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PTN78020WAZ Datasheet(PDF) 10 Page - Texas Instruments |
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PTN78020WAZ Datasheet(HTML) 10 Page - Texas Instruments |
10 / 26 page APPLICATION INFORMATION Adjusting the Output Voltage of the PTN78020x Series of Wide-Output Adjust Power Modules General R =54.9k SET W ´ 1.25 V V -V O min -R P (1) Input Voltage Considerations PTN78020W PTN78020H SLTS228B – DECEMBER 2004 – REVISED APRIL 2008 .................................................................................................................................................. www.ti.com A resistor must be connected between the VO Adjust control (pin 4) and GND (pin 7) to set the output voltage. 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 calculated using Equation 1 and the constants for the applicable product in Table 1. Figure 24 shows the placement of the required resistor. Table 1. RSET Formula Constants PRODUCT VMIN RP 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. 1. For PTN78020W output voltages lower than 10 V, the minimum input voltage is (VO + 2 V ) or 7 V, whichever is higher. 2. For PTN78020W output voltages equal to 10 V and higher, the minimum input voltage is (VO + 2.5 V ) . 3. For PTN78020W, the maximum input voltage is (10 × V O ) or 36 V, whichever is less. 4. For PTN78020H output voltages lower than 19 V, the minimum input voltage is (VO + 3 V ) or 15 V, whichever is higher. 5. For PTN78020H output voltages equal to 19 V and higher, the minimum input voltage is (VO + 4 V ) . 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 Rset for Common Output Voltages VO RSET VO Operating PRODUCT (Required) (Standard Value) (Actual) VI 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 © 2004–2008, Texas Instruments Incorporated Product Folder Link(s): PTN78020W PTN78020H |
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