MIC3000BML datasheet(65/68 Pages) MICREL

65 / 68 page

October 2004

M9999-101204

MIC3000

Micrel

RBASE

SHDN

VDD

High-Side

Low-Side

ILD

RPULLUP

PNP

SHDN

VDD

P-FET

ILD

RPULLUP

RBASE

SHDN

ILD

GND

RPULLDOWN

NPN

SHDN

ILD

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,

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

=×

(9)

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 4.7ký min. per SFP

MSA

∅ 3.3V2/4.7ký = 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 4.7Ký min. per

SFP MSA

∅ 3.3V2/4.7ký = 2.32mW.

Table 23. Contributors to Self-Heating

MIC3000BML Datasheet(PDF) 65 Page - Micrel Semiconductor

MIC3000BML Datasheet(HTML) 65 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68

Datasheet Download

Link URL