8
Detailed Description
These ICL32XXE interface ICs operate from a single +3V 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. The circuit is divided into three sections: The
charge pump, the transmitters, and the 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 0.1µF 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.
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 (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 1Mbps.
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, but only the ICL3244E receivers can three-state,
via the FORCEOFF
control line. Additionally, the ICL3244E
includes a noninverting (monitor) receiver (denoted by the
R
OUTB
label) that is always active, regardless of the state of
any control lines. Both receiver types 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.
Receiver Skew t
PHL
- t
PLH
25 - 50 - ns
Transition Region Slew Rate V
CC
=3.3V,
R
L
=3kΩ to 7kΩ,
Measured From 3V to -3V or -3V
to 3V
C
L
= 150pF to 1000pF 25 6 - 30 V/µs
C
L
= 150pF to 2500pF 25 4 8 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 - ±3-kV
NOTE:
2. An “edge” is defined as a transition through the transmitter or receiver input thresholds.
Electrical Specifications Test Conditions: V
CC
= 3V to 5.5V, C
1
- C
4
= 0.1µF; Unless Otherwise Specified.
Typicals are at T
A
= 25°C (Continued)
PARAMETER TEST CONDITIONS
TEMP
(°C) MIN TYP MAX UNITS
R
XOUT
GND ≤ V
ROUT
≤ V
CC
5kΩ
R
XIN
-25V ≤ V
RIN
≤ +25V
GND
V
CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
ICL3224E, ICL3226E, ICL3244E
