Datasheet

MAX8869
1A, Microcap, Low-Dropout,
Linear Regulator
7
Maxim Integrated
Output Voltage Selection
The MAX8869 features Dual Mode operation. Connect
SET to GND (Figure 2) for preset voltage mode (see
Ordering Information ). In adjustable mode, set the out-
put between +0.8V to +5.0V through two external resis-
tors connected as a voltage-divider to SET (Figure 3).
The output voltage is set by the following equation:
V
OUT
= V
SET
(1 + R1 / R2)
where V
SET
= +0.8V. To simplify resistor selection:
R1 = R2 (V
OUT
/ V
SET
- 1)
Since the input bias current at SET is nominally 50nA,
large resistance values can be used for R1 and R2 to
minimize power consumption without losing efficiency.
Up to 80kΩ is acceptable for R2.
In preset voltage mode, the impedance between SET
and ground should be less than 10kΩ. Otherwise, spu-
rious conditions could cause the voltage at SET to
exceed the 80mV Dual Mode threshold.
Shutdown
A logic low on SHDN disables the MAX8869. In shut-
down, the pass transistor, control circuitry, reference,
and all biases are turned off, reducing supply current to
typically 0.1µA. Connect SHDN to IN for normal opera-
tion. In shutdown, RST is low and the soft-start capaci-
tor is discharged.
RST Comparator
The MAX8869 features a low V
OUT
indicator that
asserts when the output voltage falls out of regulation.
The open-drain RST goes low when OUT falls 8%
Figure 1. Functional Diagram
Figure 2. Typical Operating Circuit with Preset Output Voltage
MOSFET DRIVER
WITH FOLDBACK
CURRENT LIMIT
SHUTDOWN
LOGIC
0.8V
REFERENCE
SS
GND
SHDN
IN
OUT
RST
SET
V
SS
6µA
736mV
THERMAL
SENSOR
OUT
DELAY TIMER
IN
3ms
SHUTDOWN
ERROR AMP
DUAL MODE
COMPARATOR
80mV
92% V
OUT
DETECTOR
V
SS
PMOS
NMOS
R1
R2
MAX8869
IN
IN
IN
IN
SHDN
SS
OUT
OUT
OUT
OUT
RST
SET
GND
ON
OFF
C
OUT
1µF
C
IN
1µF
C
SS
V
OUT
V
IN
RESET
OUTPUT
MAX8869