STCS1_08 Datasheet, PDF (10/17 Pages) STMicroelectronics – 1.5 A max constant current LED driver

Application information
8
Application information
STCS1
8.1
Reverse polarity protection
STCS1 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 11. Reverse polarity condition
V_IN
BAT46
or similar
+
V_CC
PWM
EN
DISC
DRAIN
GND FB
8.2
10/17
Thermal considerations
The STCS1 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 Table 4: 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;
– LEDs current: 500 mA;