EL6272/EL6272C pdf datasheet (

The EL6272C is a single channel laser diode current amplifier that  
provides controlled current to a grounded laser diode. The amplifier  
can provide up to 200 mA of DC or pulsed current with switching  
speeds of approximately three nanoseconds rise/fall time. 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 (virtu- 
ally ground). The current seen at this pin is then amplified by 100X to  
become a current source at pin IOUT.  
An on-chip 500 MHz oscillator is provided to allow current modula- 
tion when in read mode. This is turned on when the OSCEN pin is held  
high. Complete control of amplitude and frequency is set by two exter- 
nal resistors connected to ground at pins RFREQ and RAMP (see  
graphs in this data sheet for further explanation).