Automotive MOSFET Know-how Dependable Excessive-Present Energy.

The mobility ecosystem regularly introduces new points for automotive design, significantly 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 way 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 standard fuses, primarily based on the precept {that a} conductor overheats and melts throughout an overload situation, with Digital Fuses (eFuses). They’re able to 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 Change

The high-current energy swap is a low resistance MOSFET related in sequence to the primary energy rail and managed by logic circuitry, which integrates numerous safety, diagnostic and monitoring options. In excessive energy automotive methods, a bidirectional management is assured by way of MOSFETs in a back-to-back configuration, which provides strong energy path safety (Fig. 1).

Fig. 1. Bidirectional high-current energy swap configuration.

The present flowing within the energy rail is detected in actual time by way 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 powerful overcurrent or brief circuit happens, the controller disconnects the load, thus defending the facility provide.

At start-up, the eFuse supplies 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 delicate cost section of the majority capacitor array current on the ECU enter, withstanding a relentless present below 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 primary battery to the load of the ultimate utility.

In conclusion, the facility MOSFETs have to satisfy 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 stage 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 standard 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 delicate ignition. This requires a relentless present for producing a easy voltage rise on the ECU’s enter pins, thus avoiding any excessive voltage ringing and present spikes.

The ruggedness throughout the delicate cost section might be benchmarked with the circuit schematic proven in Fig. 2.

Fig. 2. Benchmark circuit for soft charge verification. — Fig. 2. Benchmark circuit for delicate cost verification.

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-about:

case 1 – one gadget with a present of 1.7A for 700ms;
case 2 – two gadgets 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)

Fig. 3. Benchmark measurements during soft charging (case 1). — Fig. 3. Benchmark measurements throughout delicate charging (case 1).

Fig. 4. Benchmark measurements during soft charging (case 2). — Fig. 4. Benchmark measurements throughout delicate charging (case 2).

In case 1, the linear mode ruggedness of the facility swap is examined for a protracted pulse time, which is near DC operation.

In case 2, the 2 gadgets related in parallel have the next gate threshold voltage (Vth) values:

V_th1 = 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 a number of milliseconds.

In each instances, the facility MOSFET is able to withstanding the linear mode working situations, which match the theoretical protected working space (SOA), stopping the gadget from any thermal runaway.

1. Flip-off Situation

The ability MOSFET has to resist an enormous power discharge stress at flip off. The truth is, the wire harness connecting the primary battery to the ultimate utility management board leads to 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:

Fig. 5. Measured waveforms for STL325N4LF8AG with single avalanche event at turn off. — Fig. 5. Measured waveforms for STL325N4LF8AG with single avalanche occasion at flip off.

The gadget 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 satisfy the most important obligations imposed by the worldwide ISO 7637-2 commonplace, which is said to the transients generated on the availability rail. They will vary from extreme low to excessive power or excessive to low power stage, in some instances with excessive dv/dt.

1. ISO 7637-2 Pulse 1

Pulse 1 describes the unfavourable transient noticed by electronics related in parallel with an inductive load when the connection to the facility provide is interrupted, as proven in Fig. 6.

Parameter	Worth	Unit
*U_A*	13.5	V
*U_S*	-100	V
*t_d*	2	ms
*t_r*	1 (+0/-0.5)	µs
t₁	≥ 0.5	s
t₂	200	ms
t₃	< 100	µs
*R_i*	10	Ω
*Length*	5000	pulses

Fig. 6. Voltage transient waveforms and parameters for ISO 7637-2 pulse 1 test. — Fig. 6. Voltage transient waveforms and parameters for ISO 7637-2 pulse 1 check.

The compliance to ISO 7637-2 pulse 1 was verified for STL325N4LF8AG and the measurement outcomes are proven in Fig. 7:

Fig. 7. Measured waveform of STL325N4LF8AG for ISO 7637-2 pulse 1 test (zoomed on the right). — Fig. 7. Measured waveform of STL325N4LF8AG for ISO 7637-2 pulse 1 check
(zoomed on the proper).

The experimental information present that STL325N4LF8AG can go the ISO 7637-2 pulse 1 check with out exhibiting any failure or derating of the primary parameters.

