ICL3221EM_14 Datasheet, PDF (6/12 Pages) Intersil Corporation – ±15kV ESD Protected, +3V, 1μA, 250kbps, RS-232 Transmitters/Receivers

ISL3221EM
Detailed Description
ICL3221EM interface ICs operate from a single +3V
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.
Charge-Pump
Intersil’s ICL3221EM 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 “Capacitor Selection” on page 9 and
Table 3 on page 9 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.
The transmitter output disables and assumes a high
impedance state when the device enters the power-down
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 900kbps.
Transmitter inputs float if left unconnected, and may
cause I_CC increases. Connect unused inputs to GND for
the best performance.
Receivers
The ICL3221EM device contains standard inverting
receiver that three-state via the EN or FORCEOFF
control lines. The receivers convert RS-232 signals to
CMOS output levels and accept inputs up to ±25V while
presenting the required 3kW to 7kW 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 ICL3221EM’s inverting receiver is disabled only when
EN is driven high (see Table 2).
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.
V_CC
R_XIN
-25V ≤ V_RIN ≤ +25V
GND
5kΩ
R_XOUT
GND ≤ V_ROUT ≤ V_CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
Low Power Operation
These 3V devices require a nominal supply current of
0.3mA, during normal operation (not in power-down
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 ICL3221EM is pin compatible with existing 5V
RS-232 transceivers - See the “Features” section on
page 1 for details.
This pin compatibility coupled with the low I_CC and wide
operating supply range, make the ICL3221EM 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 ICL3221EM should
work in most 5V applications.
When replacing a device in an existing 5V application, it
is acceptable to terminate C₃ to V_CC as shown on the
“Typical Operating Circuits” on page 3. Nevertheless,
terminate C₃ to GND if possible, as slightly better
performance results from this configuration.
Power-down Functionality
The already low current requirement drops significantly
when the device enters power-down mode. In
power-down, 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 power-down; refer to Table 2 for details. This
micro-power mode makes these devices ideal for battery
powered and portable applications.
Software Controlled (Manual) Power-down
The ICL3221EM device provides a pin that allows the
user to force the IC into the low power, standby state.
Driving this pin high enables normal operation, while
driving it low forces the IC into its power-down state.
Connect SHDN to V_CC if the power-down function isn’t
needed. Note that all the receiver outputs remain
enabled during shutdown (see Table 2). For the lowest
power consumption during power-down, the receivers
should also be disabled by driving the EN input high (see
next section, and Figures 2 and 3).
6
FN7552.0
December 17, 2009