ISL3232E_14 Datasheet, PDF (8/14 Pages) Intersil Corporation – QFN Packaged, ±15kV ESD Protected,+2.7V to +5.5V, 150nA, 250kbps, RS-232 Transmitters/Receivers

ISL3232E, ISL4221E, ISL4223E
TABLE 2. POWER-DOWN AND ENABLE LOGIC TRUTH TABLE (EXCLUDING ISL3232E)
RS-232 SIGNAL
PRESENT AT
RECEIVER INPUT?
FORCEOFF FORCEON EN TRANSMITTER RECEIVER INVALID
INPUT
INPUT INPUT OUTPUTS OUTPUTS OUTPUT
MODE OF OPERATION
NO
H
H
L
Active
Active
L
Normal Operation
(Auto Power-down Disabled)
NO
H
H
H
Active
High-Z
L
YES
YES
H
L
L
Active
Active
H
Normal Operation
(Auto Power-down Enabled)
H
L
H
Active
High-Z
H
NO
H
L
L
High-Z
Active
L
Power-down Due to Auto Power-down
Logic
NO
H
L
H
High-Z
High-Z
L
YES
L
X
L
High-Z
Active
H
Manual Power-down
YES
L
X
H
High-Z
High-Z
H
Manual Power-down w/Rcvr. Disabled
NO
L
X
L
High-Z
Active
L
Manual Power-down
NO
L
X
H
High-Z
High-Z
L
Manual Power-down w/Rcvr. Disabled
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
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 (Excluding
ISL3232E)
The already low current requirement drops significantly when
the device enters power-down mode. In power-down, supply
current drops to 150nA because the on-chip charge pump
turns off (V+ collapses to V_CC, V- collapses to GND) and the
transmitter outputs three-state. Receiver outputs are
unaffected by power-down; refer to Table 2 for details. This
micro-power mode makes the ISL4221E, ISL4223E ideal for
battery-powered and portable applications.
Software Controlled (Manual) Power-down
The ISL4221E, ISL4223E family provides pins that allow the
user to force the IC into the low power, standby state.
The ISL4221E, ISL4223E utilize a two pin approach where
the FORCEON and FORCEOFF inputs determine the IC’s
mode. For always enabled operation, FORCEON and
FORCEOFF are both strapped high. To switch between active
and power-down modes, under logic or software control, only
the FORCEOFF input need be driven. The FORCEON state
isn’t critical, as FORCEOFF dominates over FORCEON.
Nevertheless, if strictly manual control over power-down is
desired, the user must strap FORCEON high to disable the
automatic power-down circuitry.
Connecting FORCEOFF and FORCEON together disables
the automatic power-down feature, enabling them to function
as a manual SHUTDOWN input (see Figure 4).
The time to recover from automatic power-down mode is
typically 100µs.
PWR
MGT
LOGIC
FORCEOFF
FORCEON
INVALID
ISL4221E, ISL4223E
CPU
I/O
UART
FIGURE 4. CONNECTIONS FOR MANUAL POWER-DOWN
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
POWER
MANAGEMENT
UNIT
MASTER POWER-DOWN LINE
0.1µF
1MΩ
FORCEOFF FORCEON
ISL4221E, ISL4223E
FIGURE 5. CIRCUIT TO PREVENT AUTO POWER-DOWN
FOR 100ms AFTER FORCED POWER-UP
8
FN6045.6
May 13, 2010