iC-WKP

15 V CW P-TYPE LASER DIODE DRIVER

Rev A6, Page 6/10

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 = Vref(MDK) /

I(MD), where Vref(MDK) = Item No. 101 and I(MD) =

the monitor current of the laser diode at the desired

operating point. RM should be combined from a fixed

resistor (max. output power) and a trimmer (calibra-

tion).

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 undershoot at MDK 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(MDK)

VCC − 1.5V

VCC − 1V

VCC − 0.5V

VCC

Figure 1: Turn-on behaviour

Turn-off behaviour

iC-WKP works without a fixed undervoltage lockout,

thus the laser diode forward voltage is the prime fac-

tor 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-WKP simultaneously discharges control capacitor

CI so that no excessive laser diode currents occur

when the supply voltage again rises.

I(LD)

1ms

1,01ms

1,02ms

Time

0

100mA

200mA

V(CI)

0

1V

2V

V(LDA)

0

500mV

1.0V

1.5V

V(MDK)

VCC − 1V

VCC − 0.5V

VCC

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

overcurrent shutdown threshold, for example when the

feedback path is interrupted. If the monitor diode or

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 MDA, low

voltage occurring at pin MDK may also cause a shut-

down.