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317B Datasheet(PDF) 9 Page - Linear Technology |
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317B Datasheet(HTML) 9 Page - Linear Technology |
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9 / 16 page  9 LT1317/LT1317B Table 1. Inductors Suitable for Use with the LT1317 MAX HEIGHT PART VALUE DCR MFR (mm) COMMENT LQH3C100 10 µH 0.57 Murata-Erie 2.0 Smallest Size, Limited Current Handling DO1608-103 10 µH 0.16 Coilcraft 3.0 CD43-100 10 µH 0.18 Sumida 3.2 CD54-100 10 µH 0.10 Sumida 4.5 Best Efficiency CTX32CT-100 10 µH 0.50 Coiltronics 2.2 1210 Footprint Capacitor Selection Low ESR (Equivalent Series Resistance) capacitors should be used at the output of the LT1317. For most applications a solid tantalum in a C or D case size works well. Accept- able capacitance values range from 10 µF to 330µF with ESR falling between 0.1 Ω and 0.5Ω. If component size is an issue, tantalum capacitors in smaller case sizes can be used but they have high ESR and output voltage ripple may reach unacceptable levels. Ceramic capacitors are an alternative because of their combination of small size and low ESR. A 10 µF ceramic capacitor will work for some applications but the ex- tremely low ESR of these capacitors may cause loop stability problems. Compensation components will need APPLICATIONS INFORMATION to be adjusted to ensure a stable system for the entire input voltage range. Figure 4 shows a 2V to 3.3V converter with new values for RC and CC. Figure 5 details transient response for this circuit. Also, ceramic caps are prone to temperature effects and the designer must check loop stability over the operating temperature range (see section on Frequency Compensation). Input bypass capacitor ESR is less critical and smaller units may be used. If the input voltage source is physically near the VIN pin (<5mm), a 10µF ceramic or a 10µF A case tantalum is adequate. Diodes Most of the application circuits on this data sheet specify the Motorola MBR0520L surface mount Schottky diode. In lower current applications, a 1N4148 can be used, although efficiency will suffer due to the higher forward drop. This effect is particularly noticeable at low output voltages. For higher voltage output applications, such as LCD bias generators, the extra drop is a small percentage of the output voltage so the efficiency penalty is small. The low cost of the 1N4148 makes it attractive wherever it can be used. In through hole applications the 1N5818 is the all around best choice. VIN SW FB LT1317B L1 10 µH D1 SHDN RC 20k R2 604k 1% VOUT 3.3V R1 1M 1% CC 1500pF 1317 F04 C1 10 µF VIN 2V C2 10 µF CERAMIC D1: MBR0520 L1: SUMIDA CD43-100 VC GND Figure 4. 2V to 3.3V Converter with a 10 µF Ceramic Output Capacitor. RC and CC Have Been Adjusted to Give Optimum Transient Response. 200 µs/DIV 1317 F05 VOUT 200mV/DIV AC COUPLED ILOAD 5mA TO 200mA Figure 5. Transient Response for the Circuit of Figure 4. |
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