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3
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 (800) 531-5782 Fax: (630) 393-6902 http://www.powertrends.com
Application Notes
PT6420 Series
More Applcation Notes
Adjusting the Output Voltage of the PT6420 Series
3AMP 5V Bus Converters
The output voltage of the Power Trends PT6420 Series ISRs
may be adjusted higher or lower than the factory trimmed pre-
set voltage with the addition of a single external resistor. Table 1
accordingly gives the allowable adjustment range for each model
in the series as V
a
(min) and V
a
(max).
Adjust Up: (See note 1)
An increase in the output voltage is obtained by adding a resistor
R1, between pin 14 (V
o
adjust) and pins 11-13 (V
out
).
Adjust Down: (See note 1)
Add a resistor (R2), between pin 14 (V
o
adjust) and pins 7-10
(GND).
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor; either R1 or (R2) as appropriate.
Notes:
1. The direction in which each resistor adjusts the output of the
PT6420 series differs from many other Power Trends prod-
ucts. These output voltage adjustment notes are therefore
specific only to the PT6420 models.
2. Use only a single 1% resistor in either the R1 or (R2) loca-
tion. Place the resistor as close to the ISR as possible.
3. Never connect capacitors from V
o
adjust to either GND,
V
out
, or the Remote Sense pin. Any capacitance added to
the V
o
adjust pin will affect the stability of the ISR.
4. The PT6420 incorporates a Remote Sense (See Figure 1).
If this feature is being used, connecting the resistor R1
between pin 14 (V
o
adjust) and pin 1 (Remote Sense) can
benefit load regulation.
5. An increase in the output voltage may place additional limits
on the input voltage range of the part. The revised mini-
mum input voltage will be (V
out
+ 1.2) or 4.5V, whichever is
higher. Do not exceed 5.5Vdc.
Table 1
PT6420 ADJUSTMENT RANGE
Series Pt # PT6428 PT6424 PT6426 PT6427 PT6429 PT6425
V
o
(nom) 1.2 1.5 1.8 2.1 2.5 3.3
V
a
(min) 1.1 1.3 1.5 1.8 2.1 2.8
V
a
(max) 1.4 1.8 2.2 2.6 3.1 3.8
Figure 1
R1
Adjust Up
C1
100
µ
F
C2
100
µ
F
Vo
COMCOM
Vin
+ +
(R2)
Adj Down
L
O
A
D
PT6420
11,12,13
147,8,9,10
4,5,6
Vin Vo
GND Vo
ad
1
Vsense
The values of R1 [adjust up], and (R2) [adjust down], can
also be calculated using the following formulae.
12.45 V
o
R1 =
(V
a
– V
o
)
– 49.9 k
Ω
12.45 (2V
a
– V
o
)
– 49.9 k
Ω
(R2) =
V
o
– V
a
Where: V
o
= Original output voltage
V
a
= Adjusted output voltage
