The CS6709 is a high-speed fiber optic laser diode driver suited for applications up to 200Mbps. The CS6709 accepts differential PECL inputs, additionally a TTL/CMOS enable pin is provided for bias and modulation current control. If the enable pin is logic low, both the bias and the modulation current is set to zero. The bias and modulation current of the CS6709 can be set independently via two external resistors, and the rise/fall time can be adjusted in a similar way.
Simply leave these two pins unconnected if no adjustment is needed, then default mark/space ratio is about 42/58. An automatic power control (APC) circuit is provided to ensure constant average power in the laser diode using a monitor photodiode. A temperature compensation resistor can be adjusted to compensate the modulation current with the temperature variation. A slow-start circuit is provided to prevent laser diode damage. The slow-start time can be programed by adding an external capacitor.
Normally, the CS6709 is direct coupled to PECL inputs. However if AC coupled inputs are desired, a 2/3V DD input bias point is recommended for 3.3V/5V supply applications. The output load can be DC coupled or AC coupled in 5V supply applications, but AC coupled only in 3.3V applications.
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