PT6420 Datasheet, PDF (3/5 Pages) Texas Instruments – 3 AMP ADJUSTABLE INTEGRATED SWITCHING REGULATOR

Application Notes
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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).
Figure 1
Vin
4,5,6
Vin
C1
+
100 µF
1
Vsense
PT6420
11,12,13
Vo
GND
7,8,9,10
Vo(adj)
14
R1
Adjust Up
(R2)
Adj Down
C2
+
100 µF
COM
Vo
L
O
A
D
COM
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.
The values of R1 [adjust up], and (R2) [adjust down], can
also be calculated using the following formulae.
R1
=
12.45 V_o
(V_a – V_o)
– 49.9
kΩ
(R2)
=
12.45 (2V_a – V_o)
V_o – V_a
– 49.9 kΩ
Where: V_o = Original output voltage
V_a = Adjusted output voltage
Table 1
PT6420 ADJUSTMENT RANGE
Series Pt #
PT6428
Vo (nom)
1.2
Va (min)
1.1
Va (max)
1.4
PT6424
1.5
1.3
1.8
PT6426
1.8
1.5
2.2
PT6427
2.1
1.8
2.6
PT6429
2.5
2.1
3.1
PT6425
3.3
2.8
3.8
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 [phone] Fax: [phone] http://www.powertrends.com
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