Application Note 1001 How to Control Motor Fan Speed of AM4961 Prepared by Dong Xiang Lian System Engineering Dept. 1. Operating Diagram VPWM Voltage (VCC 28%) Lowest speed setting voltage Open Thermistor fCP=25kHz (CCP=100pF) VCPH (VCC 30%) VMIN Voltage COSC Output VCPL(VCC 16%) Low Speed 0V Full Speed Low Temperature PWM Variable High Temperature VCC 0V FG Output Figure 1. Operating Diagram of AM4961 2. Typical Application L D2 D3 OUT2 OUT1 VCC GND VMIN AM4961 D1 VPWM R1 18k R1 30k PWM R6 91k R16 39k COSC FG C2 1 µF R4 18k R13 6.2k R2 18k Q1 D4 RD C8 0.33 µF R7 56k VREF HINHB C11 100pF R10 18k C4 0.47µ F CT HALL HIN+ PGND Note: D2 and D3 are recommended to be used when the average current in coil L1 is higher than 300mA. Figure 2. Typical Application 1 BCD Semiconductor Manufacturing Limited Mar. 2011 Rev. 1. 1 1 Application Note 1001 When VPWM voltage is higher than VMIN pin voltage, fan speed is settable by VMIN pin voltage. The minimum duty cycle is settable by comparing COSC oscillating voltage and VMIN pin voltage. When VPWM voltage is lower than VMIN pin voltage, PWM control system works by comparing VMIN voltage and COSC oscillating voltage. If VMIN voltage is higher than COSC oscillating voltage, the ON duty cycle of the upper side transistor will be minimized and fan speed becomes lower. Vice versa. 100 Speed / Full Speed (%) 80 Please refer to Figure 3. 60 40 20 0 100 100 80 60 40 20 0 Output Duty Cycle (%) Figure 4. Speed/Full Speed vs. Output Duty Cycle Output Duty Cycle (%) 80 Therefore, if you wish to adjust speed, it is necessary to change VPWM voltage. 60 Please refer to Figure 5. 40 100 20 80 0 1 1.8 2 3 3.2 4 Output Duty Cycle (%) 0 VPWM Voltage (V) Figure 3. Output Duty Cycle vs. VPWM Voltage When VPWM voltage is lower than about 1.8V (the low side of COSC oscillating voltage), output duty cycle is 100%. When VPWM voltage is higher than about 3.2V (VMIN pin voltage), output duty cycle is about 18% which is the minimum duty cycle on the condition that VCC=12V. Within the range of 1.8V to 3.2V, output duty cycle will be reduced gradually, and fan speed becomes lower and lower. 60 40 20 0 0 1 2 3 4 VPWM Voltage (V) Please refer to Figure 4. Figure 5. Speed/Full Speed vs. VPWM Voltage BCD Semiconductor Manufacturing Limited Mar. 2011 Rev. 1. 1 2 Application Note 1001 2. Typical Application (Continued) D1 VCC L1 R1 27k C1 0.1µ F D2 C2 R2 1µF 10k 1 OUT2 OUT1 VCC GND 2 3 R4 39k PWM VMIN 4 VPWM R6 330k R3 7.5k CT VREF 14 13 12 11 5 COSC 6 HB 9 HALL FG RD PGND HIN+ 8 7 R7 100k D3 AM4961 HIN- 10 C5 0.47µF C4 100pF C3 0.33µF R8 68k R5 100k Note: D2 and D3 are recommended to be used when the average current in coil L1 is higher than 300mA. Figure 6. Typical Application 2 100 The VPWM voltage is changed with the input duty cycle of PWM (refer to Figure 7), therefore, the fan speed is changeable with input (refer to Figure 8). Speed / Full Speed (%) 80 3.2 VPWM Voltage (V) 2.8 2.4 60 40 20 2.0 0 100 80 60 40 20 0 1.6 PWM Duty Cycle (%) Figure 8. Speed / Full Speed vs. PWM Duty Cycle 1.2 100 80 60 40 20 0 PWM Duty Cycle (%) Figure 7. VPWM Voltage vs. PWM Duty Cycle BCD Semiconductor Manufacturing Limited Mar. 2011 Rev. 1. 1 3