Datasheet

Application information LD39050xx
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For the adjustable version, the output voltage can be adjusted from 0.8 V up to the input
voltage minus the voltage drop across the PMOS (dropout voltage), by connecting a resistor
divider between the ADJ pin and the output, thus allowing remote voltage sensing.
The resistor divider should be selected using the following equation:
V
OUT
= V
ADJ
(1 + R
1
/ R
2
) with V
ADJ
= 0.8 V (typ.)
It is recommended to use resistors with values in the range of 10 kΩ to 50 kΩ. Lower values
can also be suitable, but will increase current consumption.
6.1 Power dissipation
An internal thermal feedback loop disables the output voltage if the die temperature rises to
approximately 160 °C. This feature protects the device from excessive temperature and
allows the user to push the limits of the power handling capability of a given circuit board
without risk of damaging the device.
It is very important to use a good PC board layout to maximize power dissipation. The
thermal path for the heat generated by the device is from the die to the copper lead frame
through the package leads and exposed pad to the PC board copper. The PC board copper
acts as a heat sink. The footprint copper pads should be as wide as possible to spread and
dissipate the heat to the surrounding ambient. Feed-through vias to inner or backside
copper layers are also useful in improving the overall thermal performance of the device.
The power dissipation of the device depends on the input voltage, output voltage and output
current, and is given by:
P
D
= (V
IN
-V
OUT
) I
OUT
The junction temperature of the device is:
T
J_MAX
= T
A
+ R
thJA
x P
D
where:
T
J_MAX
is the maximum junction of the die,125 °C;
T
A
is the ambient temperature;
R
thJA
is the thermal resistance junction-to-ambient.
6.2 Enable function
The LD39050 features an enable function. When the EN voltage is higher than 2 V the
device is ON, and if it is lower than 0.8 V the device is OFF. In shutdown mode, consumption
is lower than 1 µA.
The EN pin does not have an internal pull-up, which means that it cannot be left floating if it
is not used.
6.3 Power Good function
Most applications require a flag showing that the output voltage is in the correct range.
The Power Good threshold depends on the adjust voltage. When the adjust is higher than
0.92*V
ADJ
, the Power Good (PG) pin goes to high impedance. If the adjust is below