12
FN4878.8
February 27, 2006
High Data Rates
The ICL32XX maintain the RS-232 ±5V minimum transmitter
output voltages even at high data rates. Figure 12 details a
transmitter loopback test circuit, and Figure 13 illustrates the
loopback test result at 250kbps. For this test, all transmitters
were simultaneously driving RS-232 loads in parallel with
1000pF, at 250kbps. Figure 14 shows the 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 ICL32XXE directly interfaces with 5V CMOS and TTL
logic families. Nevertheless, with the ICL32XX at 3.3V, and
the logic supply at 5V, AC, HC, and CD4000 outputs can
drive ICL32XX inputs, but ICL32XX outputs do not reach the
minimum VIH for these logic families. See Table 4 for more
information.
FIGURE 12. TRANSMITTER LOOPBACK TEST CIRCUIT
FIGURE 13. LOOPBACK TEST AT 250kbps (CL = 1000pF)
ICL32XX
VCC
C1
C2
C4
C3
+
CL
V+
V-
5K
TIN
ROUT
C1+
C1-
C2+
C2-
RIN
TOUT
+
VCC
0.1
F
VCC
FORCEOFF
FORCEON
T1IN
T1OUT
R1OUT
2
s/DIV.
VCC = +3.3V
5V/DIV.
C1 - C4 = 0.1
F
FIGURE 14. LOOPBACK TEST AT 1Mbps (CL = 250pF)
TABLE 4. LOGIC FAMILY COMPATIBILITY WITH VARIOUS
SUPPLY VOLTAGES
SYSTEM
POWER-SUPPLY
VOLTAGE
(V)
VCC
SUPPLY
VOLTAGE
(V)
COMPATIBILITY
3.3
Compatible with all CMOS
families.
5
Compatible with all TTL and
CMOS logic families.
5
3.3
Compatible with ACT and HCT
CMOS, and with TTL. ICL32XX
outputs are incompatible with AC,
HC, and CD4000 CMOS inputs.
T1IN
T1OUT
R1OUT
0.5
s/DIV.
5V/DIV.
VCC = +3.3V
C1 - C4 = 0.1
F
ICL3225, ICL3245