Why is this TVS designed like this?

elec32156

Why is this TVS designed like this? [Copy link]

 

As shown in the figure, this is the internal circuit of a 4-channel ESD protection device TPD4E001 and the application circuit of an external USB. I don't quite understand what the upper row of diodes in the device does? Why is it designed like this? Doesn't normal logic only require the lower row?

maychang

The purpose of the upper row of diodes is to ensure that the voltage of any of the four channels cannot be higher than Vcc, and the purpose of the lower row of diodes is to ensure that the voltage of any of the four channels cannot be lower than GND.

elec32156

maychang posted on 2021-9-6 16:12 The purpose of the upper row of diodes is that the voltage of any of the four channels cannot be higher than Vcc, and the purpose of the lower row of diodes is that the voltage of any of the four channels cannot be higher than Vcc...

I don't quite understand this principle. It seems that my way of thinking is different from that of the teacher. This is a TVS. I look at this circuit from the perspective of the TVS principle. When ESD comes, the small tube inside instantly breaks down in reverse and discharges the energy through GND, and the voltage of the port is clamped at a normal level. When ESD comes, the tubes in the upper row will conduct forward, and high voltage will be loaded on VCC. Isn't it bad for VCC?

In addition, how does the TVS above ensure that the voltage is not higher than VCC when high voltage comes? If I add a voltage higher than VCC to the IO port, this TVS cannot clamp the voltage below VCC. I would like to ask the teacher for guidance. I still don’t understand this principle. Thank you!

呜呼哀哉

Think about it from another angle, how can a TVS tube ensure ESD clamping at 5 points without causing short circuits at these points?

maychang

elec32156 posted on 2021-9-6 17:24 I don't quite understand this principle. It seems that my way of thinking about the problem is different from that of the teacher. This is a TVS. I look at this circuit from the perspective of the TVS principle...

In the first picture, D1 is a TVS, and the four in the upper row and the four in the lower row are high-speed diodes.

chunyang

D1 is a TVS, used to discharge high voltage surges. The other diodes are conventional diodes, connected in a way called "clamping", which discharge ESD energy through the power supply and ground loops, and only those that cannot be discharged in time are discharged through the TVS.

There are decoupling capacitors between the power supply and the ground of the system, and there are also likely to be power regulators, batteries, etc., which can absorb ESD energy. Generally, the clamping diode plays a protective role. Only when the ESD discharge or coupling is high enough, the ESD energy absorption is not timely due to the inductive distribution parameters in the system, and the port voltage will rise rapidly until it exceeds the breakdown threshold of the TVS, at which time the TVS will act.

Therefore, this type of ESD protection device can be seen as two lines of defense. The first line of defense is the clamping diode, and the second line of defense is the TVS, each doing its own thing. I think it should be clear...

elec32156

chunyang published on 2021-9-6 19:30 D1 is a TVS, used to discharge high voltage surges. The other diodes are conventional diodes, and the connection method is called "clamping", through the power supply and ground loop...

I understand. Thank you for your guidance.

baopodao

Since TVS clamps a large voltage fluctuation, only one is sufficient in circuits with a large voltage adaptation range, but two are required for clamping in circuits with a smaller voltage range.

damiaa

Clamping circuit,
when the input is higher than Vcc, the diode connected to Vcc is turned on, so that the input voltage cannot rise any further.
When the input voltage is lower than 0V, the diode connected to ground is turned on, so that the input voltage cannot drop any further.

Why add TVS instead of ordinary diode?

Because TVS responds faster, it is effective for high-frequency signal interference added to the IO port.

When there is a transient interference voltage or pulse current on the IO port, it quickly switches to the reverse conduction state in a very short time (up to 1×10-12 seconds) and clamps the circuit voltage to the required safety value, thereby effectively protecting the precision components in the electronic circuit from damage.

se7ens

This is a low-cost TVS design solution

That is, a diode is connected in series with a voltage regulator (unidirectional TVS) to achieve ESD protection function.

会飞的小母鸡

I bought an SMDJ from Jiejie Microsemiconductor before, but the battery was damaged during testing. It was obviously a problem with their product, but they insisted on nagging for a long time. There were so many questions, and the replies were very slow. The engineers handled the problem very slowly and were unwilling to cooperate. I don't want to continue purchasing from this company. I have consulted Yangjie and MDD, and it seems that we can't cooperate long-term.

bmahu001

The figure shows protection devices connected in parallel, and each device has different response time and breakdown voltage.

tjy136124

The purpose of the upper row of diodes is to ensure that the voltage of any of the four channels cannot be higher than Vcc, and the purpose of the lower row of diodes is to ensure that the voltage of any of the four channels cannot be lower than GND.

langtuodianzi