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STCS2SPR データシート(PDF) 9 Page - STMicroelectronics |
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STCS2SPR データシート(HTML) 9 Page - STMicroelectronics |
9 / 16 page STCS2 Detail description 9/16 7 Detail description The STCS2 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 %. For instance, should one need a 700 mA LEDs current, RF should be selected according to the following equation: RF = VFB / ILEDs = 100 mV / 700 mA = 142 mΩ 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 minimum rise/fall time of the current which is around 4 µs each. 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 a short delay time TD (see Figure 3). 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. 7.4 Diagnostic When STCS2 is in on mode (EN is high), the device is able to detect disconnection or fail of the LED string monitoring VDRAIN pin. If VDRAIN is lower than 75 mV the DISC pin is pulled low regardless the PWM pin status. This information can be used by the system to inform that some problem happens in the LEDs. |
同様の部品番号 - STCS2SPR |
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同様の説明 - STCS2SPR |
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