AHP2805SWES Datasheet, PDF (8/12 Pages) International Rectifier – HIGH RELIABILITY HYBRID DC/DC CONVERTERS

AHP28XXS Series
Input Filter
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
Pin 1
3.5µH
Pin 2
11.2 µfd
R _ADJ
=
1000
⋅
⎡
⎢⎣_VOUT
V _NOM
− V_NOM
⎤
− 0.25^⎥⎦
For V_NOM < V_OUT < (V_NOM + 0.25V), a resistor is connected
between the +Sense and +Output pins with the –Sense
connected to the output return as shown in Figure VI.
The resistor value (R_ADJ) is calculated as follows:
R _ADJ
=
1000
⎜⎜⎝⎛
0.25
V_OUT − V_NOM
− 1_{⎟⎟⎠⎞}
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.
Undervoltage Lockout
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
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_NOM + 0.25V) < V_OUT < (V_NOM + 0.5V), a resistor is
connected between the +Sense and –Sense pins with
the –Sense connected to the output return as shown in
Figure V. The resistor value (R_ADJ) is calculated as
follows:
V_NOM = device nominal output voltage
V_OUT = desired output voltage
R_ADJ = value of the external resistor required to
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_OUT > V_NOM+ 0.25V
AHP28XXS
Enable 2
Share
+Sense
- Sense
Return
+Vout
RADJ
To Load
Figure VI. Connection for V < V < (V + 0.25V)
NOM
OUT
NOM
AHP28XXS
Enable 2
Share
+Sense
- Sense
Return
+Vout
RADJ
To Load
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