Measuring P2 die temperature - ideas ?

jmgjmg Posts: 12,064
edited October 12 in Propeller 2 Vote Up0Vote Down
With the present thermal envelope on P2, knowing the die temperature is likely to be more important.

One possible pathway, is to use the TEST pin substrate/esd diode driven negative with a light current, and use that on-die diode as an indicator of temperature.

Q: To check if this is even feasible, can someone with a P2 device isolate TEST, and use a multimeter (diode range) to measure the -ve dirn diode drop (-0.6v), and then run various CLK speeds to change the die temperature ?

If that works, a part like onSemi's MAX1720 (SOT26+passives) can be used current fed/voltage starved to drive the diode ~ -100uA.
Then either MAX1720 V+ can be measured (should ~mirror -Vd) or the -Vd can feed to a Analog pin, via a resistor scaled to give ~ 0V at cold temps.
The on-chip resistor tolerance will matter here, as it forms a divider with the external resistor.
A benefit of the resistor ( >>10k) is it could connect to a non-boot-sensed SPI pin, to get a no-added-pin cost thermal sense path.

Other ideas :
Possible could be a part like NCT75MNR2G (OnSemi, i2c TempSense, 2x2mm0.5 ~ 26c) - but that needs i2c connections, and is not an on-die sense element.
They also have N34TS04, bumps to ~ 80c, but adds a 4kb EEPROM in a 2x3 package.

Or, use more of the Smart Pins, (10uA source, 100uA sink) & capacitor couple to TEST with a ~22~50k pulldown & use the cap as a voltage level shift
Example numbers here give
10uA Source C charge times (initial power up) - after power up, keep charge balance time > (10x Measure time). Vpin ~ +220mV during charge = LOW logic.
0.1uF 0.1u*3.3/10u = 33ms
0.33uF 0.33u*3.3/10u = 109ms

100uA sink C Measure time (100mV dV indicator) Analog voltage is initially Vio-Vd (Pulldown steals 27~12uA of the 100uA test drive)
0.1uF 0.1u*0.1/100u = 100us (Tcharge >> 1ms)
0.33uF 0.33u*0.1/100u = 330us (Tcharge >> 3.3ms)

Measure cost here is just 2 passives, but it does need a dedicated pin for P2-Temp reading.
If that does work, it makes a good skewed-current-drive use demonstration.

or, if the Resistor/Current source have stable & consistent enough tempco's, yet another smart-pin approach would be to use any/best mix of the termination choices of
1.5k/15k/150k & 1mA/100uA/10uA which I think are available going both ways (Hi & lo). That could apply to a SPI pin ?

Comments

  • 16 Comments sorted by Date Added Votes
  • I believe Peter's P2D2 board has provision for a PIC chip that contains a temperature sensor.
  • Board temp is a rather different beast than die temp though.

    I do rather like the idea of seeing if an ESD diode or the Smart Pin characteristics can be leveraged to attempt to get a rough measure of die temp.
  • You could use 2 P2s. They could measure each other, one on RCSLOW, and the other on crystal, since RCSLOW seems to have a temperature coefficient

    More seriously I think there will be analog things that reveal temperature, we don't know what measurement modes yet.
  • Lol, overclocking hoons!

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  • How accurate do you want it.

    First, you have to choose what the device is mounted on, a 2 layer board like P2D2, or a 4 layer board or perhaps your interested in comparing the two.


    There's two ways to go at this. The first way, you just need a pencil and paper and perhaps a computer. If you assume a uniform die temperature, then the thermal conductivity of the PCB (its substrate and metal traces), the package materials, and the die itself are all very well characterized. You know the overall power dissipation, and can calculate results for various assumptions which should be reasonably accurate.


    Another way is to use an IR camera and take a thermograph of the top of the package. The most simplistic result would be found under the assumption that the package is "thin" compared to its width and length, and that the temperature is uniform in the plane of the surface, then you can assume that its just an infinite sheet which means the edges don't contribute. In short, you assume the temperature at the center is the temperature of the whole thing. Since the thickness of the package and the thermal conductivity of the material are known, you can apply the heat equation and find the die temperature (under the assumption that the die is of uniform temperature and thus there actually exists a single "die temperature") An improvement in the result can possibly be made by also considering the thermal conductivity of the interface between the die and the package.


    Typical thermal imagers (without cryogenic cooling) have accuracies in the ballpark of 2C and sensitivities of around 80mk. The thermograph should be able to give you a reasonable idea of whether that simplistic set of assumptions is reasonable. The temperature should be relatively uniform except at the edges, for suitable hand-wavy definitions of center, edge and uniform.