2. ISO 7637-2 Pulse 2a

Pulse 2a describes the optimistic voltage spike that will happen when present is interrupted to a circuit in parallel with the electronics being examined, as proven in Fig. 8:

Parameter	Worth	Unit
U_P	13.5 ± 5%	V
U_S	+100 ± 5%	V
t_d	50 ± 10%	µs
t_r	1 ± 10%	µs
t₁	0.5 ± 10%	s
R_i	10 ± 10%	Ω
Length	1 ± 10%	h

Fig. 8. Voltage transient waveforms and parameters for ISO 7637-2 pulse 2a test. — Fig. 8. Voltage transient waveforms and parameters for ISO 7637-2 pulse 2a check.

The measurement outcomes for STL325N4LF8AG for ISO 7637-2 pulse 2a are proven in Fig.9:

Fig. 9. Measured waveform of STL325N4LF8AG for ISO 7637-2 pulse 2a test (zoomed on the right). — Fig. 9. Measured waveform of STL325N4LF8AG for ISO 7637-2 pulse 2a check
(zoomed on the proper).

The STL325N4LF8AG can go the check additionally on this case with out exhibiting any failure or derating of the primary parameters.

3. ISO 7637-2 Pulses 3a and 3b

Pulses 3a and 3b outline the unfavourable spikes that will happen because of switching processes, influenced by the distributed capacitance and inductance of the wiring harness, as proven in Figs. 10 and 11:

Fig. 10. Voltage transient for ISO 7637-2 pulse 3a test. — Fig. 10. Voltage transient for ISO 7637-2 pulse 3a check.

Fig. 11. Voltage transient for ISO 7637-2 pulse 3b test. — Fig. 11. Voltage transient for ISO 7637-2 pulse 3b check.

The parameters worth for the exams are reported in Tab. 2:

Parameter	Pulse 3a Worth	Pulse 3b Worth	Unit
U_P	13.5	3.5 ± 0.5	V
U_S	-150	+100 ± 5 %	V
t_d	100	50 ± 45	ns
t_r	5	5 ± 1.5	ns
t₁	100	100 ± 20 %	µs
t₄	10	10 ± 20 %	ms
t₅	90	90 ± 20 %	ms
R_i	50	50 ± 20 %	Ω
Length		1	h

Experimental information for STL325N4LF8AG related to ISO 7637-2 pulse 3a and pulse 3b are proven in Figs. 12 and 13:

Fig. 12. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 3a test (zoomed on the right). — Fig. 12. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 3a check
(zoomed on the proper).

Fig. 13. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 3b test (zoomed on the right). — Fig. 13. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 3b check
(zoomed on the proper).

The check outcomes are optimistic 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:

Fig. 14. Voltage transient for ISO 7637-2 pulse 5a test. — Fig. 14. Voltage transient for ISO 7637-2 pulse 5a check.

Fig. 15. Voltage transient for ISO 7637-2 pulse 5b test. — Fig. 15. Voltage transient for ISO 7637-2 pulse 5b check.

The parameters worth for the exams in a 12V system are reported in Tab. 3

Parameter	Pulse 5a Worth	Pulse 5b Worth	Unit
U_S	65 to 87	65 to 87	V
U_S^*		35.2	V
t_d	40 to 400	40 to 400	ms
t_r	5 to 10	5 to 10	ms
R_i	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:

Fig. 16. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 5a test. — Fig. 16. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 5a check.

Fig. 17. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 5b test. — Fig. 17. Measured waveforms of STL325N4LF8AG for ISO 7637-2 pulse 5b check.

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 aggravating situations related to eFuse functions. The gadget is ready to stand up to the aggravating working situations at start-up and turn-off. Moreover, the MOSFET efficiently passes all of the exams outlined by the worldwide commonplace ISO 7637-2 for performed transients in 12V/24V battery methods. This best-in-class habits makes the STL325N4LF8AG the perfect alternative for safer energy distribution methods in harsh automotive functions.

References

[1] R. Bojoi, F. Fusillo, A. Raciti, S. Musumeci, F. Scrimizzi and S. Rizzo, “Full-bridge DC-DC energy converter for telecom functions 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”, 2^nd IEEE Worldwide Convention on Industrial Electronics for Sustainable Vitality Methods (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.