DRV8601 Datasheet, PDF (9/20 Pages) Texas Instruments – Haptic Driver for DC Motors (ERMs) and Linear Vibrators (LRAs) with Ultra-Fast Turn-On

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 (V_PWM). A single NPN transistor can be used as a low-cost level
shifting solution. This ensures that V_IN = VDD even when V_PWM ≠ 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. R_F is normally set equal to R_I (R_F = R_I) so that an overdrive
voltage of VDD is achieved when the PWM duty cycle is set to 100%.
VDD
C_R
SE PWM
10kΩ
Shutdown
2kΩ ^Control
R_I
47kΩ
REFOUT VDD
IN2
OUT-
EN ^DRV8601
IN1
OUT+
GND
R_F
C_F
– _{LRA or}
+ ^{DC Motor}
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 V_PWM < VDD. This is often the case when V_PWM = 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 V_PWM/2 reference for the DRV8601. If the shutdown control voltage is driven by a GPIO in the
same supply domain as V_PWM, 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 V_IN is the single-ended input voltage):
V_O,DIFF
æ
= _çè V_IN
-
VPWM ö
2 ^÷ø
´
R_F
R_I
´
1
1 + sR_FC_F
(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 C_F forms a low-pass filter together with the feedback
resistor R_F, and therefore, the output differential voltage is a function of the average value of the input PWM
signal V_IN. 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 C_F 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
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