The MAX603/MAX604 from Maxim Integrated (now part of Analog Devices) are low-dropout, low-quiescent-current 500 mA linear regulators built around an internal P-channel MOSFET pass element. The P-channel topology is the point: a conventional PNP-based LDO sinks a large base current that grows as the part enters dropout, but a P-channel MOSFET is voltage-driven, so the MAX604 holds a low 15 µA typical supply current all the way into dropout. The MAX604 is the 3.3 V grade (the MAX603 is 5 V); MAX604CSA+T is the RoHS ("+"), tape-and-reel ("T") 8-pin SO option.

It is a Dual Mode regulator: tie SET to the output for the preset 3.3 V, or to an external divider for any 1.25 V to 11 V adjustable output - one part covers a fixed rail and a custom rail. The pass MOSFET delivers up to 500 mA, and dropout is low - about 240 mV at 200 mA on the 3.3 V part (320 mV at 500 mA on the 5 V MAX603) - so it regulates from an input close to the output, the behaviour a nearly-flat battery needs. A 2 µA shutdown mode (OFF̅ pin) all but disconnects the load for standby.

Protection is built in. Foldback current limiting reins in the output under fault, thermal-overload protection guards the die, and a reverse-current feature protects against current flowing back from output to input. The input range is 2.7 V to 11.5 V, and the 8-pin SO is rated to dissipate 1.8 W. Several pins are GND for heat-sinking. The MAX604 operates over the commercial 0 °C to +70 °C range (C grade).

Note: Values are taken from the Maxim MAX603/MAX604 datasheet. Confirm every parameter against the latest official documentation before committing a design.

MAX604CSA+T ships in the 8-pin SO (0.150-inch narrow SOIC, package outline 21-0041), rated to dissipate up to 1.8 W. Several pins are GND, which double as the thermal path - solder them to copper pour to carry heat away from the pass MOSFET at 500 mA. Keep the input and output traces short and wide, bypass IN and OUT close to the pins, and route the SET feedback node away from noise. The dimensional drawing below gives the full mechanical detail.

The 8-pin SO places input and output on opposite ends, with several GND pins for heat-sinking (per the MAX603/MAX604 datasheet):

• Pin 1 - IN: Supply input, 2.7 V to 11.5 V. Bypass to GND.
• Pins 2, 3, 6, 7 - GND: Ground; use as the thermal path to copper.
• Pin 4 - OFF̅: Active-low shutdown; drives the 2 µA standby.
• Pin 5 - SET: Output-set / feedback; tie to OUT for 3.3 V or to a divider for 1.25-11 V.
• Pin 8 - OUT: Regulated output; up to 500 mA.

The direct sibling is the MAX603 - the 5 V version of the same part (same pinout and behaviour, SET-selectable to adjustable). Related Maxim power-management and reference parts are listed below.

Selection Tips: Stay with the MAX604 for a 3.3 V (or 1.25-11 V adjustable) 500 mA P-channel LDO with 15 µA I_Q; choose the MAX603 for the 5 V version of the same regulator. The references (MAX6004/MAX6025) and power-path parts (MAX5087/MAX5921/MAX5980) above complement an LDO in a typical power supply.

Maxim Integrated, now part of Analog Devices, Inc. (ADI), designed the MAX603/MAX604 to bring P-channel-MOSFET LDO efficiency - flat low quiescent current into dropout - to battery and portable supplies, with Dual Mode fixed/adjustable flexibility in a small SO.

ADI maintains the datasheet, the Dual Mode and divider design guidance, and the thermal and protection specifications for the family - the documentation that turns the part into a dependable 500 mA rail for a battery system.