PT6921 datasheet(3/5 Pages) TI

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Applicatio n

Note s

PT6920 Series

More Application Notes

Adjusting the Output Voltage of the PT6920 Dual

Output Voltage ISR

Both output voltages from the Power Trends PT6920 series

ISRs can be independantly adjusted higher or lower than their

factory trimmed pre-set voltage. In each case only a single

external resistor is required to adjust either V1 (the voltage at

V1out, or V2 (the voltage at V2out). Table 1 gives the permis-

sible adjustment range for both V1 and V2 for each model in the

series as Va(min) and Va(max). Note: V2 must always be lower

than V1.

V1 Adjust Up:

To increase the output, add a resistor R4 be-

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

V1 Adjust Down:

Add a resistor (R3), between pin 16

(V1 Adjust) and pin 1 (V1 Remote Sense).

V2 Adjust Up:

Add a resistor R2 between pin 23 (V2 Adjust)

and pins 7-11 (GND).

V2 Adjust Down:

Add a resistor (R1) between pin 23 (V2 Adjust)

and pin 22 (V2 Remote Sense).

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

of the required resistor.

Notes:

1. The voltage at V1out and V2out may be adjusted

independantly.

2. V2 must always be at least 0.2V lower than V1.

3. If V1 is increased above 3.3V, the minimum input voltage to

the ISR must also be increased. The minimum required

input voltage must be (V1 + 1.2)V or 4.5V, whichever is

greater. Do not exceed 6.0V

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

Table 1

PT6920 ADJUSTMENT RANGE AND FORMULA PARAMETERS

Output Bus

V1 out

V2 out

Series Pt #

PT6921/22

PT6921

PT6922

Adj. Resistor

(R3)/R4

(R1)/R2

Vo(nom)

3.3V

2.5V

1.5

Va(min)

2.3V

1.8V

1.2

Va(max)

4.2V

3.0V

3.0

Ro (k

Ω)

12.1

10.0

9.76

Rs (k

Ω)

12.1

11.5

6.49

Figure 1

330

µF

330

µF

100

µF

(R3)

(R1)

Adj Down

Adjust Up

Vin

COM

out

PT6920

18 - 21

7 - 11

4,5,6

Vin

out

GND

2(adj)

1(sns)

1(adj)

12 - 15

out

2(sns)

STBY

Adjust V1

out

Adjust V2

out

tion to adjust V1, and in the (R1) or R2 location to adjust V2.

Place the resistor as close to the ISR as possible.

5. Never connect capacitors to either the V1 Adjust or

V2 Adjust pins. Any capacitance added to these control pins

will affect the stability of the respective regulated output.

6. To comply with the ISRs power dissipation limits, changes

made to either output voltage (V1 or V2) may affect the

maximum current available from both outputs. For more

information, consult the related applications note, “Deter-

mining the Maximum Output Current for the PT6920

Series Dual Output ISR.”

The adjust up and adjust down resistor values can also be calcu-

lated using the following formulae. Be sure to select the correct

formula parameter from Table 1 for the output and model being

adjusted.

(R1)/(R3)

Ro (Va – 1)

– Rs

Ω

Vo – Va

R2/R4

– Rs

Ω

Va – Vo

Where:

Vo = Original output voltage, (V1 or V2)

Va = Adjusted output voltage

Ro = The resistance value from Table 1

Rs = The series resistance from Table 1

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