transistor, allowing the IC to cool. The thermal sensor
turns the pass transistor on again after the junction tem-
perature cools by 15°C, resulting in a pulsed output
during continuous thermal-overload conditions.
Thermal-overload protection safeguards the MAX1589
in the event of fault conditions. For continuous opera-
tion, do not exceed the absolute maximum junction-
temperature rating of +150°C.
Operating Region and Power Dissipation
The MAX1589’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 airflow. The
power dissipated in the device is P = I
OUT
✕
(V
IN
-
V
OUT
). The maximum allowed power dissipation is:
P
MAX
= (T
J(MAX)
- T
A
) / (θ
JC
+ θ
CA
)
where T
J(MAX)
- T
A
is the temperature difference between
the MAX1589 die junction and the surrounding air, θ
JC
is
the thermal resistance of the junction to the case, and
θ
CA
is the thermal resistance from the case through the
PC board, copper traces, and other materials to the sur-
rounding air. Typical thermal resistance (θ
JC
+ θ
JA
) for a
device mounted to a 1in square, 1oz copper pad is
41°C/W for the 3mm x 3mm TDFN package, and
110°C/W for the 6-pin thin SOT23 package. For best
heatsinking, expand the copper connected to GND, or
the exposed paddle.
The MAX1589 delivers up to 500mA and operates with
an input voltage up to +3.6V. However, when using the
6-pin SOT23 version, high output currents can only be
sustained when the input-output differential voltage is
low, as shown in Figure 2.
The maximum allowed power dissipation for the 6-pin
TDFN is 1.951W at T
A
= +70°C. Figure 3 shows that the
maximum input-output differential voltage is not limited
by the TDFN package power rating.
Applications Information
Capacitor Selection and
Regulator Stability
Capacitors are required at the MAX1589’s input and
output for stable operation over the full temperature
range and with load currents up to 500mA. Connect a
1µF ceramic capacitor between IN and GND and a
4.7µF low-ESR ceramic capacitor between OUT and
GND. The input capacitor (C
IN
) lowers the source
impedance of the input supply. Use larger output
MAX1589
Low-Input-Voltage, 500mA LDO Regulator
with
RREESSEETT
in SOT and TDFN
_______________________________________________________________________________________ 7
Figure 1. Functional Diagram
