As we speak’s trade gamers are accelerating the velocity of automotive know-how innovation as they develop new ideas of electrical, linked, autonomous, and shared mobility. Main automotive megatrends for electrification and digitalization contain zone architectures, digital driving of energy gadgets, battery administration techniques, energy electronics and energy / vitality administration. The rising demand for extra energy and security in Digital Management Models (ECUs) is driving system designers to develop good energy distribution options.

Already in conventional ICE options, the brand new energy distribution idea is effectively established and good subsystems have already been launched for dependable and environment friendly options. This strongly impacts the idea of energy distribution in ECUs, implying the alternative of conventional fuses with solid-state protections. They save techniques in case of additional stress on account of ultra-high present spikes, but additionally forestall malfunctions and mishandling. The system may be restarted as soon as the chance is overcome, with out changing any digital block or fuse.

ST launched the brand new STPOWER STripFET F8 40V sequence, which completely meets the stringent necessities for digital fuse (eFuse) options by way of excessive ruggedness towards linear mode operation and vitality administration.

Energy Distribution in Automotive Methods

The foremost pattern in energy distribution techniques is the alternative of the centralized structure, which distributes the electrical energy from the battery to the person loading techniques and features a central relay and fuse field for overload safety. The brand new automotive techniques are primarily based on good energy distribution with a number of small energy distribution facilities in a decentralized structure. These small facilities talk one another with an area interconnect community (LIN) or controller space community (CAN). The modular implementation permits a zonal structure within the automobile, which strongly reduces the wire harness, thus optimizing system price and weight along with {the electrical} efficiency.

The good modules, working as digital fuses (eFuses), assure large advantages for the improved diagnostic and safety related to the actual time data trade. As well as, the solid-state switches reduce the losses of the ability distribution system, thus bettering the gas effectivity of the automobile and lowering carbon dioxide emissions. Lastly, eFuses improve the system reliability, fulfilling the stringent automotive security necessities.

The block diagram of an automotive good energy distribution system is proven in Fig. 1.

Fig. 1. Automotive smart power distribution system.
Fig. 1. Automotive good energy distribution system.

The eFuse good change integrates a management circuit pushed by a micro controller unit and an influence change. For top-power automotive techniques, the place a excessive present limitation is requested, an exterior energy change is used, consisting of excessive rugged and low on-resistance energy MOSFETs.

Choice Standards for Energy Switches

The rules for the selection of the exterior energy switches are ruggedness in linear mode when switched-on and ruggedness towards avalanche when switched-off. These options play a key position for the optimization of high-current energy distribution techniques.

A complete evaluation is described for the eFuse good change in an electrical energy steering (EPS) system. The utmost complete present reaches 160A with a cycle time of about 40 seconds and 10 seconds of pause for a sequence of 6 occasions, then 4 energy MOSFETs linked in parallel are thought-about with a double back-to-back configuration to make sure a bidirectional safety from battery to load and vice versa (Fig. 2):

Fig. 2. Smart eFuse switch.
Fig. 2. Good eFuse change.

The shunt resistor (Rshunt) is inserted to detect in actual time the present flowing within the department, then flip off and shutdown the system in case of an unintended improve in present. It additionally helps to maintain the present fixed by transferring the suggestions sign to the controller which tunes the gate-source voltage (VGS) of the MOSFET accordingly to restrict the present to the goal worth.

  • Ruggedness in Linear Mode

The ability distribution system has to supply at activate a relentless present for the comfortable charging of the ECU bulk capacitors, thus limiting the inrush present and stopping any voltage spikes. This situation determines a linear mode operation for the ability change.
The STL325N4LF8AG was examined with a devoted benchmark and measured waveforms are reported in Fig. 3:

Fig. 3. MOSFET benchmark during soft charging.
Fig. 3. MOSFET benchmark throughout comfortable charging.

On the above situations, the MOSFET is ready to stand up to the linear mode working situations with a big charging time of 700ms. Due to this fact, the protected working space (SOA) must be checked to confirm the situation may be assured as protected and dependable for the system. The theoretical SOA curves for STL325N4LF8AG are proven in Fig. 4:

Fig. 4. Theoretical STL325N4LF8AG SOA.
Fig. 4. Theoretical STL325N4LF8AG SOA.

Nevertheless, thermal instability produces fairly a extreme de-rating on the MOSFET efficiency, by considerably reducing the present dealing with functionality. This phenomenon is named Spirito impact and is attributable to the uneven distribution of present throughout the silicon die. Beneath the zero thermal coefficient (ZTC) level, if a small area is at the next temperature than the remainder of the die, it would draw extra present and dissipate extra energy turning into even hotter. This course of finally results in thermal runaway and the destruction of the MOSFET as a three-terminal quick. Burn marks will seem close to the middle of the die and near the die bonding construction.

Furthermore, these hotspots are noticed to happen extra regularly at wider energy pulses. For a time pulse of 10ms, the Spirito impact takes place at a decrease VDS (about 2V) than for the 1ms pulse (about 4V), whereas DC operation is restricted by thermal instability at any voltage, as proven in Fig. 5:

Fig. 5. De-rated STL325N4LF8AG SOA.
Fig. 5. De-rated STL325N4LF8AG SOA.