    You might be able to improve the calibration of the instrument, perhaps even approaching the sensitivity (the minimum temperature difference it can see) by comparing the device under test, with a sample that you can directly control the temperature of. In other words, if the camera, under conditions of the same ambient temperature,is used to image a device that is being heated to a known temperature, its thermograph , can be compared with the thermograph of the DUT. When the known temperature is adjusted so that the thermograph shows the same as the DUT, then that's your die temperature within the error of your ability to control (and know) the temperature, and the thermal sensitivity of the camera (give or take)

    The other way to attempt to improve the result is to improve the model. Take into account the pins and edges and bottom,and assume a nonuniform die temperature,in all three dimensions. However, that violates the assumption that the die temperature is a single number which is what was initially asked for and instead calculates a temperature field over its volume. One exception might be assuming the die has a temperature gradient across its thickness, and (while still using the assumption of infinite width and heigh) and using in addition to the original parameters, the thermal conductivity of the silicon wafer, solving for the surface temperature of the die. (Change the definition of die temperature to die surface temperature)
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  • Actually, I think the Ozzy boys have demonstrated, with freeze spray, a notable inherent ADC thermal reading. Beau indicated it should exist, and Chip has shown how to calibrated it away.

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  • How accurate do you want it.
    Good question.
    The first ideal is to be able to measure temp inside the P2 itself - yes, that is only one location on the die.
    External PCB temperature is easy, and simple enough with the devices already listed - small i2c temp sensors.

    An i2c device could be reverse-side centre mounted, right where the hand assembly solder-access hole is currently located, but that bumps to 2-sided assembly, which I have in the less-ideal basket at the moment.

    If caps on the reverse side are found to be measurably better, than on the top side, maybe double-side assembly will be more common ?

    Back to on-die sense : the on-die candidates are a reverse diode, and/or Current/resistor combination tracking.
    LFOSC is also possible, but that needs external-part help, and worse, requires that SysCLK is radically changed during temperature capture.

    It would be nice to see some diode millivolts table, read with a multimeter (drive any IP pin negative), on a real P2 device warmed/cooled.
  • Can the top of the chip be much different from the die temp?
  • Yeah, it can be.

    There is an air gap there. The die is in contact with the package, but there are also losses to the outside air too.

    Over a sustained time, more consistent heat profile, the top temp will be closely related to the die temp, and not too much different.

    What won't get seen is a spike, for example.

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  • I would be curious to see the results of using the bulk diode to measure the die temperature. This temperature would reflect the peripheral substrate near the I/O and not deep within the die. If an external supply takes the I/O below ground at a specific current then the NMOS bulk diode becomes forward biased which is closest to the substrate. If an external supply takes the I/O above the supply voltage at a specific current, then the PMOS bulk diode becomes forward biased.


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  • Put the chip in a well-insulated box, along with two temp probes: one near the top of the chip; the other, above and off to one side. Once the two temp probes read the same temperature, that should equal the die temperature.

    -Phil
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  • Here are some silicon device tests, Clamp/substrate diodes, pin pulled negative, no power
    ESD/Substrate clamp diodes  - 1k Ohms measured 416mV, so diode inject current is ~416uA, for this meter.
          NXP HCT573 :  TI HCT573   NXP 40106   Prop1.IO
    Vdd : 570mV             556mV       608mV
    OP  : 647mV             636mV       670mV     416mV
    IP  : 744mV             698mV       820mV  
    
    Hot-test TI 573,       OP diode 636mV -> 550mV heated 
    
    Looks to be large variation across process, less across same-process/different vendor.
    IP clamp is weaker than OP clamp, because the NMOS Drive structure is missing, just ESD clamps are present.
    Very consistent within a device, with 1-2mV variations btween like-pins.
  • Can you shave off the top of the chip and point one of those hand held temp sensors at the die. They read the chip top surface pretty well.
  • T Chap wrote: »
    Can you shave off the top of the chip and point one of those hand held temp sensors at the die. They read the chip top surface pretty well.

    Probably, but that's not really a run-time solution .... and you have disturbed the cooling significantly in your test.
    Someone may want to top-mount a heatsink, as seen commonly in RaspPi / NanoPi cooling solutions.
  • The die is lower than the pins. Even as a non-runtime solution the only packaging remaining will be the exposed thermal pad. To make it operational would need new package and rejumpering all the pins, including ground bonds.
    "Are we alone in the universe?"
    "Yes," said the Oracle.
    "So there's no other life out there?"
    "There is. They're alone too."
  • T Chap wrote: »
    Can you shave off the top of the chip and point one of those hand held temp sensors at the die. They read the chip top surface pretty well.

    But if you get a good reading of the temp at the center of the package, you can calculate the die temperature from that because everything you need to do that is fairly well defined.
    Particularly patient proactive practice positively predicates practically precise poly-processor Parallax Propeller programming paradigms.

    .
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