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ISL97698 データシート(PDF) 14 Page - Renesas Technology Corp |
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ISL97698 データシート(HTML) 14 Page - Renesas Technology Corp |
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14 / 21 page  ISL97698 FN8417 Rev.1.00 Page 14 of 21 Sep 7, 2017 Analog Dimming The ISL97698 controls LED brightness by changing the LED DC current level (analog dimming). Compared with PWM dimming, analog dimming eliminates audible noise and PWM dimming-related EMI concerns and provides higher electrical-to-optical efficiency because of the lower forward voltage of the LEDs at lower current. This current level can be controlled in 8-bit linear or 11-bit logarithmic fashion, and can be set to between 50µA and 25mA (with 20mA available by factory configuration, for PWM Input dimming and I2C dimming application). The source of the brightness information can come from I2C, 1-WIRE (supporting 5, 6, 7, 8, 9, 10 and 11-bit input sequences) or PWMI interfaces. There are 4 possible dimming modes: 1. PWM x SWIRE (linear 8-bit output) The default mode if SCL and SDA are pulled HIGH. If SWIRE is not going to be used for dimming control, the SWIRE pin should be tied to GND through a pull-down resistor. If PWMI is not needed, the PWMI pin should be tied HIGH. This allows 8-bit PWMI and/or SWIRE control. Additionally, 1-WIRE can be used in combination with PWMI and the resulting LED brightness will be the product of the two input values. 2. PWM x I2C (linear 8-bit output) Can be selected by setting the bits b7:b6 of register 02h to ‘10’. This is very similar to mode 1, but allows both PWMI duty cycle and I2C data to be combined to set the LED brightness. If PWMI is tied HIGH, register 00h can be written to define an 8-bit linear output (this means the default on-state is 100% LED brightness level). 3. SWIRE x I2C (logarithmic 11-bit output) Can be selected by setting the bits b7:b6 of register 02h to ‘01’, or by tying SCL LOW and SDA HIGH. If I2C is not available, this mode can be used to allow between 5 and 11-bit logarithmic control of the brightness via SWIRE. This mode can also be used to allow 11-bit control via I2C, if SWIRE is not going to be used for dimming control, or it can be the combination of the two interfaces. If SWIRE is not needed, the SWIRE pin should be tied to GND through a pull- down resistor. LED current is given by Equations 1 and 2 when N=1, 2... 2047 when N=0 The value of N will be the multiple of the I2C value from registers 00h and 01h, and the incoming SWIRE value. If the SWIRE resolution is below 11-bits, the value will be internally scaled up to 11-bits. 4. SWIRE x I2C (linear 8-bit output) Can be selected by setting the bit b7:b6 of register 02h to 00, or by tying SCL and SDA LOW. This is very similar to mode 3, but has an 8-bit linear output rather than an 11-bit logarithmic output. As such, only register 00h is needed from I2C and only 8-bits on SWIRE is required. Any additional resolution will be ignored. It can be used as a pure SWIRE or I2C to LED current controller, or with LED current defined as the multiple of the I2C and SWIRE values. Note: If SWIRE is not going to be used for dimming control, the SWIRE pin should be tied to GND through a pull-down resistor. The register settings and pin setups for different dimming modes are listed in Table 3. PWMI FREQUENCIES PWMI frequencies of up to 10kHz can be decoded at 8-bit resolution. Running at lower PWMI frequencies will result in a more efficient solution because internal oscillator speed is increased to decode higher PWMI frequencies and this requires more input power to operate. CONTENT ADAPTIVE BRIGHTNESS CONTROL (CABC) Content Adaptive Brightness Control (CABC) is a control method in which the LED brightness is adjusted depending on the image being displayed. For example, if the images being displayed only contains dark pixels, the backlight brightness can be reduced and the pixel values can be boosted simultaneously to let more light pass through TFT filter, resulting in the same perceived brightness. CABC is used to save power consumption in many applications. With different options of dimming control mode, ISL97698 provides the system designer with a great design flexibility for CABC. Maximum LED Current The maximum LED current is 25mA per channel by default. For PWMI dimming and I2C dimming applications, the ISL97698 can be factory configurable to set maximum LED current to 20mA (see“Factory Trimming Option” on page 18). ILED 50 A 1.00304^N = (EQ. 1) ILED 0 = (EQ. 2) TABLE 3. REGISTER SETTING AND PIN SETUP FOR DIFFERENT DIMMING MODES REGISTER 02h<7:6> DIMMING MODE PIN SETUP PWMI SWIRE SCL SDA 11 (default at power-on) Pure PWMI (Linear) Input Low High High Pure SWIRE (Linear) High Input High High PWMI x SWIRE (Linear) Input Input High High 10 PWMI x I2C (Linear) Input Low Input Input 01 I2C (Logarithmic) Low Low Input Input Pure SWIRE (Logarithmic) Low Input Low High SWIRE x I2C (Logarithmic) Low Input Input Input 00 I2C (Linear) Low Low Input Input Pure SWIRE (Linear) Low Input Low Low SWIRE x I2C (Linear) Low Input Input Input |
同様の部品番号 - ISL97698 |
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同様の説明 - ISL97698 |
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