Datasheet MAX1818 (Maxim) - 6
| Manufacturer | Maxim |
| Description | 500mA, Low-Dropout Linear Regulator in SOT23 |
| Pages / Page | 9 / 6 — MAX1818. Internal P-Channel Pass Transistor. Shutdown. Output Voltage … |
| File Format / Size | PDF / 1.5 Mb |
| Document Language | English |
MAX1818. Internal P-Channel Pass Transistor. Shutdown. Output Voltage Selection
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MAX1818 500mA Low-Dropout Linear Regulator in SOT23 VIN = 2.5V TO 5.5V IN CIN 1µF THERMAL SENSOR MOSFET DRIVER WITH ILIM OUT VOUT = 1.25V TO 5.0V ON SHDN COUT 3.3µF OFF SHUTDOWN 5k V LOGIC REF 1.25V ERROR R1 LOGIC SUPPLY AMPLIFIER VOLTAGE (VOUT) RPOK 100k
MAX1818
TO POK SET µC R2 93% VREF 100mV GND Figure 1. Functional Diagram
Internal P-Channel Pass Transistor
The output voltage may also be adjusted by connecting The MAX1818 features a 0.25Ω P-channel MOSFET a voltage-divider from OUT to SET to GND (Figure 2). pass transistor. Unlike similar designs using PNP pass Select R2 in the 25kΩ to 100kΩ range. Calculate R1 with transistors, P-channel MOSFETs require no base drive, the following equation: which reduces quiescent current. PNP-based regulators R1 = R2 [(VOUT / VSET) – 1] also waste considerable current in dropout when the pass where V transistor saturates, and use high base-drive currents SET = 1.25V, and VOUT may range from 1.25V to 5.0V. under large loads. The MAX1818 does not suffer from these problems and consumes only 125μA of quiescent
Shutdown
current under heavy loads as well as in dropout. Pull SHDN low to enter shutdown. During shutdown, the
Output Voltage Selection
output is disconnected from the input and supply current drops to 0.1μA. When in shutdown, POK pulls low and The MAX1818’s Dual Mode operation allows opera- OUT is high impedance. The capacitance and load at tion in either a preset voltage mode or an adjustable OUT determine the rate at which V mode. Connect SET to GND to select the preset output OUT decays. SHDN can be pulled as high as 6V, regardless of the input and voltage. The two-digit part number suffix identifies the output voltage. output voltage (see Selector Guide). For example, the MAX1818EUT33 has a preset 3.3V output voltage. www.maximintegrated.com Maxim Integrated │ 6
MAX1818
TO POK SET µC R2 93% VREF 100mV GND Figure 1. Functional Diagram
Internal P-Channel Pass Transistor
The output voltage may also be adjusted by connecting The MAX1818 features a 0.25Ω P-channel MOSFET a voltage-divider from OUT to SET to GND (Figure 2). pass transistor. Unlike similar designs using PNP pass Select R2 in the 25kΩ to 100kΩ range. Calculate R1 with transistors, P-channel MOSFETs require no base drive, the following equation: which reduces quiescent current. PNP-based regulators R1 = R2 [(VOUT / VSET) – 1] also waste considerable current in dropout when the pass where V transistor saturates, and use high base-drive currents SET = 1.25V, and VOUT may range from 1.25V to 5.0V. under large loads. The MAX1818 does not suffer from these problems and consumes only 125μA of quiescent
Shutdown
current under heavy loads as well as in dropout. Pull SHDN low to enter shutdown. During shutdown, the
Output Voltage Selection
output is disconnected from the input and supply current drops to 0.1μA. When in shutdown, POK pulls low and The MAX1818’s Dual Mode operation allows opera- OUT is high impedance. The capacitance and load at tion in either a preset voltage mode or an adjustable OUT determine the rate at which V mode. Connect SET to GND to select the preset output OUT decays. SHDN can be pulled as high as 6V, regardless of the input and voltage. The two-digit part number suffix identifies the output voltage. output voltage (see Selector Guide). For example, the MAX1818EUT33 has a preset 3.3V output voltage. www.maximintegrated.com Maxim Integrated │ 6
