Analysis of Typical Anti-Reverse Connection Circuits for Automotive Electronics

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Analysis of Typical Anti-Reverse Connection Circuits for Automotive Electronics [Copy link]

Today, let’s learn about the common automotive electronic reverse connection protection circuits.

01

Why Reverse Battery Protection?

Imagine the following scene: the car has not been driven for a long time, and the battery cannot start. At this time, a kind neighbor helps you to charge the car. The neighbors are talking and laughing, what a harmonious scene.

Suddenly, a puff of smoke came out of the car. I was happy one second, but I was confused the next. The battery was connected reversely. If the vehicle ECU does not have reverse battery protection, the repair shop will probably be overwhelmed. This is of course the most basic source of the reverse connection protection requirement, and it is also one of the series of requirements of OEMs for vehicle electronics.

02

How to Do Reverse Battery Protection?

Using schottky diode

The simplest and most effective method with low cost, mainly used on ECUs with low power consumption.

Using N-mos

Mosfet has a small Rdson and low power consumption, and is suitable for systems with large currents. As shown below, N-mos is connected in series to the ground wire. Due to the presence of mosfet, the GND level of the ECU will be raised, especially in transient conditions. Therefore, this type of device is rarely used.

Using P-mos

P-mos also has the characteristics of low power consumption and low voltage difference. It is widely used in systems with large current.

Using external fuse

Generally, this method is rarely used. There are two prerequisites. The first is to have a good relationship with the customer, at least to review it with the customer. Who would agree to burn a fuse if it is connected in reverse? The second is that all primary power supplies must be able to withstand a reverse voltage equal to the forward voltage drop of the diode without any problems.

Typical circuit analysis

The following is a widely used Pmose reverse connection protection circuit. F3920 filter is used for high frequency noise. DI3944 is used to protect Pmos and prevent Vgs from exceeding the maximum voltage. DI3950 is TVS, load dump mainly depends on it. Of course, it is necessary to distinguish whether the customer requires pulse 5A or 5B and select it reasonably. D3900 is a large inductor, combined with electrolytic capacitors, it is mainly for transient interference and noise. With it, the general CE test at low frequency is more secure.

03

Other Test Standard

In addition to the revserse battery test, the vehicle electronics must also meet other tests in terms of power line interference resistance, such as ISO7637 and ISO16750. Different revserse battery protection circuits will also have different advantages and disadvantages for the following tests.

The circuit using Schottky diode has the characteristic of reverse current blocking, so it will not discharge to the outside through the power line when the power drops. As shown in the figure below,

When interference is superimposed on the power supply, the diode can also reduce the interference amplitude at the back end and the ripple current.

04

Summary

Each solution has its own advantages and disadvantages and should be used in combination with specific application scenarios.

Reply “anti-reverse circuit” on the WeChat public account to obtain relevant information and ISO7637, ISO16750 PDF documents.

statement:

The above is just my personal opinion.

combat

This is good, I learned a lot, thank you very much

liwei198377

This is good, I learned a lot, thank you very much

liwei8377

This is good, I learned a lot, thank you very much