Features: * High-performance laser diode driver
* Voltage-controlled output current source to 150 mA per channel, requiring one external set resistor per channel
* Current-controlled output current source to 150 mA per channel
* Rise time = 1.0 ns
* Fall time = 1.1 ns
* On chip oscillator with frequency and amplitude control by use of external resistors to ground
* Oscillator to 500 MHz
* Oscillator to 100 mA pk/pk
* Single +5V supply (±10%)
* Current amplification = 100
* Disable feature for power-up protection and power savings
* TTL/CMOS control signalsApplication* DVD drives
* CD-RW applications
* Writable optical drives
* Laser diode current switchingPinout
DescriptionThe EL6257C is a high-performance four channel laser diode current amplifier that provides controlled current to a grounded laser diode.The four amplifiers can provide up to 150 mA per channel of DC or pulsed current. Channels 2, 3, and 4 must be used as the write chan-nels, with switching speeds of approximately one nanosecond rise/fall time. All four channels are summed together at the IOUT output, allow-ing 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 by 100X to become a current source at pin IOUT.
An on-chip 500 MHz oscillator EL6257C is provided to allow current modula-tion when in the read mode. This is turned on when the OSCEN pin isheld high (floating not recommended). 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). The oscillator will also turn off whenever any of the OUTEN pins for channels 2, 3, and 4 (the write channels) are low (see truth table).
Output current pulses EL6257C are enabled when an 'L' signal is applied to the OUTEN pin. No output current flows when OUTEN is 'H', and addi-tional laser diode protection is provided since the OUTEN input will float high when open. Complete IOUT shut-off is also achieved by holding the ENABLE pin low, which will override the OUTEN con-trol pins.
The external resistors EL6257C allow the user to accurately and independently set each amplifier transconductance by applying a voltage to each resistor, without restriction on the voltage range, thus ensuring broad voltage DAC compatibility. Alternatively, the IIN pin can be biased from a current DAC or other current source.
EL6257 Data Sheet
