UV Cutoff [MSXV]

Description

The Under-Voltage Cutoff board exists to disconnect the battery if the voltage falls below a certain threshold. It provides a few additional protection features, including a fuse to limit short-circuit current, inrush-current limiting, and reverse polarity protection.

It also has load switches to control the loads (fans and horn). The load switches have built-in current sensing. UV Cutoff interfaces with power distribution to control the load switches and to provide power to the comparator.

In rev 2, a "fuel-gauge" IC was added (to measure the SoC more accurately)

Reading Material

https://www.edn.com/designing-battery-management-systems/

Possible Action Items

• Read up on and analyze previous revs of UV Cutoff

• Check for supply chain issues with major ICs on current board (compile list of alternatives for out of stock parts)

• Add a charging circuit

  • Will also require active protection (over-voltage, over-temperature, and overcurrent, see section 8.3.B in ASC regs)

  • Look into BMS circuits or ICs

  • Consider drawing power from LV

• Add controller board

  • This would remove the need for the differential I2C lines

  • Increases longevity and makes it easier to add more features to UV Cutoff board in the future

• Make UV cutoff compatible with aux battery

  • Use the same PCB for both batteries, but some passives might need to change to adjust reference voltages, etc.

    • OO: If we have a set of passives for the auxiliary, in conjunction with the existing passives for the actual battery, and use jumpers that we can solder or de-solder in order to connect the UV Cutoff to any or both batteries when we want.

    • Have two sets of passives: two sets of VBAT load switches, buck converter, and jumpers after each of these.

    • AUX battery powers fan and horn but when that runs out, switches to main pack

    • the main pack may be 24V AUX is 12V, maybe we will use a 24V aux if main battery is 24 and use fewer circuitry

      • Use same battery cells and place in series to have a 24V output

        • Turnigy Sub-C 1.2V 5000mAh High Power Series NiMH Single Cell (hobbyking.com)

    • OO: Currently, UV Cutoff will only deal with power from the aux pack

• Replace the high-side P-channel MOSFET reverse polarity protection with a low-side N-channel MOSFET for reverse polarity protection?

  • N-channels have a lower on resistance, so it would be more efficient. It would also be safer on the low side. If the battery was connected backwards with a P-channel FET, then 12 V will be connected to gnd, which is a larger net so it's more likely to accidentally touch something conductive and cause a short circuit.

  • https://www.infineon.com/dgdl/Reverse-Batery-Protection-Rev2.pdf?fileId=db3a304412b407950112b41887722615#:~:text=During reverse polarity of the,the two transistors would occur.

  • OO: Current strategy is to remain with P-Channel MOSFET for Reverse Polarity Protection.

• The fuse could probably be replaced with an e-fuse to have a more precise current limit.

Block Diagram

Schematic Capture Phase

Would this circuit be better off with a Buck Converter as opposed to the current LDO (U3)?

Soft Start + Reverse Polarity Protection

• Consider smaller resistor for sense resistor.

• Consider IC for RPP

• Add test-points

• SIMULATE in Falstad!

Interface with PD

• Think about how PD is currently interfacing with UV Cutoff (especially now that IC redriver is redundant).

  • Confer with relevant person.

  • Purpose of Voltage divider at UV Cutoff Interface on PD Board

  • 

• Make this a power connector!

• Move relevant signals like VBAT IS and UV_COMP to PD board appropriately