HI-3189

FUNCTIONAL DESCRIPTION

The HI-3189 is a complete differential line driver IC. When

DATA (A) = DATA (B) or SYNC or CLOCK signal is low, the

driver forces the output to a voltage Null level (0V +/- 250 mV).

Designed to address the ARINC 429 standard, the HI-3189

has output rise and fall times that can be adjusted by the

selection of an external capacitor (CAPA or CAPB) and an

output voltage range adjustable through an externally applied

VREF signal. All logic inputs and sync control inputs are

TTL/CMOS compatible. The HI-3189 is available in 16-lead

ceramic side-brazed DIP, 16-pin Cerdip and 28-pin ceramic

LCC packages. See ordering information for available

screening options.

The device contains three main functional blocks. The first

block is a digital section used to decode the ARINC Clock,

Synchronization, and Data inputs as shown in the Functional

Block Diagram (Figure 2). This block takes these inputs and

channels the data to the Level Shifter and Slope control

Circuit. The logical relationship for these pins is presented in

Table 1.

The second functional block is a charge pump circuit used to

control the output waveform and its timing characteristics.

This is achieved through charging and discharging a capaci-

tor with a known current. The capacitor is user-selectable, and

is connected between the CAPA or CAPB pins and ground. A

Rate Select pin (digital input) is used to set the rise and fall

time. If this pin is tied to ground, the device functions in the

high-speed data rate. This mode is recommended if the user

does not have an application requiring data rate switching.

Table 2 gives recommended capacitor values for each

possible data combination.

The last functional block of the device consists of a voltage

follower and high power output differential amplifier. The

voltage follower buffers the signals presented at the charge

capacitors and presents the mirrored signal to the difference

amplifier to drive the ARINC line. Two different outputs are

available from the differential amplifiers: AMPA, AMPB, and

OUTA, OUTB. The outputs AMPA and AMPB are the direct

outputs of the power amplifier. The outputs OUTA and OUTB

include 37.5 Ohm series resistors added to minimize bus

reflections by matching the power amplifier’s output imped-

ance to the cable’s impedance of 75 Ohms. AMPA and AMPB

may be used to customize the output impedance of the

device. These outputs can also be used to enhance the

device’s drive capability, for example, when driving the

standard 10 nF // 400 Ohm load defined in the ARINC 429

specification (see output drive capability and capacitive loads

for more details). All outputs are protected from voltage spikes

with diodes connected between the output pins and the

supply lines.

Heat Sinking / Air Flow and Short

Circuit Protection

The user application will determine if and how much heat

sinking / air flow will be required for the HI-3189. Consider-

ation must be given to ambient temperature, load conditions

and output voltage swing. In addition, power increases with

increased operating frequency. Use the thermal conductivity

numbers given in the Ordering Information section to deter-

mine that the maximum allowable junction temperature of

175°C is not exceeded.

Outputs OUTA and OUTB will survive a short circuit to ground

or to each other. During a short circuit of the output to either

power supply or ground, the device must be able to dissipate

the generated heat. For example, if the output is shorted to

ground and +VS = +15V, the device must dissipate 15V x

0.165A = 2.5W. An appropriate heat sink is required in this

situation.

Note that AMPA and AMPB outputs have no internal series

resistance. Shorting these pins to either power supply or

ground may cause failure of the device. An added external

resistor will protect the circuit by limiting the current.

Three power supplies are required to operate the HI-3189 in a

typical ARINC 429 bus application: +15V for +VS, -15V for -VS

and +5V for both VREF and VLOGIC. The differential output

swing of the HI-3189 is equal to 2 x VREF. Using +5V gives a

differential output swing of 10V. If a different output voltage

swing is required, an additional power supply is needed to set

VREF.

Each power supply pin should be decoupled to ground using a

high quality 10 uF tantalum capacitor. This is especially true

when driving a large capacitive or resistive load. The decoup-

ling capacitors should be located as close to the device pins

as possible to eliminate the wiring inductance.

Power Supply Considerations

APPLICATIONS

HOLT INTEGRATED CIRCUITS

3