The BD622X series of circuits is the latest Intelligent PWM DC brush motor driver IC from Rohm Semiconductor. This high-efficiency PWM H-bridge driver offers advanced performance and reliability for a wide range of motor control applications. The series includes six models: BD6220, BD6221, BD6222, BD6225, BD6226, and BD6227. Among these, BD6226, BD6221, and BD6222 are single-channel drivers, while BD6225, BD6226, and BD6227 are dual-channel drivers. These ICs are widely used in devices such as DVD recorders, digital cameras, and video cameras due to their excellent dynamic performance and comprehensive protection features.
This article will focus on the BD6222 model to explain the key characteristics and working principles of the BD622X series motor driver.
**1. Internal Structure and Key Features**
The BD6222 boasts several notable features, including automatic conversion between speed setting voltage and PWM, with a programmable PWM frequency ranging from 20kHz to 100kHz. It also has low standby power consumption, with zero current draw when the motor is stopped. The chip includes an internal circuit to prevent through-current and misoperation during standby. Its low on-resistance (RON) is typically 1.5Ω, and it supports PWM input via the control terminal. The operating voltage range is wide, from 6V to 15V, with a maximum limit of 18V. The VREF input can vary between 3V and 15V, and the maximum drive current reaches up to 2A. Built-in protection mechanisms safeguard against overcurrent, overvoltage, overtemperature, and undervoltage conditions. The device operates reliably within a temperature range of -40°C to +85°C.
The BD6222 comes in a 25-pin HSOP package, as shown in the diagram. It integrates a PWM controller, logic control circuit, overtemperature protection, overcurrent and overvoltage protection, under-voltage lockout, MOSFET driver, and power MOSFETs. The pin functions include OUT1 and OUT2 for motor drive outputs, GND for ground connections, VREF for speed setting, RIN and FIN for direction control, VCC for the control supply, and additional pins for power supply and heat dissipation.
**2. Application Circuit and Working Principle**
The figure illustrates the BD6222 pinout and typical application circuit. The internal logic control circuit supports four motor states: forward rotation, reverse rotation, brake, and standby. These modes are controlled by the VREF, FIN, and RIN pins. The table outlines the settings for each mode and the corresponding motor behavior.
In **standby mode**, the VREF pin is set to a specific level, and both FIN and RIN are pulled low. During this state, the internal circuitry, including the output MOSFETs, is turned off. When switching to standby, the system enters an idle state automatically due to the presence of a diode.
In **forward mode**, the motor rotates when OUT1 is high and OUT2 is low. The FIN pin is set high, RIN is low, and VREF is connected to VCC. Current flows from VCC through the upper MOSFET, through the motor, and back to ground via the lower MOSFET.
In **reverse mode**, the motor rotates in the opposite direction when OUT1 is low and OUT2 is high. Here, the FIN pin is low, RIN is high, and VREF is connected to VCC. The current path reverses accordingly.
In **brake mode**, the motor stops quickly by short-circuiting the terminals. However, it’s generally recommended to use standby mode for stopping the motor, as brake mode requires more power and may lead to higher stress on the system.
Additionally, the FIN and RIN signals can be used independently in PWM mode to control the motor's operation, with frequencies ranging from 20kHz to 100kHz.
**2.2 Motor Speed Control**
The BD6222 automatically converts the speed-setting voltage (VREF) into a PWM signal, adjusting the duty cycle to control the motor speed. The relationship between VREF and the PWM duty cycle is linear. For example, when VCC is 12V and VREF is 9V, the duty cycle is approximately 75%. The carrier frequency (FPWM) typically ranges from 20kHz to 35kHz, with a typical value of 25kHz. As shown in the graph, increasing VREF increases the duty cycle, resulting in higher motor speed. When VREF equals VCC, the duty cycle reaches 100%, and the motor runs at full speed.
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