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MAX8511ETA18-T Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX8511ETA18-T Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 10 page Shutdown The MAX8510/MAX8511/MAX8512 feature a low-power shutdown mode that reduces quiescent current less than 1µA. Driving SHDN low disables the voltage refer- ence, error amplifier, gate-drive circuitry, and pass transistor (see the Functional Diagram), and the device output enters a high-impedance state. Connect SHDN to IN for normal operation. Current Limit The MAX8510/MAX8511/MAX8512 include a current limiter, which monitors and controls the pass transis- tor’s gate voltage, limiting the output current to 200mA. For design purposes, consider the current limit to be 130mA (min) to 300mA (max). The output can be shorted to ground for an indefinite amount of time without dam- aging the part. Thermal-Overload Protection Thermal-overload protection limits total power dissipation in the MAX8510/MAX8511/MAX8512. When the junction temperature exceeds TJ = +160°C, the thermal sensor signals the shutdown logic, turning off the pass transistor and allowing the IC to cool down. The thermal sensor turns the pass transistor on again after the IC’s junction temperature drops by 10°C, resulting in a pulsed output during continuous thermal-overload conditions. Thermal-overload protection is designed to protect the MAX8510/MAX8511/MAX8512 in the event of a fault con- dition. For continual operation, do not exceed the absolute maximum junction temperature rating of TJ = +150°C. Operating Region and Power Dissipation The MAX8510/MAX8511/MAX8512 maximum power dissipation depends on the thermal resistance of the case and circuit board, the temperature difference between the die junction and ambient, and the rate of airflow. The power dissipation across the device is: P = IOUT (VIN - VOUT) The maximum power dissipation is: PMAX = (TJ - TA) / ( θJC + θCA) where TJ - TA is the temperature difference between the MAX8510/MAX8511/MAX8512 die junction and the surrounding air, θJC is the thermal resistance of the package, and θCA is the thermal resistance through the PC board, copper traces, and other materials to the surrounding air. The GND pin of the MAX8510/MAX8511/MAX8512 per- forms the dual function of providing an electrical connec- tion to ground and channeling heat away. Connect the GND pin to ground using a large pad or ground plane. Noise Reduction For the MAX8510, an external 0.01µF bypass capacitor between BP and OUT with innovative noise bypass scheme reduces output noises dramatically, exhibiting 11µVRMS of output voltage noise with CBP = 0.01µF and COUT = 1µF. Startup time is minimized by a power- on circuit that precharges the bypass capacitor. Applications Information Capacitor Selection and Regulator Stability Use a 1µF capacitor on the MAX8510/MAX8511/ MAX8512 input and a 1µF capacitor on the output. Larger input capacitor values and lower ESRs provide better noise rejection and line-transient response. Reduce output noise and improve load-transient response, stability, and power-supply rejection by using large output capacitors. Note that some ceramic dielectrics exhibit large capacitance and ESR variation with temperature. With dielectrics such as Z5U and Y5V, it may be necessary to use a 2.2µF or larger output capacitor to ensure stability at temperatures below -10°C. With X7R or X5R dielectrics, 1µF is sufficient at all operating temperatures. A graph of the region of stable COUT ESR vs. load current is shown in the Typical Operating Characteristics. Use a 0.01µF bypass capacitor at BP (MAX8510) for low-output voltage noise. The leakage current going into the BP pin should be less than 10nA. Increasing the capacitance slightly decreases the output noise. Values above 0.1µF and below 0.001µF are not recommended. Noise, PSRR, and Transient Response The MAX8510/MAX8511/MAX8512 are designed to deliver ultra-low noise and high PSRR, as well as low dropout and low quiescent currents in battery-powered systems. The MAX8510 power-supply rejection is 78dB at 1kHz and 54dB at 100kHz. The MAX8511/MAX8512 PSRR is 72dB at 1kHz and 46dB at 100kHz (see the Power-Supply Rejection Ratio vs. Frequency graph in the Typical Operating Characteristics). When operating from sources other than batteries, improved supply-noise rejection and transient response can be achieved by increasing the values of the input and output bypass capacitors, and through passive fil- tering techniques. The Typical Operating Characteristics show the MAX8510/MAX8511/MAX8512 line- and load- transient responses. Ultra-Low-Noise, High PSRR, Low-Dropout, 120mA Linear Regulators _______________________________________________________________________________________ 7 |
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