The mobility ecosystem regularly introduces new points for automotive design, notably with regard to the scale, security, and reliability of digital options. Then, new options are developed to deal with the expertise challenges, including connectivity and cloud computing by means of Digital Management Models (ECUs).
Excessive-end autos use as much as tons of of ECUs and this requires extra environment friendly energy administration with safer energy paths from the automotive battery to the load factors to cut back failures. Electrical security might be enhanced by changing typical fuses, primarily based on the precept {that a} conductor overheats and melts throughout an overload situation, with Digital Fuses (eFuses). They can clamp the output voltage and limits the throughput present, appropriately supplying the load or ultimately disconnecting it within the occasion of a persistent fault. Excessive present environments impose strict constraints when it comes to dealing with high-energy discharges, so strong and dependable energy switches are wanted.
Excessive-Present Energy Swap
The high-current energy swap is a low resistance MOSFET linked in collection to the principle energy rail and managed by logic circuitry, which integrates varied safety, diagnostic and monitoring options. In excessive energy automotive methods, a bidirectional management is assured by means of MOSFETs in a back-to-back configuration, which affords strong energy path safety (Fig. 1).
The present flowing within the energy rail is detected in actual time by means of the resistor (RLIM) and stored fixed by the eFuse, which tunes the gate-source voltage (VGS) of the MOSFETs to restrict the present to the goal worth. If a robust overcurrent or brief circuit happens, the controller disconnects the load, thus defending the facility provide.
At start-up, the eFuse offers an outlined ramp-up of the output voltage to make sure the inrush present is maintained inside protected confines, thus defending each the load and the facility provide. This situation locations a extreme constraint on the facility MOSFETs which must handle the mushy cost section of the majority capacitor array current on the ECU enter, withstanding a continuing present beneath linear mode operation.
Moreover, when the load is disconnected, the facility MOSFETs are put right into a burdened situation as a result of discharge of the power saved within the parasitic stray inductance related to the wire harness which connects the principle battery to the load of the ultimate utility.
In conclusion, the facility MOSFETs have to fulfill the next necessities (Tab. 1):
| Energy MOSFET | |
| Working Situation | Requirement |
| On-state | Low conduction loss |
| Begin-up | Linear mode ruggedness |
| Flip-off | Vitality dealing with |
The brand new STPOWER STripFET F8 MOSFET expertise launched by STMicroelectronics and absolutely AEC Q101 certified displays all the important thing design enhancements which guarantee a excessive degree of energy effectivity and ruggedness for protected and dependable efficiency.
The STL325N4LF8AG is a 40V MOSFET housed in a PowerFLAT 5×6 leadless bundle with a sub-milliohm static on-resistance (RDS(on)), which is lower than 0.75mΩ. Subsequently, it’s able to offering very restricted conduction losses.
Key Parameters for MOSFET Choice
For typical automotive masses powered by the 12V lead-acid battery, the facility swap has to resist a steady present stream as much as 160 A – 200 A requested by the ECU for an influence supply within the vary of 1kW.
1. Begin-up Situation
Along with the excessive present, the facility MOSFET has to handle the pre-charge section of the majority capacitor array current on the enter of the ECU to make sure a mushy ignition. This requires a continuing present for producing a clean voltage rise on the ECU’s enter pins, thus avoiding any excessive voltage ringing and present spikes.
The ruggedness in the course of the mushy cost section might be benchmarked with the circuit schematic proven in Fig. 2.
The circuit permits to cost the load capacitance (CLOAD) with fixed present: by tuning the V1 and VDD voltage values, the present might be stored fixed, thereby setting a particular charging time for CLOAD. The check was carried out with a 94mF stack of capacitors for the load and provide voltage of 15V.
For the STL325N4LF8AG, two completely different measurement settings are thought of:
- case 1 – one system with a present of 1.7A for 700ms;
- case 2 – two units in parallel with a present of 29A every for 6ms.
The measured waveforms for the linear mode operation are proven in Figs. 3 (for case 1) and 4 (for case 2)
In case 1, the linear mode ruggedness of the facility swap is examined for an extended pulse time, which is near DC operation.
In case 2, the 2 units linked in parallel have the next gate threshold voltage (Vth) values:
- Vth1 = 1.49V @ 250µA
- th2 = 1.53V @ 250µA.
The restricted Vth unfold (within the 3% vary) produces a decent imbalance on the MOSFET currents as follows:
the place ID1 is barely greater than ID2 for the decrease Vth worth.
On this case (2), the linear mode ruggedness of the facility switches is examined at excessive present with a pulse time lasting just a few milliseconds.
In each instances, the facility MOSFET is able to withstanding the linear mode working circumstances, which match the theoretical protected working space (SOA), stopping the system from any thermal runaway.
1. Flip-off Situation
The ability MOSFET has to resist an enormous power discharge stress at flip off. In reality, the wire harness connecting the principle battery to the ultimate utility management board ends in a excessive impedance related to the parasitic stray inductance and this causes an enormous power discharge on the facility distribution methods.
This power might be managed with a single avalanche occasion at MOSFET turn-off in case of particular points for the ECU or an lively clamp which forces the MOSFET to work in linear mode once more. The STL325N4LF8AG can correctly work in a particular avalanche check at 40A, as proven in Fig. 5:
The system additionally has a rugged efficiency at turn-off when it comes to power administration.
