Transmitter Outputs when

Exiting Shutdown

Figure 7 shows a transmitter output when exiting shut-

down mode. The transmitter is loaded with 3kΩ in par-

allel with 1000pF. The transmitter output displays no

ringing or undesirable transients as it comes out of

shutdown, and is enabled only when the magnitude of

V- exceeds approximately -3V.

High Data Rates

The MAX3228E/AE and MAX3229E/AE maintain the RS-

232 ±5.0V minimum transmitter output voltage even at

high data rates. Figure 8 shows a transmitter loopback

test circuit. Figure 9 shows a loopback test result at

120kbps, and Figure 10 shows the same test at 250kbps.

For Figure 9, the transmitter was driven at 120kbps into

an RS-232 load in parallel with 1000pF. For Figure 10, a

single transmitter was driven at 250kbps, and loaded

with an RS-232 receiver in parallel with 1000pF.

Figure 8. Transmitter Loopback Test Circuit

MAX3229E/AE

5k

Ω

R1IN

R1OUT

C2-

C2+

C1-

C1+

V-

V+

C4

C3

C1

C2

0.1

μF

0.1

μF

FORCEOFF

FORCEON

INVALID

T1OUT

T1IN

GND

TO POWER-

MANAGEMENT UNIT

1000pF

Figure 9. Loopback Test Result at 120kbps

0

R_OUT

T_OUT

T_IN

-5V

5V

0

5V

5V

0

4

μs/div

Figure 10. Loopback Test Result at 250kbps

0

-5V

5V

0

5V

5V

0

R_OUT

T_OUT

T_IN

4

μs/div

Figure 7. Transmitter Outputs Exiting Shutdown or Powering Up

FORCEON =

FORCEOFF

TOUT

4

μs/div

0

2V/div

0

5V/div

±15kV ESD-Protected +2.5V to +5.5V

RS-232 Transceivers in UCSP and WLP

______________________________________________________________________________________

11