M02069 Datasheet, PDF(33/44 Page) M/A-COM Technology Solutions, Inc. – 3.3 or 5 Volt VCSEL/FP Laser Driver IC for Applications to 4.3 Gbps

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M02069 Datasheet, PDF (33/44 Pages) M/A-COM Technology Solutions, Inc. – 3.3 or 5 Volt VCSEL/FP Laser Driver IC for Applications to 4.3 Gbps

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Functional Description

3.4.1

Safety Circuitry

Safety Circuitry in the M02069 will disable the modulation and bias current and assert the FAIL output immediately

upon detecting a fault condition. In addition, the supply voltage that sources or sinks the laser current (SVCC or

SGND) will immediately go open circuit and prevent any current from passing through the laser.

Fault conditions checked by the M02069 include shorts to ground or VCC of all pins which can increase the laser

modulation or bias current.

For an initialization or power-up sequence to be successful, all the fault detection monitors must signal that the chip

is âhealthyâ.

When DIS goes low, pins are checked for shorts to ground or VCC and a FAIL condition is latched if there is a fault.

If the state of the pins is OK, a one-shot at the reset pin begins a countdown which will latch a FAIL condition if the

bias current has not stabilized to an acceptable level during the one-shot time. The one-shot can be extended with

an external capacitor connected from the RESET pin to ground.

The one-shot1 width is approximately

TONE-SHOT = 3 ms + (0.3 ms/pF)x(external capacitance).

Figure 3-7. Safety Circuit Block Diagram

DIS

If chip is âhealthyâ, then Enable

the outputs and Start 3msec

AND

Reset Pulse(one-shot)

AND

OUTPUT_ENABLE

VccOK Detection:

5v Mode:

AND

Latch for

CrudeFaults

SRlatch:

Reset

Vcc Pin

5v Hi/Lo Limits

Set

Vcc3 Pin

AND

FAILout

(open-collector)

3.3v Hi/Lo Limits

Latch for

Bias_OK

VCC_OK

ONE-SHOT:

Start

SRlatch:

3.3v Mode:

t=0

3ms + Tcap PULSE

Reset

Vcc Pin

5v Hi/Lo Limits

Vcc3 Pin

â1â

AND

RESET

NOTE: Pulse stays high

if Reset pin is GNDed.

Set

optional cap for longer T_init

3.3v Hi/Lo Limits

CrudeFaults Detection:

OutP > 300mV

Cmpc > 300mV

MODset > 300mV

IbiasOut > 300mV

(2061)

IboutCA > 300mV

(2069 â Common Anode)

IboutCC < (Vcc3 â 300mV)

(2069 â Common Cathode)

CrudeFaults_OK

BiasOK Detection:

Window Compare:

HI Limit

MPCset

LOW Limit

BIAS_OK

1.The one-shot is actually comprised of an oscillator and 10-bit counter.

02069-DSH-001-D

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