Dennis Field / dvk-mx8m-bsb - History

Include li-ion charge controller PMIC which implements VBAT UVLO, VBAT OVP, input/output OVP & OCP; completely removed the old buck-boost in favor of this fully integrated chip

The BQ25896 may be able to handle the USB-C DRP PD switch all on its own (needs further investigation).

Replace instances of VSYS with VBAT to remove redundancy

In the case where VBAT can drop below 3.3V then it may be required to use a buck-boost in place of the existing buck converter for the 3.3V rail; may need some testing. Using the +5V rail as an input would also work but would introduce additional losses. According to several sources, when a 18650 Li-ion reaches 3.3V it is practically depleted anyway. When the feedback voltage drops below the internal reference voltage the buck converter will be in its "low dropout operation" with a duty cycle of 100%, so the output voltage should closely follow the input voltage.

Add USB type C circuit with DRP PD capability, should sink near 2A @ 5-6.5V and source 550mA @ 5V

Removed the reverse current protection circuit from the last commit due to the requirement changing to only 18650 battery and USB-C being possible power sources

Next thing to add is the charging circuit when the USB-C is in sink mode/role

Include reverse polarity protection circuit along with a simulation showing its effectiveness

Protecting VBAT from when board is sinking current via USB C. Protects against reverse polarity at the DC jack.

In EmCraft's instance VBUS should only be 5V when sinking current but they must protect against the condition when VBUS>12V and DC_IN=12V. This may need testing.

Move reference designators in the schematic so that they are legible

Use "Start to sheet number*100 and use first free number" designation, any new component added to the schematic will occupy the next available number in that sheet

For example: if sheet 2 has R201-R215 and we add a new resistor it will become R216.

Assign all associated signals to their respective pins on the EmCraft i.MX8M SoM

The ERC is now at the same state as the DART SoM schematic. Need to compare various aspects of the current schematic against the EmCraft reference design. The main buck-boost will likely need to be switched to a 5V regulator, or be configured to output 5V.

A regulator will likely need to be added which will output some VBAT voltage level (3.5~4.2V) for the M.2 cards. The SIM7100 for example requires at least 3.4V!

Bring out M.2 signals to the main sheet and attach WoWWAN and RESET

Add notes regarding the WWAN M.2's USB interface. The Emcraft SoM has NAND_CE3_B available for the DISABLE pin. Still need to select which pin will be used for CONFIG_1.

Add sim card slot, ESD protection, and relevant notes regarding the expected M.2 configuration