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LTC1558CS-3.3 数据表(PDF) 14 Page - Linear Technology |
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LTC1558CS-3.3 数据表(HTML) 14 Page - Linear Technology |
14 / 20 page 14 LTC1558-3.3/LTC1558-5 Table 2. Recommended Inductors PART TYP INDUCTOR MANUFACTURER NUMBER VALUE DCR ( Ω) Sumida CD54-220 22 µH ±20% 0.18 Sumida CDRH73/74 22 µH ±20% 0.2/0.11 Capacitor Selection The LTC1558 requires a minimum VBAK capacitor of 44µF to ensure that the boost converter can regulate the output at 20mA load. The capacitor’s ESR should be small (< 0.2 Ω) to minimize voltage spikes that might incorrectly trigger the LTC1558’s internal FB comparators. Note that the LTC1558 can usually share the output capacitor with the system regulator. Thus its ratings like VMAX, IRIPPLE(RMS), etc., will all have to meet the system regulator’s specifica- tions as well. Battery Selection A primary application for the LTC1558 is a “bridging” supply, only providing backup current while the main system battery is being replaced. In these applications, the LTC1558 works well with NiCd button cells or small cylindrical cells, reducing system costs and board space. It is optimized for use with up to 512mAhr battery capacities. The LTC1558 can work with standard or memory backup specific NiCd cells. Memory backup cells can operate at higher temperatures and have lower self discharge rates. The LTC1558’s trickle charger is designed to accommo- date both memory backup cells (with low self discharge) and standard cells (with higher self discharge). Some recommended manufacturers and part numbers are listed in Table 3. APPLICATIONS INFORMATION Table 3. Button/Cylindrical NiCd 1.2V Cells PART CAPACITY MANUFACTURER NUMBER (mAhr) RSERIES (Ω) SAFT GB60 60 1.1 (Memory Backup) GB170 170 0.4 GB280 280 0.4 SAFT VB10E 100 0.038 (Standard) VB22E 220 0.022 VB30E 300 0.017 VB60E 600 0.014 Sanyo N-50AAA 55 0.055 (Standard) N-110AA 120 0.03 N-120TA 130 0.034 N-150N 170 0.027 N-200AAA 220 0.021 N-270AA 305 0.015 N-500A 500 0.09 Panasonic P-11AA 110 0.08 (Standard) The internal resistance of the backup cell increases power dissipation as the boost converter draws current from it during switching, degrading efficiency. Due to the fixed inductor peak current architecture, the LTC1558’s boost converter output power drops significantly when the NiCd cell’s internal resistance increases at the end of its charge. This is because the inductor charging time will increase due to a larger R/L time constant, decreasing the switching frequency. It is advisable, especially for batteries with high internal resistance, to include a 47 µF bypass capacitor across the battery to ensure that the boost converter can deliver the maximum output power regardless of the NiCd internal resistance. |
类似零件编号 - LTC1558CS-3.3 |
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类似说明 - LTC1558CS-3.3 |
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