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ART28XXT Series

Figure III. Synchronization Input Equivalent Circuit

Output Load Fault Protection

Parallel Operation

Although no special provision for forced current sharing

has been incorporated in the ART28XXT series, multiple

units may be operated in parallel for increased output power

applications. The 5.0 volt outputs will typically share to

within approximately 10% of their full load capability and

the dual (±15 volt) outputs will typically share to within

50% of their full load. Load sharing is a function of the

individual impedance of each output and the converter

with the highest nominal set voltage will furnish the

predominant load current.

A minimum voltage is required at the input of the converter

to initiate operation. This voltage is set to a nominal value

of 16.8 volts. To preclude the possibility of noise or other

variations at the input falsely initiating and halting converter

operation, a hysteresis of approximately 1.0 volts is

incorporated in this circuit. The converter is guaranteed to

operate at 19 Volts input under all specified conditions.

Input Undervoltage Protection

Input Filter

To attenuate input ripple current, the ART28XXT series

converters incorporate a two-stage LC input filter. The

elements of this filter comprise the dominant input load

impedance characteristic, and therefore determine the

nature of the current inrush at turn-on. The input filter

circuit elements are as shown in Figure V.

Figure V. Input Filter Circuit

Synchronization

An additional feature is a synchronization output (pin 5)

permitting multiple ART28XX converters in a system to be

synchronized to one of the converters in the set. See

Figure IV.

The sync input port permits synchronization of an ART

converter to any compatible external frequency source

operating in the band of 225 to 310 KHz. The synchronization

input is edge triggered with synchronization initiated on

the negative transition. This input signal should be a

negative going pulse referenced to the input return and

have a 20% to 80% duty cycle. Compatibility requires the

negative transition time to be less than 100 ns with minimum

pulse amplitude of +4.25 volts referred to the input return.

In the absence of an external source, the converter will

revert to its own internally set frequency.

If external

synchronization is not desired, the sync in pin may be left

open (unconnected) permitting the converter to operate at

its’ own internally set frequency.

Figure IV. Synchronization Output Equivalent Circuit

6K

2N2222

4K

10pf

Sync

Output

Input

Return

+10V

5

2

10K

To Internal

Clock

An additional feature is a synchronization output (pin 5)

permitting multiple Protection against overload or short

circuit on any output is provided in the ART28XXT converter

series. This protection is implemented by sensing primary

switching current and, when a load fault condition is

detected, pulse width is limited by the protection circuitry.

The converter is able to operate continuously with a load

fault witout damage or exceeding derating limits.

5K

2N2907A

10K

47pf

Sync

Input

Input

Return

+10V

Pin 1

Pin 2

34 µH

5.4 µfd

1.35

Ω

4.7 µH

Systems using multiple convertors may dictate operating

the group at a common switching frequency. To

accomodate this requirement, the ART28XXT converters

include a synchronization input (pin 4). Topology is

illustrated in Figure III.