Disassemble and learn BYD Han EV’s BMS high-voltage sampling board

It’s National Day soon, and I’m going to take leave this weekend to go back to my hometown in Northeast China. Many students have left messages on WeChat to ask questions, but I’m really too busy to take care of them. If you have any questions, you can describe them directly. I’ll reply to you after I see them. ha.

Today we are going to study the design of BYD Han EV's BMS high-voltage acquisition board. I briefly saw it when analyzing Han's BDU a long time ago. The installation position of this high-voltage board in the BDU is as shown below. It is a separate product, independent of the control board.

Remove the mounting screws of the splitter and the two fixing screws on the upper and lower sides of the lower housing to take it out of the BDU.

This high-voltage board is as shown below. The approximate size of the product is 140mm*90mm*20mm. This is actually the B side of the PCBA. You will find that the SHUNT is placed on the T side, so that it only passes through the furnace once and reduces the risk of tin accumulation on the body. ,Worth learning.

Turn the product over and you can see that its shell is made of black plastic and its specific composition is PA66+15GF. There is a product label on the shell, which is called high-voltage monitoring module.

Remove the casing and analyze the condition of its PCBA. The T side is as shown in the figure below. The size of the PCBA is approximately 110mm*85mm*16mm. The thickness of the PCB is 2mm. It is a 4-layer board with green oil ink. The surface treatment is gold-plated. The anti-paint is basically fully coated; the chip surface on the T side is glued. At present, BYD's BMS boards are basically glued in areas with dense pins, which increases the protection against moisture or pollution; single boards There are three connectors, all of which are plug-in types.

The B side is shown in the figure below. They are all passive devices. The conformal paint is basically fully covered. The conformal paint is a bit hard after curing. The hardness indicates that its molecular structure is relatively dense and can delay the entry of water vapor. Regarding the issue of conformal paint I am also summarizing, and there are indeed some new discoveries.

The functional module division of the entire single board is roughly as shown below: In fact, the high-voltage boards are relatively clear-cut, and it is easy to find the isolation zone. The low-voltage part is mainly isolated power supply and isolated daisy chain communication. The high-voltage part generally arranges BJB chips as the core of control and acquisition. There are also some high-voltage switches, voltage dividing resistors, etc.

The main circuit structure of this single board is as follows. The BJB chip is LTC2949, an external crystal, and an EEPROM are also mounted externally to store calibration parameters. The power chip uses SN6501. Since its output is not stable, LDO is used at both the front and rear. voltage stabilization.

Let’s look at some design details. Let’s look at the SHUNT collection first. The SHUNT size is 8420, probably 50uΩ, and the surface of the copper BAR is tin-plated. The B-side collection circuit of the PCBA is as follows. An NTC is arranged at the bottom of the SHUNT to detect its temperature. ; The filter beads arranged above the current sampling line are also positioned closer to the board to avoid damage caused by mechanical stress in the middle; some windowing treatments are done on the B side of the SHUNT welding area to increase heat conduction, and the vias should not be plugged Green oil, because there is tin leakage, the advantage is that it can reduce the bubble rate of the T-side pad, but you must pay attention to the amount of tin.

The high-voltage sampling circuit is controlled by an optical MOS. This optical MOS has been discussed specifically before and is the largest size currently available. The output end of the optical MOS is connected in parallel with a TVS tube for protection in the event of overvoltage.

The high-voltage sampling board of Han EV is very similar to the high-voltage sampling board of Song DM-i (as shown below), except that there are some changes in the connector. The interior should be made into a common platform part. In addition, the high-voltage sampling board in Seal's BMS is also A similar circuit, but integrated with the control board.

Summarize:

Recently, I have gained some new understanding of safety design, especially the design requirements in the energy storage high-voltage 1500V scenario, which will be summarized later; all the above are for reference only.