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APPLICATION INFORMATION

Adjusting the Output Voltage of the PTN78060A Wide-Output Adjust Power Modules

General

R

= 54.9 k

SET

1.25 V

|

|

V

- 3 V

O

- 5.62 kW

(1)

Input Voltage Considerations

GND

GND

PTN78060A

6

1, 7

2

Adj

GND

4

+

+

C2

C1

0.05 W

1%

C3

V

O

V

O

V

I

V

I

PTN78060A

SLTS245A – APRIL 2005 – REVISED MAY 2005

the output voltage lower than –3 V. The adjustment range is from –15 V to –3 V. If pin 4 is left open, the output

voltage defaults to the highest value, –3 V.

Table 1 gives the standard resistor value for a number of common voltages, and with the actual output voltage

that the value produces. For other output voltages, the resistor value can either be calculated using the following

formula, or simply selected from the range of values given in Table 2. Figure 18 shows the placement of the

required resistor.

The PTN78060A is a buck-boost switching regulator. In order that the output remains in regulation, the input

voltage must not exceed the output by a maximum 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's input and output voltage magnitudes.

As an example, Table 1 gives the operating input voltage range for the common output bus voltages. In addition,

the Electrical Characteristics define the available output voltage adjust range for various input voltages.

Voltages

Operating

(Required)

(Standard Value)

(Actual)

–15 V

100

Ω

–14.997 V

9 V to 17 V

–12 V

2 k

Ω

–12.006 V

9 V to 20 V

–5 V

28.7 k

Ω

–5.000 V

9 V to 27 V

–3.3 V

221 k

Ω

–3.303 V

9 V to 28.7 V

(1)

A 0.05-W rated resistor may be used. The tolerance should be 1%, with a temperature stability of 100 ppm/°C (or

better). Place the resistor as close to the regulator as possible. Connect the resistor directly between pins 4 and 7

using dedicated PCB traces.

(2)

stability of the regulator.

8