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TPS54521RHLT Datasheet(PDF) 11 Page - Texas Instruments |
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TPS54521RHLT Datasheet(HTML) 11 Page - Texas Instruments |
11 / 41 page TPS54521 www.ti.com SLVS981C – JUNE 2010 – REVISED AUGUST 2013 TYPICAL CHARACTERISTICS (continued) The device reduces the external component count by integrating the boot recharge circuit. The bias voltage for the integrated high-side MOSFET is supplied by a capacitor between the BOOT and PH pins. The boot capacitor voltage is monitored by a BOOT to PH UVLO (BOOT-PH UVLO) circuit allowing PH pin to be pulled low to recharge the boot capacitor. The device can operate at 100% duty cycle, as long as the boot capacitor voltage is higher than the preset BOOT-PH UVLO threshold, which is typically 2.1V. The output voltage can be stepped down to as low as the 0.8V voltage reference (Vref). The device has a power good comparator (PWRGD) with hysteresis which monitors the output voltage through the VSENSE pin. The PWRGD pin is an open drain MOSFET which is pulled low when the VSENSE pin voltage is less than 91% or greater than 109% of the reference voltage Vref and floats high when the VSENSE pin voltage is 94% to 106% of the Vref. The SS/TR (slow start/tracking) pin is used to minimize inrush currents or provide power supply sequencing during power up. A small value capacitor or resistor divider should be attached to the pin for slow start or critical power supply sequencing requirements. The device is protected from output overvoltage, overload and thermal fault conditions. The device minimizes excessive output overvoltage transients by taking advantage of the overvoltage circuit power good comparator. When the overvoltage comparator is activated, the high-side MOSFET is turned off and prevented from turning on until the VSENSE pin voltage is lower than 106% of the Vref. The device implements both high-side MOSFET overload protection and bidirectional low-side MOSFET overload protections which help control the inductor current and avoid current runaway. If the overcurrent condition has lasted for more than the hiccup wait time, the device will shut down and restart after the hiccup time. The device also shuts down if the junction temperature is higher than thermal shutdown trip point. The device is restarted under control of the slow start circuit automatically when the junction temperature drops 5°C typically below the thermal shutdown trip point. DETAILED DESCRIPTION Fixed Frequency PWM Control The device uses adjustable, fixed frequency, peak current mode control. The output voltage is compared through external resistors on the VSENSE pin to an internal voltage reference by an error amplifier which drives the COMP pin. An internal oscillator initiates the turn on of the high-side power switch. The error amplifier output is converted into a current reference which is compared to the high-side power switch current. When the power switch current reaches the current reference generated by the COMP voltage level, the high-side power switch is turned off and the low-side power switch is turned on. Continuous Current Mode Operation (CCM) As a synchronous buck converter, the device normally works in CCM (Continuous Conduction Mode) under all load conditions. VIN and Power VIN Pins (VIN and PVIN) The device allows for a variety of applications by using the VIN and PVIN pins together or separately. The VIN pin voltage supplies the internal control circuits of the device. The PVIN pin voltage provides the input voltage to the power converter system. If tied together, the input voltage for VIN and PVIN can range from 4.5V to 17V. If using the VIN separately from PVIN, the VIN pin must be between 4.5V and 17V, and the PVIN pin can range from as low as 1.6V to 17V. A voltage divider connected to the EN pin can adjust either input voltage UVLO appropriately. Adjusting the input voltage UVLO on the PVIN pin helps to provide consistent power up behavior. Voltage Reference The voltage reference system produces a precise voltage reference by scaling the output of a temperature stable bandgap circuit. Copyright © 2010–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links :TPS54521 |
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