Cooling Considerations

The 0PA4350 has shown reliable and repetitive behavior at 77K. However, some considerations must be taken into account. If the chip is kept off when cooled it is possible to encounter problems when attempting to power-up the chip at 77K. The chip will either consume a lot of current or very little. However, after some attempts it will consume the correct value. From that moment forth, if a soft-start voltage regulator is used (we are using a REG103 from Burr-Brown), which rises the voltage slowly (in ~1 ms), it will be possible to turn on the chip as many times as desired in repetition (see test bench in Fig. 2).

However, requiring multiple attempts is not desirable. The solution is as simple as keeping the chip on while cooling. If we use a soft-start voltage regulator when cold, the chip can be turned on and off in a repeatedly manner without requiring previous attempts. It appears that keeping the chip powered during cooling minimized the lattice distortion resulting from possible thermal stresses.

Figure 1. OPA435Q in a previous version of the EMIR fan-out board.
Figure 2. Test bench used to obtain parameters in cryogenics.

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