A detailed comparability between the theoretical SOA curve at regular state situation (as worst case) and the related de-rated curve with the Spirito impact is proven in Fig. 6:

Fig. 6. Comparison of DC SOA curves.
Fig. 6. Comparability of DC SOA curves.

By together with the Spirito impact, for a VDS of 10V, the utmost present the STL325N4LF8AG can deal with beneath DC operation drastically goes from theoretical 19A all the way down to 1A.
The linear mode working situation related to the pre-charging part of the majority capacitor of the ECU may be reported on the de-rated DC curve of the SOA, by assuming 700ms equal to a gradual state situation. The imply worth of the ability managed by the MOSFET may be calculated as under reported (Eq. 1):

PD = ID x VDS_(imply) = 1.7 x (15 : 2) = 1.7 x 7.5 = 12.75 W (1)

the place: PD is the ability dissipated in the course of the pre-charging part;
ID the fixed drain present of the MOSFET;
VDS_(imply) the imply worth of the drain voltage of the MOSFET in the course of the charging time.

The linear mode level is in a protected area of the SOA, subsequently the STL325N4LF8AG reveals the ruggedness obligatory for avoiding the thermal runaway.

A complete comparability of the SOA curves of an equal AEC Q101 MOSFET (identical breakdown voltage and on-resistance in an equal bundle) from one of many essential rivals is proven in Fig. 7:

Fig. 7. SOA comparison for STL325N4LF8AG and competing device.
Fig. 7. SOA comparability for STL325N4LF8AG and competing system.

The STripFET F8 MOSFET reveals wider SOA areas for pulse occasions ranging from 1ms, displaying larger margin particularly at 10ms.

Evaluating the DC curves at 7.5V, the next values may be obtained:

  • ID = 1.9A for ST’s F8 MOSFET;
  • ID = 1.8A for competitor’s MOSFET.

Therefore, the STripFET F8 MOSFET reveals good steady-state efficiency with excessive ruggedness in linear mode operation completely aligned with the competitors.

Ruggedness towards Avalanche

At flip off the present lasts for a number of microseconds, which deposits appreciable vitality into the eFuse and the ability switches.

In truth, the wire harness that connects the primary battery to the ultimate software management board ends in a excessive impedance related to the parasitic stray inductance. This produces a sustained voltage spike which leads the MOSFET to the avalanche area.

The eFuse failure mode at flip off is then related to the breakdown of the drain−supply junction of the MOSFET.

For the EPS system, a parasitic inductance of 7µH can roughly be thought-about at each drain and supply connection, then the next testing circuit may be thought-about (Fig. 8):

Fig. 8. Schematic circuit for MOSFET testing at turn off.
Fig. 8. Schematic circuit for MOSFET testing at flip off.

The take a look at was carried out on the following situations associated to the one energy change present profile, proven in Fig. 9:

Fig. 9. Current profile of the single power switch.
Fig. 9. Present profile of the one energy change.

At flip off, the MOSFET enters the avalanche mode, by reaching a most worth of the drain-source voltage of 47.2V which exceeds the breakdown voltage. On this situation, the system has to handle a single pulse avalanche vitality (EAS) of 16.8mJ for an avalanche time (tAV) of 20µs, as proven in Fig. 10:

Fig. 10. MOSFET benchmark during avalanche.
Fig. 10. MOSFET benchmark throughout avalanche.

The avalanche situation is dependable and protected for the MOSFET if the working temperature stays decrease than absolutely the most score worth (equal to 175⁰C).

On this case, the EAS vitality for tAV = 20µs determines an influence dissipation (PD) given by (Eq. 2):

PD = = 840 W (2)

From the datasheet, the thermal impedance worth related to tAV = 20µs is the next (Eq. 3):

Zth = Okay (@ 20µs) x RthJC = 0.023 x 0.8 = 0.018 ⁰C/W (3)

Then, the temperature variation (DT) is given by (Eq. 4):

DT = PD x Zth = 15 ⁰C (4)

and, with an preliminary junction temperature (TJ_in ) of 25⁰C, the working temperature (TJ_oper) in avalanche situation turns into (Eq. 5):

TJ_oper TJ_oper = TJ_in + DT = 25 + 15 = 40 pC (5)

This ensures the STL325N4LF8AG system can safely handle the discharge vitality within the eFuse system.

A complete comparability of the assured EAS values of an equal AEC Q101 MOSFETs from the primary rivals is reported in Tab. 1:

IAV
[A]
EAS
[mJ</sub]
ΔEAS (ST vs Comp)
[%]
ST30
60
1170
590
Competitor 129706+ 66
Competitor 230
60
800
400
+46
+47

Tab. 1. Avalanche vitality comparability with competing gadgets.

Then, the innovation launched with new trench buildings to ST’s STripFET F8 know-how deeply will increase the efficiency not solely in switching, but additionally in avalanche situations, making the MOSFET function in protected and dependable mode.

Conclusions

Experimental knowledge exhibit the STL325N4LF8AG can stand up to the annoying situations related to eFuse purposes. Greatest-in-class conduct makes the STripFET F8 MOSFET the best alternative for protected and dependable energy distribution techniques in harsh excessive present automotive purposes.


 





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