9

FN6045.2

April 13, 2007

Operation Down to 2.7V

typically ensure inter operability with RS-232 devices.

High Data Rates

transmitter output voltages even at high data rates. Figure 9

details a transmitter loopback test circuit, and Figure 10

illustrates the loopback test result at 120kBps. For this test,

all transmitters were simultaneously driving RS-232 loads in

parallel with 1000pF, at 120kBps. Figure 11 shows the

loopback results for a single transmitter driving 1000pF and

an RS-232 load at 250kBps. The static transmitters were

also loaded with an RS-232 receiver.

Interconnection with 3V and 5V Logic

The ISL422XE directly interface with 5V CMOS and TTL

logic families. Nevertheless, with the ISL422XE at 3.3V, and

the logic supply at 5V, AC, HC, and CD4000 outputs can

drive ISL422XE inputs, but ISL422XE outputs do not reach

more information.

FIGURE 9. TRANSMITTER LOOPBACK TEST CIRCUIT

TIME (20

μs/DIV.)

T1

T2

2V/DIV.

5V/DIV.

FORCEOFF

FIGURE 8. TRANSMITTER OUTPUTS WHEN EXITING

POWERDOWN

C1 - C4 = 0.1

μF

ISL422XE

FORCEOFF

+

+

+

+

1000pF

V+

V-

5k

C1+

C1-

C2+

C2-

+

0.1

μF

FORCEON

FIGURE 10. LOOPBACK TEST AT 120kBps

FIGURE 11. LOOPBACK TEST AT 250kBps

TABLE 3.

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. ISL422XE

outputs are incompatible with AC,

HC, and CD4000 CMOS inputs.

5

μs/DIV.

5V/DIV.

C1 - C4 = 0.1

μF

2

μs/DIV.

5V/DIV.

C1 - C4 = 0.1

μF

ISL4221E, ISL4223E