500mA Low-Dropout Linear Regulator in UCSP
V
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
(POWER DISSIPATION LIMIT)
OUT
R1 = R2
- 1
1.25V
V
= 2.5V TO 5.5V
IN
V
OUT
600
400
200
0
IN
OUT
T
T
= +85°C
= +70°C
MAXIMUM RECOMMENDED
OUTPUT CURRENT
A
A
C
C
OUT
3.3µF
IN
1µF
R
1
MAX1819
ON
SHDN
POK
SET
V
OUT
= 1.8V
OFF
V
OUT
= 2.5V
V
OUT
= 3.3V
R
2
GND
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
INPUT VOLTAGE (V)
Figure 3. Power Operating Regions—Maximum Output vs.
Supply Voltage
Figure 2. Adjustable Output Using External Feedback
Resistors
Operating Region and Power Dissipation
The MAX1819’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
POK Output
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 signal, connect a pullup resistor from
POK to OUT. A 100kΩ resistor works well for most appli-
cations. POK can be used as a power-OK signal to a
microcontroller (µC), or drive an external LED to indicate
power failure. When the MAX1819 is shut down, POK is
held low independent of the output voltage. If unused,
leave POK grounded or unconnected.
power dissipated in the device is P = I
× (V
-
IN
OUT
V
). The maximum allowed power dissipation is
OUT
840mW at T = +70°C or:
A
P
MAX
= (T
- T ) / ( θ + θ
)
BA
J(MAX)
A
JB
where T - T is the temperature difference between
J
A
the MAX1819 die junction and the surrounding air, θ
JB
is the thermal resistance of the junction to the base,
and θ is the thermal resistance through the PC
Current Limit
The MAX1819 monitors and controls the pass transis-
tor’s gate voltage, limiting the output current to 1.0A
(typ). This current limit doubles when the output voltage
is within 4% of the nominal value to improve perfor-
mance with large load transients.
BA
board, copper traces, and other materials to the sur-
rounding air. For best heatsinking, the copper area
should be equally shared between the IN, OUT, and
GND pins.
The MAX1819 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.
Thermal Overload Protection
Thermal overload protection limits total power dissipa-
tion in the MAX1819. When the junction temperature
exceeds T = +170°C, a thermal sensor turns off the
J
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 MAX1819 in
the event of fault conditions. For continuous operation,
do not exceed the absolute maximum junction-temper-
ature rating of T = +150°C.
J
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