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ISL58327 датащи(PDF) 8 Page - Intersil Corporation |
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ISL58327 датащи(HTML) 8 Page - Intersil Corporation |
8 / 15 page ISL58327 8 FN6577.2 July 29, 2013 Application Information Input Optical Power The ISL58327 has a photo detector in an octagon shape (shown in PD pattern) with 700µm diameter. It is sensitive from 400nm to 1000nm for light power monitoring application, which is a perfect choice for Light Automatic Power control. This wide range of sensitivity also allows the ISL58327 to be used for white balance control in systems such as LED based LCoS or DLP pico projectors. Current generated by the photo detector, is amplified by a trans-impedance amplifier (TIA). The TIA has four feedback resistors; the user can choose which feedback resistor is used for HIGH or LOW gain applications by the setting in tia_gain register. Once an appropriate resistor is selected for the required TIA gain, the optical signal is then amplified by the TIA, which feeds into the fine gain stage. HIGH gain channel and LOW gain channel TIA gains can be individually set through the TIA register. The HIGH gain and LOW gain channels have the same gain adjustment range (20dB) and can be individually controlled. In applications, if light power is modulated between 2 power levels, the user can choose between HIGH gain channel for low power level and LOW gain channel for high power. It can provide the best resolution when power is low yet the amplifier circuit is not saturated when the power is high. If users do not need to monitor two power levels, there is no need to switch between the HIGH gain channel and LOW gain channel. The selection of HIGH gain or LOW gain signal path can be done with fast hardware switching or by setting the register bit “h/l”. When changing HIGH Gain or LOW Gain signal paths by hardware switching, “h/l” bit needs to be “1”; when changing it with the register (soft switching), the HL pin needs to be driven by digital HIGH because HL and “h/l” are AND’ed for TIA gain control. Regardless of the channel gain settings, the dynamic range of TIA is determined by the photo detector sensitivity with respect to wavelength. For example, in a 445nm application when TIA = 01b gain is selected, the maximum input optical power is limited to 2mW for blue light laser, but this limitation is reduced to 1.45mW with a 638nm laser. This is because the photo detector has a higher optical-to-electrical conversion efficiency at longer wavelengths. Higher than the maximum input limitation, the TIA or whole device will still be working but it may yield a distorted output and a long falling time, while the circuits recover from saturation. Detector Pattern Gain Control The ISL58327 channel gain is set through a 12-bit DAC, separated into 2 registers. Each wavelength has two 12-bit gain registers; one for HIGH gain applications and the other for LOW gain applications. The selection of HIGH gain or LOW Gain is done by fast hardware switching through the HL pin or “h/l” register bit. All gain registers of HIGH Gain and LOW Gain channels are capable of update at anytime through the serial interface. The 12-bit gain registers provide a total of 25dB of adjustment range; +16dB to -5.5dB reference to fine gain setting 7FFh. All settings will be reset to default at power-on. The user needs to load all gain settings after the ISL58327 is powered up. Overall differential output signal gain can be estimated by using Equations 1 through 3: Blue Laser Diode(445nm) Red Laser Diode (638nm) Green Laser Diode(530nm) Where: Code is 12 bits fine gain code in decimal (0 ~ 4095) and TIA is the factor shown in Table 2. Output Configuration The ISL58327 has two differential outputs: OUTP is a positive and OUTN is a negative swing output. OUTP and OUTN outputs are referenced to VREF. VREF can be externally supplied or from the internally generated 2.1V. With respect to the input optical signal, OUTP swings up from the reference voltage and OUTN swings down from the reference voltage. Both OUTP and OUTN have the same linear output dynamic range up to 1.4V swing TABLE 1. MAXIMUM INPUT POWER vs TIA RESISTOR TIA_Gain (tia_h/tia_l) (445nm) mW (638nm) mW (532nm) mW 00b 5.0 3.65 5.30 01b 2.5 1.82 2.65 10b 1.25 0.91 1.33 11b 0.44 0.32 0.47 TABLE 2. TIA FACTOR IN EQUATIONS tia_h, tia_l SETTINGS TIA FACTOR IN EQUATION 00b 500 01b 1000 10b 2000 11b 5400 300µm 300µm 700µm 700µm Gain (mV/ W 1.88 TIA 256 Code + ------------------------------- = (EQ. 1) Gain (mV/ W 2.57 TIA 256 Code + ------------------------------- = (EQ. 2) Gain (mV/ W 1.76 TIA 256 Code + ------------------------------- = (EQ. 3) |
Аналогичный номер детали - ISL58327 |
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Аналогичное описание - ISL58327 |
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