10

When using minimum required capacitor values, make sure

that capacitor values do not degrade excessively with

temperature. If in doubt, use capacitors with a larger nominal

value. The capacitor’s equivalent series resistance (ESR)

usually rises at low temperatures and it influences the

amount of ripple on V+ and V-.

Power Supply Decoupling

adequate. In applications that are particularly sensitive to

Connect the bypass capacitor as close as possible to the IC.

Operation Down to 2.7V

typically ensure inter operability with RS-232 devices.

Transmitter Outputs when Exiting

Powerdown

Figure 10 shows the response of two transmitter outputs

when exiting powerdown mode. As they activate, the two

transmitter outputs properly go to opposite RS-232 levels,

with no glitching, ringing, nor undesirable transients. Each

transmitter is loaded with 3k

Ω in parallel with 2500pF. Note

that the transmitters enable only when the magnitude of the

supplies exceed approximately 3V.

High Data Rates

transmitter output voltages even at high data rates. Figure

11 details a transmitter loopback test circuit, and Figure 12

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 13 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.

TIME (20µs/DIV.)

T1

T2

2V/DIV

5V/DIV

FORCEOFF

FIGURE 10. TRANSMITTER OUTPUTS WHEN EXITING

POWERDOWN

C1 - C4 = 0.1µF

FIGURE 12. LOOPBACK TEST AT 120kbps

FIGURE 13. LOOPBACK TEST AT 250kbps

ICL3238E

FORCEOFF

+

+

+

+

1000pF

V+

V-

5k

C1+

C1-

C2+

C2-

+

0.1µF

FORCEON

FIGURE 11. TRANSMITTER LOOPBACK TEST CIRCUIT

5µs/DIV.

5V/DIV.

C1 - C4 = 0.1µF

2µs/DIV.

5V/DIV.

C1 - C4 = 0.1µF

ICL3238E