19-0226; Rev 1; 8/09
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-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.
____________________________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
MAX253
______________Ordering Information
PART
MAX253CPA
MAX253CSA
MAX253CUA
MAX253C/D
MAX253EPA
MAX253ESA
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
-55°C to +125°C
PIN-PACKAGE
8 Plastic DIP
8 SO
8 μMAX
Dice*
8 Plastic DIP
8 SO
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
V
CC
D1
1
C3
C2
V
IN
5V
C1
OUTPUT
5V @ 200mA
__________________Pin Configuration
TOP VIEW
D1
GND1
1
2
MAX253
3
FREQUENCY
SWITCH
FS
GND1
2
D2
GND2
7
8
8
7
D2
GND2
V
CC
N.C.
FS 3
SD 4
MAX253
6
5
DIP/SO/μMAX
µMAX is a registered trademark of Maxim Integrated Products, Inc.
________________________________________________________________
Maxim Integrated Products
1
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.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
