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MAX3646

155Mbps to 622Mbps SFF/SFP Laser Driver with Extinction Ratio Control

Maxim Integrated 

155Mbps to 622Mbps SFF/SFP

Laser Driver with Extinction Ratio Control

Pin Description

PIN

1

2, 5, 14, 17

3

4

6

7

8

9

10, 12

11

13

15

16

18

19

20

21

22

23

24

—

NAME

FUNCTION

Modulation-Current Compensation from Temperature. A resistor at this pin sets the temperature

MODTCOMP coefficient of the modulation current when above the threshold temperature. Leave open for zero

temperature compensation.

VCC

+3.3V Supply Voltage

IN+

Noninverted Data Input

IN-

Inverted Data Input

TX_DISABLE

Transmitter Disable, TTL. Laser output is disabled when TX_DISABLE is asserted high or left

unconnected. The laser output is enabled when this pin is asserted low.

PC_MON

Photodiode-Current Monitor Output. Current out of this pin develops a ground-referenced voltage

across an external resistor that is proportional to the monitor diode current.

BC_MON

Bias-Current Monitor Output. Current out of this pin develops a ground-referenced voltage across

an external resistor that is proportional to the bias current.

SHUTDOWN

Shutdown Driver Output. Voltage output to control an external transistor for optional shutdown

circuitry.

GND

Ground

TX_FAULT Open-Collector Transmit Fault Indicator (Table 1)

BIAS

OUT-

OUT+

MD

Laser Bias-Current Output

Inverted Modulation-Current Output. IMOD flows into this pin when input data is low.

Noninverted Modulation-Current Output. IMOD flows into this pin when input data is high.

Monitor Photodiode Input. Connect this pin to the anode of a monitor photodiode. A capacitor to

ground is required to filter the high-speed AC monitor photocurrent.

APCFILT1

Connect a capacitor (CAPC) between pin 19 (APCFILT1) and pin 20 (APCFILT2) to set the dominant

pole of the APC feedback loop.

APCFILT2

APCSET

MODSET

(See Pin 19)

A resistor connected from this pin to ground sets the desired average optical power. The total

capacitive load at the APCSET pin should be no more than 10pF. Minimize metal resistance for

ground connections.

A resistor connected from this pin to ground sets the desired constant portion of the modulation

current. The total capacitive load at the MODSET pin should be no more than 10pF. Minimize

metal resistance for ground connections.

MODBCOMP

Modulation-Current Compensation from Bias. Couples the bias current to the modulation current.

Mirrors IBIAS through an external resistor. Leave open for zero-coupling.

TH_TEMP

Threshold for Temperature Compensation. A resistor at this pin programs the temperature above

which compensation is added to the modulation current.

Exposed Pad. Solder the exposed pad to the circuit board ground for specified thermal and

EP

electrical performance.

6 _______________________________________________________________________________________

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