±50V Isolated, 3.0V to 5.5V,

250kbps, 2 TX/2 RX, RS-232 Transceiver

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7

AC waveforms are rectified on the isolated side of the

Capacitor C6 filters the output of the rectifier. See the

Typical Operating Circuit.

The power controller works in a dual power mode. Power

is maximum when the isolated power supply is below its

regulation point. Power is reduced when the isolated

power supply is above its regulation point.

Dual Charge-Pump Voltage Converter

The RS-232 drivers are powered from a regulated dual

charge pump that provides output voltages of +5.5V (dou-

bling charge pump) and -5.5V (inverting charge pump)

operate in a discontinuous mode. If the output voltages

are less than 5.5V, the charge pumps are enabled. If

the output voltages exceed 5.5V, the charge pumps

are disabled. Each charge pump requires a flying

capacitor (C3, C4) and a reservoir capacitor (C7, C8)

to generate the V+ and V- supplies.

RS-232 Transmitters

The transmitters are inverting level translators that convert

TTL/CMOS-logic levels to ±5.0V EIA/TIA-232-compliant

levels. They guarantee a 250kbps data rate with worst-

case loads of 3k

Ω in parallel with 1000pF to ISOCOM. In

shutdown, the transmitters are disabled and the outputs

are forced into a high-impedance state. When powered

off or shut down, the outputs can be driven up to ±12V

relative to ISOCOM. The transmitter inputs do not have

pullup resistors. All unused inputs should be connected

RS-232 Receivers

The receivers convert RS-232 signals to CMOS-logic

output levels. The receivers’ outputs are forced into a

high-impedance state when the device is in shutdown.

This allows a single UART to multiplex between differ-

ent protocols.

Low-Power Shutdown Mode

Shutdown mode is obtained by driving SHDN low. In

shutdown, the devices typically draw only 20µA of sup-

ply current and no power is transferred across the iso-

lation capacitors. The charge pumps are disabled, and

the receiver outputs and transmitter outputs are high

impedance. When exiting shutdown the charge pumps

and transmitter outputs are fully operational in typically

down mode is not used.

Applications Information

Power Isolation Capacitors

The values for capacitors C1 and C2 are important for

proper operation of the device. These capacitors

should be 0.047µF for 4.5V to 5.5V operation, and

0.47µF for 3.0V to 3.6V operation. Smaller values result

in insufficient supply voltage on the isolated side.

Larger values are not allowed.

Capacitor C9 provides an AC feedback path for proper

controller operation. Connect C9 from ISOCOM to GND.

The values for C1, C2, and C9 determine the maximum

frequency and amplitude of the voltage difference

between the local and isolated ground. Table 1 shows

proper capacitance values.

LOAD CURRENT PER TRANSMITTER (mA)

7

6

4

5

2

3

1

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

-6

08

T1

T2

Figure 2. Transmitter Output Voltage vs. Load Current per

Transmitter

100

µs/div

2V/div

T2OUT

SHDN

5V/div

T1OUT

Figure 3. Transmitter Outputs when Exiting Shutdown or

Powering Up