MIC3001GML Micrel Inc, MIC3001GML Datasheet - Page 72

• Manufacturer Part Number: MIC3001GML
• Description: IC FOM MANAGEMENT W/CALIBR 24MLF
• Manufacturer: Micrel Inc
• Type: Transceiverr

Specifications of MIC3001GML

• Protocol: SDHj Sonet
• Voltage - Supply: 3 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 24-MLF®, QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Number Of Drivers/receivers: -
• Other names: 576-1753-5; MIC3001GML

Micrel, Inc.
SY89307 5.0V/ 3.3V 2.5Gbps VCSEL Driver
The modulation level of the SY89307 driver is controlled by
the voltage applied to the VCTRL pin (Type (c) above).
The circuit shown in Figure 32 allows the MIC3001’s V
output to control the SY89307’s output swing. VCTRL is
simply the DAC output voltage. The circuit operates as a
DAC-controlled voltage source. See section above on
SY88912 for R
Laser Drivers Programmed via a Sink Current
The modulation level of some laser diode drivers is
controlled by a current sourced out of the RSET pin (Type
(b) above). The circuit shown in Figure 33 allows the
MIC3001’s V
The circuit operates as a DAC-controlled current sink. The
current sink is formed by the V
transistor, and current sense resistor. The op-amp acts to
force the voltage drop across RSET to be equal to the DAC
output voltage.
The current through R
I
where b is the DC gain of Q1
The higher the gain of the transistor, the closer I
to the current in R
noise that might be present on V
shown give a 100ms time constant. See section above on
SY88912 for R
August 2004
RSET
= V
MOD
+/R
Figure 32. Controlling the SY89307
MOD
FLTR
FLTR
SET
outputs to control the set current, ISET.
, C
. I
SET
, C
Modulation Current
SET
FLTR
FLTR
. R
SET
is given by the equation:
FLTR
.
is therefore regulated as
and SHDN.
and C
MOD
DDA
buffer amplifier, external
FLTR
or V
act to eliminate any
(13)
MOD
. The values
SET
will be
MOD
72
Drivers with Monitor Outputs
Laser diode driver ICs have been introduced with
monitor outputs. These outputs provide ground-referred
signals that mirror critical signals like laser bias current,
modulation current or monitor photodiode current, an
analog of transmitted power. Generally, these outputs
source a current into an external resistor to generate a
ground-referenced voltage. Using these outputs with
the MIC3001 is straightforward since the MIC3001’s
VILD+/– and VMPD inputs are polarity programmable,
Shutdown Output
The shutdown output, SHDN, can be used in two ways:
as an enable or on/off control for the laser driver IC,
and/or to control a redundant switch in the laser current
path. The redundant switch provides a means for the
MIC3001 to shut off the laser current even if the bias
transistor or modulator is damaged or fails. SHDN is
active any time the MIC3001 shuts down the laser, i.e.,
if the TXDISABLE function is asserted in hardware or
software, or if the fault detection circuits trigger laser
shutdown. The shutdown output, SHDN, is essentially a
logic
programmable polarity allows SHDN to drive either
high-side or low-side switches or active-high or active-
low enable inputs without the need for external
inversion circuits. If an active-low and an active-high
shutdown signal are required, an external inverter will
be necessary. Examples of redundant switch circuits
are shown in Figure 34.
Figure 33. Controlling the Modulation Current
output
with
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via a Sink Current
programmable
or [phone]
M9999-082404-A
polarity.
MIC3001
The