EL6216 pdf datasheet (3-Channe

The EL6216 is a high-performance
three channel laser driver that provides
controlled current to a grounded laser
diode. Write channels 2 and 3 should be used as the write
channels, with switching speeds of approximately one
nanosecond rise/fall time. All three channels are summed
together at the IOUT output, allowing the user to create
multilevel waveforms in order to optimize laser diode
performance. The level of the output current is set by an
analog voltage applied to an external resistor which converts
the voltage into a current at the IIN pin (virtually ground). The
current seen at this pin is then amplified to become a current
source at pin IOUT.
An on-chip 500MHz oscillator is provided to allow output
current modulation when in any mode. This is turned on
when the OSCEN pin is held high. Complete control of
amplitude and frequency is set by two external resistors
connected to ground at pins RFREQ and RAMP (see graphs
in this data sheet for further explanation).