5

Detailed Description

The ISL8563 operates from a single +3V to +5.5V supply,

guarantees a 250kbps minimum data rate, requires only four

small external 0.1

µF capacitors, features low power

consumption, and meets all ElA/TIA-562 and EIA/TIA-232

specifications. The circuit is divided into three sections: The

charge pump, the transmitters, and the receivers.

Charge-Pump

Intersil’s new ISL8563 utilizes regulated on-chip dual charge

pumps as voltage doublers, and voltage inverters to

generate

low as 3.0V. This allows these devices 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 0.1

µF capacitors for the

range. 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-562/232

output levels. Coupled with the on-chip

±5.5V supplies,

these transmitters deliver true RS-562/232 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.

full load conditions (3k

transmitter operating at full speed. Under more typical

transmitter easily operates at 900kbps.

Unused transmitter inputs may be left unconnected because

Forcing the ISL8563 into power down disables the pull-up

resistors to further minimize power.

Receivers

The ISL8563 contains standard inverting receivers that

three-state via the EN control line. All the receivers convert

RS-562/232 signals to CMOS output levels and accept

inputs up to

±25V while presenting the required 3kΩ to 7kΩ

input impedance (see Figure 3) even if the power is off

hysteresis (even in powerdown) to increase noise immunity

and decrease errors due to slow input signal transitions.

The ISL8563 inverting receivers disable only when EN is

driven high. Standard receivers driving powered down

peripherals must be disabled to prevent current flow through

the peripheral’s protection diodes (see Figures 4 and 5).

Powerdown Functionality

This 3V device requires a nominal supply current of 0.3mA

during normal operation (not in powerdown mode). This is

considerably less than the 5mA to 11mA current required by

5V 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-

collapses to GND), the transmitter outputs three-state, and

the transmitter input pull-ups disable. This micro-power

mode makes the ISL8563 ideal for battery powered and

portable applications.

Software Controlled (Manual) Powerdown

The ISL8563, is forced into its low power, stand by state via

a simple shutdown (SHDN) pin. Driving this pin high enables

normal operation, while driving it low forces the IC into its

function isn’t needed. Note that all the receiver outputs

remain enabled during shutdown (see Table 2). For the

lowest power consumption during powerdown, the receivers

should also be disabled by driving the EN input high (see

next section, and Figures 4 and 5). The time required to exit

powerdown, and resume transmission is less than 30

µs.

Receiver ENABLE Control

ThedevicealsofeaturesanEN input to control the receiver

outputs. Driving EN high disables all the receiver outputs

placing them 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

enable input has no effect on transmitters.

GND

5k

Ω

-25V

GND

FIGURE 3. INVERTING RECEIVER CONNECTIONS

TABLE 2. POWERDOWN AND ENABLE LOGIC TRUTH TABLE

SHDN INPUT

EN INPUT

TRANSMITTER OUTPUTS

RECEIVER OUTPUTS

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

ISL8563