According to MAX14655 datasheet, the external adjustable OVLO threshold range is from +4V to +20V. The part’s operating input voltage is up to 28V, I’m wondering why we get 20V limitation for the OVLO?

The 20V limitation is coming from the internal vs external OVLO selection threshold. The OVLO pin is used to select the internal vs external based on the threshold called VOLVLO_SELECT. For example, the internal OVLO selection point is 0.3V at OVLO pin. The external resistor divider is compared with the internal reference of 1.2V. Then if one set the external ratio vs internal more than 4:1, the internal OVLO would trip before the external one is selected. MAX14653 has the higher internal OVLO so it could go up higher than 20V.

According to MAX14655 datasheet, the external adjustable OVLO threshold range is from +4V to +20V. The part’s operating input voltage is up to 28V, I’m wondering why we get 20V limitation for the OVLO?

The 20V limitation is coming from the internal vs external OVLO selection threshold. The OVLO pin is used to select the internal vs external based on the threshold called VOLVLO_SELECT. For example, the internal OVLO selection point is 0.3V at OVLO pin. The external resistor divider is compared with the internal reference of 1.2V. Then if one set the external ratio vs internal more than 4:1, the internal OVLO would trip before the external one is selected. MAX14653 has the higher internal OVLO so it could go up higher than 20V.