SY88904 データシートの表示（PDF） - Micrel

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SY88904

FIBER OPTIC MODULE CONTROLLER WITH APC

Micrel 

Micrel, Inc.

SY88904

DLEOTGAICILDEDIADGERSACMRIPTION

The SY88904 is an integrated control circuit for laser

diode modules intended for high-frequency fiber-optic

applications. The device is designed to operate with the

SY88902 laser diode driver providing Automatic Power

Control (APC) which provides bias and modulation current

control, laser diode driver enable and monitor diode interface.

The device also interfaces with the SY88903 high-speed

limiting amplifier providing chatter-free Loss of Signal

function. The system functions provided include laser diode

over-current detection, module fault signal and transmit

disable control. The SY88904 also provides power up cycling

of laser diode current and the fault detect signal.

Laser Diode Supply Current

The SY88904 provides the adjustable drive current for

the laser diode, DC bias.

Laser Diode Over-Current Detection

The SY88904 provides the ability to set an upper limit

fail point for the laser diode. ILIMIT SET sets an upper limit

for the average current present at the IBIAS pin.

Monitor Diode

The MD pin on the SY88904 provides low frequency

light intensity, laser power out feedback from the monitor

diode in the laser diode package. This feedback is used to

adjust the IBIAS level through the Automatic Power Control

circuit to maintain a near constant power output from the

laser diode. The SY88904 will also generate a fault if the

MD pin receives photo current less than IPINSET or is no

longer connected to the monitor diode.

Laser Diode Driver Enable

The SY88904 provides a TX_Out pin used to control the

output of the laser diode driver, through the Enable pin , of

the SY88902. This is a single ended PECL output.

Module Fault

The SY88904 provides an open collector output,

TX_Fault, that indicates to the host system that the module

is in a fault condition. The SY88904 will assert TX_Fault

when a low VCC condition is detected, when the monitor

diode is not connected or when a laser diode over-current

condition is detected. The SY88904 will attempt to clear a

TX_Fault condition if the device is power cycled or a reset

cycle is initiated with TX_Disable. When the SY88904 is in

a TX_Fault condition Ibias will be removed, TX_Out will be

negated and fault detection will be disabled.

Power Up Sequence, TX_Disable asserted

The SY88904 will power up in a TX_Fault condition and

will remain in a fault condition while TX_Disable is asserted.

Power Up Sequence, TX_Disable negated

The SY88904 will power up in a TX_Fault condition and

will remain in a fault condition until VCC is within operational

limits, at which time an initialization sequence will be started.

TX_Disable Cycle, TX_Fault Negated

When the SY88904 is not in a TX_Fault condition, a

rising edge of TX_Disable will cause the SY88904 to enter

a TX_Fault condition. The falling edge of TX_Disable will

cause a power up sequence to be started.

TX_Disable Cycle, TX_Fault Asserted

When the SY88904 is in a TX_Fault condition, the falling

edge of TX_Disable will cause an initialization sequence to

be started.

TX_Disable Cycle, during an initialization cycle

A rising edge of TX_Disable will cause the SY88904 to

terminate the current initialization cycle and remain in a

TX_Fault condition. The falling edge of TX_Disable will cause

the initialization sequence to be restarted.

Initialization Sequence

The initialization sequence consists of a delay, set by

the RC time constant on the Rwin input, followed by a

power up sequence.

Power Up Sequence

A power up sequence will negate TX_Fault and then

ramp up Ibias, controlled by the capacitor on the Rwin input

and an internal 1mA current, followed by TX_OUT being

negated and fault checking. If a fault occurs at this time the

module will enter a TX_Fault conditions, otherwise the

module will be ready for operation.

M9999-081005

hbwhelp@micrel.com or (408) 955-1690

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