
10
FN4910.18
March 8, 2005
Detailed Description
ICL32XXE interface ICs operate from a single +3V to +5.5V 
supply, guarantee a 250kbps minimum data rate, require 
only four small external 0.1
μ
F capacitors, feature low power 
consumption, and meet all ElA RS-232C and V.28 
specifications. The circuit is divided into three sections: 
charge pump, transmitters and receivers.
Charge-Pump
Intersil’s new ICL32XXE family utilizes 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 these devices 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 0.1
μ
F capacitors 
for the voltage doubler and inverter functions at V
CC
 = 3.3V. 
See the “Capacitor Selection” section, and Table 3 for 
capacitor recommendations for other operating conditions. 
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.
Except for the ICL3232E, all transmitter outputs disable and 
assume a high impedance state when the device enters the 
powerdown mode (see Table 2). These outputs may be 
driven to 
±
12V when disabled.
All devices guarantee a 250kbps data rate for full load 
conditions (3k
 and 1000pF), V
CC
≥
 3.0V, with one 
transmitter operating at full speed. Under more typical 
conditions of V
CC
≥
 3.3V, R
L
 = 3k
, 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 ICL32XXE devices contain standard inverting 
receivers that three-state (except for the ICL3232E) via the 
EN or FORCEOFF control lines. Additionally, the two 
ICL324XE 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 3k
 to 7k
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 ICL3221E, ICL3222E, ICL3223E, ICL3241E inverting 
receivers disable only when EN is driven high. ICL3243E 
receivers disable during forced (manual) powerdown, but not 
during automatic powerdown (see Table 2).
ICL3241E and ICL3243E monitor receivers remain active 
even during manual powerdown and forced receiver disable, 
making them extremely useful for Ring Indicator monitoring. 
Standard receivers driving powered down peripherals must be 
disabled to prevent current flow through the peripheral’s 
protection diodes (see Figures 2 and 3). This renders them 
useless for wake up functions, but the corresponding monitor 
receiver can be dedicated to this task as shown in Figure 3.
Low Power Operation
These 3V devices require a nominal supply current of 
0.3mA, even at V
CC
= 5.5V, during normal operation (not in 
powerdown mode). This is considerably less than the 5mA 
to 11mA current required by comparable 5V RS-232 devices, 
allowing users to reduce system power simply by switching 
to this new family.
Pin Compatible Replacements for 5V Devices
The ICL3221E, ICL3222E, ICL3232E are pin compatible 
with existing 5V RS-232 transceivers - see the 
Features
section on the front page for details.
This pin compatibility coupled with the low I
CC
 and wide 
operating supply range, make the ICL32XXE potential lower 
power, higher performance drop-in replacements for existing 
5V applications. As long as the 
±
5V RS-232 output swings 
are acceptable, and transmitter input pull-up resistors aren’t 
required, the IICL32XXE should work in most 5V 
applications.
When replacing a device in an existing 5V application, it is 
acceptable to terminate C
3
 to V
CC
 as shown on the 
Typical 
Operating Circuit
. Nevertheless, terminate C
3
 to GND if 
possible, as slightly better performance results from this 
configuration. 
Powerdown Functionality 
(Except ICL3232E)
The already low current requirement drops significantly 
when the device enters powerdown mode. In powerdown, 
supply current drops to 1μA, because the on-chip charge 
pump turns off (V+ collapses to V
CC
, V- collapses to GND), 
and the transmitter outputs three-state. Inverting receiver 
outputs may or may not disable in powerdown; refer to 
Table 2 for details. This micro-power mode makes these 
devices ideal for battery powered and portable applications.
R
XOUT
GND 
≤
 V
ROUT
≤
 V
CC
5k
R
XIN
-25V 
≤
 V
RIN
≤
 +25V
GND
V
CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
ICL3221E, ICL3222E, ICL3223E, ICL3232E, ICL3241E, ICL3243E