Can you let us know how you got 272 mA max estimate. You are using the Operating Current Used by Internal Circuitry (ICCQ) and Output Buffer Current per Output Pair (ICCN) for total supply current if i am understanding correctly.
Can you let us know all the test conditions you are using. The VCCQ value, and if while checking you are checking with the load connected or unconnected.
I hope you have not shorted any of the device outputs as it can lead to a permanent damage to the device.
Note 7 in the datasheet was used to arrive at a number of 272
7. Total output current per output pair is approximated by the following expression that includes device current plus load current: CY7B991: ICCN = [(4 + 0.11F) + [((835 – 3F)/Z) + (.0022FC)]N] × 1.1 CY7B992: ICCN = [(3.5 + 0.17F) + [((1160 – 2.8F)/Z) + (.0025FC)]N] × 1.1
environment variables of F=80, C=50 and N=8,
Thanks for your support!
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Thank You for the update. The note in the datasheet can be used as a guideline for calculation of ICCN as it is not 100 % accurate and is deduced by making some approximations. So the ICCN value should be near enough 272 mA. any value like 290 or 300 should be a good enough ceiling for supply current across a large sample of parts and would be sure not to exceed across the full temperature range for this device as you asked. You can select 300 mA as the ceiling value. or say 290 mA also, as it provides enough buffer to the approx calculation.
I hope this clarifies your query.