ADM206/ADM207/ADM208/ADM211/ADM213

Rev. D | Page 12 of 16

Shutdown (SD)

The ADM2xx feature a control input that may be used to

disable the part and reduce the power consump-ion to less than

5 ΩW. This is very useful in battery-operated systems. During

shutdown, the charge pump is turned off, the transmitters are

disabled, and all receivers except R4 and R5 on the ADM213 are

put into a high impedance disabled state. Receivers R4 and R5

on the ADM213 remain enabled during shutdown. This feature

allows monitoring external activity while the device is in a low

power shutdown mode. The shutdown control input is active

high on all parts except the ADM213, where it is active low. See

Table 5 and Table 6.

Enable Input

The ADM211 and ADM213 feature an enable input used to

enable or disable the receiver outputs. The enable input is active

low on the ADM211 and active high on the ADM213. See

Table 5 and Table 6. When the receivers are disabled, their

outputs are placed in a high impedance state. This function

allows the outputs to be connected directly to a microprocessor

data bus. It can also be used to allow receivers from different

devices to share a common data line. The timing diagram for

the enable function is shown in Figure 22.

3V

0V

3.5V

0.8V

* POLARITY OF EN IS REVERSED FOR ADM213.

EN*

Figure 22. Enable Timing

APPLICATION HINTS

Driving Long Cables

In accordance with the EIA-232-E standard, long cables are

permissible provided the total load capacitance does not exceed

2500 pF. For longer cables that do exceed this, it is possible to

trade off baud rate for cable length. Large load capacitances cause

a reduction in slew rate, and therefore the maximum transmis-

sion baud rate is decreased. The ADM2xx are designed to

minimize the slew rate reduction that occurs as load

capacitance increases.

For the receivers, it is important that a high level of noise

immunity be inbuilt so that slow rise and fall times do not cause

multiple output transitions as the signal passes slowly through

the transition region. The ADM2xx have 0.65 V of hysteresis to

guard against this. This ensures that even in noisy environments

error-free reception can be achieved.

High Baud Rate Operation

The ADM2xx feature high slew rates, permitting data

transmission at rates well in excess of the EIA-232-E

specification. The drivers maintain ±5 V signal levels at data

rates up to 120 kB/s under worst-case loading conditions.