MAX253C(2009) Ver la hoja de datos (PDF) - Maxim Integrated
Número de pieza
componentes Descripción
Lista de partido
MAX253C Datasheet PDF : 17 Pages
| |||
Transformer Driver for
Isolated RS-485 Interface
_____________________Pin Description
PIN NAME
1
D1
2 GND1
3
FS
4
SD
5 N.C.
6
VCC
7 GND2
8
D2
FUNCTION
Open drain of N-channel transformer drive 1.
Ground. Connect both GND1 and GND2
to ground.
Frequency switch. If FS = VCC or open,
switch frequency = 350kHz; if FS = 0V,
switch frequency = 200kHz.
Shutdown. Ground for normal operation,
tie high for shutdown.
Not internally connected.
+5V supply voltage.
Ground. Connect both GND1 and GND2
to ground.
Open drain of N-channel transformer drive 2.
VIN
5V
C1
0.1µF
6
VCC
4 SD
ON / OFF
MAX253
R1
50Ω
1
D1
R2
50Ω
3
FREQUENCY
SWITCH
FS
GND1
2
8
D2
GND2
7
Figure 1. Test Circuit
C1
MAX253
FREQUENCY
SWITCH
FS
OSC
400kHz/
700kHz
VIN 5V
F/F
VCC
D1
Q
N
T
D2
Q
N
SD
GND2 GND1
5V @ 200mA
ISO OUTPUT
C3
C2
ISO
GND
ON / OFF
Figure 2. Block Diagram
_______________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 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-
quency (see 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 float to the high-fre-
quency state if not connected.
_______________________________________________________________________________________ 5
Share Link: 