ICL3221 INTERSIL [Intersil Corporation], ICL3221 Datasheet - Page 11

• Manufacturer Part Number: ICL3221
• Description: 1 Microamp Supply-Current, +3V to +5.5V, 250kbps, RS-232 Transmitters/Receivers
• Manufacturer: INTERSIL [Intersil Corporation]

Detailed Description
ICL32XX interface ICs operate from a single +3V to +5.5V
supply, guarantee a 250kbps minimum data rate, require
only four small external 0.1 F 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 ICL32XX family utilizes regulated on-chip dual
charge pumps as voltage doublers, and voltage inverters to
generate 5.5V transmitter supplies from a V
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 F capacitors for the
voltage doubler and inverter functions at V
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 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 (3k and 1000pF), V
transmitter operating at full speed. Under more typical
conditions of V
transmitter easily operates at 900kbps.
Transmitter inputs float if left unconnected, and may cause
I
performance.
Receivers
All the ICL32XX devices contain standard inverting receivers
that tristate (except for the ICL3232) via the EN or
FORCEOFF control lines. Additionally, the two ICL324X
products include noninverting (monitor) receivers (denoted
by the R
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
receivers’ Schmitt trigger input stage uses hysteresis to
increase noise immunity and decrease errors due to slow
input signal transitions.
CC
increases. Connect unused inputs to GND for the best
OUTB
label) that are always active, regardless of the
CC
3.3V, R
3-11
L
= 3k , and C
CC
3.0V, with one
CC
CC
L
= 0V). The
= 250pF, one
CC
= 3.3V. See
supply as
ICL3221 thru ICL3243
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 Figure 3.
Powerdown Functionality (Except
ICL3232)
This 3V family of RS-232 interface devices requires a
nominal supply current of 0.3mA during normal operation
(not in powerdown mode). This is considerably less than the
5mA to 11mA current required of 5V RS-232 devices. The
already low current requirement drops significantly when the
device enters powerdown mode. In powerdown, supply
current drops to 1 A, because the on-chip charge pump
turns off (V+ collapses to V
the transmitter outputs tristate. 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.
Software Controlled (Manual) Powerdown
Most devices in the ICL32XX family provide pins that allow
the user to force the IC into the low power, standby state.
On the ICL3222 and ICL3241, the powerdown control is via
a simple shutdown (SHDN) pin. Driving this pin high enables
normal operation, while driving it low forces the IC into it’s
powerdown state. Connect SHDN to V
function isn’t needed. Note that all the receiver outputs
remain enabled during shutdown (see Table 2). For the
lowest power consumption during powerdown, the receivers
should also be disabled by driving the EN input high (see
next section, and Figures 2 and 3).
The ICL3221, ICL3223, and ICL3243 utilize a two pin
approach where the FORCEON and FORCEOFF inputs
determine the IC’s mode. For always enabled operation,
FORCEON and FORCEOFF are both strapped high. To
switch between active and powerdown modes, under logic or
software control, only the FORCEOFF input need be driven.
FIGURE 1. INVERTING RECEIVER CONNECTIONS
-25V
V
RIN
R
GND
V
XIN
CC
+25V
5k
CC
, V- collapses to GND), and
GND
CC
R
if the powerdown
XOUT
V
ROUT
V
CC