MIC3000 Datasheet, PDF (65/68 Pages) Micrel Semiconductor – SFP Management IC

MIC3000
V_DD
R_PULLUP
R_BASE
SHDN
Q1
PNP
ILD
ILD
R_BASE
SHDN
Q1
NPN
R_PULLDOWN
High-Side
SHDN
Low-Side
SHDN
V_DD
R_PULLUP
Q1
P-FET
ILD
ILD
Q1
N-FET
R_PULLUP
GND
GND
Figure 33. Redundant Switch Circuits
Temperature Sensing
The MIC3000 can measure and report its own internal
temperature or the temperature of a remote PN junction or
“thermal diode”. In either case it is important to note that any
board-mounted semiconductor device tends to track the
ground plane temperature around it. The dominant thermal
path to the sensor is often the ground pin. The ground pin
usually connects to the leadframe paddle on which the die is
mounted. Typical semiconductor packages, being non-con-
ductive plastic, insulate the device from the ambient air.
The advantage to using a remote sensor is that the tempera-
ture may be sensed at a specific location, such as in the
proximity of the laser diode, or away from any heat sources
where it will more closely track the transceiver’s case tem-
perature. The measured temperature is reported via the
digital diagnostics registers and is used to index the tempera-
ture compensation tables. (Note: SFF-8472 does not specify
the meaning of the reported temperature information or the
location from which it is taken. This information is to be
specified in the transceiver vendor’s datasheet.)
Micrel
Remote Sensing
For remote temperature sensing using the XPN pin, most
small-signal PNP transistors with characteristics similar to
the JEDEC 2N3906 will perform well as thermal diodes. Table
22 lists several examples of such parts that Micrel has tested
for use with the MIC3000. Other transistors equivalent to
these should also work well.
Vendor
Part Number
Fairchild Semiconductor MMBT3906
Package
SOT-23
On Semiconductor
Infineon Technologies
MMBT3906L
SOT-23
SMBT3906/MMBT3906 SOT-23
Samsung Semiconductor KST3906-TF
SOT-23
Table 22. Transistors Suitable for
Use as Remote Diodes
Minimizing Errors
Self-Heating
One concern when measuring temperature is to avoid errors
induced by self-heating. Self-heating is caused by power
dissipation within the MIC3000. It is directly proportional to
the internal power dissipation and the junction-to-ambient
thermal resistance, θ_JA. The dissipation in the MIC3000 must
be calculated and reduced to a temperature offset. The power
dissipation, PDISS, includes the effect of quiescent current
and all currents flowing into or out of any signal pins, espe-
cially V_BIAS and V_MOD. The temperature rise caused by self-
heating is given by:
∆t = P_DISS × θ_JA
(9)
θ_JA is given in the “Operating Ratings” section above as
43°C/W. The possible contributors to self-heating are listed in
Table 23.
The numbers given in Table 23 suggest that the power
dissipation in a typical application will be no more than a few
tens of milliwatts, leading to self-heating on the order of 1°C.
Description
Quiescent power
SHDN current
TXFAULT current
V_BIAS current
V_MOD current
RSOUT current
DATA current
RXLOS current
Magnitude
Notes
I_DD × V_DD
I_OL × V_OL
I_OL × V_OL
Typically V_DD = 3.3V, I_DD = 2.7mA → 3.3V × 2.7mA = 8.91mW.
Negligible if MOSFET is used as shutdown device.
WMSorAst_→ca3s.e3Vis_2/V4D.7Dk²_Ω/R=_{PU2L.L3U2Pm; WRP. ULLUP} is 4.7kΩ min. per SFP
V_BIAS × I_VBIAS or (V_DD–V_BIAS) × I_VBIAS
V_MOD × I_VMOD or (V_DD–V_MOD) × I_VMOD
I_OL × V_OL
I_OL × V_OL × duty_cycle
I_OL × V_OL
Worst-case is V_REF × 10mA = 1.22V × 10mA = 12.3mW.
Worst-case is V_REF × 10mA = 1.22V × 10mA = 12.3mW.
Only for rate-agile applications using RSIN/RSOUT.
May be negligible; Depends on bus speed, pullup current,
and bus activity.
WSFoPrsMt cSaAse_→is3V.3_{DVD22//4R.7PUkΩLLU=P2; .R32PmULWLU.P} is 4.7KΩ min. per
Table 23. Contributors to Self-Heating
October 2004
65
M9999-101204