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|Description||1 Microamp Supply-Current, +3V to +5.5V, 250kbps, RS-232 Transmitters/Receivers|
|ICL3221CA Datasheet PDF : 28 Pages |
ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243
ICL32XX 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:
charge pump, transmitters and receivers.
Intersil’s new ICL32XX family utilizes regulated on-chip dual
charge pumps as voltage doublers, and voltage inverters to
generate ±5.5V transmitter supplies from a VCC 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 VCC = 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.
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 ICL3232, 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 (3kΩ and 1000pF), VCC ≥ 3.0V, with one
transmitter operating at full speed. Under more typical
conditions of VCC ≥ 3.3V, RL = 3kΩ, and CL = 250pF, one
transmitter easily operates at 900kbps.
Transmitter inputs float if left unconnected, and may cause
ICC increases. Connect unused inputs to GND for the best
All the ICL32XX devices contain standard inverting receivers
that three-state (except for the ICL3232) via the EN or
FORCEOFF control lines. Additionally, the two ICL324X
products include noninverting (monitor) receivers (denoted
by the ROUTB 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 (VCC = 0V). The
receivers’ Schmitt trigger input stage uses hysteresis to
increase noise immunity and decrease errors due to slow
input signal transitions.
The ICL3221/22/23/41 inverting receivers disable only when
EN is driven high. ICL3243 receivers disable during forced
(manual) powerdown, but not during automatic powerdown
(See Table 2).
ICL324X 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
-25V ≤ VRIN ≤ +25V
GND ≤ VROUT ≤ VCC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
Low Power Operation
These 3V devices require a nominal supply current of
0.3mA, even at VCC = 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 ICL3221/22/32 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 Icc and wide
operating supply range, make the ICL32XX 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 ICL32XX should work in most 5V applications.
When replacing a device in an existing 5V application, it is
acceptable to terminate C3 to VCC as shown on the Typical
Operating Circuit. Nevertheless, terminate C3 to GND if
possible, as slightly better performance results from this
Powerdown Functionality (Except ICL3232)
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 VCC, 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.
March 1, 2006
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