Although not directly stated in the datasheet the exposed pad of the MAX2623 TSOP package variants should be connected to ground.
MAX26239
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The MAX26239/MAX26240 are small, synchronous, buck-boost converters with integrated H-bridge switches. These ICs provide a fixed-output regulation voltage...
Datasheet
MAX26239 on Analog.com
Although not directly stated in the datasheet the exposed pad of the MAX2623 TSOP package variants should be connected to ground.