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ADP2116ACPZ-R7 数据表(PDF) 26 Page - Analog Devices |
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ADP2116ACPZ-R7 数据表(HTML) 26 Page - Analog Devices |
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26 / 36 page ![]() ADP2116 Rev. 0 | Page 26 of 36 EXTERNAL COMPONENTS SELECTION INPUT CAPACITOR SELECTION The input current to a buck converter is pulsating in nature. The current is zero when the high-side switch is off and approximately equal to the load current when the high-side switch is on. Because this pulsation occurs at reasonably high frequencies (300 kHz to 1.2 MHz), the input bypass capacitor supplies most of the high frequency current (ripple current), allowing the input power source to supply only the average (dc) current. The input capacitor needs a sufficient ripple current rating to handle the input ripple, as well as an ESR that is low enough to mitigate the input voltage ripple. For the ADP2116, place a 22 μF, 6.3 V X5R ceramic capacitor close to the VINx pin for each channel. X5R or X7R dielectrics are recommended with a voltage rating of 6.3 V or 10 V. Y5V and Z5U dielectrics are not recommended due to their poor temperature and dc bias characteristics. VDD RC FILTER It is recommended that the input power, VIN, be apply to the VDD pin through a low-pass RC filter, as shown in Figure 68. Connecting a 10 Ω resistor in series with VIN and a 1 μF, 6.3 V X5R (or X7R) ceramic capacitor between VDD and GND creates a 16 kHz (−3 dB) low-pass filter that effectively attenuates voltage glitches on the input power rail caused by the switching regulator. This provides a clean power supply to the internal, sensitive analog and digital circuits in the ADP2116, ensuring robust operation. VDD GND ADP2116 1µF 10 Ω VIN Figure 68. Low-Pass Filter at VDD INDUCTOR SELECTION The high switching frequency of the ADP2116 allows for minimal output voltage ripple even with small inductors. The size of the inductor is a trade-off between efficiency and transient response. A small inductor leads to larger inductor current ripple that provides excellent transient response but degrades efficiency. Due to the high switching frequency of the ADP2116, shielded ferrite core inductors are recommended for their low core losses and low EMI. As a guideline, the inductor peak-to-peak current ripple, ΔIL, is typically set to be one-third of the maximum load current for optimal transient response and efficiency. 3 ) ( ) (MAX LOAD SW IN OUT IN OUT L I L f V V V V I ≈ × × − × = Δ ) ( ) ( 3 MAX LOAD IN SW OUT IN OUT IDEAL I V f V V V L × × − × × = ⇒ (5) where: VIN is the input voltage on the VINx terminal. VOUT is the desired output voltage. fSW is the converter switching frequency. The internal slope compensation introduces additional limitations on the optimal inductor value for stable operation because the internal ramp is scaled for each VOUT setting. The limits for different VIN, VOUT, and fSW combinations are listed in Table 8. Table 8. Minimum and Maximum Inductor Values fSW (kHz) VIN (V) VOUT (V) Min L (μH) Max L (μH) 300 5 3.3 6.8 10 300 5 2.5 5.6 15 300 3.3 2.5 5.6 6.8 300 5 1.8 4.7 12 300 3.3 1.8 4.7 8.2 300 5 1.5 2.2 12 300 3.3 1.5 2.2 8.2 300 5 1.2 2.2 10 300 3.3 1.2 2.2 8.2 300 5 0.8 1.5 6.8 300 3.3 0.8 1.5 6.8 600 5 3.3 3.3 4.7 600 5 2.5 3.3 6.8 600 3.3 2.5 3.3 3.3 600 5 1.8 2.2 6.8 600 3.3 1.8 2.2 3.3 600 5 1.5 1.5 5.6 600 3.3 1.5 1.5 4.7 600 5 1.2 1.5 4.7 600 3.3 1.2 1.5 3.3 600 5 0.8 1.0 3.3 600 3.3 0.8 1.0 3.3 1200 5 2.5 1.0 3.3 1200 5 1.8 1.0 3.3 1200 3.3 1.8 1.0 2.2 1200 5 1.5 0.8 2.2 1200 3.3 1.5 0.8 2.2 1200 5 1.2 0.8 2.2 1200 3.3 1.2 0.8 2.2 1200 5 0.8 0.47 1.5 1200 3.3 0.8 0.47 1.5 |
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