DRV8801-Q1_15 Datasheet, PDF (11/19 Pages) Texas Instruments – DMOS FULL-BRIDGE MOTOR DRIVERS

DRV8801-Q1
www.ti.com
SLVSAS7A – FEBRUARY 2011 – REVISED JANUARY 2014
APPLICATION INFORMATION
Power Dissipation
First-order approximation of power dissipation in the DRV8801-Q1 can be calculated by examining the power
dissipation in the full-bridge during each of the operation modes. DRV8801-Q1 uses synchronous rectification.
During the decay cycle, the body diode is shorted by the low-r_DS(on) driver, which in turn reduces power
dissipation in the full-bridge. In order to prevent shootthrough (high-side and low-side drivers on the same side
are ON at the same time), DRV8801-Q1 implements a 500-ns typical crossover delay time. During this period,
the body diode in the decay current path conducts the current until the DMOS driver turns on. High-current and
high-ambient-temperature applications should take this into consideration. In addition, motor parameters and
switching losses can add power dissipation that could affect critical applications.
Drive Current
This current path is through the high-side sourcing DMOS driver, motor winding, and low-side sinking DMOS
driver. Power dissipation I²R loses in one source and one sink DMOS driver, as shown in Equation 1.
P_D = I² (r_DS(on)Source + r_DS(on)Sink )
(1)
DRV8801-Q1
VBB
4
1
3
2
1 Drive Current
2 Fast decay with synchronous rectification (reverse)
3 Slow decay with synchronous rectification (brake) Low Side
4 Slow decay with synchronous rectification (brake) High Side
Figure 5. Current Path
Fast Decay With Synchronous Rectification
This decay mode is equivalent to a phase change where the opposite drivers are switched on. When in fast
decay, the motor current is not allowed to go negative (direction change). Instead, as the current approaches
zero, the drivers turn off. The power calculation is the same as the drive-current calculation (see Equation 1).
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