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CDRH103RNP-2R2N Datasheet(PDF) 11 Page - Skyworks Solutions Inc. |
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CDRH103RNP-2R2N Datasheet(HTML) 11 Page - Skyworks Solutions Inc. |
11 / 19 page 11 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 201998B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 AAT1162 12V, 1.5A Step-Down DC/DC Converter DATA SHEET The external resistors set the output voltage according to the following equation: ⎛⎞ VOUT = 0.6V 1 + ⎝⎠ R1 R2 or ⎛⎞ ⎝⎠ R1 = -1 · R2 VOUT VREF Table 1 shows the resistor selection for different output voltage settings. VOUT (V) R2 = 5.9(kΩ) R1 (kΩ) R2 = 59(kΩ) R1 (kΩ) 0.8 1.96 19.6 0.9 2.94 29.4 1.0 3.92 39.2 1.1 4.99 49.9 1.2 5.90 59.0 1.3 6.81 68.1 1.4 7.87 78.7 1.5 8.87 88.7 1.8 11.8 118 1.85 12.4 124 2.0 13.7 137 2.5 18.7 187 3.3 26.7 267 5.0 43.2 432 Table 1: Resistor Selection for Different Output Voltage Settings. Standard 1% Resistors are Substituted for Calculated Values. Inductor Selection For most designs, the AAT1162 operates with inductors of 2μH to 4.7μH. Low inductance values are physically smaller, but require faster switching, which results in some efficiency loss. The inductor value can be derived from the following equation: VOUT 3.3 L1 = · 3.8µH Where ∆IL is inductor ripple current. Large value induc- tors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current approximately 32% of the maximum load current 1.5A, or ∆IL = 480mA. For output voltages above 3.3V, the minimum recommended inductor is 3.8μH. For 3.3V and below, use a 2 to 3.8μH inductor. For optimum voltage- positioning load transients, choose an inductor with DC series resistance in the 15mΩ to 20mΩ range. For higher efficiency at heavy loads (above 1A), or minimal load regulation (but some transient overshoot), the resistance should be kept below 18mΩ. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (1.5A + 280mA). Table 2 lists some typical surface mount inductors that meet target applications for the AAT1162. Manufacturer’s specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the satura- tion characteristics. The inductor should not show any appreciable saturation under normal load conditions. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. For example, the 4.7μH WE-TPC series inductor selected from Wurth has an 38mΩ DCR and a 2.4ADC current rating. At full load, the inductor DC loss is 85mW which gives only a 1.1% loss in efficiency for a 1.5A, 5V output. Input Capacitor Selection The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency shall be less than the input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 10μF ceramic capacitor is sufficient for most applications. |
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