Datasheet

DRV8840

www.ti.com

SLVSAB7C –MAY 2010–REVISED AUGUST 2013

Table 3. Pin Functions (continued)

RELATIVE CURRENT

I[4..0]

(% FULL-SCALE CHOPPING CURRENT)

0x17h 90%

0x18h 92%

0x19h 94%

0x1Ah 96%

0x1Bh 97%

0x1Ch 98%

0x1Dh 99%

0x1Eh 100%

0x1Fh 100%

Decay Mode and Braking

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 Figure 2 as case 1. The current flow direction shown

indicates the state when the xENBL pin is high.

Once the chopping current threshold is reached, the H-bridge can operate in two different states, fast decay or

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 Figure 2 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 Figure 2 as case 3.

Figure 2. Decay Mode

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