NZQFN28 datasheet(9/20 Pages) ROITHNER

9 / 20 page

iC-NZ

FAIL-SAFE LASER DIODE DRIVER

Rev B2, Page 9/20

DESCRIPTION OF FUNCTIONS

iC-NZ is a three-channel laser diode pulse regulator

which is single-failure-proof and able to maintain a se-

lected laser class. The device includes the following

functions:

• Monitoring of the laser current

• Switching of three laser light intensity levels which

are regulated separately

• Single-failure-proof via laser light monitoring using a

second monitor diode and shut-down of the laser in

the event of error via three separate, independent

switches

• External error messaging

• Pulses of up to 155 MHz in controlled burst mode,

during which a previously set operating point is main-

tained

• Extension of the laser current with few external com-

ponents

• Operation of blue laser diodes possible

To simplify the initial operation of iC-NZ the following

passage ﬁrst outlines the basic steps involved and then

goes on to provide details referring to the demo board

available for evaluation. A HL6339G HITACHI laser

diode has been used here by way of example.

Monitoring the laser current

iC-NZ monitors the laser current ﬂowing from pin LDA

(Figure 5). The DC current threshold is set using a

resistor at pin RSI. If this threshold is exceeded, the

device is shut down for safety reasons.

IRS

x500

VDD

VREF

NEN

LDA

LDAOK

NSEN

SDIS

−

0.5V

ILDA

FINITE STATE MACHINE

VDD

RSI

CURRENT MONITOR

RSI

CLDA

NSEN

SDIS

Figure 5: Monitoring the laser current

When dimensioning resistor RSI the following applies:

Imax (LDA) = 500 ×

0.5 V

RSI

Short pulses with higher currents are also possible as

the DC current is monitored. Capacitor CLDA supplies

the current for short, higher pulses.

Demo board

According to the manufacturer’s speciﬁcations laser

diode HL6339G requires a maximum current of 70 mA

for an optical power of 5 mW. For this maximum 70 mA

current RSI is calculated as:

RSI = 500 ×

0.5 V

70 mA

= 3.5 k Ω

Switching up to three laser power levels

The following steps must be taken to set the required

optical power:

1. Enabling the system

2. Calibrating the low and middle channels

3. Calibrating the high channel

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