ISL4223E INTERSIL [Intersil Corporation], ISL4223E Datasheet - Page 6

• Manufacturer Part Number: ISL4223E
• Description: QFN Packaged, +/-15kV ESD Protected, +2.7V to +5.5V, 150Nanoamp, 250kBps, RS-232 Transmitters/Receivers
• Manufacturer: INTERSIL [Intersil Corporation]

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 transmitter outputs disable and assume a high
impedance state when the device enters the powerdown
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
transmitter operating at full speed. Under more typical
conditions of V
transmitter easily operates at 900kBps.
Transmitter inputs float if left unconnected, and may cause
I
performance.
Receivers
All the ISL422XE devices contain standard inverting
receivers that 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
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 ISL422XE 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.
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
CC
increases. Connect unused inputs to GND for the best
CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
-25V ≤ V
= 0V). The receivers’ Schmitt trigger input stage
RIN
R
GND
CC
V
XIN
CC
≤ +25V
CC
≥ 3.3V, R
= 5.5V, during normal operation (not in
5kΩ
L
= 3kΩ, and C
6
CC
≥ 3.0V, with one
GND ≤ V
R
XOUT
L
ROUT
= 250pF, one
≤ V
ISL4221E, ISL4223E
CC
11mA current required by comparable 5V RS-232 devices,
allowing users to reduce system power simply by switching
to this new family.
Powerdown Functionality
The already low current requirement drops significantly
when the device enters powerdown mode. In powerdown,
supply current drops to 150nA, because the on-chip charge
pump turns off (V+ collapses to V
and the transmitter outputs three-state. Receiver outputs are
unaffected by powerdown; refer to Table 2 for details. This
micro-power mode makes the ISL422XE ideal for battery
powered and portable applications.
Software Controlled (Manual) Powerdown
The ISL422XE family provides pins that allow the user to
force the IC into the low power, standby state.
The ISL422XE utilize a two pin approach where the
FORCEON and FORCEOFF inputs determine the IC’s
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
POWERED
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
DOWN
UART
POWERED
DOWN
V
UART
WAKE-UP
GND
CC
LOGIC
V
TO
CC
R
T
PERIPHERAL
X
X
TRANSITION
DETECTOR
Rx
Tx
V
CC
V
OUT
EN = V
SHDN = GND
V
OUT
= HI-Z
V
R
CC
OUT
T
CC
= V
IN
CC
CC
INVALID
, V- collapses to GND),
RS-232 CHIP
ISL422XE
V
OLD
CURRENT
FLOW
CC
R
T
OUT
IN