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ISL3232EIRZ

P1-P3P4-P6P7-P9P10-P12P13-P14
7
FN6045.6
May 13, 2010
Detailed Description
The ISL4221E, ISL4223E and ISL3232E operate from a
single +2.7V to +5.5V supply, guarantee a 250kbps minimum
data rate, require only four small external 0.1µF capacitors,
feature low power consumption, and meet all ElA RS-232C
and V.28 specifications even with V
CC
= 3.0V. The circuit is
divided into three sections: The charge pump, the transmitters
and the receivers.
Charge-Pump
Intersil’s new RS-232 devices utilize regulated on-chip dual
charge pumps as voltage doublers, and voltage inverters to
generate ±5.5V transmitter supplies from a V
CC
supply as
low as 3.0V. This allows them to maintain RS-232 compliant
output levels over the ±10% tolerance range of 3.3V
powered systems. The efficient on-chip power supplies
require only four small, external 0.1µF capacitors for the
voltage doubler and inverter functions. The charge pumps
operate discontinuously (i.e., they turn off as soon as the V+
and V- supplies are pumped up to the nominal values),
resulting in significant power savings.
Transmitters
The transmitters are proprietary, low dropout, inverting drivers
that translate TTL/CMOS inputs to EIA/TIA-232 output levels.
Coupled with the on-chip ±5.5V supplies, these transmitters
deliver true RS-232 levels over a wide range of single supply
system voltages.
All ISL4221E, ISL4223E transmitter outputs disable and
assume a high impedance state when the device enters the
power-down mode (see Table 2). These outputs may be driven
to ±12V when disabled.
The devices guarantee a 250kbps data rate for full load
conditions (3kΩ and 1000pF), V
CC
≥ 3.0V, with one
transmitter operating at full speed. Under more typical
conditions of V
CC
≥ 3.3V, R
L
= 3kΩ, and C
L
= 250pF, one
transmitter easily operates at 900kbps.
Transmitter inputs float if left unconnected, and may cause
I
CC
increases. Connect unused inputs to GND for the best
performance.
Receivers
All these RS-232 devices contain standard inverting receivers,
and the ISL4221E, ISL4223E receivers three-state via the EN
control line. All the receivers 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
CC
= 0V). The receivers’ Schmitt trigger
input stage uses hysteresis to increase noise immunity and
decrease errors due to slow input signal transitions.
Receivers driving a powered down UART must be disabled to
prevent current flow through, and possible damage to, the
UART’s protection diodes (see Figures 2 and 3). This can be
accomplished on the ISL4221E, ISL4223E by driving the EN
input high whenever the UART powers down. Figure 3 also
shows that the INVALID
output can be used to determine
when the UART should be powered down. When the RS-232
cable is disconnected, INVALID
switches low indicating that
the UART is no longer needed. Reconnecting the cable drives
INVALID
back high, indicating that the UART should be
powered up.
R
XOUT
GND ≤ V
ROUT
≤ V
CC
5kΩ
R
XIN
-25V ≤ V
RIN
≤ +25V
GND
V
CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
OLD
V
CC
POWERED
GND
SHDN
= GND
V
CC
Rx
Tx
V
CC
CURRENT
V
OUT
=
V
CC
FLOW
RS-232 CHIP
DOWN
UART
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
ISL4221E, ISL4223E
TRANSITION
R
X
T
X
INVALID
R
OUT
T
IN
V
CC
V
CC
TO
R
IN
T
OUT
V
OUT
=
HI-Z
POWERED
DETECTOR
DOWN
UART
WAKE-UP
LOGIC
EN
= V
CC
ISL3232E, ISL4221E, ISL4223E
8
FN6045.6
May 13, 2010
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.
TABLE 2. POWER-DOWN AND ENABLE LOGIC TRUTH TABLE (EXCLUDING ISL3232E)
RS-232 SIGNAL
PRESENT AT
RECEIVER INPUT?
FORCEOFF
INPUT
FORCEON
INPUT
EN
INPUT
TRANSMITTER
OUTPUTS
RECEIVER
OUTPUTS
INVALID
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 H L L Active Active H Normal Operation
(Auto Power-down Enabled)
YES 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
FIGURE 4. CONNECTIONS FOR MANUAL POWER-DOWN
WHEN NO VALID RECEIVER SIGNALS ARE
PRESENT
PWR
FORCEOFF
INVALID
CPU
I/O
FORCEON
ISL4221E, ISL4223E
MGT
LOGIC
UART
FIGURE 5. CIRCUIT TO PREVENT AUTO POWER-DOWN
FOR 100ms AFTER FORCED POWER-UP
ISL4221E, ISL4223E
FORCEOFF
FORCEON
POWER
MASTER POWER-DOWN LINE
1MΩ
0.1µF
MANAGEMENT
UNIT
ISL3232E, ISL4221E, ISL4223E
9
FN6045.6
May 13, 2010
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-
.
FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS
0.3V
-0.3V
-2.7V
2.7V
INVALID LEVEL - POWER-DOWN OCCURS AFTER 30µs
VALID RS-232 LEVEL - ISL4221E, ISL4223E IS ACTIVE
VALID RS-232 LEVEL - ISL4221E, ISL4223E IS ACTIVE
INDETERMINATE - POWER-DOWN MAY OR
INDETERMINATE - POWER-DOWN MAY OR
MAY NOT OCCUR
MAY NOT OCCUR
RECEIVER
INPUTS
TRANSMITTER
OUTPUTS
INVALID
OUTPUT
V+
V
CC
0
V-
V
CC
0
t
INVL
t
INVH
INVALID
REGION
}
FIGURE 7. AUTOMATIC POWER-DOWN AND INVALID
TIMING DIAGRAMS
AUTOPWDN
PWR UP
ISL3232E, ISL4221E, ISL4223E
P1-P3P4-P6P7-P9P10-P12P13-P14

ISL3232EIRZ

Mfr. #:
Buy ISL3232EIRZ
Manufacturer:
Renesas / Intersil
Description:
RS-232 Interface IC 3V RS-232 2TX/2RX TRANSC 16LD 5X5
Lifecycle:
New from this manufacturer.
Delivery:
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