ISL3232E Datasheet, PDF (9/14 Pages) Intersil Corporation – QFN Packaged, ±15kV ESD Protected, +2.7V to +5.5V, 150nA, 250kbps, RS-232 +2.7V to +5.5V, 150nA, 250kbps, RS-232

ISL3232E, ISL4221E, ISL4223E
2.7V
0.3V
-0.3V
-2.7V
VALID RS-232 LEVEL - ISL4221E, ISL4223E IS ACTIVE
INDETERMINATE - POWER-DOWN MAY OR
MAY NOT OCCUR
INVALID LEVEL - POWER-DOWN OCCURS AFTER 30µs
INDETERMINATE - POWER-DOWN MAY OR
MAY NOT OCCUR
VALID RS-232 LEVEL - ISL4221E, ISL4223E IS ACTIVE
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS
RECEIVER
INPUTS
INVALID
} _REGION
TRANSMITTER
OUTPUTS
INVALID ^VCC
OUTPUT ₀
V+
t_INVL
AUTOPWDN
V_CC
0
V-
t_INVH
PWR UP
FIGURE 7. AUTOMATIC POWER-DOWN AND INVALID
TIMING DIAGRAMS
Automatic Power-down (Excluding ISL3232E)
Even greater power savings is available by using the
automatic power-down function. When no valid RS-232
voltages (see Figure 6) are sensed on any receiver input for
30µs, the charge pump and transmitters power-down,
thereby reducing supply current to 150nA. 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 ISL4221E, ISL4223E powers back up
whenever it detects a valid RS-232 voltage level on any
receiver input. This automatic power-down feature provides
additional system power savings without changes to the
existing operating system.
Automatic power-down operates when the FORCEON input is
low, and the FORCEOFF input is high. Tying FORCEON high
disables automatic power-down, but manual power-down is
always available via the overriding FORCEOFF input. Table 2
summarizes the automatic power-down functionality.
Some applications may need more time to wake up from
shutdown. If automatic power-down is being utilized, the
RS-232 device will re-enter power-down if valid receiver
levels aren’t reestablished within 30µs of the ISL4221E,
ISL4223E powering up. Figure 5 illustrates a circuit that
keeps the ISL4221E, ISL4223E from initiating automatic
power-down for 100ms after powering up. This gives the
slow-to-wake peripheral circuit time to re-establish valid
RS-232 output levels.
The time to recover from automatic power-down mode is
typically 100µs.
INVALID Output (Excluding ISL3232E)
The INVALID output always indicates whether or not a valid
RS-232 signal (see Figure 6) is present at any of the
receiver inputs (see Table 2), giving the user an easy way to
determine when the interface block should power down.
Invalid receiver levels occur whenever the driving
peripheral’s outputs are shut off (powered down) or when the
RS-232 interface cable is disconnected. In the case of a
disconnected interface cable where all the receiver inputs
are floating (but pulled to GND by the internal receiver pull
down resistors), the INVALID logic detects the invalid levels
and drives the output low. The power management logic
then uses this indicator to power-down the interface block.
Reconnecting the cable restores valid levels at the receiver
inputs, INVALID switches high, and the power management
logic wakes up the interface block. INVALID can also be
used to indicate the DTR or RING INDICATOR signal, as
long as the other receiver inputs are floating, or driven to
GND (as in the case of a powered down driver).
INVALID switches low after invalid levels have persisted on all
of the receiver inputs for more than 30µs (see Figure 7).
INVALID switches back high 1µs after detecting a valid
RS-232 level on a receiver input. INVALID operates in all
modes (forced or automatic power-down, or forced on), so it is
also useful for systems employing manual power-down
circuitry. When automatic power-down is utilized, INVALID = 0
indicates that the ISL4221E, ISL4223E is in power-down
mode.
Capacitor Selection
The charge pumps require 0.1µF, or greater, capacitors for
proper operation. Increasing the capacitor values (by a
factor of 2) reduces ripple on the transmitter outputs and
slightly reduces power consumption.
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-.
9
FN6045.6
May 13, 2010