6

Detailed Description

ICL3238E operates from a single +3V to +5.5V supply,

guarantees a 250kbps minimum data rate, requires only four

features low power consumption, and meets all EIA/TIA-232

and V.28 specifications. The circuit is divided into three

sections: The charge pump, the transmitters, and the

receivers.

Charge-Pump

Intersil’s new ICL32XXE family utilizes 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 these devices to maintain

RS-232 compliant output levels over the

±10% tolerance

range of 3.3V powered systems. The efficient on-chip power

See the “Capacitor Selection” section, and Table 3 for

capacitor recommendations for other operating conditions.

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.

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.

All devices guarantee a 250kbps data rate for full load

conditions (3k

transmitter operating at full speed. Under more typical

transmitter easily operates at 1Mbps.

Transmitter inputs incorporate an active positive feedback

resistor that maintains the last driven input state in the

absence of a forcing signal. Unused transmitter inputs may

be left unconnected.

Receivers

The ICL3238E contains both standard inverting, three-state

receivers, and a single noninverting (monitor) receiver

regardless of the state of any control lines. Both receiver

types convert RS-232 signals to CMOS output levels and

accept inputs up to

±25V while presenting the required 3kΩ

to 7k

Ω input impedance (see Figure 1) even if the power is

uses hysteresis to increase noise immunity and decrease

errors due to slow input signal transitions.

The inverting receivers disable during forced (manual)

powerdown, but not during automatic powerdown (see

Table 2). Conversely, the monitor receiver remains active

TABLE 2. POWERDOWN LOGIC TRUTH TABLE

RCVR OR

XMTR

EDGE

WITHIN 30

SEC?

FORCEOFF

INPUT

FORCEON

INPUT

TRANSMITTER

OUTPUTS

RECEIVER

OUTPUTS

OUTPUT

RS-232

LEVEL

PRESENT

AT

RECEIVER

INPUT?

INVALID

OUTPUT

MODE OF OPERATION

No

H

H

Active

Active

Active

No

L

Normal Operation (Enhanced

Auto Powerdown Disabled)

No

H

H

Active

Active

Active

Yes

H

Yes

H

L

Active

Active

Active

No

L

Normal Operation (Enhanced

Auto Powerdown Enabled)

Yes

H

L

Active

Active

Active

Yes

H

No

H

L

High-Z

Active

Active

No

L

Powerdown Due to Enhanced

Auto Powerdown Logic

No

H

L

High-Z

Active

Active

Yes

H

X

L

X

High-Z

High-Z

Active

No

L

Manual Powerdown

X

L

X

High-Z

High-Z

Active

Yes

H

INVALID DRIVING FORCEON AND FORCEOFF (EMULATES AUTOMATIC POWERDOWN)

X

Note 7

Note 7

Active

Active

Active

Yes

H

Normal Operation

X

Note 7

Note 7

High-Z

High-Z

Active

No

L

Forced Auto Powerdown

NOTE:

7. Input is connected to INVALID Output.

ICL3238E