ISL3232E Datasheet, PDF (7/14 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
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.
V_CC
R_XIN
-25V ≤ V_RIN ≤ +25V
5kΩ
GND
R_XOUT
GND ≤ V_ROUT ≤ V_CC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
V_CC
V_CC
V_CC
CURRENT
FLOW
Rx
POWERED
DOWN
UART
Tx
GND
V_OUT = V_CC
SHDN = GND
OLD
RS-232 CHIP
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
V_CC
TRANSITION
DETECTOR
TO
WAKE-UP
LOGIC
V_CC
ISL4221E, ISL4223E
INVALID
R_X
POWERED
DOWN
UART _TX
V_OUT = HI-Z
R_OUT
T_IN
EN = V_CC
R_IN
T_OUT
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
7
FN6045.6
May 13, 2010