STCS1A Datasheet, PDF (12/19 Pages) STMicroelectronics – 1.5 A max constant current LED driver

Application information
8
Application information
STCS1A
8.1
Reverse polarity protection
STCS1A must be protected from reverse connection of the supply voltage. Since the current
sunk from V_CC pin is in the range of 450 µA a small diode connected to V_CC is able to
protect the chip. Care must be taken for the whole application circuit, especially for the
LEDs, in fact, in case a negative voltage is applied between V_IN and GND, a negative
voltage will be applied to the LED string that must have a total breakdown voltage higher
than the negative applied voltage in order to avoid any damage.
Figure 15. Reverse polarity condition
V_IN
BAT46
or similar
+
V_CC
PWM
DRAIN
EN
DISC
SLOPE GND FB
8.2
12/19
Thermal considerations
The STCS1A is able to control a LED current up to 1.5 A and able to sustain a voltage on
the drain pin up to 40 V. Those operating conditions are however limited by thermal
constraints, the thermal resistances shown in the Thermal data section are the typical ones,
in particular R_thJA depends on the copper area and the number of layers of the printed
circuit board under the pad. DFN8 and PowerSO-8 have an exposed die attach pad which
enhances the thermal conductivity enabling high power application.
The power dissipation in the device can be calculated as follow:
P_D = (V_DRAIN - V_FB) x I_LED + (V_CC x I_CC)
basing on this and on the thermal resistance and ambient temperature, the junction
temperature can be calculated as:
T_J = R_thJA x P_D + T_A
A typical application could be:
– Input voltage: 12 V;
– 3 white LEDs with an typical V_F=3.6 V;