ICL3310 Datasheet, PDF (5/9 Pages) Intersil Corporation – +3V to +5.5V, 1 Microamp, 250kbps, RS-232 Transmitter/Receiver

ICL3310
Transmitter inputs float if left unconnected (there are no pull-
up resistors), and may cause I_CC increases. Connect
unused inputs to GND for the best performance.
TABLE 2. POWERDOWN AND ENABLE LOGIC TRUTH TABLE
SHDN TRANSMITTER RECEIVER
INPUT OUTPUTS OUTPUTS MODE OF OPERATION
H
Active
Active Normal Operation
L
High-Z
High-Z Manual Powerdown
Receivers
The ICL3310 contains standard inverting receivers that
three-state via the SHDN control line. Receivers driving
powered down peripherals must be disabled to prevent
current flow through the peripheral’s protection diodes (see
Figures 2 and 3).
All the receivers convert RS-232 signals to CMOS output
levels and accept inputs up to ±30V 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.
V_CC
R_XIN
-25V ≤ V_RIN ≤ +25V
5kΩ
GND
R_XOUT
GND ≤ V_ROUT ≤ V_CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
Low Power Operation
This 3V device requires 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 11mA
current required by comparable 5V RS-232 devices,
allowing users to reduce system power simply by replacing
the old style device with the ICL3310.
Low Power, Pin Compatible Replacement
Pin compatibility with existing 5V products (e.g., MAX222),
coupled with the wide operating supply range, make the
ICL3310 a potential lower power, higher performance drop-
in replacement for existing 5V applications. As long as the
±5V RS-232 output swings are acceptable, and transmitter
pull-up resistors aren’t required, the ICL3310 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 Circuit”. Nevertheless, terminate C₃ to GND if
possible, as slightly better performance results from this
configuration.
Powerdown Functionality
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 and receiver outputs three-state. This
micro-power mode makes these devices ideal for battery
powered and portable applications.
Software Controlled (Manual) Powerdown
The ICL3310 may be forced into its low power, standby state
via a simple shutdown (SHDN) pin (see Figure 4). Driving
this pin high enables normal operation, while driving it low
forces the IC into it’s powerdown state. The time required to
exit powerdown, and resume transmission is less than 50µs.
Connect SHDN to V_CC if the powerdown function isn’t
needed.
V_CC
V_CC
V_CC
CURRENT
FLOW
V_OUT = V_CC
Rx
POWERED
DOWN
UART
GND
Tx
SHDN = GND
OLD
RS-232 CHIP
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
V_CC
TRANSITION
DETECTOR
TO
WAKE-UP
LOGIC
V_CC
ICL3310
V-
R_X
POWERED
DOWN
UART _TX
V_OUT = HI-Z
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
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