M61880FP

Rev.1.0, Sep.19.2003, page 12 of 20

Application Example

1. Example of sample-and-hold type self-APC circuit

20

19

18

17

16

15

14

13

12

11

50k

2.5V

COMP

2RM

1RM

ENB

DATA

PD

5V

LD

NC

100pF

36

Ω

10

Ω

5V

RO

Connected to prevent overshoot and undershoot when

LD current rises and falls. Optimal values depend on

the type of laser used and the board pattern.

1.5k

Ω

150

Ω

NC

S/H

5V

0.047µF

1

2

3

4

5

6

7

8

9

10

1.5V

Vcc2

Digital

GND2

Digital

Vcc1

Analog

GND1

Analog

TTL input

Charge/

discharge

control circuit

Reference

voltage

2. Example of controlling sample-and-hold circuit by means of

DATA signal

When the M61880 is used in optical communications, etc., (when the

S/H signal cannot be supplied), the DATA signal

can be used as a sample-and-hold control signal.

In this case, the

S/H pin should be fixed at “L”. If value CH of the hold capacitor connected to the CH pin is 0.047µF,

switching at around 20 Mbps is possible.

3. Examples of varying LD switching drive current by means of external control

(1) Varying the monitoring load resistance value (resistance connected between pins 11 and 12)

The LD drive current can be varied by varying the resistance between pins 11 and 12 in the circuit in 1. above.

(2) Varying the voltage applied to the Vr pin

The LD drive current can be varied by applying an external voltage (within the reference voltage input range) to pin

6 in the circuit in 1. above. A maximum multiplication factor of 2/0.35 = 5.7 times can be obtained as the LD drive

current ratio in this case.