ISL4238E Intersil Corporation, ISL4238E Datasheet - Page 13

• Manufacturer Part Number: ISL4238E
• Description: QFN Packaged, 15kV Esd Protected, +2.7V to +5.5V, 10Nanoamp, 250kbps/ 1Mbps, RS-232 Transceivers With Enhanced Automatic Powerdown
• Manufacturer: Intersil Corporation

Mouse Driveability
The ISL424XE are specifically designed to power a serial
mouse while operating from low voltage supplies. Figure 11
shows the transmitter output voltages under increasing load
current. The on-chip switching regulator ensures the
transmitters will supply at least
conditions (15mA for paralleled V+ transmitters, 7.3mA for
single V- transmitter).
High Data Rates
The ISL4238E/4XE maintain the RS-232
transmitter output voltages even at high data rates. Figure
12 details a transmitter loopback test circuit, and Figure 13
illustrates the ISL4238E/44E loopback test result at
120kbps. For this test, all transmitters were simultaneously
driving RS-232 loads in parallel with 1000pF, at 120kbps.
Figure 14 shows the ISL4238E/44E loopback results for a
single transmitter driving 1000pF and an RS-232 load at
250kbps. Figure 15 illustrates the ISL4245E loopback test
result at 250kbps. For this test, all transmitters were
simultaneously driving RS-232 loads in parallel with 1000pF,
at 250kbps. Figure 16 shows the ISL4245E loopback results
5V/DIV
2V/DIV
FIGURE 10. TRANSMITTER OUTPUTS WHEN EXITING
FIGURE 11. TRANSMITTER OUTPUT VOLTAGE vs LOAD
-1
-2
-3
-4
-5
-6
6
5
4
3
2
1
0
0
V
C1 - C4 = 0.1µF
V
CC
CC
1
= +3.3V
POWERDOWN
CURRENT (PER TRANSMITTER, i.e., DOUBLE
CURRENT AXIS FOR TOTAL V
FORCEOFF
LOAD CURRENT PER TRANSMITTER (mA)
V
T1
T2
T3
CC
2
= 3.0V
3
ISL424XE
V
V
OUT
OUT
TIME (20µs/DIV.)
4
+
-
13
±
5V during worst case
5
6
±
7
5V minimum
OUT+
ISL4238E, ISL4244E, ISL4245E
V
V
OUT
OUT
8
CURRENT)
+
-
T2
T1
9
10
for a single transmitter driving 250pF and an RS-232 load at
1Mbps. The static transmitters were also loaded with an
RS-232 receiver.
5V/DIV.
5V/DIV.
R1
T1
R1
T1
FIGURE 13. ISL4238E/44E LOOPBACK TEST AT 120kbps
FIGURE 14. ISL4238E/44E LOOPBACK TEST AT 250kbps
T1
FIGURE 12. TRANSMITTER LOOPBACK TEST CIRCUIT
OUT
OUT
T1
OUT
OUT
IN
IN
V
V
C
C
CC
CC
1
2
V
C1 - C4 = 0.1µF
V
C1 - C4 = 0.1µF
+
+
CC
CC
= +3.3V
= +3.3V
0.1µF
C1+
C1-
C2+
C2-
T
R
FORCEON
FORCEOFF
IN
OUT
+
(C
L
ISL4238E/4XE
= 1000pF)
V
CC
5µs/DIV.
2µs/DIV.
T
OUT
R
V+
5k
V-
IN
+
+
C
C
C
3
4
L