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.
APPLICATIONS
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.
Power Supply Considerations
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.
HOLT INTEGRATED CIRCUITS
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HOLTIC [ HOLT INTEGRATED CIRCUITS ]
