AHP28XXD Datasheet, PDF (8/11 Pages) International Rectifier – HIGH RELIABILITY HYBRID DC/DC CONVERTERS

AHP28XXD Series
Input Filter
The AHP28XXD series converters incorporate a single stage
LC input filter whose elements dominate the input load
impedance characteristic during the turn-on sequence. The
input circuit is as shown in Figure IV.
Figure IV. Input Filter Circuit
Pin 1
3.5µH
Figure V. Connection for V_OUT Adjustment
AHP28xxD
12
Enable 2
Share
Trim
- Vout
Return
+ Vout
7
R_{ADJ -}
+
To
Loads
Pin 2
11.2 µfd
Connect R_adj to + to increase, - to decrease
Table 1. Output Voltage Trim Values and Limits
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
By use of the trim pin (10), the magnitude of output voltages
can be adjusted over a limited range in either a positive or
negative direction. Connecting a resistor between the trim
pin and either the output return or the positive output will
raise or lower the magnitude of output voltages. The span
of output voltage adjustment is restricted to the limits shown
in Table I.
8
AHP2805D
AHP2812D
AHP2815D
Vout
5.5
5.4
5.3
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.583
Radj
0
12.5K
33.3K
75K
200K
∞
190K
65K
23K
2.5K
0
Vout
12.5
12.4
12.3
12.2
12.1
12.0
11.7
11.3
10.8
10.6
10.417
Radj
0
47.5K
127K
285K
760K
∞
975K
288K
72.9K
29.9K
0
Vout
15.5
15.4
15.3
15.2
15.1
15.0
14.6
14.0
13.5
13.0
12.917
Radj
0
62.5K
167K
375K
1.0M
∞
1.2M
325K
117K
12.5K
0
Note that the nominal magnitude of output voltage resides in
the middle of the table and the corresponding resistor value
is set to ∞. To set the magnitude greater than nominal, the
adjust resistor is connected to output return. To set the
magnitude less than nominal, the adjust resistor is connected
to the positive output. (Refer to Figure V.)
For output voltage settings that are within the limits, but
between those listed in Table I, it is suggested that the
resistor values be determined empirically by selection or by
use of a variable resistor. The value thus determined can
then be replaced with a good quality fixed resistor for
permanent installation.
When use of this adjust feature is elected, the user should
be aware that the temperature performance of the converter
output voltage will be affected by the temperature
performance of the resistor selected as the adjustment
element and therefore, is advised to employ resistors with a
tight temperature coefficient of resistance.
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