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TPS62150 Datasheet(PDF) 11 Page - Texas Instruments |
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TPS62150 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 43 page OUT ON IN V t 400 ns V = ´ 11 TPS62150, TPS62150A, TPS62151, TPS62152, TPS62153 www.ti.com SLVSAL5D – NOVEMBER 2011 – REVISED SEPTEMBER 2016 Product Folder Links: TPS62150 TPS62150A TPS62151 TPS62152 TPS62153 Submit Documentation Feedback Copyright © 2011–2016, Texas Instruments Incorporated 8.3.5 Frequency Selection (FSW) To get high power density with a very small solution size, a high switching frequency allows the use of small external components for the output filter. However, switching losses increase with the switching frequency. If efficiency is the key parameter, more than solution size, the switching frequency can be set to half (1.25 MHz typical) by pulling FSW to High. It is mandatory to start with FSW = Low to limit inrush current, which connecting FSW to VOUT or PG can accomplish. Running with lower frequency produces higher efficiency, but also creates higher output-voltage ripple. Pull FSW to Low for high-frequency operation (2.5 MHz typical). To get low ripple and full output current at the lower switching frequency, the recommended minimum inductor value is 2.2 µH. An application can change the switching frequency during operation, if needed. An internally connected pulldown resistor of about 400 kΩ on this pin acts the same way as one on the DEF pin (see Pin-Selectable Output Voltage (DEF)). 8.3.6 Undervoltage Lockout (UVLO) If the input voltage drops, the undervoltage lockout prevents faulty operation of the device by switching off both the power FETs. The typical undervoltage-lockout threshold setting is 2.7 V. The device is fully operational for voltages above the UVLO threshold and turns off if the input voltage trips the threshold. The converter starts operation again once the input voltage exceeds the threshold by a hysteresis of typically 200 mV. 8.3.7 Thermal Shutdown An internal temperature sensor monitors the junction temperature (TJ) of the device. If TJ exceeds 160°C (typ), the device goes into thermal shutdown. Both the high-side and low-side power FETs turn off and PG goes into the high-impedance state. When TJ decreases below the hysteresis level, the converter resumes normal operation, beginning with soft start. To avoid unstable conditions, the device implements a hysteresis of typically 20°C on the thermal shutdown temperature. 8.4 Device Functional Modes 8.4.1 Pulse-Width Modulation (PWM) Operation The TPS6215x operates using pulse-width modulation in continuous-conduction mode (CCM) with a nominal switching frequency of 2.5 MHz or 1.25 MHz, selectable with the FSW pin. The frequency variation in the PWM mode is controlled and depends on VIN, VOUT, and the inductance. The device operates in PWM mode as long the output current is higher than half the inductor ripple current. To maintain high efficiency at light loads, the device enters power-save mode at the boundary of discontinuous conduction mode (DCM). This happens if the output current becomes smaller than half the inductor ripple current. 8.4.2 Power-Save Mode Operation The TPS6215x enters its built-in power-save mode seamlessly if the load current decreases. This secures a high efficiency in light load operation. The device remains in power-save mode as long as the inductor current is discontinuous. In power-save mode, the switching frequency decreases linearly with the load current, maintaining high efficiency. The transition into and out of power-save mode happens within the entire regulation scheme and is seamless in both directions. TPS6215x includes a fixed on-time circuitry. An estimate for this on-time, in steady-state operation with FSW=Low, is: space (1) space For very small output voltages, an absolute minimum on-time of about 80 ns is kept to limit switching losses. The operating frequency is thereby reduced from its nominal value, which keeps efficiency high. Also, the off-time can reach its minimum value at high duty cycles. The output voltage remains regulated in such cases. Using tON, the typical peak inductor current in power-save mode is approximated by: space |
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