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ISL83220E Datasheet(PDF) 5 Page - Intersil Corporation

Part No. ISL83220E
Description  /-15kV ESD Protected, 3V to 5.5V, 1Microamp, 250kbps, RS-232 Transmitters/Receivers
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Maker  INTERSIL [Intersil Corporation]
Homepage  http://www.intersil.com/cda/home
Logo INTERSIL - Intersil Corporation

ISL83220E Datasheet(HTML) 5 Page - Intersil Corporation

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5
Receivers
The ISL83220E device contains a standard inverting
receiver that three-states via the EN control line. 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
(VCC = 0V). The receiver’s Schmitt trigger input stage uses
hysteresis to increase noise immunity and decrease errors
due to slow input signal transitions.
The ISL83220E receiver disables only when EN is driven
high. (see Table 2). This allows the receiver to monitor
external devices, like a modem, even when the ISL83220E is
in its 1
µA powerdown state.
Standard receivers driving powered down peripherals must
be disabled to prevent current flow through the peripheral’s
protection diodes (see Figures 2). This renders them
useless for wake up functions.
Operation down to 2.7V
ISL83220E transmitter outputs meet RS-562 levels (
±3.7V)
with VCC as low as 2.7V. RS-562 levels typically ensure inter
operability with RS-232 devices.
Powerdown Functionality
This 3V family of RS-232 interface devices requires a
nominal supply current of 0.3mA during normal operation
(not in powerdown mode), which is considerably less than
the 5mA to 11mA current required of 5V RS-232 devices.
The already low current requirement drops significantly
when the device enters powerdown mode. In powerdown,
supply current drops to 1
µA, because the on-chip charge
pump turns off (V+ collapses to VCC, V- collapses to GND),
and the transmitter outputs three-state. This micro-power
mode makes these devices ideal for battery powered and
portable applications.
Software Controlled (Manual) Powerdown
On the ISL83220E, the powerdown control is via a simple
shutdown (SHDN) pin. Driving this pin high enables normal
operation, while driving it low forces the IC into it’s
powerdown state. Connect SHDN to VCC if the powerdown
function isn’t needed. Note that the receiver output remains
enabled during shutdown (see Table 2). For the lowest
power consumption during powerdown, the receiver should
also be disabled by driving the EN input high (see next
section). The time to recover from manual powerdown mode
is typically 100
µs.
Receiver ENABLE Control
The ISL83220E also features an EN input to control the
receiver output. Driving EN high disables the receiver output
placing it in a high impedance state. This is useful to
eliminate supply current, due to a receiver output forward
biasing the protection diode, when driving the input of a
powered down (VCC = GND) peripheral (see Figure 2).
Capacitor Selection
The charge pumps require 0.1
µF capacitors for 3.3V
operation. Do not use values smaller than 0.1
µF. 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
-.
R1OUT
GND
≤ VROUT ≤ VCC
5k
R1IN
-25V
≤ VRIN ≤ +25V
GND
VCC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
TABLE 2. POWERDOWN AND ENABLE LOGIC TRUTH TABLE
SHDN
INPUT
EN
INPUT
TRANSMITTER
OUTPUT
RECEIVER
OUTPUT
MODE OF
OPERATION
L
L
High-Z
Active
Manual
Powerdown
L
H
High-Z
High-Z
Manual
Powerdown
w/Rcvr. Disabled
H
L
Active
Active
Normal
Operation
H
H
Active
High-Z
Normal
Operation
w/Rcvr. Disabled
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
OLD
VCC
POWERED
GND
SHDN = GND
VCC
Rx
Tx
VCC
CURRENT
VOUT = VCC
FLOW
RS-232 CHIP
DOWN
UART
ISL83220E


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