PT6526LT datasheet(5/12 Pages) TI

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Application Notes

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PT6520 Series

Adjusting the Output Voltage of the PT6520

Series of Integrated Switching Regulators

The output voltage of the PT6520 series of integrated

switching regulators (ISRs) may be adjusted higher or

lower than the factory trimmed pre-set voltage with the

addition of a single external resistor. 1 Table 1 gives the

allowable adjustment range for each model in the series as

Va (min) and Va (max).

Adjust Up:

An increase in the output voltage is obtained

by adding a resistor R2, between pin 14 (Vo adjust) and

pins 7-10 (GND).

Adjust Down:

Add a resistor (R1), between pin 14 (Vo ad-

just) and pin 1 Vo(sense) 3.

Refer to Figure 1 and Table 2 for both the placement and value

of the required resistor, either (R1) or R2 as appropriate.

The values of (R1) [adjust down], and R2 [adjust up], can

also be calculated using the following formulas.

Ro ( Va –Vr )

(R1)

Vo – Va

– Rs

kΩ

Ro ·Vr

– Rs

kΩ

Va – Vo

Where: Vo = Original output voltage

Va = Adjusted output voltage

Vr = The reference voltage (Table 1)

Ro = The multiplier resistance (Table 1)

Rs = The internal series resistance (Table 1)

Figure 1

out

(R1)

Adj Down

Adj

COM

Vin

COM

PT6520

11,12,13

7,8,9,10

4,5,6

Vin

Vout

GND

Vo(adj)

STBY

Vo(sense)

Table 1

ADJUSTMENT AND FORMULA PARAMETERS

Series Pt #

PT6527

PT6522

PT6526

PT6525

PT6523

PT6521

Vo (nom)

1.2

1.5

1.8

2.1

2.5

3.3

Va (min)

1.09

1.47

1.75

1.95

2.25

2.75

Va (max)

1.52

1.73

2.05

2.45

2.85

3.75

Vr (V)

0.8

1.27

Ro (k

Ω

Ω)

10.0

10.2

10.0

Rs (k

Ω

Ω)

24.9

49.9

33.2

24.9

Notes:

1. Use only a single 1% resistor in either the (R1) or R2

location. Place the resistor as close to the ISR as

possible.

2. Never connect capacitors from Vo adjust to either

GND, Vout, or the Remote Sense pin. Capacitance

added to the Vo adjust pin will affect the stability of

the ISR.

3. If the Remote Sense feature is not being used, the

resistor (R1) may be connected between pin 14 (Vo

adjust) and pins 11–13 (Vout).

4. Adjusting the output voltage of the PT6523 (2.5V

model) higher than the factory pre-trimmed output

voltage may increase the minimum input voltage

specified for the part. This model must comply with

the following requirements.

PT6523:

Vin(min) = (Va + 0.5)V or 3.1V, whichever is greater.

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