ISL4238E Intersil Corporation, ISL4238E Datasheet - Page 9

• Manufacturer Part Number: ISL4238E
• Description: QFN Packaged, 15kV Esd Protected, +2.7V to +5.5V, 10Nanoamp, 250kbps/ 1Mbps, RS-232 Transceivers With Enhanced Automatic Powerdown
• Manufacturer: Intersil Corporation

NOTE:
Transmitter inputs on the ISL424XE float if left unconnected,
and may cause I
GND for the best performance. ISL4238E transmitter inputs
incorporate an active positive feedback resistor that
maintains the last input state in the absence of a forcing
signal, so unused transmitter inputs may be left
unconnected.
Receivers
ISL4238E/4XE devices contain standard inverting receivers
which can tristate via the FORCEOFF control line.
Additionally, they include a noninverting (monitor) receiver
(denoted by the R
regardless of the state of any control lines. Both receiver
types 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
uses hysteresis to increase noise immunity and decrease
errors due to slow input signal transitions.
The ISL4238E/4XE inverting receivers disable during forced
(manual) powerdown, but not during automatic powerdown
(see Table 2). Conversely, the monitor receiver remains
active even during manual powerdown making it extremely
useful for Ring Indicator monitoring. Standard receivers
driving powered down peripherals must be disabled to
INVALID DRIVING FORCEON AND FORCEOFF (EMULATES AUTOMATIC POWERDOWN)
8. Input is connected to INVALID Output.
WITHIN 30
RCVR OR
XMTR
EDGE
SEC?
YES
YES
NO
NO
NO
NO
CC
X
X
X
X
FIGURE 1. INVERTING RECEIVER CONNECTIONS
-25V ≤ V
= 0V). The receivers’ Schmitt trigger input stage
RIN
FORCEOFF
R
GND
V
NOTE 8
NOTE 8
XIN
INPUT
CC
CC
≤ +25V
OUTB
H
H
H
H
H
H
L
L
increases. Connect unused inputs to
label) that is always active,
5kΩ
FORCEON
NOTE 8
NOTE 8
INPUT
9
H
H
L
L
L
L
X
X
GND ≤ V
TRANSMITTER
OUTPUTS
R
TABLE 2. POWERDOWN LOGIC TRUTH TABLE
XOUT
High-Z
High-Z
High-Z
High-Z
High-Z
Active
Active
Active
Active
Active
ISL4238E, ISL4244E, ISL4245E
ROUT
≤ V
CC
RECEIVER
OUTPUTS
High-Z
High-Z
High-Z
Active
Active
Active
Active
Active
Active
Active
OUTPUTS
R
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
OUTB
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.
Low Power Operation
These 3V devices require a nominal supply current of
0.3mA, even at V
powerdown 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.
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
POWERED
DOWN
RECEIVER
UART
PRESENT
GND
INPUT?
RS-232
LEVEL
V
YES
YES
YES
YES
YES
NO
NO
NO
NO
NO
AT
CC
PERIPHERAL
CC
Rx
Tx
V
= 5.5V, during normal operation (not in
INVALID
OUTPUT
CC
SHDN = GND
H
H
H
H
H
V
L
L
L
L
L
OUT
= V
Normal Operation
Normal Operation (Enhanced
Auto Powerdown Disabled)
Normal Operation (Enhanced
Auto Powerdown Enabled)
Powerdown Due to Enhanced
Auto Powerdown Logic
Manual Powerdown
Forced Auto Powerdown
CC
MODE OF OPERATION
RS-232 CHIP
OLD
V
CURRENT
FLOW
CC