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IS31LT3354-STLS2 Datasheet(PDF) 7 Page - Integrated Silicon Solution, Inc |
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IS31LT3354-STLS2 Datasheet(HTML) 7 Page - Integrated Silicon Solution, Inc |
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7 / 12 page  IS31LT3354 Integrated Silicon Solution, Inc. – www.issi.com Rev. A, 09/01/2011 7 APPLICATION INFORMATION Setting nominal average output current with external resistor RS The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected between VIN and ISENSE and is given by: IOUT nom = 0.1/RS The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the typical application circuit shown on page 1: RS (Ω) Nominal average output current (mA) 0.05 2000 0.083 1200 0.15 667 0.3 333 Vsense is divided into two ranges to improve current accuracy, please refer to bin information on page 3. The above values assume that the ADJ pin is floating and at a nominal voltage of VREF =1.2V. It is possible to use different values of RS if the ADJ pin is driven from an external voltage. Rs need to be chosen 1% accuracy resistor with enough power tolerance and good temperature characteristic to ensure stable output current. Output current adjustment by external DC control voltage The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current to a value above or below the nominal average value defined by RS. ADJ GND SN3354 DC The nominal average output current in this case is given by: IOUTdc = 0.083*VADJ/RS [for 0.3V< VADJ <1.2V] Note that 100% brightness setting corresponds to VADJ = VREF. When driving the ADJ pin above 1.2V, the current will be clamped to 100% brightness automatically. The input impedance of the ADJ pin is 500kΩ ±25%. Output current adjustment by PWM control Directly driving ADJ input A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as shown below, to adjust the output current to a value below the nominal average value set by resistor RS ,the signal range is from 0V~5V. The PWM signal must have the driving ability to drive internal 500KΩ pull-up resistor. ADJ GND SN3354 0v 5v Driving the ADJ input from a microcontroller Another possibility is to drive the chip from the open drain output of a microcontroller. The diagram below shows one method of doing this: The diode and resistor suppress possible high amplitude negative spikes on the ADJ input resulting from the drain-source capacitance of the FET. Negative spikes at the input to the chip should be avoided as they may cause errors in output current or erratic device operation. See the section on PWM dimming for more details of the various modes of control using high frequency and low frequency PWM signals. Shutdown mode Taking the ADJ pin to a voltage below 0.2V will turn off the output and supply current will fall to a low standby level of 95μA nominal. IS31LT3354 IS31LT3354 IS31LT3354 |
Similar Part No. - IS31LT3354-STLS2 |
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Similar Description - IS31LT3354-STLS2 |
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