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TPS74401KTWR Datasheet(PDF) 11 Page - Texas Instruments |
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TPS74401KTWR Datasheet(HTML) 11 Page - Texas Instruments |
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11 / 22 page  www.ti.com DROPOUT VOLTAGE Reference SimplifiedBlock Diagram BIAS FB IN V IN V =3.3V 5% BIAS ± V =3.3V 5% V =1.5V I =1.5A Efficiency=45% IN OUT OUT ± V 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) TPS74401 SBVS066D – DECEMBER 2005 – REVISED AUGUST 2006 The TPS74401 offers industry-leading dropout performance, making it well-suited for high-current low VIN/low VOUT applications. The extremely low dropout of the TPS74401 allows the device to be used in place of a DC/DC converter and still achieve good efficiencies. This efficiency allows users 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 TPS74401. The first specification (see Figure 28) is referred to as VIN Dropout and is for users that wish to apply an external bias voltage to achieve low dropout. This specification assumes Figure 29. Typical Application of the TPS74401 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 TPS74401 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 TPS74401 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), the soft-start capacitance (CSS), and the internal Figure 28. Typical Application of the TPS74401 reference voltage (VREF), and can be calculated Using an Auxiliary Bias Rail using Equation 1: The second specification (see Figure 29) is referred to as VBIAS Dropout and is for users that wish to tie IN and BIAS together. This option allows the device If large output capacitors are used, the device to be used in applications where an auxiliary bias current limit (ICL) and the output capacitor may set voltage is not available or low dropout is not the start-up time. In this case, the start-up time is required. Dropout is limited by BIAS in these given by Equation 2: applications because VBIAS provides the gate drive to the pass FET and therefore must be 1.4V above VOUT. 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. 11 Submit Documentation Feedback |
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