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TPS61165DRVTG4 Datasheet(PDF) 11 Page - Texas Instruments |
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TPS61165DRVTG4 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 33 page out in out out out s ripple (V V ) I C V F V - = ´ ´ 11 TPS61165 www.ti.com SLVS790D – NOVEMBER 2007 – REVISED APRIL 2016 Product Folder Links: TPS61165 Submit Documentation Feedback Copyright © 2007–2016, Texas Instruments Incorporated Application Information (continued) Inductor values can have ±20% tolerance with no current bias. When the inductor current approaches saturation level, its inductance can decrease 20% to 35% from the 0A value depending on how the inductor vendor defines saturation current. Using an inductor with a smaller inductance value forces discontinuous PWM when the inductor current ramps down to zero before the end of each switching cycle. This reduces the maximum output current of the boost convert, causes large input voltage ripple, and reduces efficiency. Large inductance value provides much more output current and higher conversion efficiency. For these reasons, a 10- μH to 22-μH inductor value range is recommended. A 22- μH inductor optimized the efficiency for most application while maintaining low inductor peak to peak ripple. Table 2 lists the recommended inductor for the TPS61165. When recommending inductor value, the factory has considered –40% and 20% tolerance from its nominal value. TPS61165 has built-in slope compensation to avoid subharmonic oscillation associated with current mode control. If the inductor value is lower than 10 μH, the slope compensation may not be adequate, and the loop can be unstable. Therefore, customers need to verify the inductor in their application if it is different from the recommended values. Table 2. Recommended Inductors for TPS61165 PART NUMBER L ( μH) DCR MAX (m Ω) SATURATION CURRENT (A) SIZE (L × W × H mm) VENDOR A915_Y-100M 10 90 1.3 5.2 × 5.2 × 3.0 TOKO VLCF5020T-100M1R1-1 10 237 1.1 5 × 5 × 2.0 TDK CDRH4D22/HP 10 144 1.2 5 × 5 × 2.4 Sumida LQH43PN100MR0 10 247 0.84 4.5 × 3.2 × 2.0 Murata 9.1.3 Schottky Diode Selection The high switching frequency of the TPS61165 demands a high-speed rectification for optimum efficiency. Ensure that the average and peak current rating of the diode exceeds the average output current and peak inductor current. In addition, the reverse breakdown voltage of the diode must exceed the open LED protection voltage. The ONSemi MBR0540 and the ZETEX ZHCS400 are recommended for TPS61165. 9.1.4 Compensation Capacitor Selection The compensation capacitor C3 (see Functional Block Diagram), connected from COMP pin to GND, is used to stabilize the feedback loop of the TPS61165. A 220-nF ceramic capacitor is suitable for most applications. 9.1.5 Input and Output Capacitor Selection The output capacitor is mainly selected to meet the requirements for the output ripple and loop stability. This ripple voltage is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated as shown in Equation 4. where • Vripple = peak-to-peak output ripple (4) The additional output ripple component caused by ESR is calculated as shown in Equation 4. Vripple_ESR= Iout × RESR (5) Due to its low ESR, Vripple_ESR can be neglected for ceramic capacitors, but must be considered if tantalum or electrolytic capacitors are used. Care must be taken when evaluating a ceramic capacitors derating under dc bias, aging and AC signal. For example, larger form factor capacitors (in 1206 size) have self-resonant frequencies in the range of the switching frequency. So the effective capacitance is significantly lower. The dc bias can also significantly reduce capacitance. Ceramic capacitors can loss as much as 50% of its capacitance at its rated voltage. Therefore, leave the margin on the voltage rating to ensure adequate capacitance at the required output voltage. |
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