PT6935 datasheet(9/12 Pages) TI

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Application Notes

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

Adjusting the Output Voltage of the PT6935

Dual Output Voltage ISRs

Each output voltage from the PT6935 series of ISRs can be

independantly adjusted higher or lower than the factory

trimmed pre-set voltage. The voltages, Vo1 and Vo2 may

each be adjusted either up or down using a single external

resistor 1. 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 2.

Vo1 Adjust Up:

To increase the output, add a resistor R4

between pin 16 (V1 Adjust) and pins 7-11 (GND) 1.

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

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

Vo2 Adjust Up:

Add a resistor R2 between pin 23

(Vo2 Adjust) and pins 7-11 (GND) 1.

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

(Vo2 Adjust) and pin 22 (Vo2 Sense) 1.

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

the required resistor.

Notes:

1. 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.

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

3. Both the Vo1 and Vo2 may be adjusted down to an

alternative bus voltage by making, (R3) or (R1)

respectively, a zero ohm link. Refer to the Table 1

footnotes for guidance.

Figure 1

(R3)

(R1)

Adj Down

Adjust Up

COM

PT6935

18 - 21

7 - 11

4,5,6

Vin

GND

2(adj)

1(sns)

1 (adj)

12 - 15

2(sns)

STBY

Adjust Vo

4. Adjusting the Vo1 output voltage of either the PT6935

(2.5V/1.8V model) or PT6939 (2.5V/1.2V) higher than

the factory pre-trimmed output voltage, may increase

the minimum input voltage specified for the part. These

models must comply with the following requirements.

PT6935/PT6939:

Vin(min) =(Va + 0.6)V or 3.1V,

whichever is greater.

5. 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.

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

power dissipation in the regulator, and change the

maximum current available at either output. Consult

the note on p.2 of the data sheet regarding Vo1/Vo2

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)

10 (Va – Vr )

– Rs

Ω

Vo – Va

(R2) or (R4)

10 · Vr

– Rs

Ω

Va – Vo

Where: Vo = Original output voltage, (Vo1 or Vo2)

Va = Adjusted output voltage

Vr = The reference voltage from Table 1

Rs = The series resistance from Table 1

PT6935 Series

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