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PTB48500 Datasheet(PDF) 11 Page - Texas Instruments |
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PTB48500 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 17 page www.ti.com APPLICATION INFORMATION ADJUSTING THE LOWER OUTPUT CALCULATION OF THE ADJUST RESISTOR R 1 [Adjust Up] + Rp Va Va * Vo * Rs kW (1) R 2 [Adjust Down] + Rn Va Vo * Va * Rs kW (2) +VO PTB4850x 6 9 COM 7 VO2 VO2Adj R1 Adjust Up PTB4850x 6 9 COM 7 +VO VO2 VO2Adj (R2) Adj Down PTB48500 PTB48501 PTB48502 SLTS218C – SEPTEMBER 2003 – REVISED AUGUST 2006 VOLTAGE OF THE PTB4850x The value of the adjust resistor is calculated using The PTB4850x series of DC/DC converters are one of the following equations. Use the equation for designed to produce two logic-level supply voltages R1 to adjust up, or (R2) to adjust down. for use with the AC-7 ADSL chipset. The magnitude of lowest output voltage (Vo2) can be adjusted higher or lower by up to 10% or —20% of the nominal. The adjustment method uses a single external resistor.1 The value of the resistor determines the amount of adjustment, and its placement determines whether the voltage is increased or decreased. The resistor values can be calculated using the appropriate Where: formula (see Equation 1 and Equation 2), or simply Vo = Magitude of the original output voltage selected from the range of values given in Table 2. The placement of each resistor is as follows. Va = Magnitude of the adjusted voltage Rp = Adjust-up constant from Table 1 Adjust Up: To increase the magnitude of both output voltages, place a resistor R1 between Vo2 Adj Rn = Adjust-down constant from Table 1 (pin 9) and the Vo2 (pin 6) voltage rail; see Rs = Internal series resistor from Table 1 Figure 17. Table 1. Adjustment Range and Formula Parameters Part No. PTB48500(1)A PTB48502A Vo(nom) 1.2 V 1.2 V Va(min) 0.96 V 0.84 V Va(max) 1.32 V 1.32 V Rp (kΩ) 1.648 1.196 Rn (kΩ) 4.624 3.598 Rs (kΩ) 18.2V 13.0 NOTES: 1. A 0.05 W rated resistor may be used. The tolerance should be 1%, with a temperature Figure 17. Adjust Up stability of 100 ppm/ °C or better. Place the resistor in either the R1 or (R2) location, as close Adjust Down: To decrease the magnitude of both to the converter as possible. output voltages, add a resistor (R2), between Vo2 Adj 2. Never connect capacitors to the Vo2 Adj pin. (pin 9) and the COM (pin 7) voltage rail; see Capacitance added to this pin can affect the Figure 18. stability of the regulated output. Table 2. Adjust Resistor Values Part No. PTB4850xA PTB48502A % Adjust Va (V) R1 / (R2)(1) R1 / (R2)(1) –21 0.848 N/A (0.5) k Ω –20 0.960 (0.3) k Ω (1.4) k Ω –19 0.972 (1.5) k Ω (2.3) k Ω –18 0.984 (2.9) k Ω (3.4) k Ω –17 0.996 (4.4) k Ω (4.6) k Ω –16 1.008 (6.1) k Ω (5.9) k Ω –15 1.020 (8.0) k Ω (7.4) k Ω –14 1.032 (10.2) k Ω (9.1) k Ω Figure 18. Adjust Down (1) R1 =Adjust up, (R2) =Adjust down 11 Submit Documentation Feedback |
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Similar Description - PTB48500_06 |
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