7
FN8037.7
June 10, 2010
Detailed Description
The ISL4241E and ISL4243E both operate from a single
+2.7V to +5.5V supply, guarantee a 250kbps minimum data
rate, require only four small external 0.1µF capacitors,
feature low power consumption, and meet all ElA RS-232C
and V.28 specifications even with V
CC
= 3.0V. The circuit is
divided into three sections: The charge pump, the
transmitters, and the receivers.
Charge-Pump
Intersil’s new ISL4241E, ISL4243E devices utilize regulated
on-chip dual charge pumps as voltage doublers, and voltage
inverters to generate ±5.5V transmitter supplies from a V
CC
supply as low as 3.0V. This allows them to maintain RS-232
compliant output levels over the ±10% tolerance range of
3.3V powered systems. The efficient on-chip power supplies
require only four small, external 0.1µF capacitors for the
voltage doubler and inverter functions. The charge pumps
operate discontinuously (i.e., they turn off as soon as the V+
and V- supplies are pumped up to the nominal values),
resulting in significant power savings.
Transmitters
The transmitters are proprietary, low dropout, inverting
drivers that translate TTL/CMOS inputs to EIA/TIA-232
output levels. Coupled with the on-chip ±5.5V supplies,
these transmitters deliver true RS-232 levels over a wide
range of single supply system voltages.
All transmitter outputs disable and assume a high
impedance state when the device enters the power-down
mode (see Table 2). These outputs may be driven to ±12V
when disabled.
The devices guarantee a 250kbps data rate for full load
conditions (3kΩ and 1000pF), V
CC
≥ 3.0V, with one
transmitter operating at full speed. Under more typical
conditions of V
CC
≥ 3.3V, R
L
= 3kΩ, and C
L
= 250pF, one
transmitter easily operates at 900kbps.
Transmitter inputs float if left unconnected, and may cause
I
CC
increases. Connect unused inputs to GND for the best
performance.
Receivers
All the ISL4241E, ISL4243E’s devices contain standard
inverting receivers that are three-state via the EN
or
FORCEOFF
control lines. Additionally, the ISL4241E,
ISL4243E’s products include noninverting (monitor)
receivers (denoted by the R
OUTB
label) that are always
active, regardless of the state of any control lines. All the
receivers convert RS-232 signals to CMOS output levels and
accept inputs up to ±25V while presenting the required 3kΩ
to 7kΩ input impedance (see Figure 1) even if the power is
off (V
CC
= 0V). The receivers’ Schmitt trigger input stage
uses hysteresis to increase noise immunity and decrease
errors due to slow input signal transitions.
The ISL4241E inverting receivers disable only when EN
is
driven high. ISL4243E receivers disable during forced
(manual) power-down, but not during automatic power-down
(see Table 2).
Transition Region Slew Rate V
CC
= 3V to 3.6V, R
L
= 3kΩ to 7kΩ,
Measured From 3V to -3V or -3V to 3V
C
L
= 150pF to
2500pF
25 4 9 30 V/µs
Full 4 8 30 V/µs
C
L
= 150pF to
1000pF
25 6 11 30 V/µs
Full 6 10 30 V/µs
ESD PERFORMANCE
RS-232 Pins (T
OUT
, R
IN
) Human Body Model 25 - ±15 - kV
IEC61000-4-2 Contact Discharge 25 - ±8 - kV
IEC61000-4-2 Air Gap Discharge 25 - ±15 - kV
All Other Pins Human Body Model 25 - ±2 - kV
NOTE:
3. Transmitter skew is measured at the transmitter zero crossing points.
4. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature limits established by characterization
and are not production tested.
Electrical Specifications Test Conditions: V
CC
= 3V to 5.5V, C
1
to C
4
= 0.1µF; Unless Otherwise Specified.
Typicals are at T
A
= +25°C (Continued)
PARAMETER TEST CONDITIONS
TEMP
(°C)
MIN
(Note 4) TYP
MAX
(Note 4) UNITS
R
XOUT
GND ≤ V
ROUT
≤ V
CC
5kΩ
R
XIN
-25V ≤ V
RIN
≤ +25V
GND
V
CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
ISL4241E, ISL4243E
