Datasheet
APPLICATION INFORMATION
Adjusting the Output Voltage of the PTN78060 Wide-Output Adjust Power Modules
General
R =54.9k
SET
W ´
1.25 V
V -V
O min
-R
P
(1)
Input Voltage Considerations
PTN78060W , PTN78060H
SLTS229B – NOVEMBER 2004 – REVISED JUNE 2009 ...................................................................................................................................................
www.ti.com
A resistor must be connected between the V
O
Adjust control (pin 4) and GND (pin 1) to set the output voltage.
The adjustment range is from 2.5 V to 12.6 V for PTN78060W. The adjustment range is from 11.85 V to 22 V for
PTN78060H. If pin 4 is left open, the output voltage defaults to the lowest value.
Table 2 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 Equation 1
and the constants for the applicable product in Table 1 . Alternatilvey, R
SET
can be simply selected from the range
of values given in Table 3 and Table 4 . Figure 27 shows the placement of the required resistor.
Table 1. R
SET
Formula Constants
PRODUCT V
MIN
R
P
PTN780x0W 2.5 V 6.49 k Ω
PTN780x0H 11.824 V 6.65 k Ω
The PTN78060 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.
For satisfactory performance, the operating input voltage range of the PTN78060x must adhere to the following
requirements.
1. For PTN78060W output voltages lower than 10 V, the minimum input voltage is (V
O
+ 2 V ) or 7 V, whichever
is higher.
2. For PTN78060W output voltages equal to 10 V and higher, the minimum input voltage is (V
O
+ 2.5 V ).
3. The maximum input voltage for PTN78060W is (10 × V
O
) or 36 V, whichever is less.
4. For PTN78060H output voltages lower than 19 V, the minimum input voltage is (V
O
+ 3 V) or 15 V, whichever
is higher.
5. For PTN78060H output voltages equal to 19 V and higher, the minimum input voltage is (V
O
+ 4 V ) .
As an example, 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.
Table 2. Standard Values of R
set
for Common Output Voltages
V
O
R
SET
V
O
Operating
PRODUCT
(Required) (Standard Value) (Actual) V
I
Range
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 Submit Documentation Feedback Copyright © 2004 – 2009, Texas Instruments Incorporated
Product Folder Link(s): PTN78060W PTN78060H