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TPS61087QDRCRQ1 Datasheet(PDF) 8 Page - Texas Instruments |
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TPS61087QDRCRQ1 Datasheet(HTML) 8 Page - Texas Instruments |
8 / 30 page 8 TPS61087-Q1 SLVSB50B – DECEMBER 2011 – REVISED JUNE 2016 www.ti.com Product Folder Links: TPS61087-Q1 Submit Documentation Feedback Copyright © 2011–2016, Texas Instruments Incorporated 7.3 Feature Description 7.3.1 Soft Start The boost converter has an adjustable soft start to prevent high inrush current during start-up. To minimize the inrush current during start-up an external capacitor, connected to the SS pin and charged with a constant current, is used to slowly ramp up the internal current limit of the boost converter. When the EN pin is pulled high, the soft-start capacitor (CSS) is immediately charged to 0.3 V. The capacitor is then charged at a constant current of 10 μA typically until the output of the boost converter VS has reached its Power Good threshold (roughly 98% of VS nominal value). During this time, the SS voltage directly controls the peak inductor current, starting with 0 A at VSS = 0.3 V up to the full current limit at VSS = 800 mV. The maximum load current is available after the soft start is completed. As the size of the capacitor increases the ramp of the current limit slows and the soft-start time increases. A 100-nF capacitor is usually sufficient for most of the applications. When the EN pin is pulled low, the soft-start capacitor is discharged to ground. 7.3.2 Frequency Select Pin (FREQ) The switching frequency of the device is set using the frequency select pin (FREQ) to 650 kHz (FREQ = low) or 1.2 MHz (FREQ = high). Higher switching frequency improves load transient response but slightly reduces the efficiency. Another benefit of higher switching frequency is a lower output ripple voltage. Unless light load efficiency is a major concern, TI recommends using a 1.2-MHz switching frequency. 7.3.3 Undervoltage Lockout (UVLO) To avoid misoperation of the device at low input voltages, an undervoltage lockout is included, which disables the device if the input voltage falls below 2.4 V. 7.3.4 Thermal Shutdown A thermal shutdown is implemented to prevent damages due to excessive heat and power dissipation. Typically the thermal shutdown happens at a junction temperature of 150°C. When the thermal shutdown is triggered, the device stops switching until the junction temperature falls below typically 136°C. Then the device starts switching again. 7.3.5 Overvoltage Prevention If overvoltage is detected on the FB pin (typically 3% above the nominal value of 1.238 V) the part stops switching immediately until the voltage on this pin drops to its nominal value. This prevents overvoltage on the output and secures the circuits connected to the output from excessive overvoltage. 7.4 Device Functional Modes The converter operates in continuous conduction mode (CCM) as soon as the input current increases above half the ripple current in the inductor; for lower load currents, the converter switches into discontinuous conduction mode (DCM). If the load is further reduced, the part starts to skip pulses to maintain the output voltage. |
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