In-depth Analysis of Automotive Blower Design: Why Dual Resistors Have Become Mainstream? An Explanation of the Logic Behind the Solution Using TLE9879 and Seven MOSFETs

1. The role of the blower in automotive air conditioning

The automotive blower is an indispensable component in the air conditioning system, primarily responsible for driving air circulation within the air conditioning ducts, thereby achieving cooling, heating, and ventilation functions inside the vehicle. As shown in the figure below, in a typical air conditioning system, the HVAC Blower represents the blower. It can be seen that its installation position is relatively close to the passenger compartment and the driver's seat.

Currently, blower motors are primarily categorized into two types: Brush DC (BDC) motors and Three-phase Brushless DC (BLDC) motors. Among them, brushed blowers, often referred to as "speed regulators," are still widely used in existing vehicle models. However, BLDC motors, with their high efficiency, long lifespan, excellent mechanical noise performance, and high EMC ratings, are gradually becoming the mainstream in the market.

II. Typical design indicators (taking a 12V system three-phase BLDC as an example)

Operating voltage: 9V~16V

Power range: Typically 200W to 400W

Speed range: approximately 800rpm to 4000rpm

Speed regulation method: PWM or LIN control

Functional requirements: It must have the ability to operate in both downwind and upwind conditions

Noise requirements: Low noise levels must be maintained throughout the entire process of startup, operation, and shutdown

III. Main technical difficulties

For three-phase BLDC blowers, two major challenges are particularly prominent:

1) The noise requirements are extremely strict

The high requirements here are not only reflected in the decibel values, but more crucially, in the subjective comfort level of the human ear. In other words, the sound pressure of each frequency band needs to be relatively coordinated, and there should not be any particular frequency of noise that stands out. That is, the sound level curves that vary with rotational speed should be close to each other. If a single-resistance sampling scheme is adopted, the difficulty of meeting this requirement will further increase.

2) EMC level challenge

If the goal is to achieve EMC Level 4 or Level 5, it places very high demands on circuit design and layout, making it a challenging task.

IV. Interpretation of the Plan

The core components of this solution include: TLE9879QXA40, IPD70N03S4L-04 × 7, and a dual-channel operational amplifier (OPA).

1) Main control chip: TLE9879QXA40

This chip is an intelligent pre-drive motor control SoC launched by Infineon. Its Flash capacity is twice that of the TLE9877, and the specific parameters are shown in the figure below. Thanks to the highly integrated nature of the TLE9879, the overall PCBA design of this blower is quite compact.

2) Power device: IPD70N03S4L-04 × 7

One of them is used for reverse polarity protection, while the remaining six constitute a three-phase bridge arm drive. The specifications of this MOSFET are 30V voltage tolerance and 4.3mΩ internal resistance. From the perspective of selection, it may be due to cost control considerations.

3) Current sampling: External dual-channel operational amplifier

A noteworthy detail is that the TLE9879 only integrates one operational amplifier internally, thus requiring two additional external operational amplifiers to achieve dual-resistor sampling in this solution. This design choice also indirectly indicates that in blower applications with high noise requirements, the single-resistor solution still faces significant challenges. This is also the reason why many blower designs currently commonly adopt the dual-resistor solution. However, it should be noted that there are also mass-produced single-resistor solutions on the market, such as ELMOS's E523.06.