6

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

Standard receivers driving powered down peripherals must

be disabled to prevent current flow through the peripheral’s

protection diodes (see Figure 2). This renders them useless

for wake up functions.

Operation Down to 2.7V

ISL83220E transmitter outputs meet RS-562 levels (±3.7V),

typically ensure interoperability 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

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

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

Capacitor Selection

The charge pumps require 0.1

μF capacitors for 3.3V

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

-.

Power Supply Decoupling

In most circumstances a 0.1

μF bypass capacitor is

adequate. In applications that are particularly sensitive to

Connect the bypass capacitor as close as possible to the IC.

GND

5k

Ω

-25V

GND

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

POWERED

GND

SHDN = GND

Rx

Tx

CURRENT

FLOW

RS-232 CHIP

DOWN

UART

ISL83220E