iC-HK

155MHz LASER SWITCH

Rev 21.11.01, Page 10/13

Layout advise

iC-HK can be used in a wide range of applications from CW to over 150 MHz. Very fast switches have thus been

integrated, which have to be properly blocked to prevent ringing. A small blocking capacitor is therefore required

for iC-WK between pin 2 (CI) and 3 (AGND) and also at pin 4 (CI) of iC-HK (cf. Figure 19). Increasing capacitor

CLDA might also help to suppress ringing.

If the connection between the laser diode and iC-HK (LDK Pin 7) is loaded inductively, a small capacitor CLD in

parallel with the laser diode is recommended to suppress current spikes.

With higher pulse frequencies it is advisable to use separate grounds for iC-WK, iC-HK, capacitor C1 and

resistors Rkx respectively.

The connection between VCC and LDA (dashed line) is necessary for laser currents >70mA.

Device

Typical value

Comment

CVCC

100nF

Power supply blocking capacitor for iC-WK

CVDD

100nF

Power supply blocking capacitor for iC-HK

CLDA

1µF

Laser diode supply smoothing capacitor

CLD

2.2nF

Laser diode ESD protection, filtering with inductive loads; to be

mounted directly across the laser diode

CI

47nF..

Averaging capacitor for V(CI)-control by iC-WK

CM

MDA smoothing capacitor, has to be calculated

C1

22pF

CI smoothing capacitor (used with current limitation)

LED

V

V(VCC

V(GND

Load for iC-WK output stage; LED must be capable of 45mA; may be

replaced by a resistor or even jumpered

DGND

V

Ground shift at iC-WK to increase V(CI)

RGND

0

S .. 100S

Ground shift at iC-WK to increase V(CI)

RM

200

S .. 50kS

Set point of monitor current (mean value)

RK1

0

S ..

Set point of current through channel 1

RK2

0

S ..

Set point of current through channel 2

RCI

1k

S

Decoupling of pin CI at iC-WK and iC-HK for laser current limitation