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TPS60231 Datasheet(PDF) 9 Page - Texas Instruments |
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TPS60231 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 16 page www.ti.com EN1 + EN2 VO ILED 0 V 0 A 0 V 20 ms/div VI = 3.6 V , ILED = 20 mA, 3 LED’s Connected, TA = 255C DETAILED DESCRIPTION OPERATION LED CURRENT ADJUSTMENT (ISET) R ISET + V ISET I LED K TPS60231 SLVS544 – OCTOBER 2004 STARTUP TIMING Figure 11. The TPS60231 uses a fractional conversion charge pump to generate a supply voltage for the integrated current sinks. These current sinks are used to ensure a constant current for each LED. Depending on the input voltage and programmed LED current, the charge pump either operates in the 1x mode or in the 1.5x mode. By switching automatically between these two modes, the circuit optimizes power conversion efficiency as well as extends operating time by allowing the discharge of the battery completely. The charge pump can generate 75 mA of output current, so each of the 3 LED outputs can be powered with up to 25 mA of current. The maximum LED current is set by a resistor connected to the ISET pin. This resistor programs a reference current, which is current mirrored to set the LED current. Applying a PWM signal to the EN1 pin and/or the EN2 pin controls the LED brightness. See a detailed description in the section Analog Dimming Using ISET Pin. A resistor programs a reference current, which is current mirrored to set the LED current. The voltage at the ISET pin depends on the status of EN1 and EN2. The current in each LED is typically 260 times the current through the resistor at ISET. VISET— Voltage from ISET pin (0.2 V, 0.4 V or 0.6 V) to GND, see Table 1 ILED— Current per LED from Dx pin to GND K — Dx to ISET current ratio (typically 260) The LED current varies linearly from 0 mA to ILED(max) mA by applying a PMW signal with 0% to 100% duty cycle. The LED brightness can however also be controlled by an analog control signal that is fed into the ISET pin. 9 |
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