Datasheet MAX1735 (Maxim) - 6

200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23
IN THERMAL CIN SENSOR NMOS PASS TRANSISTOR SHUTDOWN LOGIC OUT
MAX1735
ON SHDN GND OFF MAX1735 COUT ON ERROR AMPLIFIER R1 VREF -1.25V SET Dual Mode COMPARATOR R2 -270mV GND Figure 1. Functional Diagram
Detailed Description
comparator selects the feedback path based on VSET. Connect SET to GND to use the internal feedback path, The MAX1735 is a low-dropout negative linear voltage setting the output voltage to the preset value. If an regulator. It features Dual Mode operation, allowing a external voltage-divider is used, see Output Voltage fixed -5.0V, -3.0V, or -2.5V output voltage or an Selection. adjustable output from -1.25V to -5.5V. The regulator is guaranteed to supply 200mA of output current. It fea-
Internal N-Channel MOSFET
tures 60dB power-supply rejection for noise-sensitive The MAX1735 features an N-channel MOSFET pass applications and a low 85µA operating current that opti- transistor. Unlike similar designs using NPN bipolar mizes it for battery-operated devices. pass transistors, N-channel MOSFETs require extreme- As Figure 1 illustrates, the device consists of an internal ly low drive currents, reducing overall quiescent cur- -1.25V reference, an error amplifier, an N-channel rent. Also, NPN-based regulators consume still more MOSFET, an internal precision-trimmed feedback volt- base current in dropout conditions when the pass tran- age-divider, and a Dual Mode comparator. sistor saturates. The MAX1735 does not suffer from these problems, consuming only 125µA total current at The -1.25V reference is connected to the inverting input full load and in dropout. of the error amplifier. The error amplifier compares the reference voltage with the selected feedback voltage
Output Voltage Selection
and amplifies the difference. The error amplifier drives The MAX1735 features Dual Mode operation, allowing for the MOSFET to control the output voltage. a preset or adjustable output voltage. In preset voltage The feedback voltage for regulation is generated by mode, the output of the MAX1735 is set to -5.0V, -3.0V, or either an internal or external resistive voltage-divider -2.5V (see Ordering Information). Select this mode by connected from OUT to SET. The internal Dual Mode connecting SET to GND (Figure 2).
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