DRV8818_15 Datasheet, PDF (15/31 Pages) Texas Instruments – DRV8818 Stepper Motor Controller IC

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DRV8818
SLVSAX9D – SEPTEMBER 2011 – REVISED JANUARY 2015
8.3.5.3 Undervoltage Lockout (UVLO)
If at any time the voltage on the VM or VCC pins falls below the VM or VCC undervoltage lockout threshold
voltage, all circuitry in the device will be disabled, and the indexer will be reset to the home state. Operation will
resume when VM and VCC both rise above their UVLO thresholds.
8.4 Device Functional Modes
8.4.1 RESETn, ENABLEn and SLEEPn Operation
The RESETn pin, when driven active low, resets the step table to the home position. It also disables the H-bridge
drivers. The STEP input is ignored while RESETn is active.
The ENABLEn pin is used to control the output drivers. When ENABLEn is low, the output H-bridges are
enabled. When ENABLEn is high, the H-bridges are disabled and the outputs are in a high-impedance state.
Note that when ENABLEn is high, the input pins and control logic, including the indexer (STEP and DIR pins) are
still functional.
The SLEEPn pin is used to put the device into a low power state. If SLEEPn is low, the H-bridges are disabled,
the gate drive charge pump is stopped, and all internal clocks are stopped. In this state all inputs are ignored
until the SLEEPn pin returns high.
8.4.2 Decay Modes
The DRV8818 supports three different decay modes: slow decay, fast decay, and mixed decay. The current
through the motor windings is regulated using a fixed off time scheme.
This means that the current will increase until it reaches the current chopping threshold (I_TRIP), after which it will
enter the set decay mode for a fixed period of time. The cycle will then repeat after the decay period expires.
The blanking time t_BLANK defines the minimum drive time for the current chopping. I_TRIP is ignored during t_BLANK,
so the winding current may overshoot the trip level.
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