The principle and use of transient suppression diode TVS

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The principle and use of transient suppression diode TVS [Copy link]

1. Basic principles of TVS

TVS (transient voltage suppressor diode), also known as avalanche breakdown diode, is a device that uses its avalanche breakdown characteristics to suppress transient power. As shown in the figure below, a TVS is connected in reverse parallel between the power supply circuit and the subsequent circuit. The power supply voltage normally does not exceed the maximum operating voltage of the TVS, so the TVS has almost no effect on the circuit. When the power supply voltage is higher than the TVS breakdown threshold for some reason, the TVS will be instantly broken down. At this time, a large current will flow through the TVS to GND, consuming the instantaneous high power, so the subsequent voltage will also decrease. The voltage after the decrease is called the clamping voltage.

2. TVS basic parameters

1. Maximum operating voltage VRWM

Since TVS is used in anti-parallel and does not work under normal circumstances, its maximum working voltage is its working peak reverse voltage, and VRWM cannot exceed the maximum working voltage of the protected circuit. This voltage is also its rated voltage in some manufacturers.

2. Breakdown voltage VBR

VBR is the breakdown voltage, which is defined as the voltage corresponding to a certain reverse current IT, which is generally 1 to 10 mA. Data sheets generally divide it into maximum breakdown voltage VBR (min) and minimum breakdown voltage VBR (max), and sometimes the rated voltage is between the two.

3. Peak pulse current IPP

The peak pulse current generally refers to the peak current corresponding to the applied 10/1000μs current waveform.

4. Clamping voltage VC

The clamping voltage VC refers to the peak voltage measured across the TVS when the specified 10/1000μs current waveform is applied to the TVS, which means that under the specified current conditions, the voltage after passing through the TVS will not exceed the clamping voltage.

5. Forward voltage drop VF

VF is Forward Voltage, which refers to the forward voltage drop of TVS, which is similar to the forward voltage drop of an ordinary diode.

6. Leakage current IR

IR refers to leakage current. Even if the voltage across the TVS is lower than its maximum operating voltage VRWM, there will be a small current passing through the TVS. This current is the leakage current of the TVS. The lower the rated voltage of the TVS, the greater the leakage current. The leakage current of a 5V TVS can reach several hundred microamperes, while the leakage current of a 12V TVS is generally less than 10uA.

7. Peak pulse power Ppp

Peak pulse power is the pulse power under given conditions, Ppp=VC*Ipp

3. Key points for TVS selection

1. Packaging & Power

The package is related to power. The package should be selected based on the estimated power. Ppp=VC*Ipp. When the power cannot be estimated, the largest package can be used if the PCB and cost allow.

2. One-way and two-way

Bidirectional TVS can absorb high power of instantaneous pulses in both positive and negative directions, so it can be used in AC scenarios. At the same time, bidirectional TVS is different from single-phase TVS in parameters such as interstage capacitance, which will be introduced in a subsequent article.

3. Application scenarios

The selection also depends on its application scenario. For example, TVS can be used at the power input port as well as for the protection of CAN, USB and other signals. When used for high-speed signals, the interstage capacitance of TVS is also a factor that needs to be considered. A special article will be written later to introduce the interstage capacitance.

4. VRWM and VC

VRWM and VC are the primary considerations. For example, if a 5V power supply is used to power a chip with a maximum withstand voltage of 11V, then when we choose a parallel TVS, we can choose a TVS with a rated voltage of 6.8V. Its maximum operating voltage VRWM is 5.8V, the maximum breakdown voltage VBR(max) is 7.14V, and the clamping voltage VC is 10.5V. After clamping, it does not exceed the maximum withstand voltage of 11V.

At the same time, we should also be aware of a problem. The above example is stuck at the clamping voltage limit. With the increasing number of low-power scenarios in recent years, the voltage of ICs has become lower and lower, and their maximum withstand voltage has also become lower and lower. If the withstand voltage of the subsequent chip is only 8V or even 7V under 5V power supply, how to perform overvoltage protection? In addition to TVS, an OVP protection circuit needs to be added. I will write an article to introduce OVP circuits and integrated OVP chips later.

5. Leakage current IR

In low-power scenarios or for ADC acquisition, the power consumption or error caused by leakage current cannot be ignored, especially in low-power applications where the voltage is low and the TVS with low rated voltage has a large leakage current. Therefore, leakage current is also an object that needs to be considered.

4. Other parameters and applications

Only the above basic content is introduced, as shown in the figure below: integrated TVS array and application scenario.

xutong

I don't know how to build a TVS simulation. I usually use Zener to simulate this thing.