350mA, 16.5V Input,
Low-Dropout Linear Regulators
MAX1658/MAX1659
IN
SHDN
P
1.21V
REFERENCE
THERMAL
SENSOR
ERROR
AMPLIFIER
MOSFET
DRIVER
WITH
CURRENT
LIMIT
P
OUT
R1
SET
R2
DUAL-MODE
COMPARATOR
MAX1658
MAX1659
65mV
GND
Figure 1. Functional Diagram
_______________Detailed Description
The MAX1658/MAX1659 are micropower, low-dropout
linear regulators featuring Dual Mode™ operation,
which allows them to deliver an adjustable (1.25V to
16.5V) or preset (3.3V for the MAX1658, 5V for
MAX1659) output. They supply up to 350mA while
requiring only 120µA of supply current (typically 30µA
with no load). The devices include thermal shutdown
circuitry, output current limiting, a P-channel pass tran-
sistor, a Dual Mode comparator, and a feedback volt-
age divider. Figure 1 shows the functional diagram.
The 1.21V reference is connected to the amplifier’s
inverting input. The error amplifier compares this refer-
ence with the selected feedback voltage and amplifies
6
the difference. The error signal applies the drive to the
P-channel pass transistor. If the feedback voltage is
lower than the reference voltage, the transistor’s gate is
pulled lower, increasing output current.
The output voltage is fed back through an internal
resistor network or an external user-selected network.
The Dual Mode comparator examines the voltage at the
SET pin and selects either the internal or external feed-
back path. If SET is below 65mV, internal feedback sets
the MAX1658’s output voltage to 3.3V and the
MAX1659’s to 5V. Otherwise, external feedback is used
for an adjustable output between 1.25V and 16.5V.
Additional features include internal current limiting,
reverse battery protection, thermal-overload protection,
and a 1µA shutdown mode.
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