Datasheet MAX882, MAX883, MAX884 (Maxim) - 7

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