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参数资料
| 型号： | MIC3000BMLTR |
| 厂商： | MICREL INC |
| 元件分类： | 数字传输电路 |
| 英文描述： | ATM/SONET/SDH SUPPORT CIRCUIT, QCC24 |
| 封装： | 4 X 4 MM, MLF-24 |
| 文件页数： | 62/68页 |
| 文件大小： | 444K |
| 代理商： | MIC3000BMLTR |
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October 2004
65
M9999-101204
MIC3000
Micrel
RBASE
SHDN
VDD
High-Side
Low-Side
ILD
RPULLUP
Q1
PNP
SHDN
VDD
Q1
P-FET
ILD
RPULLUP
RBASE
SHDN
ILD
GND
RPULLDOWN
Q1
NPN
SHDN
ILD
Q1
N-FET
GND
RPULLUP
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.)
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
Package
Fairchild Semiconductor
MMBT3906
SOT-23
On Semiconductor
MMBT3906L
SOT-23
Infineon Technologies
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 VBIAS and VMOD. The temperature rise caused by self-
heating is given by:
tPDISS
JA
=×
θ
(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
Magnitude
Notes
Quiescent power
IDD ∞ VDD
Typically VDD = 3.3V, IDD = 2.7mA 3.3V ∞ 2.7mA = 8.91mW.
SHDN current
IOL ∞ VOL
Negligible if MOSFET is used as shutdown device.
TXFAULT current
IOL ∞ VOL
Worst case is VDD2/RPULLUP; RPULLUP is 4.7k min. per SFP
MSA
3.3V2/4.7k = 2.32mW.
VBIAS current
VBIAS ∞ IVBIAS or (VDD–VBIAS) ∞ IVBIAS
Worst-case is VREF ∞ 10mA = 1.22V ∞ 10mA = 12.3mW.
VMOD current
VMOD ∞ IVMOD or (VDD–VMOD) ∞ IVMOD
Worst-case is VREF ∞ 10mA = 1.22V ∞ 10mA = 12.3mW.
RSOUT current
IOL ∞ VOL
Only for rate-agile applications using RSIN/RSOUT.
DATA current
IOL ∞ VOL ∞ duty_cycle
May be negligible; Depends on bus speed, pullup current,
and bus activity.
RXLOS current
IOL ∞ VOL
Worst case is VDD2/RPULLUP; RPULLUP is 4.7K min. per
SFP MSA
3.3V2/4.7k = 2.32mW.
Table 23. Contributors to Self-Heating
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