MAX253ESA Maxim Integrated Products, MAX253ESA Datasheet - Page 6

• Manufacturer Part Number: MAX253ESA
• Description: IC XFRMR DRIVER RS485 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Driverr

Specifications of MAX253ESA

• Number Of Drivers/receivers: 1/0
• Protocol: RS232, RS485
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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 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-
Transformer Driver for
Isolated RS-485 Interface
Figure 1. Test Circuit
Figure 2. Block Diagram
6
_______________Detailed Description
_______________________________________________________________________________________
FREQUENCY
SWITCH
C1
FS
400kHz/
700kHz
MAX253
OSC
V
5V
IN
FREQUENCY
ON / OFF
T
SWITCH
F / F
Q
Q
C1
0.1µF
4
3
SD
ON / OFF
V
SD
IN
FS
V
CC
GND1
5V
MAX253
2
V
GND2
CC
6
GND2
7
GND1
D1
D2
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.
1
8
50Ω
N
N
R1
D1
D2
50Ω
R2
C3
ISO
GND
5V @ 200mA
C2
ISO OUTPUT