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AHP28XXS Series

Input Filter

Undervoltage Lockout

The AHP28XXS series converters incorporate a single stage

LC input filter whose elements dominate the input load

impedance characteristic during the turn-on. The input circuit

is as shown in Figure IV.

Figure IV. Input Filter Circuit

A minimum voltage is required at the input of the converter

to initiate operation. This voltage is set to 14.0

± 0.5 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. Thus if the input voltage droops to 13.0

± 0.5 volts,

the converter will shut down and remain inoperative until the

input voltage returns to

≈14.0 volts.

Output Voltage Adjust

Input Over-Voltage Protection

One additional protection feature is incorporated into the

AHP input circuit. It is an input over-voltage protection. The

output will shutdown and restart at approximately 110% of

the maximum rated input voltage. This protection feature is

unique to the AHP.

Pin 1

Pin 2

3.5µH

11.2 µfd

In addition to permitting close voltage regulation of remotely

located loads, it is possible to utilize the converter sense

pins to incrementally increase the output voltage over a

limited range. The adjustments made possible by this

method are intended as a means to “trim” the output to a

voltage setting for some particular application, but are not

intended to create an adjustable output converter. These

output voltage setting variations are obtained by connecting

an appropriate resistor value in the locations as shown in

Figure V or Figure VI depending on the desired output

voltage. The range of adjustment and corresponding range

of resistance values can be determined by use of the

equations presented below.

For (V

connected between the +Sense and –Sense pins with

the –Sense connected to the output return as shown in

Figure V. The resistor value (R

follows:

⎥

⎦

⎤

⎢

⎣

⎡

−

−

⋅

=

25

.

0

1000

NOM

OUT

NOM

ADJ

V

V

V

R

For V

between the +Sense and +Output pins with the –Sense

connected to the output return as shown in Figure VI.

The resistor value (R

⎟⎟⎠

⎞

⎜⎜⎝

⎛

−

−

=

1

25

.

0

1000

NOM

OUT

ADJ

V

V

R

V

V

R

achieve the desired Vout

Finding a resistor value for a particular output voltage, is

simply a matter of substituting the desired output voltage

and the nominal device voltage into the equation and solving

for the corresponding resistor value.

Figure V. Connection for V

Figure VI. Connection for V

Enable 2

Share

+Sense

- Sense

Return

+Vout

AHP28XXS

To Load

Enable 2

Share

+Sense

- Sense

Return

+Vout

AHP28XXS

To Load