DRV8870_16 Datasheet, PDF (9/25 Pages) Texas Instruments – Brushed DC Motor Driver

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DRV8870
SLVSCY8A – AUGUST 2015 – REVISED JANUARY 2016
I_TRIP (A)
VREF (V)
A_v u R_ISEN (:)
VREF (V)
10 u R_ISEN (:)
(1)
For example, if VREF = 3.3 V and a R_ISEN = 0.15 Ω, the DRV8870 will limit motor current to 2.2 A no matter how
much load torque is applied. For guidelines on selecting a sense resistor, see Sense Resistor.
When I_TRIP has been reached, the device enforces slow current decay by enabling both low-side FETs, and it
does this for time t_OFF (typically 25 µs).
I_TRIP
t_BLANK
t_DRIVE
t_OFF
Figure 5. Current Regulation Time Periods
After t_OFF has elapsed, the output is re-enabled according to the two inputs INx. The drive time (t_DRIVE) until
reaching another I_TRIP event heavily depends on the VM voltage, the motor’s back-EMF, and the motor’s
inductance.
7.3.4 Dead Time
When an output changes from driving high to driving low, or driving low to driving high, dead time is automatically
inserted to prevent shoot-through. t_DEAD is the time in the middle when the output is High-Z. If the output pin is
measured during t_DEAD, the voltage will depend on the direction of current. If current is leaving the pin, the
voltage will be a diode drop below ground. If current is entering the pin, the voltage will be a diode drop above
VM. This diode is the body diode of the high-side or low-side FET.
IN1
IN2
OUT1
t_PD
t_R
t_DEAD
t_PD
t_F
t_DEAD
OUT2
t_PD
t_F
t_DEAD
t_PD
t_R
t_DEAD
Figure 6. Propagation Delay Time
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