The LTC2937 can get its VDD power either from the VPWR regulator or an external source. When VDD drops below the undervoltage lockout (UVLO) level but stays above about 1V, the chip can still pull the EN1–EN6 outputs low using internal NMOS transistors. This helps keep the outputs in a known low state instead of floating. However, as VDD drops further, these pulldowns get weaker. If the external pull-up is strong enough, it might eventually override the weak pulldown, causing the EN outputs to rise or become unstable.