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TPS73225DBVR Datasheet(PDF) 11 Page - Texas Instruments |
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TPS73225DBVR Datasheet(HTML) 11 Page - Texas Instruments |
11 / 23 page www.ti.com APPLICATION INFORMATION INPUT AND OUTPUT CAPACITOR TPS732xx GND EN NR IN OUT V IN V OUT Optional input capacitor. May improve source impedance, noise, or PSRR. Optional output capacitor. May improve load transient, noise, or PSRR. Optional bypass capacitor to reduce output noise. OUTPUT NOISE V N + 32mVRMS (R 1 ) R2) R 2 + 32mVRMS V OUT V REF (1) TPS732xx GND EN FB IN OUT V IN V OUT V OUT = × 1.204 (R 1 + R2) R 1 R 1 C FB R 2 Optional input capacitor. May improve source impedance, noise, or PSRR. Optional output capacitor. May improve load transient, noise, or PSRR. Optional capacitor reduces output noise and improves transient response. V N(mVRMS) + 27 mVRMS V V OUT(V) (2) TPS732xx SBVS037I – AUGUST 2003 – REVISED MAY 2006 in addition to the internal 8k Ω resistor, presents the The TPS732xx belongs to a family of new generation same impedance to the error amp as the 27k Ω LDO regulators that use an NMOS pass transistor to bandgap reference output. This impedance helps achieve ultra-low-dropout performance, reverse compensate for leakages into the error amp current blockage, and freedom from output capacitor terminals. constraints. These features, combined with low noise and an enable input, make the TPS732xx ideal for portable applications. This regulator family offers a REQUIREMENTS wide selection of fixed output voltage versions and an adjustable output version. All versions have Although an input capacitor is not required for thermal and over-current protection, including stability, it is good analog design practice to connect foldback current limit. a 0.1µF to 1µF low ESR capacitor across the input supply near the regulator. This counteracts reactive Figure 31 shows the basic circuit connections for the input sources and improves transient response, fixed voltage models. Figure 32 gives the noise rejection, and ripple rejection. A higher-value connections for the adjustable output version capacitor may be necessary if large, fast rise-time (TPS73201). load transients are anticipated or the device is located several inches from the power source. The TPS732xx does not require an output capacitor for stability and has maximum phase margin with no capacitor. 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 31. Typical Application Circuit for Fixed-Voltage Versions A precision band-gap reference is used to generate the internal reference voltage, VREF. This reference is the dominant noise source within the TPS732xx and it generates approximately 32µVRMS (10Hz to 100kHz) at the reference output (NR). 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: Since the value of VREF is 1.2V, this relationship reduces to: Figure 32. Typical Application Circuit for Adjustable-Voltage Versions for the case of no CNR. R1 and R2 can be calculated for any output voltage An internal 27k Ω resistor in series with the noise using the formula shown in Figure 32. Sample reduction pin (NR) forms a low-pass filter for the resistor values for common output voltages are voltage reference when an external noise reduction shown in Figure 2. capacitor, CNR, is connected from NR to ground. For CNR = 10nF, the total noise in the 10Hz to 100kHz For best accuracy, make the parallel combination of bandwidth is reduced by a factor of ~3.2, giving the R1 and R2 approximately euqal to 19kΩ. This 19kΩ, approximate relationship: 11 Submit Documentation Feedback |
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