Application Notes

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Using the Margin Up/Down Controls on the

PT5800 & PT5810 Regulator Series

The PT5800 & PT5810 series of integrated switching

regulator modules incorporate Margin Up* (pin 4) and

Margin Dn* (pin 3) control inputs. These controls allow the

either up or down, by a nominal 5%. This provides a

convenient method for dynamically testing the load

circuit’s power supply voltage over its operating margin

or range. Note that the ±5% change is also applied to any

Adjust (pin 1).

The 5% adjustment is made by driving the appropriate

margin control input directly to the ground reference at

a MOSFET or a p-channel JFET is recommended for this

purpose. Adjustments of less than 5% can also be accom-

modated by adding series resistors to the control inputs

(See Figure 6-1). The value of the resistor can be selected

from Table 6-1, or calculated using the following formula.

Resistor Value Calculation

To reduce the margin adjustment to something less than

same. The formulas is as follows.

499

– 99.8

k

Ω

∆%

Where

∆% = The desired amount of margin adjust in

percent.

Notes:

1. The Margin Up* and Margin Dn* controls were not

intended to be activated simultaneously. If they are

their affects on the output voltage may not completely

cancel, resulting in a slight shift in the output voltage

set point.

2. When possible use the Sense(-) (pin 8) as the ground

reference. This will produce a more accurate adjustment

of the output voltage at the load circuit terminals. GND

(pins 9-13) can be used if the Sense(-) pin is connected

to GND near the regulator.

C

out

+

C

in

+5V

GND

MargDn

L

O

A

D

Q

2

Sense(–)

+V

OUT

GND

PT5800

18

14–17

8

29–13

5, 6, 7

V

OUT

V

IN

GND

SNS(+)

SNS(–)

INHIBIT*

Q

1

4

3

MARG

DN*

MARG

UP*

+

MargUp

0V

+V

o

R

D

R

U

0V

Figure 6-1; Margin Up/Down Application Schematic

Table 6-1; Margin Up/Down Resistor Values

PADDING RESISTOR VALUES

% Adjust

5

0.0k

Ω

4

24.9k

Ω

3

66.5k

Ω

2

150.0k

Ω

1

397.0k

Ω

PT5800 & PT5810 Series