MC14C89B, AB

5

MOTOROLA ANALOG IC DEVICE DATA

APPLICATIONS INFORMATION

Description

The MC14C89AB and MC14C89B are designed to be

direct replacements for the MC1489A and MC1489. Both

devices meet all EIA–232 specifications and also the faster

EIA–562 and CCITT V.28 specifications. Noise pulse

rejection circuitry eliminates the need for most response

control filter capacitors but does not exclude the possibility as

filtering is still possible at the Response Control (RC) pins.

Also, the Response Control pins allow for a user defined

selection of the threshold voltages. The MC14C89AB and

MC14C89B are manufactured with a bipolar technology

using low power techniques and consume at most 700

mA,

plus load currents with a +5.0 V supply.

Outputs

The output low or high voltage depends on the state of the

inputs, the load current, the bias of the Response Control

pins, and the supply voltage. Table 1 applies to each receiver,

regardless of how many other receivers within the package

are supplying load current.

Table 1. Function Table

Receivers

Input*

Output*

H

L

L

H

*The asterisk denotes A, B, C, or D.

Receiver Inputs and Response Control

The receiver inputs determine the state of the outputs in

accordance with Table 1. The nominal VIL and VIH

thresholds are 0.95 V and 1.90 V respectively for the

MC14C89AB. For the MC14C89B, the nominal VIL and VIH

thresholds are 0.95 and 1.30, respectively. The inputs are

able to withstand

±30 V referenced to ground. Should the

input voltage exceed ground by more than

± 30 V, excessive

currents will flow at the input pin. Open input pins will

generate a logic high output, but good design practices

dictate that inputs should never be left open.

The Response Control (RC) pins are coupled to the inputs

through a resistor string. The RC pins provide for adjustment

of the threshold voltages of the IC while preserving the

amount of hysteresis. Figure 10 shows a typical application

to adjust the threshold voltages. The RC pins also provide

access to an internal resistor string which permits low pass

filtering of the input signal within the IC. Like the input pins,

the RC pins should not be taken above or below ground by

more than

±30 V or excessive currents will flow at these pins.

The dependence of the low level threshold voltage (VIL) upon

RRC and Vbat can be described by the following equation:

V

IL ]

V

0.09 *

V

bat

505

W

R

RC

(1.6)

) 2.02 kW

(1)

5.32 k

W ) 6.67

106

W2

R

RC

505

W

VIH can be found by calculating for VIL using equation (1)

then adding the hysteresis for each device (0.35 for the

MC14C89B or 0.95 V for the MC14C89AB). Figure 7 plots

equation (1) for two values of Vbat and a range of RRC.

If an RC pin is to be used for low pass filtering, the

capacitor chosen can be calculated by the equation,

C

RC ]

1

2.02 k

W 2p f*3dB

(2)

of the low pass filter.

Figure 9. Application to Adjust Thresholds

Input Pin

Response Control Pin

Vbat

RRC

–

+

Another feature of the MC14C89AB and MC14C89B is

input noise rejection. The inputs have the ability to ignore

pulses which exceed the VIH and VIL thresholds but are less

than 1.0

ms in duration. As the duration of the pulse exceeds

1.0

ms, the noise pulse may still be ignored depending on its

amplitude. Figure 8 is a graph showing typical input noise

rejection as a function of pulse amplitude and pulse duration.

Figure 8 reflects data taken for an input with an unconnected

RC pin and applied to the MC14C89AB and MC14C89B.

Operating Temperature Range

The ambient operating temperature range is listed as

–40

°C to +85°C, and the devices are designed to meet the

EIA–232–E, EIA–562 and CCITT V.28 specifications over

this temperature range. The timing characteristics are

guaranteed to meet the specifications at +25

°C. The

maximum ambient operating temperature is listed as +85

°C.

However, a lower ambient may be required depending on

system use (i.e., specifically how many receivers within a

package are used), and at what current levels they are

operating. The maximum power which may be dissipated

within the package is determined by:

PD(max) +

T

J(max)

–T

A

RqJA

where: R

θJA =

TJ(max) =

TA =

PD =

where: VCC =

VOH, VOL =

ICC =

thermal resistance (typ., 100

°C/W for the

DIP and 125

°C/W for the SOIC packages);

maximum operating junction temperature

(150

°C); and

ambient temperature.

{[(VCC – VOH)IOH] or

[(VOL)IOL]}each receiver + (VCCICC)

positive supply voltage;

measured or estimated from Figure 2

and 3;

measured quiescent supply current.

As indicated, the first term (in brackets) must be calculated

and summed for each of the four receivers, while the last

term is common to the entire package.