PT6420_14 Datasheet, PDF (3/6 Pages) Texas Instruments – Adjustable Output Voltage

Application Notes
PT6420 Series
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
products. 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)
location. 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
minimum input voltage will be (V_out + 1.2) or 4.5V,
whichever is higher. Do not exceed 5.5Vdc.
Figure 1
Vin
4,5,6
Vin
C1
+
1 0 0 µF
1
Vsense
PT6420
11,12,13
Vo
GND
Vo(adj)
7,8,9,10
14
R1
Adjust
Up
C2
+
1 0 0 µF
(R2)
Adj Down
COM
Vo
L
O
A
D
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
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
For technical support and more information, see inside back cover or visit www.ti.com/powertrends