Texas Instruments Evaluation Module for DRV8841 DRV8841EVM DRV8841EVM 데이터 시트
제품 코드
DRV8841EVM
SLVSAC0E – MAY 2010 – REVISED AUGUST 2013
Note that when both xI bits are 1, the H-bridge is disabled and no current flows.
Example:
If a 0.25-
Ω sense resistor is used and the VREF pin is 2.5 V, the chopping current will be 2 A at the 100%
setting (xI1, xI0 = 00). At the 71% setting (xI1, xI0 = 01) the current will be 2 A x 0.71 = 1.42 A, and at the
38% setting (xI1, xI0 = 10) the current will be 2 A x 0.38 = 0.76 A. If (xI1, xI0 = 11) the bridge will be disabled
and no current will flow.
38% setting (xI1, xI0 = 10) the current will be 2 A x 0.38 = 0.76 A. If (xI1, xI0 = 11) the bridge will be disabled
and no current will flow.
Decay Mode
During PWM current chopping, the H-bridge is enabled to drive current through the motor winding until the PWM
current chopping threshold is reached. This is shown in
current chopping threshold is reached. This is shown in
as case 1. The current flow direction shown
indicates the state when the xIN1 pin is high and the xIN2 pin is low.
Once the chopping current threshold is reached, the H-bridge can operate in two different states, fast decay or
slow decay.
slow decay.
In fast decay mode, once the PWM chopping current level has been reached, the H-bridge reverses state to
allow winding current to flow in a reverse direction. As the winding current approaches zero, the bridge is
disabled to prevent any reverse current flow. Fast decay mode is shown in
allow winding current to flow in a reverse direction. As the winding current approaches zero, the bridge is
disabled to prevent any reverse current flow. Fast decay mode is shown in
as case 2.
In slow decay mode, winding current is re-circulated by enabling both of the low-side FETs in the bridge. This is
shown in
shown in
as case 3.
Figure 2. Decay Mode
The DRV8841 supports fast decay, slow decay and a mixed decay mode. Slow, fast, or mixed decay mode is
selected by the state of the DECAY pin - logic low selects slow decay, open selects mixed decay operation, and
logic high sets fast decay mode. The DECAY pin has both an internal pullup resistor of approximately 130 k
selected by the state of the DECAY pin - logic low selects slow decay, open selects mixed decay operation, and
logic high sets fast decay mode. The DECAY pin has both an internal pullup resistor of approximately 130 k
Ω
and an internal pulldown resistor of approximately 80 k
Ω. This sets the mixed decay mode if the pin is left open
or undriven. Note that the DECAY pin sets the decay mode for both H-bridges.
Mixed decay mode begins as fast decay, but at a fixed period of time (75% of the PWM cycle) switches to slow
decay mode for the remainder of the fixed PWM period.
decay mode for the remainder of the fixed PWM period.
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