eFuse Parts Selection
eFuse IC: TPS25983 (
)
This eFuse IC was selected because…
Its wide 2 - 18 A current limit range allows flexibility without needing to parallelize any eFuses.
Has functionality for overcurrent, under/overvoltage, slew rate control, reverse current (via external FET). (Note that we will be implementing undervoltage protection ourselves so that the EN/UVLO pin can be used as an EN pin for switching of outputs.)
Monitoring functionality for current and fault state.
Works for 12V and 24V systems.
It’s on the more pricy side of TI eFuses but the wide current range and flexibility in voltage will allow us to save costs by requiring fewer ICs if we can keep the same system working into the next-generation vehicle.
Calculated Component Values for eFuse Protection Functions
Overcurrent Limit
According to the datasheet, the formula for determining the resistance of a particular current limit is…
For a current limit range of 2 - 18 A, a range of possible goes from 81.610 Ω to 772.487 Ω.
On the BBPDU, we will be using a digital POT IC to be able to easily change the current limit through code. Its selection is described in a section below.
Overcurrent Blanking Interval
Current Monitoring Resistor
Retry # of Attempts
Retry Delay
Slew Rate
Overvoltage Lockout
Gate Resistance (for external FET)
Digital POT IC: AD5258BRMZ1 (
)
The current limit is set on the eFuse IC using a resistance from the ILIM pin to ground. In order to allow this limit to be easily adjustable without replacing components or opening up the PCB’s enclosure, we will use a digital potentiometer/rheostat IC.
This digital POT IC features a range from about 150 Ω - 1150 Ω, which covers the range of resistances calculated above that we need to be able to set the eFuse. It doesn’t fully cover the lower end of resistance values, but that is for very high current limits that we are unlikely to set.
Another potential option could be the AD8400. It has a smaller package, more resistance positions, and a smaller package, but is significantly more expensive.
External FET:
The TP25983 offers the ability to drive the gate of an external FET to block reverse current.