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MAX8863REUK+T Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX8863REUK+T Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 10 page Low-Dropout, 120mA Linear Regulators 8 Operating Region and Power Dissipation Maximum power dissipation of the MAX8863/MAX8864 depends on the thermal resistance of the case and cir- cuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipation across the device is P = IOUT (VIN - VOUT). The resulting maximum power dissipation is: PMAX = (TJ - TA) / θJA where (TJ - TA) is the temperature difference between the MAX8863/MAX8864 die junction and the surround- ing air, and θJA is the thermal resistance of the chosen package to the surrounding air. The GND pin of the MAX8863/MAX8864 performs the dual function of providing an electrical connection to ground and channeling heat away. Connect the GND pin to ground using a large pad or ground plane. Reverse Battery Protection The MAX8863/MAX8864 have a unique protection scheme that limits the reverse supply current to less than 1mA when either VIN or VSHDN falls below ground. The circuitry monitors the polarity of these two pins, dis- connecting the internal circuitry and parasitic diodes when the battery is reversed. This feature prevents the device from overheating and damaging the battery. VIN > 5.5V Minimum Load Current When operating the MAX8863/MAX8864 with an input voltage above 5.5V, a minimum load current of 20µA is required to maintain regulation in preset voltage mode. When setting the output with external resistors, the min- imum current through the external feedback resistors and load must be 30µA. __________Applications Information Capacitor Selection and Regulator Stability Normally, use a 1µF capacitor on the input and a 1µF capacitor on the output of the MAX8863/MAX8864. Larger input capacitor values and lower ESR provide better supply-noise rejection and transient response. A higher-value input capacitor (10µF) may be necessary if large, fast transients are anticipated and the device is located several inches from the power source. Improve load-transient response, stability, and power-supply rejection by using large output capacitors. For stable operation over the full temperature range, with load cur- rents up to 120mA, a minimum of 1µF is recommended. Noise The MAX8863/MAX8864 exhibit 350µVRMS noise during normal operation. When using the MAX8863/MAX8864 in applications that include analog-to-digital converters of greater than 12 bits, consider the ADC’s power-sup- ply rejection specifications (see the Output Noise DC to 1MHz photo in the Typical Operating Characteristics). Power-Supply Rejection and Operation from Sources Other than Batteries The MAX8863/MAX8864 are designed to deliver low dropout voltages and low quiescent currents in battery- powered systems. Power-supply rejection is 62dB at low frequencies and rolls off above 300Hz. As the fre- quency increases above 20kHz, the output capacitor is the major contributor to the rejection of power-supply noise (see the Power-Supply Rejection Ratio vs. Ripple Frequency graph in the Typical Operating Characteristics). When operating from sources other than batteries, improve supply-noise rejection and transient response by increasing the values of the input and output capac- itors, and using passive filtering techniques (see the supply and load-transient responses in the Typical Operating Characteristics). Load Transient Considerations The MAX8863/MAX8864 load-transient response graphs (see Typical Operating Characteristics) show two components of the output response: a DC shift of the output voltage due to the different load currents, and the transient response. Typical overshoot for step changes in the load current from 0mA to 50mA is 12mV. Increasing the output capacitor’s value and decreasing its ESR attenuates transient spikes. |
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