Detail description

STCS2A

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Detail description

The STCS2A is a BiCMOS constant current source designed to provide a precise constant

current starting from a varying input voltage source. The main target is to replace discrete

components solution for driving LEDs in low voltage applications such as 5 V, 12 V or 24 V

giving benefits in terms of precision, integration and reliability.

7.1

Current setting

The current is set with an external sensing resistor connected to the FB pin. The feedback

voltage is 100 mV, then a low resistor value can be chosen reducing power dissipation. A

value between 1 mA and 2 A can be set according to the resistor value the resulting output

current has a tolerance of ± 10%.

the following equation:

7.2

Enable

When the enable pin is low the device completely off thus reducing current consumption to

less than 1 µA. When in shutdown mode, the internal main switch is off.

7.3

PWM dimming

The PWM input allows implementing PWM dimming on the LED current; when the PWM

input is high the main switch will be on and vice versa. A typical frequency range for the

input is from few Hertz to 50 kHz. The maximum dimming frequency is limited by the

Above 50 kHz the current waveforms starts assuming a triangular shape.

While the PWM input is switching, the overall circuitry remains on, this is needed in order to

implement two important features: short delay time and controlled slope for the current.

Since the PWM pin is controlling just the main switch, the overall circuitry is always on and it

is able to control the delay time between the PWM input signal and the output current in the

range of few µs, this is important to implement synchronization among several light LED

sources.

characteristics). A controlled rise time has two main benefits: reducing EMI noise and avoid

current spike at turn on.

condition an overshoot can be present on the LED current before the system goes into

regulation.