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MAX8881EUT50-T Datasheet(PDF) 5 Page - Maxim Integrated Products |
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MAX8881EUT50-T Datasheet(HTML) 5 Page - Maxim Integrated Products |
5 / 12 page 12V, Ultra-Low-IQ, Low-Dropout Linear Regulators with POK _______________________________________________________________________________________ 5 Detailed Description The MAX8880/MAX8881 are low-dropout, low-quies- cent current linear regulators designed primarily for battery-powered applications (Figure 1). The MAX8880 provides an adjustable output voltage from 1.25V to 5V using an external resistor-divider. The MAX8881 is available in factory preset output voltages of 1.8V, 2.5V, 3.3V, and 5V. Both devices have a +1.25V reference, error amplifier, MOSFET driver, and P-channel pass transistor (Figure 2). Low-Dropout Regulator The 1.25V reference is connected to the error amplifi- er’s inverting input. The error amplifier compares this reference 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 reference voltage, the pass-transistor gate is pulled lower, allowing more current to pass, increasing the output voltage. If the feedback voltage is higher than the reference voltage, the pass-transistor gate is driven higher, allowing less current to pass to the out- put. The output voltage is fed back through either an internal resistor voltage divider by externally connect- ing FB to OUT (MAX8881), or an external resistor net- work connected to FB (MAX8880). Additional blocks include an output current limiter, reverse battery pro- tection, a thermal sensor, shutdown logic, and a POK comparator to indicate when the output is out of regula- tion (Figure 2). Internal P-Channel Pass Transistor The MAX8880/MAX8881 feature a 2 Ω P-channel MOS- FET pass transistor. This provides advantages over similar designs using PNP pass transistors, including longer battery life. The P-channel MOSFET requires no base drive, which reduces quiescent current consider- ably. PNP-based regulators waste considerable current in dropout when the pass transistor saturates. They also use high base-drive currents under large loads. The MAX8880/MAX8881 do not suffer from these prob- lems and consume only 3.5µA of supply current (see Typical Operating Characteristics). Dropout Voltage A regulator’s minimum input-output differential (or dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Because the MAX8880/MAX8881 use a P-channel MOSFET pass transistor, their dropout voltage is RDS(ON) (2 Ω) multi- plied by the load current (see Electrical Characteristics). IN R2* 100k OUT FB GND C2 4.7 μF C1 1 μF SHDN 2.5V TO 12V REGULATION OK POK MAX8881 VIN VOUT *OPTIONAL Figure 1. Standard Application Circuit PIN MAX888_ (SOT) MAX888_ (TDFN) NAME FUNCTION 1 4 IN Input Voltage. Bypass with a 1µF capacitor to GND. 2 2 GND Ground 3 3 OUT Output Voltage. Bypass with a 4.7µF capacitor (<0.5 Ω ESR) to GND for load currents up to 200mA. For load currents up to 40mA, 1µF is acceptable. 41 FB Feedback Set Point, 1.25V (MAX8880 only). Output sense, connect to OUT externally (MAX8881 only). 5 5 SHDN ON/OFF Control. Regulator is ON when V SHDN > 2V. If unused, connect to IN. If reverse battery protection of the SHDN input is desired, connect a 100k Ω resistor in series with SHDN. 6 6 POK POK Output, Open Drain. Low when OUT is out of regulation or in shutdown. Connect POK to OUT through a high-value resistor for a simple error — — EP Exposed paddle (TDFN only). Connect to the circuit ground plane. Pin Description |
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Similar Description - MAX8881EUT50-T |
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