NZQFN28 datasheet(2/20 Pages) ROITHNER

2 / 20 page

iC-NZ

FAIL-SAFE LASER DIODE DRIVER

Rev B2, Page 2/20

DESCRIPTION

Three-channel laser diode pulse regulator iC-NZ en-

ables the continuous wave operation of laser diodes

and spike-free switching with deﬁned current pulses

in a frequency range of up to 155 MHz. The three

channels can be accumulatively pulsed via inputs

LENL, LENM and LENH. The peak optical power of

the laser diodes is regulated separately for high, mid-

dle and low levels and adjusted using the three exter-

nal resistors RMH, RMM and RML.

The iC is activated via pin EN which triggers a self-

test of the device. The system is enabled if no errors

are detected. Any errors are signaled at pin NERR.

The (average) current monitor can be set using ex-

ternal resistor RSI. Overcurrent is signalled at NERR,

causing the iC to be shut down.

To ensure that the selected laser class is maintained

a second monitor input SMD (safety monitor diode)

is needed. This optional photo diode monitors the

laser power. Exceeding the monitor window, set-up

by RSMD, triggers a permanent reset. This is re-

ported at output NERR and can be deleted when the

system is restarted at EN.

For high pulse frequencies the device can be

switched into controlled burst mode at input REGEN.

A previously settled operating point is maintained

throughout the burst phase.

When the iC is switched on all safety-relevant sig-

nals pertinent to the current monitor, SMD and con-

trol unit are checked. These units are in turn mon-

itored for the following: overcurrent, short circuits,

open pins and whether the laser is switched off in

terms of output power. With the exception of the lat-

ter these checks are carried out intermittently dur-

ing operation. So that the device is single-failure-

proof various safety check routines are also imple-

mented. To this end a second SMD (safety monitor

diode) monitoring the laser power is required. The

laser power must stay within a deﬁned range during

operation (thus maintaining the laser class). If this

range is left, the system is shut down and an error

message is generated.

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