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AME5130AEEVADJZ Fiches technique(PDF) 7 Page - Analog Microelectronics |
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AME5130AEEVADJZ Fiches technique(HTML) 7 Page - Analog Microelectronics |
7 / 16 page AME, Inc. 7 AME5130 Micropower Step-Up DC/DC Converter n Electrical Specifications The AME5130 features a constant off-time control scheme. Operation can be best understood by referring to Figure 3. When the voltage at the FB pin is less than 0.9V, the Enable Comp in Figure 3 enables the device and the NMOS switch is turmed on pulling the SW pin to ground. When the NMOS switch is on, current is sup- plied by the output capacitor C OUT. Once the current in the inductor reaches the peak current limit, the 400ns One Shot turns off the NMOS switch. The SW voltage will then rise to the output voltage plus a diode drop and the inductor current will begin to decrease as shown in Figure 3. During this time the energy stored in the induc- tor is transferred to C OUT and the load. After the 400ns off-time the NMOS switch is turned on and energy is stored in the inductor again. This energy transfer from the inductor to the output causes a stepping effect in the output ripple. This cycle is continued until the voltage at FB reaches 1.23V. When FB reaches this voltage, the enable com- parator then disables the device turning off the NMOS switch and reducing the Iq of the device to 64 µA. The load current is then supplied solely by C OUT indicated by the gradually decreasing slope at the output. When the FB pin drops slightly below 1.23V, the enable com- parator enables the device and begins the cycle de- scribed previously. The RUN pin can be used to turn off the AME5130 and reduce the Iq to 0.01 µA. In shutdown mode the output voltage will be a diode drop lower than the input voltage. n Application Information INDUCTOR SELECTION The appropriate inductor for a given application is calculated using the following equation: Where V D is the schottky diode voltage, I CL is the switch current limit found in the Typical Performance Char- acteristics section, and T OFF is the switch off time. When using this equation be sure to use in minimum input volt- age for the application, such as for battery powered ap- plications. Choosing inductors with low ESR decrease power lossed and increase efficiency. Care should be taken when choosing an inductor. For applications that require an input voltage that approaches the output voltage, such as when converting a Li-ion bat- tery voltage to 5V, the 400ns off time may not be enough time to discharge the energy in the inductor and transfer the energy to the output capacitor and load. This can cause a ramping effect in the inductor current waveform and an increased ripple on the output voltage. Using a smaller inductor will cause the I PK to increase and will increase the output voltage ripple further. This can be solved by adding a 4.7pF capacitor across the R1 feed- back resistor (Figure 3) and slightly increasing the out- put capacitor. A smaller inductor can then be used to ensure proper discharge in the 400ns off time. DIODE SELECTION To maintain high efficiency, the average current rating of the schottky diode should be larger than the peak in- ductor current, I PK. Schottky diodes with a low forward drop and fast switching speeds are ideal for increasing efficiency in portable applications. Choose a reverse break- down of the schottky diode larger than the output volt- age. OFF CL D IN(min) OUT T I V V V L + − = |
Numéro de pièce similaire - AME5130AEEVADJZ |
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Description similaire - AME5130AEEVADJZ |
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