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MAX6481BL25BD3 Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX6481BL25BD3 Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 24 page 300mA LDO Linear Regulators with Internal Microprocessor Reset Circuit ______________________________________________________________________________________ 11 cool. The thermal sensor turns the pass transistor on again after the IC’s junction temperature cools by 20°C, resulting in a pulsed output during continuous thermal overload conditions. Thermal overload protection is designed to protect the MAX6469–MAX6484 in the event of fault conditions. For continuous operation, do not exceed the absolute maximum junction temperature rating of TJMAX = +150°C. Operating Region and Power Dissipation The MAX6469–MAX6484’s maximum power dissipation depends on the thermal resistance of the case and cir- cuit board, the temperature difference between the die junction and the ambient air, and the rate of airflow. The power dissipation across the device is: P = IOUT (VIN - VOUT) The maximum power dissipation is: PMAX = (TJ - TA) / (ØJB + ØBA) where TJ - TA is the temperature difference between the die junction and the surrounding air, ØJB (or ØJC) is the thermal resistance of the package, and ØBA is the ther- mal resistance through the PC board, copper traces, and other materials to the surrounding air. The MAX6469–MAX6476 TDFN package ØJC = 41°C/W, and the MAX6469–MAX6476 SOT package ØJC = 110°C/W. The MAX6469–MAX6484’s ground pin (GND) performs the dual function of providing an electrical connection to the system ground and channeling heat away. Connect GND to the system ground using a large pad or ground plane. For continuous operation, do not exceed the absolute maximum junction temperature rating of TJMAX = +150°C. Applications Information Output Voltage Selection The MAX6469–MAX6484 feature dual-mode operation: they operate in either a preset output voltage mode or an adjustable mode. In preset voltage mode, internal feedback resistors set the MAX6469–MAX6484’s output from +1.5V to +3.3V (Table 1). Select this mode by con- necting SET to ground (MAX6469–MAX6472/ MAX6477–MAX6480). In adjustable mode, select an output between 1.25V and 5.5V using two external resistors connected as a voltage-divider to SET (Figure 1). The output voltage is set by the following equation: VOUT = VSET (1 + R1 / R2) where VSET = 1.23V. To simplify resistor selection: R1 = R2 (VOUT / VSET - 1) Choose R2 = 50kΩ to maintain stability, accuracy and high-frequency power-supply rejection. Avoid selecting resistor values greater than 100kΩ. In preset voltage mode, the impedance between SET and ground should always be less than 50kΩ. In most applications, con- nect SET directly to ground. Low-Noise UCSP Output MAX6477–MAX6484 UCSP products include internal fil- tering to yield low output noise without an additional external bypass capacitor. The devices yield 75µVRMS (typ) output noise (for VOUT = 3.0V) and 150µVRMS (for VOUT = 3.3V). This low-noise feature makes the MAX6477–MAX6484 ideal for audio applications. Capacitor Selection and Regulator Stability For stable operation over the full temperature range and with load currents up to 300mA, use a 3.3µF (min) ceramic output capacitor with an ESR <0.2Ω. To reduce noise and improve load transient response, sta- bility, and power-supply rejection, use large output capacitor values such as 10µF. Note that some ceramic capacitors exhibit large capac- itance and ESR variation with temperature. With capaci- tor dielectrics such as Z5U and Y5V, use 4.7µF or more to ensure stability over temperature. With X7R or X5R capacitor dielectrics, 3.3µF should be sufficient at all operating temperatures. Higher ESR capacitors require more capacitance to maintain stability. A graph of the Region of Stable ESR vs. Load Current is shown in the Typical Operating Characteristics. To improve power-supply rejection and transient response, use a 1µF capacitor between IN and GND. The MAX6469–MAX6484 remain stable with purely resistive loads or current loads up to 300mA. Reset Transient Immunity The reset circuit is relatively immune to short-duration, falling VOUT transients. The Typical Operating Characteristics section shows a graph of the Maximum Transient Duration vs. Reset Threshold Overdrive for which reset is not asserted. The graph was produced using falling VOUT transients starting at VOUT and end- ing below the reset threshold by the magnitude indicat- ed (reset threshold overdrive). The graph shows the maximum pulse width that a falling VOUT transient can typically have without triggering a reset pulse. As the amplitude of the transient increases (i.e., goes further below the reset threshold), the maximum allowable pulse width decreases. Typically, a VOUT transient that goes only 10mV below the reset threshold and lasts for 75µs does not trigger a reset pulse. |
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