitch Frequency

150 200 300

FS Input Leakage Current

10 pA

Start-Up Voltage 2.5 2.2 V

CONDITIONS

FS = V

CC

Low

High

SD = V

CC

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 (V

CC

+ 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 (T

A

= +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

MAX253

Transformer Driver for

Isolated RS-485 Interface

_______________________________________________________________________________________

3

__________________________________________Typical Operating Characteristics

(Circuit of Figure 6, VIN= 5V ±10%, TA = +25°C, unless otherwise noted.)

OUTPUT RESISTANCE vs. TEMPERATURE

(FS = LOW)

10.5
MEASURED AT TP1

10.0

9.5

9.0

8.5

8.0

7.5

OUTPUT RESISTANCE (Ω)

7.0

6.5

6.0

-40 0 8040 120

-60 -20 60 140

VIN = 4.5V

VIN = 5.0V

20 100

TEMPERATURE (°C)

D1, D2 FREQUENCY vs. TEMPERATURE

(FS = LOW)

260

240

220

200

FREQUENCY (kHz)

180

160

VIN = 6.0V

VIN = 5.0V

VIN = 4.5V

-40 0 8040 120

-60 -20 60 140

20 100

TEMPERATURE (°C)

VIN = 5.5V

plot01

OUTPUT RESISTANCE (Ω)

plot04

FREQUENCY (kHz)

OUTPUT RESISTANCE vs. TEMPERATURE

(FS = HIGH)

15

MEASURED AT TP1

12

VIN = 4.5V

VIN = 5.0V

9

6

-40 0 8040 120

-60 -20 60 140

20 100

TEMPERATURE (°C)

D1, D2 FREQUENCY vs. TEMPERATURE

(FS = HIGH)

480

440

400

360

320

280

VIN = 6.0V

VIN = 5.5V

VIN = 5.0V

VIN = 4.5V

-40 0 8040 120

-60 -20 60 140

20 100

TEMPERATURE (°C)

plot02

SHUTDOWN CURRENT (μA)

plot05

SUPPLY CURRENT (μA)

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

1.0

INCLUDES SWITCH LEAKAGE CURRENTS

0.8

0.6

0.4

0.2

0

-40 0 8040 120

-60 -20 60 140

20 100

TEMPERATURE (°C)

SUPPLY CURRENT vs. TEMPERATURE

(FS = LOW)

600

550

500

450

400

350

300

250

-40 0 8040 120

-60 -20 60 140

VIN = 6.0V

VIN = 5.5V

VIN = 5.0V

VIN = 4.5V

20 100

TEMPERATURE (°C)

plot03

plot06

SUPPLY CURRENT vs. TEMPERATURE

(FS = HIGH)

850

800

750

700

650

600

550

SUPPLY CURRENT (μA)

500

450

400

-40 0 8040 120

-60 -20 60 140

20 100

TEMPERATURE (°C)

VIN = 6.0V

VIN = 5.5V

VIN = 5.0V

VIN = 4.5V

plot07

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT

(FS = LOW)

100

90

80

70

60

50

40

30

20

10

0

0 40 120 200

20 60 140100 180

VIN = 4.5V

80 160

LOAD CURRENT (mA)

VIN = 5.5V

plot08

MAX253

Transformer Driver for
Isolated RS-485 Interface

4 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 6, VIN= 5V ±10%, TA = +25°C, unless otherwise noted.)

EFFICIENCY vs. LOAD CURRENT

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0 40 120 200

20 60 140100 180

(FS = HIGH)

VIN = 5.5V

VIN = 4.5V

80 160

LOAD CURRENT (mA)

SWITCHING WAVEFORMS

(TWO CYCLES)

10

plot09

9

8

7

6

5

4

OUTPUT VOLTAGE (V)

3

2

1

0

OUTPUT VOLTAGE vs. LOAD CURRENT

(FS = LOW)

CIRCUIT OF FIGURE 7
V

= 3.3V

IN

TURNS RATIO = 1:2.1

CIRCUIT OF FIGURE 6

= 5.0V

V

IN

TURNS RATIO = 1:1.3

CIRCUIT OF FIGURE 6

= 5.0V

V

IN

TURNS RATIO = 1:1

MEASURED AT TP1

80

20 60 140

0 40 220

D1

12 0100 160 180 200

LOAD CURRENT (mA)

OUTPUT VOLTAGE vs. LOAD CURRENT

10

plot10

CIRCUIT OF FIGURE 7

9

V

= 3.3V

IN

TURNS RATIO = 1:2.1

8

7

6

5

4

OUTPUT VOLTAGE (V)

CIRCUIT OF FIGURE 6

3

V

= 5.0V

IN

2

TURNS RATIO = 1:1

1

0

20 60 140

0 40 220

SWITCHING WAVEFORMS

(BREAK BEFORE MAKE)

(FS = HIGH)

CIRCUIT OF FIGURE 6

= 5.0V

V

IN

TURNS RATIO = 1:1.3

MEASURED AT TP1

80

12 0100 160 180 200

LOAD CURRENT (mA)

plot11

D1

D2

CIRCUIT OF FIGURE 1

CIRCUIT OF FIGURE 1

TIME FROM SHUTDOWN TO POWER-UP

SD

TP1 (OUTPUT VOLTAGE)

CIRCUIT OF FIGURE 6

D2

MAX253

Transformer Driver for

Isolated RS-485 Interface

_______________________________________________________________________________________ 5

__________________Pin Configuration _____________________Pin Description

Not internally connected.N.C.5

5V supply voltage.V

CC

6

GND27

Open drain of N-channel transformer drive 2.D28

SD4

FS3

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 V

FS

= 0V,

switch frequency = 200kHz.
Shutdown. Ground for normal operation,

connect high for shutdown.

Ground. Connect both GND1 and GND2
to ground.

TOP VIEW

GND1

D1

1

2

FS

3

SD

4

DIP/SO/μMAX

+

MAX253

8

D2

GND2

7

V

6

CC

5

N.C.

MAX253

Transformer Driver for
Isolated RS-485 Interface

6 _______________________________________________________________________________________

_______________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 trans­former, optocouplers, and the appropriate Maxim inter­face product (as described in the

Isolated RS-485/RS-

232 Data Interface

section).

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 ground­referenced output switches. Internal delays ensure
break-before-make action between the two switches.

Ground SD for normal operation. When high, SD dis­ables all internal circuitry, including the oscillator and
both power switches.

Pulling FS low reduces the oscillator frequency and low­ers 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 high­frequency state if not connected.

MAX253

D1

D2FS

GND1 GND2

V

CC

1

8

4

6

27

3

SD

FREQUENCY

SWITCH

ON / OFF

R2

50Ω

R1

50Ω

V

IN

5V

C1

0.1µF

Figure 1. Test Circuit

MAX253

D1

D2

FS

GND2 GND1

V

CC

FREQUENCY

SWITCH

C3

C1

C2

5V @ 200mA

ISO OUTPUT

5V

N

N

Q

Q

OSC

F / F

V

IN

SD

ON / OFF

400kHz/
700kHz

T

ISO
GND

Figure 2. Block Diagram