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MAX884CSA Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX884CSA Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 16 page 5V/3.3V or Adjustable, Low-Dropout, Low IQ, 200mA Linear Regulators _______________________________________________________________________________________ 7 _______________Detailed Description The MAX882/MAX883/MAX884 are micropower, low- dropout linear regulators designed primarily for battery- powered applications. They feature Dual-Mode™ operation, allowing a fixed output of 5V for the MAX883 and 3.3V for the MAX882/MAX884, or an adjustable output from 1.25V to 11V. These devices supply up to 200mA while requiring less than 15µA quiescent current. As illus- trated in Figure 1, they consist of a 1.20V reference, error amplifier, MOSFET driver, P-channel pass transistor, dual- mode comparator and feedback voltage divider. The 1.20V reference is connected to the error amplifier’s inverting input. The error amplifier compares this refer- ence with the selected feedback voltage and amplifies the difference. The MOSFET driver reads the error signal and applies the appropriate drive to the P-channel pass transistor. If the feedback voltage is lower than the refer- ence, the pass transistor’s gate is pulled lower, allowing more current to pass and increasing the output voltage. If the feedback voltage is too high, the pass transistor gate is pulled up, allowing less current to pass to the output. The output voltage is fed back through either an inter- nal resistor voltage divider connected to the OUT pin, or an external resistor network connected to the SET pin. The dual-mode comparator examines the SET pin voltage and selects the feedback path used. If the SET pin is below 65mV, internal feedback is used and the output voltage is regulated to 5V for the MAX883 or 3.3V for the MAX882/MAX884. Additional blocks include a foldback current limiter, reverse-current pro- tection, a thermal sensor, shutdown or standby logic, and a low-battery-detection comparator. Internal P-Channel Pass Transistor The MAX882/MAX883/MAX884 feature a 200mA P- channel MOSFET pass transistor. This provides several advantages over similar designs using PNP pass tran- sistors, including longer battery life. The P-channel MOSFET requires no base drive, which reduces quiescent current considerably. PNP based reg- ulators waste large amounts of current in dropout when the pass transistor saturates. They also use high base- drive currents under large loads. The MAX882/MAX883/ MAX884 do not suffer from these problems and consume only 11µA of quiescent current during light loads, heavy loads, and dropout. Output Voltage Selection The MAX882/MAX883/MAX884 feature Dual Mode™ operation. In preset voltage mode, the MAX883’s out- put is set to 5V and the MAX882/MAX884’s output is set to 3.3V, using internal trimmed feedback resistors. Select this mode by connecting SET to ground. In preset voltage mode, impedances between SET and ground should be less than 100k Ω. Otherwise, spurious conditions could cause the voltage at SET to exceed the 65mV dual-mode threshold. ______________________________________________________________Pin Description LBO SET GND OUT LBI OFF STBY IN 1 1 Low-Battery Output is an open-drain output that goes low when LBI is less than 1.2V. Connect to IN or OUT through a pull-up resistor. LBO is undefined during shutdown mode (MAX883/MAX884). 2 2 Feedback for setting the output voltage. Connect to GND to set the output voltage to the prese- lected 3.3V or 5V. Connect to an external resistor network for adjustable-output operation. 3, 6 3, 6 Ground pins—also function as heatsinks in the SO package. All GND pins must be soldered to the circuit board for proper power dissipation. Connect to large copper pads or planes to channel heat from the IC. 4 4 Regulator Output. Fixed or adjustable from 1.25V to 11.0V. Sources up to 200mA. Bypass with a 2.2µF capacitor. 8 8 Low-Battery comparator Input. Tie to IN when not used. — 7 Shutdown. Active-low logic input. In OFF mode, supply current is reduced below 1µA and VOUT = 0V 7 — Standby. Active-low comparator input. Connect to GND to disable the output or to IN for normal operation. A resistor network (from IN) can be used to set a standby mode threshold. 5 5 Regulator Input. Supply voltage can range from 2.7V to 11.5V. NAME PIN FUNCTION MAX883/ MAX884 MAX882 |
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