Transceivers with ±15kV ESD Protection

______________________________________________________________________________________

21

product of 9.5V-µs. The commercially available trans-

formers for the MAX845 listed in Table 5 meet that

requirement. In most cases, use half of the center-tapped

primary winding with the MAX3535E and leave the other

end of the primary floating. Most of the transformers in

Table 5 are 1:1:1 or 1:1:1:1 turns ratio.

For +3.3V operation (+3.6V maximum) the required pri-

mary ET product is 6.2V-µs. All of the previously men-

tioned transformers meet this requirement. Table 6 lists

some other transformers with step-up turns ratios

specifically tailored for +3.3V operation. Most of the

transformers in Table 6 are 1:1:1.3:1.3.

By using a HALO TGM-010 or Midcom 95061 trans-

former, it becomes possible to build a complete isolated

RS-485/RS-422 transceiver with a maximum thickness

less than 0.1in. To minimize power consumption, select

the turns ratio of the transformer to produce the minimum

light loads on the isolated side, ensure that the voltage at

rent with full load on the RS-485 driver. Using a TGM250

A slight step-down transformer can result in extra power

savings in some situations. A custom wound sample

transformer with 23 primary turns and 20:20 secondary

turns on a Ferronics 11-050B core operates well with a

Table 4. Transformers for the MXL1535E/MAX3535E

MANUFACTURER

PART NUMBER

ISOLATION VOLTAGE (1s)

PHONE NUMBER

Cooper Electronic Technologies, Inc.

CTX01-14659

500V

561-241-7876

Cooper Electronic Technologies, Inc.

CTX01-14608

561-241-7876

EPCOS AG (Germany)

(USA)

B78304-A1477-A3

500V

0 89-626-2-80-00

800-888-7724

Midcom, Inc.

31160R

1250V

605-886-4385

Pulse FEE (France)

P1597

500V

33-3-85-35-04-04

Sumida Corporation (Japan)

S-167-5779

100V

03-3667-3320

Transpower Technologies, Inc.

TTI7780-SM

500V

775-852-0145

Table 5. Transformers for MAX3535E at +5V

MANUFACTURER

PART

NUMBER

ISOLATION

VOLTAGE (1s)

PHONE

NUMBER

WEBSITE

TGM-010

TGM-250

TGM-350

HALO Electronics, Inc.

TGM-450

650-903-3800

www.haloelectronics.com/6pin.html

BH Electronics, Inc.

500-1749

952-894-9590

www.bhelectronics.com/PDFs/DC-

DCConverterTransformers.pdf

Coilcraft, Inc.

U6982-C

800-322-2645

44-1236-730595

www.coilcraft.com/minitrans.cfm

7825355

1500V

Newport/C&D Technologies

7625335

4000V

520-295-4300

www.dc-dc.com/products/productline.asp?ED=9

Midcom, Inc.

95061

1250V

605-886-4385

www.midcom-inc.com

PCA Electronics, Inc.

EPC3115S-5

700V DC

818-894-5791

www.pca.com/Datasheets/EPC3117S-X.pdf

Rhombus Industries, Inc.

T-1110

714-898-0960

www.rhombus-ind.com/pt-cat/maxim.pdf

Premier Magnetics, Inc.

PM-SM15

949-452-0511

www.premiermag.com/pdf/pmsm15.pdf