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LTC1558CS8-3.3 数据表(PDF) 7 Page - Linear Technology |
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LTC1558CS8-3.3 数据表(HTML) 7 Page - Linear Technology |
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7 / 20 page  7 LTC1558-3.3/LTC1558-5 SWITCHING WAVEFORMS Cold Power Boot-Up Description 1. The VBAT voltage increases and turns on the QEXT body diode. VBAK follows VBAT by one body diode drop. 2. VBAK increases above the system regulator’s minimum input voltage. The system regulator wakes up and starts ramping up the system power supply. RESET remains asserted from VCC = 1V. 3. The LTC1558’s internal bandgap wakes up. The LTC1558’s internal boost converter does not turn on as RESET remains asserted. Once VFB is greater than (VREF – 6%), BACKUP is deasserted after the tPHL delay time. QEXT turns on and VBAK = VBAT. 4. RESET is asserted for a further 200ms after VCC exceeds – 6% of its rated value. Backup Mode Description 1. Trigger into Backup Mode. The main battery fails and VFB drops 7.5% below the LTC1558’s internal VREF. The BACKUP pin is asserted after a tRISE delay time and the LTC1558’s boost converter is turned on. 2. Backup Mode. The LTC1558’s boost converter charges and discharges the inductor with 165mA peak current. If VFB doesn’t recover above (VREF – 7.5%) (due to a heavy load), the boost converter increases peak charg- ing current to 330mA. When VFB rises above (VREF – 7.5%), the boost converter stops but the BACKUP pin remains asserted. 3. Recovery from Backup Mode. While the boost con- verter is running, the main battery is restored. This causes the external MOSFET’s body diode to conduct and VFB is pulled higher than (VREF – 6%). BACKUP deasserts and the boost converter finishes its last cycle. 4. Trigger into UVLO. During backup, the 1.2V NiCd cell grows weak and its terminal voltage falls. The LOBAT pin is asserted to give an early warning when the cell voltage drops below 1V. RESET is asserted when the cell voltage drops below 0.9V and the LTC1558 enters UVLO mode. Backup Mode (Main Battery Discharged) INDUCTOR CURRENT RESET BACKUP VFB VNICD LOBAT 1558 SW03 tRISE tRISE – 7.5% 1.2V – 7.5% – 7.5% 1V 0.9V –6% BOOST CONVERTER OUTPUT tFALL tRISE tRISE 4 3 2 1 |
类似零件编号 - LTC1558CS8-3.3 |
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类似说明 - LTC1558CS8-3.3 |
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