PT6400 Datasheet, PDF (3/5 Pages) Texas Instruments – 3 AMP ADJUSTABLE INTEGRATED SWITCHING REGULATOR

Application Notes
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PT6400 Series
More Applcation Notes
Adjusting the Output Voltage of the PT6400 Series
3AMP 5V Bus Converters
The output voltage of the Power Trends PT6400 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 12 (V_o adjust) and pins 9-11 (V_out).
Adjust Down: (See note 1)
Add a resistor (R2), between pin 12 (V_o adjust) and pins 5-8
(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
PT6400 series differs from many other Power Trends prod-
ucts. These output voltage adjustment notes are therefore
specific only to the PT6400 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 or
V_out. Any capacitance added to the V_o adjust pin will affect
the stability of the ISR.
4. 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.
Figure 1
Vin
2,3,4
Vin
C1
+
1 0 0 µF
PT6400
9,10,11
Vo
GND
5,6,7,8
Vo(adj)
12
R1
Adjust Up
(R2)
Adj Down
C2
+
100 µF
COM
Vo
COM
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) _{– 49.9 kΩ}
V_o – V_a
Where: V_o = Original output voltage
V_a = Adjusted output voltage
Table 1
PT6400 ADJUSTMENT RANGE
Series Pt #
PT6408
Vo (nom)
1.2
Va (min)
1.1
Va (max)
1.4
PT6404
1.5
1.3
1.8
PT6406
1.8
1.5
2.2
PT6407
2.1
1.8
2.6
PT6409
2.5
2.1
3.1
PT6405
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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