Compliance to ISO 7637-2
For 12V/24V battery methods, automotive eFuse switches have to meet the most important obligations imposed by the worldwide ISO 7637-2 normal, which is expounded to the transients generated on the availability rail. They will vary from extreme low to excessive power or excessive to low power degree, in some instances with excessive dv/dt.
1. ISO 7637-2 Pulse 1
Pulse 1 describes the unfavorable transient noticed by electronics linked in parallel with an inductive load when the connection to the facility provide is interrupted, as proven in Fig. 6.
| Parameter | Worth | Unit |
| UA | 13.5 | V |
| US | -100 | V |
| td | 2 | ms |
| tr | 1 (+0/-0.5) | µs |
| t1 | ≥ 0.5 | s |
| t2 | 200 | ms |
| t3 | < 100 | µs |
| Ri | 10 | Ω |
| Period | 5000 | pulses |
The compliance to ISO 7637-2 pulse 1 was verified for STL325N4LF8AG and the measurement outcomes are proven in Fig. 7:
(zoomed on the suitable).
The experimental knowledge present that STL325N4LF8AG can move the ISO 7637-2 pulse 1 check with out displaying any failure or derating of the principle parameters.
2. ISO 7637-2 Pulse 2a
Pulse 2a describes the constructive voltage spike which will happen when present is interrupted to a circuit in parallel with the electronics being examined, as proven in Fig. 8:
| Parameter | Worth | Unit |
| UP | 13.5 ± 5% | V |
| US | +100 ± 5% | V |
| td | 50 ± 10% | µs |
| tr | 1 ± 10% | µs |
| t1 | 0.5 ± 10% | s |
| Ri | 10 ± 10% | Ω |
| Period | 1 ± 10% | h |
The measurement outcomes for STL325N4LF8AG for ISO 7637-2 pulse 2a are proven in Fig.9:
(zoomed on the suitable).
The STL325N4LF8AG can move the check additionally on this case with out displaying any failure or derating of the principle parameters.
3. ISO 7637-2 Pulses 3a and 3b
Pulses 3a and 3b outline the unfavorable spikes which will happen because of switching processes, influenced by the distributed capacitance and inductance of the wiring harness, as proven in Figs. 10 and 11:
The parameters worth for the exams are reported in Tab. 2:
| Parameter | Pulse 3a
Worth |
Pulse 3b
Worth |
Unit |
| UP | 13.5 | 3.5 ± 0.5 | V |
| US | -150 | +100 ± 5 % | V |
| td | 100 | 50 ± 45 | ns |
| tr | 5 | 5 ± 1.5 | ns |
| t1 | 100 | 100 ± 20 % | µs |
| t4 | 10 | 10 ± 20 % | ms |
| t5 | 90 | 90 ± 20 % | ms |
| Ri | 50 | 50 ± 20 % | Ω |
| Period | 1 | h |
Experimental knowledge for STL325N4LF8AG related to ISO 7637-2 pulse 3a and pulse 3b are proven in Figs. 12 and 13:
(zoomed on the suitable).
(zoomed on the suitable).
The check outcomes are constructive for STL325N4LF8AG for each pulse 3a and 3b too.
4. ISO 7637-2 Pulses 5a and 5b (Load Dump)
Pulses 5a and 5b are a simulation of load dump transient, occurring within the occasion of a discharged battery being disconnected whereas the alternator is producing charging present and with different masses remaining on the alternator circuit, as proven in Figs. 14 and 15:
The parameters worth for the exams in a 12V system are reported in Tab. 3
| Parameter | Pulse 5a
Worth |
Pulse 5b
Worth |
Unit |
| US | 65 to 87 | 65 to 87 | V |
| US* | 35.2 | V | |
| td | 40 to 400 | 40 to 400 | ms |
| tr | 5 to 10 | 5 to 10 | ms |
| Ri | 0.5 to 4 | 0.5 to 4 | Ω |
The measured waveforms of STL325N4LF8AG with ISO 7637-2 pulse 3a and pulse 3b are proven in Figs. 17 and 18:
Then, the STL325N4LF8AG can present a safety to load dump too.
Conclusions
The STL325N4LF8AG manufactured with the brand new STripFET F8 expertise is tailor-made for withstanding all of the disturbing circumstances related to eFuse purposes. The system is ready to face up to the disturbing working circumstances at start-up and turn-off. Moreover, the MOSFET efficiently passes all of the exams outlined by the worldwide normal ISO 7637-2 for performed transients in 12V/24V battery methods. This best-in-class habits makes the STL325N4LF8AG the best selection for safer energy distribution methods in harsh automotive purposes.
References
[1] R. Bojoi, F. Fusillo, A. Raciti, S. Musumeci, F. Scrimizzi and S. Rizzo, “Full-bridge DC-DC energy converter for telecom purposes with superior trench gate MOSFETs”, IEEE Worldwide Telecommunications Vitality Convention (INTELEC), Turin 2018.
[2] S. Musumeci, F. Scrimizzi, G. Longo, C. Mistretta and D. Cavallaro, “Trench-gate MOSFET utility as lively fuse in low voltage battery administration system”, 2nd IEEE Worldwide Convention on Industrial Electronics for Sustainable Vitality Programs (IESES), 2020.
[3] G. Breglio, F. Frisina, A. Magrì and P. Spirito, “Electro-thermal instability in low voltage energy MOS: experimental characterization”, IEEE ISPSD, Toronto 1999.
