8

details a transmitter loopback test circuit, and Figure 6

illustrates the standard speed loopback test result for a

single transmitter driving 1000pF and an RS-232 load at

250kbps. Figure 7 shows the megabaud loopback results for

a single transmitter driving 250pF and an RS-232 load at

1Mbps. The static transmitters were also loaded with an

RS-232 receiver.

Interconnection with 3V and 5V Logic

The ICL3237 directly interfaces with most 5V logic families,

including ACT and HCT CMOS. See Table 4 for more

information on possible combinations of interconnections.

FIGURE 5. TRANSMITTER LOOPBACK TEST CIRCUIT

TIME (20

µs/DIV.)

T1

T2

2V/DIV.

5V/DIV.

SHDN

FIGURE 4. TRANSMITTER OUTPUTS WHEN EXITING

POWERDOWN

C1 - C4 = 0.1

µF

ICL3237

+

+

+

+

V+

V-

5K

C1+

C1-

C2+

C2-

+

0.1

µF

EN

SHDN

MBAUD

TABLE 4. LOGIC FAMILY COMPATIBILITY WITH VARIOUS

SUPPLY VOLTAGES

SYSTEM

POWER-SUPPLY

VOLTAGE

(V)

SUPPLY

VOLTAGE

(V)

COMPATIBILITY

3.3

3.3

Compatible with all CMOS

families.

5

5

Compatible with all TTL and

CMOS logic families.

5

3.3

Compatible with ACT and HCT

CMOS, and with TTL.

Incompatible with AC, HC, or

CD4000 CMOS.

2

µs/DIV.

5V/DIV.

C1 - C4 = 0.1

µF

MBAUD = GND

0.5

µs/DIV.

5V/DIV.

C1 - C4 = 0.1

µF

ICL3237