Sound Generator for Cellular Phone # Technical Documentation: BU8793KN - 3-Phase Brushless Motor Pre-Driver IC
Manufacturer : ROHM Semiconductor
Document Version : 1.0
Last Updated : October 2023
---
## 1. Application Scenarios
### 1.1 Typical Use Cases
The BU8793KN is a 3-phase brushless DC (BLDC) motor pre-driver IC designed for sensorless control applications. It integrates a PWM control circuit, a Hall comparator, and a charge pump circuit, making it suitable for driving external N-channel power MOSFETs in a 3-phase bridge configuration.
Primary Applications Include:
- Fan and Blower Systems : CPU cooling fans, HVAC blowers, and ventilation fans where compact, efficient, and reliable motor control is required.
- Small Appliance Motors : Used in devices such as air purifiers, range hoods, and small pumps that utilize BLDC motors for improved efficiency and noise reduction.
- Light Industrial Automation : Low-power conveyor belts, small robotic actuators, and positioning systems where sensorless control simplifies design and reduces component count.
### 1.2 Industry Applications
- Consumer Electronics : Cooling solutions for gaming consoles, projectors, and audio equipment.
- Automotive : Auxiliary systems like cabin air blowers or small pump drives in non-critical, low-voltage domains (typically requiring additional qualification).
- IT & Telecommunications : Server cooling fans and fan trays in networking equipment, where reliability and power efficiency are paramount.
- Industrial Equipment : Control of small BLDC motors in packaging machinery, textile equipment, and other light-duty industrial tools.
### 1.3 Practical Advantages and Limitations
Advantages:
- Integrated Design : Combines a pre-driver, PWM controller, and Hall signal comparator, reducing external component count and board space.
- Sensorless Operation : Eliminates the need for physical Hall sensors, lowering system cost and improving reliability by removing a potential failure point.
- Wide Operating Voltage : Typically operates from a 7V to 18V supply, making it compatible with common 12V systems.
- Built-in Protection Features : Includes under-voltage lockout (UVLO) and over-current protection (via external sense resistor), enhancing system robustness.
- Low Standby Current : Suitable for battery-operated or energy-sensitive applications.
Limitations:
- Limited Current Drive : As a pre-driver, it requires external MOSFETs. The gate drive current (typically ~100mA source/200mA sink) may not be sufficient for very large MOSFETs with high gate charge without careful selection.
- Sensorless Constraints : Startup and very low-speed operation can be challenging for sensorless algorithms, potentially causing hesitation or cogging under high load at start.
- Fixed Functionality : Lacks programmability. Control parameters like PWM frequency or dead time are often set by external RC components, offering flexibility but requiring careful tuning.
- Thermal Management : The SOP30 package has a moderate thermal performance. In high ambient temperatures or high PWM frequency applications, junction temperature must be monitored.
---
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
| Pitfall | Potential Consequence | Recommended Solution |
| :--- | :--- | :--- |
| Insufficient Gate Drive | High switching losses in MOSFETs, potential overheating. | Select MOSFETs with total gate charge (Qg) compatible with the IC's drive capability. Use gate resistors to control rise/fall times and prevent ringing. |
| Poor Back-EMF Sensing | Incorrect commutation, motor stalling, especially at startup. | Ensure proper RC filtering on the BEMF sensing inputs (VS pins). Adjust filter time constant based on motor electrical time constant. Implement a robust startup routine (e.g., align-and-go). |
|
