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LP8866S-Q1 Datasheet(PDF) 17 Page - Texas Instruments |
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LP8866S-Q1 Datasheet(HTML) 17 Page - Texas Instruments |
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17 / 82 page  Table 7-1. Boost Frequency Selection R_BST_FSET (kΩ) BOOST FREQUENCY (kHz) 3.92 400 4.75 200 5.76 303 7.87 100 11 500 17.8 1818 42.2 2000 124 2222 7.3.6.1 Boost Cycle-by-Cycle Current Limit The voltage between ISNS and ISNSGND is used for both boost DC/DC controller's current sensing and cycle- by-cycle current limit settings. When the cycle-by-cycle current limit is reached, the controller will turn off the switching MOSFET immediately and turn on it again in next siwtching cycle. This cycle-by-cycle current limit could be used as a common protection for all related DC/DC components (inductor, schottky diode and switching MOSFET) to avoid current running over their max limit. Cycle-by-Cycle current limit won't trigger any faults of the device. CYCLE _ LIMIT ISNS SENSE V I = R (1) where • VISNS = 200 mV 7.3.6.2 Controller Min On/Off Time The device boost DC/DC controller has minimum on/off time as below table. Minimum off time should be specially taken care in system design. The SW node rising time plus falling time should be higher than minimum off time to avoid controller not turning off the MOSFET. Table 7-2. Controller Minimum On/Off Time Frequency (kHz) Minimum Switch OFF Time (ns) Minimum Switch ON Time (ns) 100 to 500 150 150 1818 to 2222 40 110 7.3.6.3 Boost Adaptive Voltage Control The LP8866S-Q1 boost DC/DC converter generates the anode voltage for the LEDs. During normal operation, boost output voltage is adjusted automatically based on the LED current sink headroom voltages. This is called adaptive boost control. The number of used LED outputs is set by LED_SET pin and only the active LED outputs are monitored to control the adaptive boost voltage. Any LED strings with open or short faults are also removed from the adaptive voltage control loop. The LED driver pin voltages are periodically monitored by the control loop and the boost voltage is raised if any of the LED outputs falls below the VHEADROOM threshold. The boost voltage is lowered until any of the LED outputs touch the VHEADROOM threshold. See Figure 7-4 for how the boost voltage automatically scales based on the OUTx-pin voltage, VHEADROOM and VHEADROOM_HYS. www.ti.com LP8866S-Q1 SNVSBD1A – AUGUST 2020 – REVISED FEBRUARY 2021 Copyright © 2021 Texas Instruments Incorporated Submit Document Feedback 17 Product Folder Links: LP8866S-Q1 |
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