ISL3241E_14 Datasheet, PDF (9/16 Pages) Intersil Corporation – QFN Packaged, ±15kV ESD Protected, +2.7V to +3.6V,250kbps, RS-232 Transmitters/Receivers with Separate Logic Supply Pin

ISL3241E, ISL3243E
RS-232
SIGNAL
PRESENT
AT
RECEIVER
INPUT?
ISL3241E
N/A
N/A
N/A
N/A
ISL3243E
NO
YES
NO
YES
NO
TABLE 2. POWER-DOWN AND ENABLE LOGIC TRUTH TABLE (NOTE: “H” = V_L)
SHDN OR
FORCEOFF
INPUT
FORCEON EN TRANSMITTER
INPUT INPUT OUTPUTS
RECEIVER
OUTPUTS
R_OUTB
OUTPUTS
INVALID
OUTPUT
MODE OF OPERATION
L
N/A
L
High-Z
Active
Active
N/A Manual Power-down
L
N/A
H
High-Z
High-Z
Active
N/A Manual Power-down w/Rcvr. Disabled
H
N/A
L
Active
Active
Active
N/A Normal Operation
H
N/A
H
Active
High-Z
Active
N/A Normal Operation w/Rcvr. Disabled
H
H
N.A.
Active
Active
Active
L
Normal Operation
(Auto Powerdown Disabled)
H
L
N.A.
Active
Active
Active
H
Normal Operation
(Auto Power-down Enabled)
H
L
N.A.
High-Z
Active
Active
L
Power-down Due to Auto Power-down
Logic
L
X
N.A.
High-Z
High-Z
Active
H
Manual Power-down
L
X
N.A.
High-Z
High-Z
Active
L
Manual Power-down
ISL324xE monitor receivers remain active even during manual
powerdown, making them extremely useful for Ring Indicator
monitoring. Standard receivers driving powered down
peripherals must be disabled to prevent current flow through
the peripheral’s protection diodes (see Figures 5 and 6). This
renders them useless for wake up functions, but the
corresponding monitor receiver can be dedicated to this task
as shown in Figure 6.
Low Power Operation
These 3V devices require a nominal supply current of 0.3mA,
even at V_CC = 3.6V, 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.
Power-down Functionality
The already low current requirement drops significantly when
the device enters powerdown mode. In powerdown, supply
current drops to less than 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
disable only in manual powerdown (ISL3243E) or when EN =
V_L (ISL3241E); refer to Table 2 for details. This micro-power
mode makes the ISL324xE ideal for battery powered and
portable applications.
V_CC
V_CC
V_CC
POWERED
DOWN
UART
GND
V_OUT = V_CC
Rx
Tx
SHDN = GND
CURRENT
FLOW
OLD
RS-232 CHIP
FIGURE 5. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
9
FN6768.2
June 18, 2012