ICL3207_05 Datasheet, PDF (6/11 Pages) Intersil Corporation – Low Power, +3V to +5.5V, 250kbps, RS-232 Transmitters/Receivers

ICL3207, ICL3217
Receivers
The ICL32X7 each contain inverting receivers that 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.
Receivers on the ICL3207 are always active. The ICL3217
receivers disable when in the automatic powerdown state,
thereby eliminating the possible current path through a
shutdown peripheral’s input protection diode (see Figures 2
and 3).
V_CC
R_XIN
-25V ≤ V_RIN ≤ +25V
5kΩ
GND
R_XOUT
GND ≤ V_ROUT ≤ V_CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
V_CC
V_CC
V_CC
CURRENT
FLOW
Rx
POWERED
DOWN
UART
Tx
GND
V_OUT = V_CC
SHDN = GND
OLD
RS-232 CHIP
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
Low Power Operation
These 3V devices require 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 ICL3207.
Low Power, Pin Compatible Replacement
Pin compatibility with existing 5V products (e.g., MAX207),
coupled with the wide operating supply range, make the
ICL32X7 potential lower power, higher performance drop-in
replacements for existing ‘2X7 5V applications. As long as
the ±5V RS-232 output swings are acceptable, the ICL32X7
devices should work in most 5V applications.
V_CC
TRANSITION
DETECTOR
TO
WAKE-UP
LOGIC
V_CC
ICL3217
V-
R_X
POWERED
DOWN
UART _TX
V_OUT = HI-Z*
* IN AUTOMATIC
POWERDOWN
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
When replacing a ‘207 or ‘237 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.
Automatic Powerdown (ICL3217 Only)
Even greater power savings is available by using the
ICL3217 which features an automatic powerdown function.
When no valid RS-232 voltages (see Figure 4) are sensed
on any receiver input for 30µs, the ICL3217 automatically
enters its powerdown state (see Figure 5). 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 receiver and transmitter outputs three-state (see
Table 2). This micro-power mode makes the ICL3217 ideal
for battery powered and portable applications. Invalid
receiver levels occur whenever the driving peripheral’s
outputs are shut off (powered down) or when the RS-232
interface cable is disconnected. The ICL3217 powers back
up whenever it detects a valid RS-232 voltage level on any
receiver input (such as when the RS-232 cable is
reconnected). The time to recover from automatic powerdown
mode is typically 100µs.
TABLE 2. ICL3217 AUTOMATIC POWERDOWN OPERATION
RS-232 SIGNAL
PRESENT AT
RECEIVER
INPUT?
MODE
TRANSMITTER RECEIVER
OF
OUTPUTS OUTPUTS OPERATION
YES
Active
Active Normal
Operation
NO
High-Z
High-Z Powerdown
Due to Auto
Powerdown
Logic
6