![](http://datasheet.mmic.net.cn/Intersil/ICL3237EIA-T_datasheet_97462/ICL3237EIA-T_7.png)
7
Receiver ENABLE Control
This device also features an EN input to control the receiver
outputs. Driving EN high disables all the inverting (standard)
receiver outputs placing them in a high impedance state.
This is useful to eliminate supply current, due to a receiver
output forward biasing the protection diode, when driving the
input of a powered down (VCC = GND) peripheral (see
Figure 2). The enable input has no effect on transmitter nor
monitor (ROUTB) outputs.
MegaBaud Selection
In normal operating mode (MBAUD = GND), the ICL3237E
transmitters guarantee a 250kbps data rate with worst-case
loads of 3k
in parallel with 1000pF. This provides
compatibility with PC-to-PC communication software, such
as Laplink.
For higher speed serial communications, the ICL3237E
features MegaBaud operation. In MegaBaud operating mode
(MBAUD = VCC), the ICL3237E transmitters guarantee a
1Mbps data rate with worst-case loads of 3k
in parallel with
250pF for 3.0V < VCC < 4.5V. For 5V ±10% operation, the
ICL3237E transmitters guarantee a 1Mbps data rate with
worst-case loads of 3k
in parallel with 1000pF.
Capacitor Selection
The charge pumps require 0.1
F capacitors for 3.3V (5%
tolerance) operation. For other supply voltages refer to Table
3 for capacitor values. Do not use values smaller than those
listed in Table 3. Increasing the capacitor values (by a factor
of 2) reduces ripple on the transmitter outputs and slightly
reduces power consumption. C2, C3, and C4 can be
increased without increasing C1’s value, however, do not
increase C1 without also increasing C2, C3, and C4 to
maintain the proper ratios (C1 to the other capacitors).
When using minimum required capacitor values, make sure
that capacitor values do not degrade excessively with
temperature. If in doubt, use capacitors with a larger nominal
value. The capacitor’s equivalent series resistance (ESR)
usually rises at low temperatures and it influences the
amount of ripple on V+ and V-.
Power Supply Decoupling
In most circumstances a 0.1
F bypass capacitor is
adequate. In applications that are particularly sensitive to
power supply noise, decouple VCC to ground with a
capacitor of the same value as the charge-pump capacitor C1.
Connect the bypass capacitor as close as possible to the IC.
TABLE 2. POWERDOWN AND ENABLE LOGIC TRUTH TABLE
SHDN INPUT
EN INPUT
TRANSMITTER OUTPUTS
RECEIVER OUTPUTS
ROUTB OUTPUT
MODE OF OPERATION
L
High-Z
Active
Manual Powerdown
L
H
High-Z
Active
Manual Powerdown w/Rcvr. Disabled
H
L
Active
Normal Operation
H
Active
High-Z
Active
Normal Operation w/Rcvr. Disabled
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
OLD
VCC
POWERED
GND
SHDN = GND
VCC
Rx
Tx
VCC
CURRENT
VOUT = VCC
FLOW
RS-232 CHIP
DOWN
UART
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
ICL3237E
TRANSITION
RX
TX
R1OUTB
R1OUT
T1IN
VCC
TO
R1IN
T1OUT
VOUT = HI-Z
POWERED
SHDN = GND, EN = VCC
DETECTOR
DOWN
UART
WAKE-UP
LOGIC
TABLE 3. REQUIRED CAPACITOR VALUES
VCC
(V)
C1
(
F)
C2, C3, C4
(
F)
3.0 to 3.6 (3.3V
±10%)
0.22
3.15 to 3.6 (3.3V
±5%)
0.1
4.5 to 5.5
0.047
0.33
3.0 to 5.5
0.22
1.0
ICL3237E
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