ISL4270E Datasheet, PDF (10/13 Pages) Intersil Corporation – QFN Packaged, ±15kV ESD Protected, +3V to +5.5V, 300nA, 250kbps, RS-232 Transceivers with Enhanced Automatic Powerdown and a Separate Logic Supply

ISL4270E
5V/DIV
FORCEOFF
5V/DIV.
T1
T1_IN
2V/DIV
T2
V_CC = +3.3V
C1 - C4 = 0.1μF
TIME (20μs/DIV.)
FIGURE 8. TRANSMITTER OUTPUTS WHEN EXITING
POWERDOWN
High Data Rates
The ISL4270E maintains the RS-232 ±5V minimum
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.
V_CC
0.1μF
+
+
C₁
+
C₂
V_CC
C1+
V_CC
V_{L V+}
C1-
ISL4270E
C2+
V-
C2-
T_IN
T_OUT
R_OUT
R_IN
FORCEON
5K
FORCEOFF
+
C₃
+C⁴
1000pF
FIGURE 9. TRANSMITTER LOOPBACK TEST CIRCUIT
T1_OUT
R1_OUT
V_CC = +3.3V
C1 - C4 = 0.1μF
5μs/DIV.
FIGURE 10. LOOPBACK TEST AT 120kbps
5V/DIV.
T1_IN
T1_OUT
R1_OUT
V_CC = +3.3V
C1 - C4 = 0.1μF
2μs/DIV.
FIGURE 11. LOOPBACK TEST AT 250kbps
Interconnection with 3V and 5V Logic
Standard 3.3V powered RS-232 devices interface well with
3V and 5V powered TTL compatible logic families (e.g., ACT
and HCT), but the logic outputs (e.g., R_OUTS) fail to reach
the V_IH level of 5V powered CMOS families like HC, AC, and
CD4000. The ISL4270E V_L supply pin solves this problem.
By connecting V_L to the same supply (1.8V to 5V) powering
the logic device, the ISL4270E logic outputs will swing from
GND to the logic V_CC.
10
FN6041.2
June 16, 2010