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APPLICATION INFORMATION

Adjusting the Output Voltage of the PTN78020x Series of Wide-Output Adjust Power Modules

General

R

= 54.9 k

SET

1.25 V

V

- V

O

min

- R

P

(1)

Input Voltage Considerations

PTN78020W

PTN78020H

SLTS228A – DECEMBER 2004 – REVISED APRIL 2005

The adjustment range is from 2.5 V to 12.6 V for PTN78020W. The adjustment range is from 11.85 V to 22 V for

PTN78020H. 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 a number of standard voltages, with the actual

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

placement of the required resistor.

PRODUCT

PTN780x0W

2.5 V

6.49 k

Ω

PTN780x0H

11.824 V

6.65 k

Ω

The PTN78020 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.

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 PTN78020x must adhere to

the following requirements.

is higher.

3. For PTN78020W, the maximum input voltage is (10

× V

whichever is higher.

Table 2 gives the operating input voltage range for the common output bus voltages. In addition, the Electrical

Characteristics table defines the available output voltage adjust range for various input voltages.

Operating

PRODUCT

(Required)

(Standard Value)

(Actual)

2.5 V

Open

2.5 V

7 V to 25 V

3.3 V

78.7 k

Ω

3.306 V

7 V to 33 V

PTN780x0W

5 V

21 k

Ω

4.996 V

7 V to 36 V

12 V

732

Ω

12.002 V

14.5 V to 36 V

12 V

383 k

Ω

12.000 V

15 V to 36 V

15 V

15 k

Ω

14.994 V

18 V to 36 V

PTN780x0H

18 V

4.42 k

Ω

18.023 V

21 V to 36 V

22 V

95.3

21.998 V

26 V to 36 V

10