MAX6329/MAX6349
logic low on MR asserts reset while the regulator is still
within tolerance.
Reset remains asserted while MR is low and for the
reset timeout period (100ms min) after MR returns high.
The MR input has an internal pullup of 20kΩ (typ) to
OUT. This input can be driven with TTL/CMOS logic
levels or with open-drain/collector outputs. Connect a
normally open momentary switch from MR to GND to
create a manual reset function; external debounce cir-
cuitry is not required. If MR is driven from long cables
or the device is used in a noisy environment, connect a
0.1µF capacitor from MR to GND to provide additional
noise immunity.
Reverse Leakage Protection
An internal circuit monitors the input and output volt-
ages. When the output voltage is greater than the input
voltage, the internal pass transistor and parasitic
diodes turn off. OUT powers the device. There is no
leakage path from OUT to IN. Therefore, the output can
be powered from an auxiliary supply such as a backup
battery without any need for additional blocking diodes.
Current Limit
The MAX6329/MAX6349 include a current limiter that
monitors and controls the pass transistor’s gate voltage,
limiting the output current to 350mA (typ). The output can
be shorted to ground for an indefinite period without
damaging the part.
Thermal Overload Protection
When the junction temperature exceeds T
J
= +160°C,
the thermal sensor signals the shutdown logic, turning
off the pass transistor and allowing the IC to cool. The
thermal sensor will turn the pass transistor on again
after the IC’s junction temperature cools by 20°C,
resulting in a pulsed output during continuous thermal-
overload conditions. Thermal overload protection is
designed to protect the MAX6329/MAX6349 in the
event of fault conditions. For continuous operation, do
not exceed the absolute maximum junction temperature
rating of T
J
= +150°C.
Operating Region and Power Dissipation
The MAX6329/MAX6349s’ maximum power dissipation
depends on the thermal resistance of the case and cir-
cuit board, the temperature difference between the die
junction and the ambient air, and the rate of airflow.
The power dissipation across the device is:
P = I
OUT
(V
IN
- V
OUT
)
The maximum power dissipation is:
P
MAX
= (T
J
- T
A
) / (θ
JB
+ θ
BA
)
where T
J
- T
A
is the temperature difference between the
die junction and the surrounding air, θ
JB
(or θ
JC
) is the
thermal resistance of the package, and θ
BA
is the ther-
mal resistance through the printed circuit board, copper
traces, and other materials to the surrounding air.
The MAX6329/MAX6349s’ ground pin (GND) performs
the dual function of providing an electrical connection
to the system ground and channeling heat away.
Connect GND to the system ground using a large pad
or ground plane.
Applications Information
Output Voltage Selection
The MAX6329/MAX6349 feature dual mode operation:
they operate in either a preset voltage mode or an
adjustable mode. In preset voltage mode, internal
feedback resistors set the MAX6329/MAX6349 to
+3.3V, +2.5V, or +1.8V (see Selector Guide). Select this
mode by connecting SET to ground. In adjustable
mode, select an output between 1.23V to 5.0V using
two external resistors connected as a voltage divider to
SET (Figure 1). The output voltage is set by the following
equation:
V
OUT
= V
SET
(1 + R1/R2)
where V
SET
= 1.23V. To simplify resistor selection:
R1 = R2 (V
OUT
/V
SET
- 1)
Choose R2 ≥ 100kΩ to optimize power consumption,
accuracy, and high-frequency power-supply rejection.
Since the V
SET
tolerance is typically less than ±30mV,
the output can be set using fixed resistors instead of
variable resistors. In preset voltage mode, impedance
between SET and ground should be less than 50kΩ.
150mA, SOT23, Low Dropout Linear Regulators
with Internal Microprocessor Reset Circuit
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