MAX253ESA Maxim Integrated Products, MAX253ESA Datasheet - Page 15

• 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

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 gen-
erated by connecting additional diodes to the 1/4 and
3/4 tap points on the secondary. For 5V only applica-
tions, the MAX187 is recommended.
The transformer primary used with the MAX253 must be
a center-tapped winding with sufficient ET product to
prevent saturation at the worst-case lowest selected
frequency. The MAX253’s guaranteed minimum fre-
quency with the FS pin held low is 150kHz, equating to
a maximum period of 6.67µs. The required ET product
Table 2. Typical Transformer Characteristics
*CT = Center Tapped
Table 3. Transformer, Transformer Core, and Optocoupler Suppliers
______________Component Selection
Figure
Turns Ratio
Typical
Windings
Primary ET
Product
BH Electronics
Phone: [phone]
FAX: [phone]
Coilcraft
Phone: [phone]
FAX: [phone]
Coiltronics
Phone: [phone]
FAX: [phone]
CHARACTERISTIC
TRANSFORMERS
Primary
Secondary
FS Low
FS High
______________________________________________________________________________________
Transformer Selection
9a
1CT*:1
44CT
44
18.3V-µs
11V-µs
5V to ±10V
Philips Components
Phone: [phone]
FAX: [phone]
Magnetics Inc.
Phone: [phone]
FAX: [phone]
Fair-Rite Products
Phone: [phone]
FAX: [phone]
TRANSFORMER CORES
2, 3, 5, 6
1CT:1.3CT
44CT
56CT
18.3V-µs
11V-µs
Isolated RS-485 Interface
5V to 5V
for half the primary is simply the product of the maxi-
mum supply voltage and half the maximum period.
With FS connected high, the guaranteed minimum fre-
quency is 250kHz, giving a maximum period of 4µs.
The secondary winding may or may not be center
tapped, depending on the rectifier topology used. The
phasing of the secondary winding is not critical. In
some applications, multiple secondaries might be
required. Half-wave rectification could be used, but is
discouraged because it normally adds a DC imbalance
to the magnetic flux in the core, reducing the ET prod-
uct. If the DC load is imbalanced, full-wave rectification
is recommended, as shown in Figure 9b.
The transformer turns ratio must be set to provide the
minimum required output voltage at the maximum
anticipated load with the minimum expected input volt-
Transformer Driver for
4, 7
1CT:2.1CT
28CT
56CT
12V-µs
7.2V-µs
3.3V to 5V
Quality Technology
Phone: [phone]
FAX: [phone]
Sharp Electronics
Phone: [phone]
FAX: [phone]
Siemens Components
Phone: [phone]
FAX: [phone]
8
1CT:5CT
44CT
220CT
18.3V-µs
11V-µs
5V to 24V
OPTOCOUPLERS
10
1CT:1.5CT:3CT
44CT
66CT, 132CT
18.3V-µs
11V-µs
5V to ±5V; ±12V
15