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TLV1117LV18DCYR Datasheet(PDF) 10 Page - Texas Instruments |
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TLV1117LV18DCYR Datasheet(HTML) 10 Page - Texas Instruments |
10 / 19 page TLV1117LV Series SBVS160A – MAY 2011 – REVISED SEPTEMBER 2011 www.ti.com APPLICATION INFORMATION The TLV1117LV is a low quiescent current linear regulator designed for high current applications. Unlike typical high current linear regulators, the TLV1117LV series consume significantly less quiescent current. These devices deliver excellent line and load transient performance. The device is low noise, and exhibits a very good power-supply rejection ratio (PSRR). As a result, it is ideal for high current applications that require very sensitive power-supply rails. This family of regulators offers both current limit and thermal protection. The operating junction temperature range of the device is –40°C to +125°C. Input and Output Capacitor Requirements For stability, 1.0- μF ceramic capacitors are required at the output. Higher-valued capacitors improve transient performance. X5R- and X7R-type ceramic capacitors are recommended because these capacitors have minimal variation in value and equivalent series resistance (ESR) over temperature. Unlike traditional linear regulators that need a minimum ESR for stability, the TLV1117LV series are ensured to be stable with no ESR. Therefore, cost-effective ceramic capacitors can be used with these devices. Effective output capacitance that takes bias, temperature, and aging effects into consideration must be greater than 0.5 μF to ensure stability of the device. Although an input capacitor is not required for stability, it is good analog design practice to connect a 0.1- μF to 1.0- μF, low-ESR capacitor across the IN pin and GND pin of the regulator. This capacitor counteracts reactive input sources and improves transient response, noise rejection, and ripple rejection. A higher-value capacitor may be necessary if large, fast rise-time load transients are anticipated, or if the device is not located physically close to the power source. If source impedance is greater than 2 Ω, a 0.1-μF input capacitor may also be necessary to ensure stability. Board Layout Recommendations to Improve PSRR and Noise Performance Input and output capacitors should be placed as close to the device pins as possible. To improve characteristic ac performance such as PSRR, output noise, and transient response, it is recommended that the board be designed with separate ground planes for VIN and VOUT, with the ground plane connected only at the GND pin of the device. In addition, the ground connection for the output capacitor should be connected directly to the GND pin of the device. Higher value ESR capacitors may degrade PSRR performance. Internal Current Limit The TLV1117LV internal current limit helps to protect the regulator during fault conditions. During current limit, the output sources a fixed amount of current that is largely independent of the output voltage. In such a case, the output voltage is not regulated, and can be calculated by the formula: VOUT = ILIMIT × RLOAD. The PMOS pass transistor dissipates (VIN – VOUT) × ILIMIT until thermal shutdown is triggered and the device turns off. As the device cools down, it is turned on by the internal thermal shutdown circuit. If the fault condition continues, the device cycles between current limit and thermal shutdown. See the Thermal Information section for more details The PMOS pass element in the TLV1117LV device has a built-in body diode that conducts current when the voltage at OUT exceeds the voltage at IN. This current is not limited; if extended reverse voltage operation is anticipated, external limiting to 5% of the rated output current is recommended. Dropout Voltage The TLV1117LV uses a PMOS pass transistor to achieve low dropout. When (VIN – VOUT) is less than the dropout voltage (VDO), the PMOS pass device is in the linear region of operation and the input-to-output resistance is the RDS(ON) of the PMOS pass element. VDO scales approximately with output current because the PMOS device behaves as a resistor in dropout. As with any linear regulator, PSRR and transient response are degraded as (VIN – VOUT) approaches dropout Transient Response As with any regulator, increasing the size of the output capacitor reduces over-/undershoot magnitude. 10 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated |
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