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LT3430-1 Datasheet(PDF) 9 Page - Linear Technology |
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LT3430-1 Datasheet(HTML) 9 Page - Linear Technology |
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9 / 28 page  LT3430/LT3430-1 9 34301fa APPLICATIONS INFORMATION tion should be used if resistors are increased beyond the suggested values and short-circuit conditions occur with high input voltage. High frequency pickup will increase and the protection accorded by frequency and current foldback will decrease. Choosing the Inductor For most applications, the output inductor will fall into the range of 5µH to 47µH (10µH to 100µH for LT3430-1). Lower values are chosen to reduce physical size of the inductor. Higher values allow more output current because they reduce peak current seen by the LT3430/LT3430-1 switch, which has a 3A limit. Higher values also reduce output ripple voltage. When choosing an inductor you will need to consider output ripple voltage, maximum load current, peak induc- tor current and fault current in the inductor. In addition, other factors such as core and copper losses, allowable component height, EMI, saturation and cost should also be considered. The following procedure is suggested as a way of handling these somewhat complicated and conflicting requirements. Output Ripple Voltage Figure 3 shows a comparison of output ripple voltage for the LT3430/LT3430-1 using either a tantalum or ceramic output capacitor. It can be seen from Figure 3 that output ripple voltage can be significantly reduced by using the ceramic output capacitor; the significant decrease in out- put ripple voltage is due to the very low ESR of ceramic capacitors. Output ripple voltage is determined by ripple current (ILP-P) through the inductor and the high frequency impedance of the output capacitor. At high frequencies, the impedance of the tantalum capacitor is dominated by its effective series resistance (ESR). Tantalum Output Capacitor The typical method for reducing output ripple voltage when using a tantalum output capacitor is to increase the inductor value (to reduce the ripple current in the inductor). The following equations will help in choosing the required – – + + 1.2V BUFFER VSW L1 VC GND TO SYNC CIRCUIT 3430 F02 TO FREQUENCY SHIFTING R3 1k R4 2k R1 C1 R2 OUTPUT 5V ERROR AMPLIFIER FB 1.4V Q1 LT3430 Q2 + Figure 2. Frequency and Current Limit Foldback Figure 3. LT3430 Output Ripple Voltage Waveforms. Ceramic vs Tantalum Output Capacitors VIN = 40V VOUT = 5V L = 22 µH 3430 F03 2 µs/DIV 20mV/DIV VOUT USING 100 µF CERAMIC OUTPUT CAPACITOR VOUT USING 100 µF 0.08Ω TANTALUM OUTPUT CAPACITOR 20mV/DIV |
Similar Part No. - LT3430-1_15 |
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Similar Description - LT3430-1_15 |
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