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TPS73701DCQR Datasheet(PDF) 10 Page - Texas Instruments |
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TPS73701DCQR Datasheet(HTML) 10 Page - Texas Instruments |
10 / 18 page www.ti.com APPLICATION INFORMATION INPUT AND OUTPUT CAPACITOR TPS737xx GND EN IN OUT V IN V OUT OUTPUT NOISE TPS737xx GND EN FB IN OUT V IN V OUT V = OUT ´ 1.204 (R +R ) 1 2 R 1 R 1 C FB R 2 V N + 32mVRMS (R 1 ) R2) R 2 + 32mVRMS V OUT V REF (1) V N mVRMS + 27 mVRMS V V OUT (V) (2) TPS737xx SBVS067C – JANUARY 2006 – REVISED AUGUST 2006 The TPS737xx belongs to a family of new generation LDO regulators that use an NMOS pass transistor to REQUIREMENTS achieve ultra-low-dropout performance, reverse current blockage, and freedom from output capacitor Although an input capacitor is not required for constraints. These features combined with an enable stability, it is good analog design practice to connect input make the TPS737xx ideal for portable a 0.1 µF to 1µF low equivalent series resistance applications. This regulator family offers a wide (ESR) capacitor across the input supply near the selection of fixed output voltage versions and an regulator. This capacitor counteracts reactive input adjustable output version. All versions have thermal sources and improves transient response, noise and over-current protection, including foldback rejection, and ripple rejection. A higher-value current limit. capacitor may be necessary if large, fast rise-time load transients are anticipated or the device is Figure 25 shows the basic circuit connections for the located several inches from the power source. fixed voltage models. Figure 26 gives the connections for the adjustable output version The TPS737xx requires a 1.0µF output capacitor for (TPS73701). stability. It is designed to be stable for all available types and values of capacitors. In applications where VIN – VOUT < 0.5V and multiple low ESR capacitors are in parallel, ringing may occur when the product of COUT and total ESR drops below 50nΩF. Total ESR includes all parasitic resistances, including capacitor ESR and board, socket, and solder joint resistance. In most applications, the sum of capacitor ESR and trace resistance will meet this requirement. Figure 25. Typical Application Circuit for Fixed-Voltage Versions A precision bandgap reference is used to generate the internal reference voltage, VREF. This reference is the dominant noise source within the TPS737xx and it generates approximately 32 µV RMS (10Hz to 100kHz) at its output. The regulator control loop gains up the reference noise with the same gain as the reference voltage, so that the noise voltage of the regulator is approximately given by: Figure 26. Typical Application Circuit for Adjustable-Voltage Versions Since the value of VREF is 1.2V, this relationship reduces to: R1 and R2 can be calculated for any output voltage using the formula shown in Figure 26. Sample resistor values for common output voltages are shown in Figure 2. Connecting a feedback capacitor, CFB, from the For best accuracy, make the parallel combination of output to the FB pin reduces output noise and R1 and R2 approximately equal to 19kΩ. This 19kΩ, improve load transient performance. This capacitor in addition to the internal 8k Ω resistor, presents the should be limited to 0.1µF. same impedance to the error amp as the 27k Ω bandgap reference output. This impedance helps The TPS737xx uses an internal charge pump to compensate for leakages into the error amp develop an internal supply voltage sufficient to drive terminals. the gate of the NMOS pass element above VOUT. The charge pump generates ~250 µV of switching noise at ~2MHz; however, charge-pump noise contribution is negligible at the output of the regulator for most values of IOUT and COUT. 10 Submit Documentation Feedback |
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