Soft Saturation | PartQuest™ Explore

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Darrell
Designer10

Darrell

Member for

10 years 6 months

624

designs

10

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Big fan of VHDL-AMS

Description

This example shows the performance of an ON Semiconductor NCV8876 Automotive Grade Start-Stop Boost Controller. For vehicles with Start-Stop capability, the engine (ICE) is turned off during idle periods, for the purpose of fuel economy. But low-voltage nuisance drop-out of key electronic functions must be avoided during engine re-start. The NCV8876 is designed specifically for this purpose. It uses current-mode control, with many integrated functions to reduce the complexity of the external boost circuit.Simulation results show the output to the load during battery drop-out and recovery. Note that in this application, the output voltage (dark blue waveform) is maintained above 6.4V during the drop-out transient, and regulates at 6.8V during sustained low voltage (4V) battery operation (orange waveform).This circuit also demonstrates the value of soft-saturation inductor components from Coilcraft. The load current for the XAL4030-332 inductor in this application is 4A during nominal 12V operation. But during boost operation, the current reaches 6.6A peak (light blue waveform). This could saturate a typical inductor if it were sized for the nominal load, resulting in a collapse of the effective inductance. But notice that the actual instantaneous inductance (green waveform) only drops to 2.2uH, for this nominal 3.3uH part. This relatively small percentage drop in inductance can easily be accommodated by the converter design.To learn more about the NCV8876 from ON Semiconductor, click here: http://www.onsemi.com/pub_link/Collateral/NCV8876-D.PDFTo learn more about molded core soft saturation technology from Coilcraft, see page 4 of this document: http://www.coilcraft.com/pdfs/Doc1140_Beyond_the_data_sheet_Part1.pdf

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NCV8876 - Overcurrent Protection

Mike Donnelly
Designer19

Mike Donnelly

Member for

10 years 6 months

1,563

designs

10

groups

Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

This example demonstrates the overcurrent protection capabilities of the ON Semiconductor NCV8876. It complements the design: https://www.systemvision.com/design/ncv8876-automotive-start-stop-boost-controller, which shows the performance of the device in normal operation. But in this design, the inductor element proves inadequate for boost operation under a heavy load condition. Inductance collapse, caused by core saturation, could lead to damaging peak current levels in multiple electronic components, were it not for the “hiccup-mode” overcurrent protection feature of the NCV8876. Simulation results show that the boost output voltage (dark blue waveform) falls to approximately 5V when the battery voltage (orange waveform) drops to 6V. This is in contrast to the nominal circuit operation, in which the NCV8876 would enter boost control mode and maintains a 6.8V boost output level. But because of the low drop-out voltage of the NCV59302 VLDO, the 5V regulated output voltage is only slightly reduced. The current through the 2.3 Ohm load resistor is maintained at just under 2.2A throughout the entire operation.While this load level is within the current rating of the inductor (2.3A RMS Max.), it is approaching the saturation inductance “cliff” for this traditional (i.e. non-soft-saturating) part. So when the NCV8876 activates boost control, it switches on the Power MOSFET briefly, effectively grounding the low side of the inductor through the small current sense resistance (0.03 Ohms). With the nominal 3.3uH inductance value, this would result in a slow current build-up (V/L = di/dt = 6V/3.3uH = 1.8A/us). But in this case the inductance collapses with further current increase, and the di/dt value becomes very large. The inductor current spikes to well over 10A (light blue waveform), and the corresponding inductance crashes to a small fraction of its nominal value (green waveform).The current spikes could have gone much higher, possibly resulting in damage to the NVGS3130 Power MOSFET, which has a rated pulse current maximum of 19A. If you zoom in on the magenta waveform, you'll see the Ids current rising, slowly at first while the inductance is intact, but then rapidly rising to over 11A as the inductance collapses, all in just 100ns! Fortunately the gate voltage (brown waveform) is cut off to prevent further current rise. This is thanks to the overcurrent protection feature of the NCV8876. When an overcurrent condition is detected, the device immediately goes into “hiccup-mode”, in which the gate drive is turned off and remains off for a count of 1024 clock cycles. After the mandatory hiccup period, the NCV8876 reattempts boost operation, but with continued overcurrent monitoring. Note that the current spikes are repeated with just over a 2ms period, because the clock is programmed to just over 2 us period (450 kHz switching frequency) in this design.To learn more about the capabilities of the ON Semiconductor NCV8876, click here: http://www.onsemi.com/pub_link/Collateral/NCV8876-D.PDFTo learn more about the benefits of Coilcraft's molded core soft saturation technology for reducing problems with current spikes, see page 4 of this document: http://www.coilcraft.com/pdfs/Doc1140_Beyond_the_data_sheet_Part1.pdf

About text formats

NCV8876 - Automotive Start-Stop Boost Controller

Darrell
Designer10

Darrell

Member for

10 years 6 months

624

designs

10

groups

Big fan of VHDL-AMS

Description

This example shows the performance of an ON Semiconductor NCV8876 Automotive Grade Start-Stop Boost Controller. For vehicles with Start-Stop capability, the engine (ICE) is turned off during idle periods, for the purpose of fuel economy. But low-voltage nuisance drop-out of key electronic functions must be avoided during engine re-start. The NCV8876 is designed specifically for this purpose. It uses current-mode control, with many integrated functions to reduce the complexity of the external boost circuit.Simulation results show the output to the load during battery drop-out and recovery. Note that in this application, the output voltage (dark blue waveform) is maintained above 6.4V during the drop-out transient, and regulates at 6.8V during sustained low voltage (4V) battery operation (orange waveform).This circuit also demonstrates the value of soft-saturation inductor components from Coilcraft. The load current for the inductor in this application is 4A during nominal 12V operation. But during boost operation, the current reaches 6.6A peak (light blue waveform). This could saturate a typical inductor if it were sized for the nominal load, resulting in a collapse of the effective inductance. But notice that the actual instantaneous inductance (green waveform) only drops to 2.2uH, for the nominal 3.3uH part. This relatively small percentage drop in inductance can easily be accommodated by the converter design.

About text formats

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NCV8876 - Automotive Start-Stop Boost Controller

DarrellDesigner10

Darrell

Member for

NCV8876 - Overcurrent Protection

Mike DonnellyDesigner19

Mike Donnelly

Member for

NCV8876 - Automotive Start-Stop Boost Controller

DarrellDesigner10

Darrell

Member for

Darrell
Designer10

Mike Donnelly
Designer19

Darrell
Designer10