AHP270XXD Series
Input Filter
The AHP270XXD 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.
Table 1. Output Voltage Trim Values and Limits
AHP27005D
V
out
5.5
5.4
5.3
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.583
R
adj
0
12.5K
33.3K
75K
200K
∞
190K
65K
23K
2.5K
0
AHP27012D
V
out
12.5
12.4
12.3
12.2
12.1
12.0
11.7
11.3
10.8
10.6
10.417
R
adj
0
47.5K
127K
285K
760K
∞
975K
288K
72.9K
29.9K
0
AHP27015D
V
out
15.5
15.4
15.3
15.2
15.1
15.0
14.6
14.0
13.5
13.0
12.917
R
adj
0
62.5K
167K
375K
1.0M
∞
1.2M
325K
117K
12.5K
0
Figure IV. Input Filter Circuit
8.4µH
Pin 1
0.54µfd
Pin 2
Input Overvoltage Protection
One additional protection feature is incorporated into the
AHP input circuit. It is an input over-voltage protection. The
output will shutdown and start at approximately 110% of the
maximum rated input voltage.
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.)
Undervoltage Lockout
A minimum voltage is required at the input of the converter
to initiate operation. This voltage is set to 150V
±
5.0V. To
preclude the possibility of noise or other variations at the
input falsely initiating and halting converter operation, a
hysteresis of approximately 10V is incorporated in this circuit.
Thus if the input voltage droops to 140V
±
5.0V, the converter
will shut down and remain inoperative until the input voltage
returns to
≈
150V.
Figure V. Connection for V
OUT
Adjustment
12
Enable 2
Share
AHP270XXD
Trim
- Vout
Return
+ Vout
R
ADJ
-
+
To
Loads
7
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.
Connect R
adj
to + to increase, - to decrease
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.
8
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