APPLICATION INFORMATION

Adjusting the Output Voltage of the PTN78000 Wide-Output Adjust Power Modules

General

R

=54.9k

SET

1.25 V

V -V

O

min

-R

P

(1)

Input Voltage Considerations

PTN78000W, PTN78000H

The adjustment range is from 2.5 V to 12.6 V for PTN78000W. The adjustment range is from 11.85 V to 22 V for

PTN78000H. If pin 4 is left open, the output voltage defaults to the lowest value.

Table 2 gives the preferred value of the external resistor for several standard voltages, with the actual output

voltage that the value provides. For other output voltages, the value of the required resistor can be calculated

selected from the range of values given in Table 3. Figure 27 shows the placement of the required resistor.

PRODUCT

PTN780x0W

2.5

6.49

PTN780x0H

11.824

6.65

The PTN78000 is a step-down switching regulator. In order that the output remains in regulation, the input

voltage must exceed the output by a minimum differential voltage. (Please refer to the input voltage range

requirements in the electrical characteristics table.)

Another consideration is the pulse width modulation (PWM) range of the regulator's internal control circuit. For

stable operation, its operating duty cycle should not be lower than some minimum percentage. This defines the

maximum advisable ratio between the regulator input and output voltage magnitudes.

As an example, for satisfactory performance, the operating input voltage range of the PTN78000x must adhere to

the following requirements.

is higher.

whichever is higher.

10

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