iC-WJB

2.7 V LASER DIODE DRIVER

Rev E1, Page 10/12

2.7..6V

ISET

4

KLD

AMD

7

CI

3

CWD

2

GND

1

IN

6

LD MD

8

VCC

5

WDOG

REF

iC−WJB

VMOD

0..1.3V

R1

2nF

C3

CI

22nF

RSET

27k

Ω

100nF

C2

C1

47uF

27k

Ω

R3

0..2

Ω

Figure 11: Analogue modulation during CW operation

Analogue modulation during CW operation

The modulation cut-off frequency is determined by the

capacitor CI as well as by the operating point set with

the resistor RSET. With CI = 100 nF and RSET = R3 =

15 kΩ the cut-off frequency is approx. 30 kHz, with CI =

22 nF and the same resitor value of about 150 kHz.

The laser power can also be modulated by adapting a

current source, e.g. by using an operational amplifier

with a current output (OTA). To limit the current at pin

ISET while turning on the power supply for the OTA cir-

cuitry, however, RSET should be connected to the OTA

output (instead of to GND). The maximum current pos-

sible at ISET must be taken into consideration when

dimensioning the capacitor CI.

PC board layout

The ground connections of the external components

CI, CWD and RSET have to be directly connected at

the IC with the GND terminal.

DEMO BOARD

For the devices iC-WJ/WJZ/WJB a Demo Board is

available for test purpose. The following figures show

the schematic diagram and the component side of the

test PCB.