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TPS74201KTWR Datasheet(PDF) 11 Page - Texas Instruments |
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TPS74201KTWR Datasheet(HTML) 11 Page - Texas Instruments |
11 / 26 page www.ti.com DROPOUT VOLTAGE Reference SimplifiedBlock Diagram V OUT OUT BIAS FB IN V IN V =3.3V 5% BIAS ± V =3.3V 5V V =1.5V I =1.5A Efficiency=45% IN OUT OUT ± PROGRAMMABLE SOFT-START Reference SimplifiedBlock Diagram V OUT OUT BIAS FB IN V =5V 5% BIAS ± V =1.8V V =1.5V I =1.5A Efficiency=83% IN OUT OUT t SS + V REF C SS I SS (1) t SSCL + V OUT(NOM) C OUT I CL(MIN) (2) TPS74201 SBVS064F – DECEMBER 2005 – REVISED OCTOBER 2007 The TPS74201 offers industry-leading dropout performance, making it well-suited for high-current low VIN/low VOUT applications. The extremely low dropout of the TPS74201 allows the device to be used in place of a DC/DC converter and still achieve good efficiencies. This efficiency allows the user to rethink the power architecture for their applications to achieve the smallest, simplest, and lowest cost solution. There are two different specifications for dropout voltage with the TPS74201. The first specification (see Figure 27) is referred to as VIN Dropout and is for users who wish to apply an external bias voltage to achieve low dropout. This specification assumes Figure 28. Typical Application of the TPS74201 that VBIAS is at least 1.62V above VOUT, which is the Without an Auxiliary Bias case for VBIAS when powered by a 3.3V rail with 5% tolerance and with VOUT = 1.5V. If VBIAS is higher than 3.3V × 0.95 or V OUT is less than 1.5V, VIN dropout is less than specified. The TPS74201 features a programmable, monotonic, voltage-controlled soft-start that is set with an external capacitor (CSS). This feature is important for many applications because it eliminates power-up initialization problems when powering FPGAs, DSPs, or other processors. The controlled voltage ramp of the output also reduces peak inrush current during start-up, minimizing start-up transients to the input power bus. To achieve a linear and monotonic soft-start, the TPS74201 error amplifier tracks the voltage ramp of the external soft-start capacitor until the voltage exceeds the internal reference. The soft-start ramp time depends on the soft-start charging current (ISS), soft-start capacitance (CSS), and the internal Figure 27. Typical Application of the TPS74201 reference voltage (VREF), and can be calculated using Using an Auxiliary Bias Rail Equation 1: The second specification (see Figure 28) is referred to as VBIAS Dropout and is for users who wish to tie IN and BIAS together. This option allows the device If large output capacitors are used, the device current to be used in applications where an auxiliary bias limit (ICL) and the output capacitor may set the voltage is not available or low dropout is not required. start-up time. In this case, the start-up time is given Dropout is limited by BIAS in these applications by Equation 2: because VBIAS provides the gate drive to the pass FET and therefore must be 1.4V above VOUT. Because of this usage, IN and BIAS tied together easily consume huge power. Pay attention not to exceed the power rating of the IC package. VOUT(NOM) is the nominal set output voltage as set by the user, COUT is the output capacitance, and ICL(MIN) is the minimum current limit for the device. In applications where monotonic startup is required, the soft-start time given by Equation 1 should be set to be greater than Equation 2. Copyright © 2005–2007, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): TPS74201 |
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