Application Notes

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

PT5800 & PT5810 Series

Adjusting the Output Voltage of the PT5800 &

PT5810 Step-Down Series of Regulators

Using Margin Up/ Margin Down

The Margin Up* (pin 4) and Margin Dn* (pin 3) control

inputs allow the output voltage to be easily adjusted by

up to ±5% of the nominal set-point voltage. To activate,

simply connect the appropriate control input to the Sense(–)

(pin 8), or the local starpoint ground. Either a logic level

MOSFET or a p-channel JFET is recommended for this

purpose. For further information see the related applica-

tion note on this feature.

Using the ‘V

o

Adjust’ Control

For a more permanent and precise adjustment, use the

adjustment in any increment by up to ±10% of the set-

point. The adjustment method requires the addition of a

single external resistor. Table 5-1 gives the allowable

be calculated using the formulas given below, or simply

selected from the range of values provided in Table 5-2.

Refer to Figure 5-1 for the placement of the required

Adjust Up: An increase in the output voltage is obtained

Sense(–) (pin 8). See Figure 5-1.

and Sense(+) (pin 18). See Figure 5-1.

Figure 5-1; V

o

Adjust Resistor Placement

also be calculated using the following formulas. Again, use

Figure 5-1for the placement of the required resistor;

=

– 24.9

k

Ω

=

– 24.9

k

Ω

Table 5-1

ISR OUTPUT VOLTAGE ADJUSTMENT RANGE AND FORMULA PARAMETERS

Series Pt. No.

5.0V Bus

PT5801

PT5802

PT5803

PT5804

PT5805

PT5806

3.3V Bus

N/A

PT5813

PT5814

PT5815

PT5816

Vo (nom)

3.3V

2.5V

1.8V

1.5V

1.2V

1.0V

Va (min)

2.6V

2.0V

1.52V

1.31V

1.1V

0.94V

Va (max)

3.63V

2.8V #

2.1V

1.82V

1.52V

1.32V

Vr

0.8V

0.8V

0.8V

0.8V

0.8V

0.8V

Ro (k

Ω

Ω

Ω

Ω

Ω)

10.2

10.7

10.2

9.76

10.0

10.2

# The PT5812 should not be adjusted higher than its nominal output voltage of 2.5V. See note 4.

Notes:

possible.

the stability of the ISR.

3. If the remote sense feature is not being used, the adjust

of Sense (+).

PT5800/5810

9–13

1

18

14–17

8

C

OUT

330µF

GND

V

OUT

Sense (+) [Note 3]

Sense (–)

(R

Adj Down

V

GND

Sense(+)

Sense(–)

V

OUT

R

1

Adjust Up

4. The PT5812 may not be adjusted higher than the

nominal output voltage of 2.5V. There is insufficient

an increase in the output voltage.