Datasheet

Application information ST1L05, ST1L05A, ST1L05B, ST1L05C, ST1L05D
16/24 Doc ID 14492 Rev 2
6.1 Power dissipation
An internal thermal feedback loop disables the output voltage if the die temperature rises to
approximately 165 °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 the 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
I
-V
O
) I
O
The junction temperature of device will be:
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 (ST1L05B, ST1L05C and ST1L05D only)
The ST1L05B, ST1L05C and ST1L05D 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 has an internal pull-up, which means that it can be left floating if it is not used.
6.3 Power Good function (ST1L05B and ST1L05D only)
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
0.92*V
ADJ
the PG pin goes in low impedance. If the device is functioning well, the Power
Good pin is at high impedance.
If the output voltage is fixed using an external or internal resistor divider, the Power Good
threshold is 0.92*V
O
.
The use of the Power Good function requires an external pull-up resistor, which must be
connected between the PG pin and V
I
or V
O
. The typical current capability of the PG pin is
up to 6 mA. The use of a pull-up resistor for PG in the range of 100 kΩ to 1 MΩ is
recommended. If the Power Good function is not used, the PG pin must remain floating.