MAX1818 Maxim, MAX1818 Datasheet - Page 7

• Manufacturer Part Number: MAX1818
• Description: 500mA Low-Dropout Linear Regulator in SOT23
• Manufacturer: Maxim

The power OK (POK) output pulls low when OUT is less
than 93% of the nominal regulation voltage. Once OUT
exceeds 93% of the nominal voltage, POK goes high
impedance. POK is an open-drain N-channel output. To
obtain a voltage output, connect a pullup resistor from
POK to OUT. A 100kΩ resistor works well for most appli-
cations. POK can be used as a power-okay (POK) signal
to a microcontroller (µC), or drive an external LED to indi-
cate power failure. When the MAX1818 is shut down,
POK is held low independent of the output voltage. If
unused, leave POK grounded or unconnected.
The MAX1818 monitors and controls the pass transis-
tor’s gate voltage, limiting the output current to 0.8A
(typ). This current limit doubles when the output voltage
is within 4% of the nominal value to improve perfor-
mance with large load transients.
Thermal overload protection limits total power dissipa-
tion in the MAX1818. When the junction temperature
exceeds T
pass transistor, allowing the IC to cool. The thermal
sensor turns the pass transistor on again after the junc-
tion temperature cools by 20°C, resulting in a pulsed
output during continuous thermal overload conditions.
Thermal overload protection protects the MAX1818 in
Figure 2. Adjustable Output Using External Feedback
Resistors
V
IN
= 2.5V TO 5.5V
ON
OFF
1µF
C
J
IN
= +170°C, a thermal sensor turns off the
Thermal Overload Protection
_______________________________________________________________________________________
IN
SHDN
POK
MAX1818
GND
OUT
SET
Current Limit
C
3.3µF
OUT
POK Output
R1 = R2
V
1.25V
R
R
2
OUT
1
V
- 1
OUT
Linear Regulator in SOT23
the event of fault conditions. For continuous operation,
do not exceed the absolute maximum junction-temper-
ature rating of T
The MAX1818’s maximum power dissipation depends
on the thermal resistance of the IC package and circuit
board, the temperature difference between the die
junction and ambient air, and the rate of air flow. The
power dissipated in the device is P = I
V
800mW at T
where T
the MAX1818 die junction and the surrounding air, θ
is the thermal resistance of the junction to the case,
and θ
through the PC board, copper traces, and other materi-
als to the surrounding air. For best heatsinking, the
copper area should be equally shared between the IN,
OUT, and GND pins.
The MAX1818 delivers up to 0.5A RMS and operates
with input voltages up to +5.5V, but not simultaneously.
High output currents can only be sustained when input-
output differential voltages are low, as shown in Figure 3.
Figure 3. Power Operating Regions: Maximum Output vs.
Supply Voltage
OUT
Operating Region and Power Dissipation
). The maximum allowed power dissipation is
500mA Low-Dropout
CA
J
P
- T
is the thermal resistance from the case
600
400
200
MAX
A
0
A
2.5
= +70°C or:
MAXIMUM RECOMMENDED
OUTPUT CURRENT
is the temperature difference between
J
= (T
V
= +150°C.
OUT
MAXIMUM OUTPUT CURRENT
3.0
(POWER DISSIPATION LIMIT)
= 1.8V
J(MAX)
V
vs. INPUT VOLTAGE
OUT
3.5
INPUT VOLTAGE (V)
= 2.5V
4.0
- T
A
V
OUT
4.5
) / ( θ
= 3.3V
5.0
JC
T
T
A
A
= +85°C
= +70°C
+ θ
5.5
CA
OUT
6.0
)
× (V
IN
JC
7
-