SLTS062B datasheet(3/7 Pages) TI

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Application Notes

For technical support and more information, see inside back cover or visit www.ti.com

PT6920/PT6930 Series

Adjusting the Output Voltage of the PT6920 and

PT6930 Dual Output Voltage ISRs

Each output voltage from the PT6920 and PT6930 series

of ISRs can be independantly adjusted higher or lower than

the factory trimmed pre-set voltage. Vo1 or Vo2 may each

be adjusted either up or down using a single external resis-

tor 2. Table 1 gives the adjustment range for both Vo1 and

Vo2 for each model in the series as Va(min) and Va(max).

Note that Vo2 must always be lower than Vo1 3.

Vo1 Adjust Up:

To increase the output, add a resistor R4

between pin 16 (V1 Adjust) and pins 7-11 (GND) 2.

Vo1 Adjust Down: Add a resistor (R3), between pin 16

(Vo1 Adjust) and pin 1 (Vo1 Sense) 2.

Vo2 Adjust Up:

Add a resistor R2 between pin 23

(Vo2 Adjust) and pins 7-11 (GND) 2.

Vo2 Adjust Down: Add a resistor (R1) between pin 23

(Vo2 Adjust) and pin 22 (Vo2 Sense) 2.

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

the required resistor.

Notes:

1. The output voltages, Vo1 and Vo2, may be adjusted

independantly.

2. Use only a single 1% resistor in either the (R3) or R4

location to adjust Vo1, and in the (R1) or R2 location to

adjust Vo2. Place the resistor as close to the ISR as

possible.

3. Vo2 must always be at least 0.2V lower than Vo1.

4. Vo2 on both the PT6921 and PT6931 models may be

adjusted from 2.5V to 1.8V by simply connecting pin

22 (Vo2 Sense) to pin 23 (Vo2 Adjust). For more

details, consult the data sheet.

Table 1

PT6920 ADJUSTMENT RANGE AND FORMULA PARAMETERS

Output Bus

Vo1

Vo2

Series Pt #

Standard Case

PT6921/22

PT6921

PT6922

Excalibur Case

PT6931/32

PT6931

PT6932

PT6933

Adj. Resistor

(R3)/R4

(R1)/R2

Vo(nom)

3.3V

2.5V

1.5V

1.8V

Va(min)

2.3V

1.8V

1.2V

Va(max)

3.6V

3.0V

1.02V

1.0V

Ro (k

Ω

Ω)

12.1

10.0

9.76

10.0

Rs (k

Ω

Ω)

12.1

11.5

6.49

3.32

Figure 1

(R3)

(R1)

Adj Down

Adjust Up

Vin

COM

PT6920

18 - 21

7 - 11

4,5,6

Vin

out

GND

V o

2(adj)

1(sns)

1(adj)

12 - 15

out

2(sns)

STBY

Adjust V1

out

Adjust V2

out

5. If Vo1 is increased above 3.3V, the minimum input voltage

to the ISR must also be increased. The minimum

required input voltage must be (Vo1 + 1.2)V or 4.5V,

whichever is greater. Do not exceed 5.5V

6. Never connect capacitors to either the Vo1 Adjust or Vo2

Adjust pins. Any capacitance added to these control pins

will affect the stability of the respective regulated output.

7. Adjusting either voltage (Vo1 or Vo2) may increase the

power dissipation in the regulator, and correspondingly

change the maximum current available at either output.

Consult the factory for application assistance.

The adjust up and adjust down resistor values can also be

calculated using the following formulas. Be sure to select

the correct formula parameter from Table 1 for the output

and model being adjusted.

(R1) or (R3)

Ro (Va – Vr) –R

Ω

Vo – Va

R2 or R4

Vr . Ro

– Rs

Ω

Va – Vo

Where:

Vo = Original output voltage, (Vo1 or Vo2)

Va = Adjusted output voltage

Vr = The reference voltage from Table 1

Ro = The resistance value from Table 1

Rs = The series resistance from Table 1

Not Recommended For New Designs

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