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PT5813C Datasheet(PDF) 8 Page - Texas Instruments |
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PT5813C Datasheet(HTML) 8 Page - Texas Instruments |
8 / 11 page Application Notes For technical support and more information, see inside back cover or visit www.ti.com PT5800 & PT5810 Series Adjusting the Output Voltage of the PT5800 & PT5810 Step-Down Series of Regulators Using Margin Up/ Margin Down The Margin Up* (pin 4) and Margin Dn* (pin 3) control inputs allow the output voltage to be easily adjusted by up to ±5 % of the nominal set-point voltage. To activate, simply connect the appropriate control input to the Sense(–) (pin 8), or the local starpoint ground. Either a logic level MOSFET or a p-channel JFET is recommended for this purpose. For further information see the related applica- tion note on this feature. Using the ‘V o Adjust’ Control For a more permanent and precise adjustment, use the Vo Adjust control (pin 1). The Vo Adjust control allows adjustment in any increment by up to ±10% of the set- point. The adjustment method requires the addition of a single external resistor. Table 5-1 gives the allowable adjustment range for each model of the series as Va (min) and Va (max). The value of the external resistor can either be calculated using the formulas given below, or simply selected from the range of values provided in Table 5-2. Refer to Figure 5-1 for the placement of the required resistor. Use the resistor R1 to adjust up, and the resistor (R2) to adjust down. Adjust Up: An increase in the output voltage is obtained by adding a resistor R1, between Vo Adjust (pin 1) and Sense(–) (pin 8). See Figure 5-1. Adjust Down: Add a resistor (R2), between Vo Adjust (pin 1) and Sense(+) (pin 18). See Figure 5-1. Figure 5-1; V o Adjust Resistor Placement Vo Adjust Resistor Calculations The values of R1 [adjust up] and (R2) [adjust down] can also be calculated using the following formulas. Again, use Figure 5-1for the placement of the required resistor; either R1 or (R2) as appropriate. R1 = Vr · Ro – 24.9 k Ω Va – Vo (R2) = Ro (Va – Vr) – 24.9 k Ω Vo – Va Where: Vo = Original output voltage Va = Adjusted output voltage Vr = The reference voltage in Table 5-1 Ro = The resistance constant in Table 5-1 Table 5-1 ISR OUTPUT VOLTAGE ADJUSTMENT RANGE AND FORMULA PARAMETERS Series Pt. No. 5.0V Bus PT5801 PT5802 PT5803 PT5804 PT5805 PT5806 3.3V Bus N/A PT5812 4 PT5813 PT5814 PT5815 PT5816 Vo (nom) 3.3 V 2.5 V 1.8 V 1.5 V 1.2 V 1.0 V Va (min) 2.6 V 2.0 V 1.52 V 1.31 V 1.1 V 0.94 V Va (max) 3.63 V 2.8 V # 2.1 V 1.82 V 1.52 V 1.32 V Vr 0.8 V 0.8 V 0.8 V 0.8 V 0.8 V 0.8 V Ro (k Ω Ω Ω Ω Ω) 10.2 10.7 10.2 9.76 10.0 10.2 # The PT5812 should not be adjusted higher than its nominal output voltage of 2.5 V. See note 4. Notes: 1. Use a 1% (or better) tolerance resistor in either the R1 or (R2) location. Place the resistor as close to the ISR as possible. 2. Never connect capacitors from Vo Adjust to either GND or Vout. Any capacitance added to the Vo Adjust pin will affect the stability of the ISR. 3. If the remote sense feature is not being used, the adjust resistor (R2) can be connected to Vout, (pins 14-17) instead of Sense (+). PT5800/5810 9–13 1 18 14–17 8 C OUT 330 µF GND V OUT Sense (+) [Note 3] Sense (–) (R 2) Adj Down V O Adj GND Sense(+) Sense(–) V OUT R 1 Adjust Up 4. The PT5812 may not be adjusted higher than the nominal output voltage of 2.5 V. There is insufficient input voltage between Vin and Vout to accommodate an increase in the output voltage. |
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