iC-WKM

M-TYPE CW LASER DIODE DRIVER

Rev C2, Page 9/12

SAFETY INSTRUCTIONS

Laser light can damage the human eye and the

eyes of animals! Do not look at any laser light di-

rectly or through any optical lens. When handling a

laser diode, do not look directly at the light generated

by it. Wear appropriate safety glasses to prevent light

from entering the eye even by reflection.

FUNCTION DESCRIPTION

Setting the output power

The output power is simply set by RM = V(MDA) / I(MD);

with V(MDA) = Item-No. 101 and I(MD) = monitor cur-

rent of the laser diode at the desired operating point.

RM should be combined from fixed resistor (max. output

power) and a trimmer (calibration).

Turn-on behaviour

After switching the supply voltage on, the output stage

remains disabled until the internal enabling flip-flop is

set by a sufficiently high voltage at VCC.

A quick soft start follows; the transition to controlled CW

operation is gradual and primarily determined by the

values of CI and RM. CI is properly dimensioned when

the voltage overshoot at MDA is at a minimum.

0

50us

100us

150us

200us

250us

Time

0

100mA

200mA

V(CI)

I(LD)

0

1V

2V

V(LDA)

0

500mV

1,0V

1,5V

V(MDA)

−100mV

0

100mV

200mV

Figure 1: Turn-on behaviour

Turn-off behaviour

iC-WKM works without a fixed undervoltage lockout,

thus the laser diode forward voltage is the prime factor

determining the lowest possible supply voltage.

If the voltage drops below this value, the output stage

is forcibly saturated and the laser current decreases.

iC-WKM simultaneously discharges the control capaci-

tor CI so that no excessive laser diode currents occur

when the supply voltage rises again.

I(LD)

1000us

1,01ms

1,02ms

Time

0

100mA

200mA

V(CI)

0

1V

2V

V(LDA)

0

500mV

1,0V

1,5V

V(MDA)

−100mV

0

100mV

200mV

Figure 2: Turn-off behaviour

Disruptions in operation

The power control is shut down with excessive driver

temperature or when the laser current reaches the over-

current shutdown threshold, for example when the feed-

back is interrupted. If the monitor diode or the bias

resistor RM fail, the device is shut down in less than

600 µs, provided that the supply voltage applied is high

enough.

When modulating the laser current via pin MDK, exces-

sive voltage occurring at pin MDA also may cause a

shutdown.