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DRV8601 Datasheet(PDF) 9 Page - Texas Instruments |
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DRV8601 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 21 page VDD GND LRA or DC Motor VDD C R OUT- OUT+ IN2 REFOUT IN1 EN DRV8601 SE PWM Shutdown Control 10k 47k 2k R I R F C F + – PWM F O,DIFF IN I F F R V 1 V = V 2 R 1 + sR C æ ö - ´ ´ ç ÷ è ø DRV8601 www.ti.com SLOS629B – JULY 2010 – REVISED JANUARY 2012 PSEUDO-DIFFERENTIAL FEEDBACK WITH LEVEL-SHIFTER This configuration is desirable when a regulated supply voltage for the DRV8601 (VDD) is availble, but that voltage is different than the PWM input voltage (VPWM). A single NPN transistor can be used as a low-cost level shifting solution. This ensures that VIN = VDD even when VPWM ≠ VDD. A regulated supply for the DRV8601 is still recommended in this scenario. If the supply voltage varies, the PWM level shifter output will follow, and this will, in turn, cause a change in vibration strength. However, if the variance is acceptable, the DRV8601 will still operate properly when connected directly to a battery, for example. A 50% duty cycle will still translate to zero vibration strength across the life cycle of the battery. RF is normally set equal to RI (RF = RI) so that an overdrive voltage of VDD is achieved when the PWM duty cycle is set to 100%. Figure 16. Pseudo-Differential Feedback with Level-Shifter DIFFERENTIAL FEEDBACK WITH EXTERNAL REFERENCE This configuration is useful for connecting the DRV8601 to an unregulated power supply, most commonly a battery. The gain can then be independently set so that the required motor overdrive voltage can be achieved even when VPWM < VDD. This is often the case when VPWM = 1.8 V, and the desired overdrive voltage is 3.0 V or above. Note that VDD must be greater than or equal to the desired overdrive voltage. A resistor divider can be used to create a VPWM/2 reference for the DRV8601. If the shutdown control voltage is driven by a GPIO in the same supply domain as VPWM, it can be used to supply the resistor divider as in Figure 17 so that no current is drawn by the divider in shutdown. In this configuration, feedback is taken from both output pins. The output voltage is given by Equation 3 (where s is the Laplace Transform variable and VIN is the single-ended input voltage): (3) Note that this differs from Equation 1 for the pseudo-differential configuration by a factor of 2 because of differential feedback. The optional feedback capacitor CF forms a low-pass filter together with the feedback resistor RF, and therefore, the output differential voltage is a function of the average value of the input PWM signal VIN. When driving a motor, design the cutoff frequency of the low-pass filter to be sufficiently lower than the PWM frequency in order to eliminate the PWM frequency and its harmonics from entering the motor. This is desirable when driving motors which do not sufficiently reject the PWM frequency by themselves. When driving a linear vibrator in this configuration, if the feedback capacitor CF is used, care must be taken to make sure that the low-pass cutoff frequency is higher than the resonant frequency of the linear vibrator. Copyright © 2010–2012, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Link(s): DRV8601 |
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