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IMOTOR

VMOTOR

Control Input

(xIN1 or xIN2)

ITRIP

tOFF

Figure 9-5. Off-Time Current-Regulation

The current chopping threshold (ITRIP) is set through a combination of the VREF voltage (VVREF) and IPROPI

output resistor (RIPROPI). This is done by comparing the voltage drop across the external RIPROPI resistor to

VVREF with an internal comparator.

ITRIP (A) x AIPROPI (μA/A) = VVREF (V) / RIPROPI (Ω)

(3)

For example, if VVREF = 3.3 V, RIPROPI = 10 kΩ, and AIPROPI = 200 μA/A, then ITRIP will be approximately 1.65 A.

When VVM ≥ 3.6 V, VVREF can have be set to a voltage up to 3.6 V. When VVM < 3.6 V, VVREF must be ≤ VVM.

The fixed off-time current chopping scheme supports up to 100% duty cycle current regulation since the H-bridge

automatically enables after the tOFF period and does not require a new control input edge on the xINx pins to

reset the outputs. When the motor current exceeds the ITRIP threshold, the outputs will enter a current chopping

mode with a fixed off time (tOFF). During tOFF, the H-bridge enters a brake/low-side slow decay state (both

low-side MOSFETs ON) for tOFF duration after IOUT exceeds ITRIP. After tOFF, the outputs re-enable according to

the control inputs if IOUT is less than ITRIP. If IOUT is still greater than ITRIP, the H-bridge enters another period

of brake/low-side slow decay for tOFF. If the state of the xINx control pins changes during the tOFF time, the

remainder of the tOFF time is ignored, and the outputs will again follow the inputs.

The ITRIP comparator has both a blanking time (tBLANK) and a deglitch time (tDEG). The internal blanking time

helps to prevent voltage and current transients during output switching from effecting the current regulation.

These transients may be caused by a capacitor inside the motor or on the connections to the motor terminals.

The internal deglitch time ensures that transient conditions do not prematurely trigger the current regulation. In

certain cases where the transient conditions are longer than the deglitch time, placing a 10-nF capacitor on the

IPROPI pin, close to the device, will help filter the transients on IPROPI output so current regulation does not

prematurely trigger. The capacitor value can be adjusted as needed, however large capacitor values may slow

down the response time of the current regulation circuitry.

The internal current regulation and current feedback can be disabled by tying IPROPI to GND and setting the

VREF pin voltage greater than GND. If current feedback is required and current regulation is not required, set

VVREF and RIPROPI such that VIPROPI never reaches the VVREF threshold. For proper operation of the current

regulation circuit, VVREF must be within the range of the VREF pin voltages specified in the Recommended

Operating Conditions table.

9.4.3 Protection Circuits

The DRV8411A is fully protected against undervoltage, overcurrent and overtemperature events.

9.4.3.1 Overcurrent Protection (OCP)

An analog current limit circuit on each FET limits the current through the FET by limiting the gate drive internally.

If this current limit persists for longer than the OCP deglitch time (tOCP), all FETs in the H-bridge will disable and

the nFAULT pin will assert low. The driver re-enables after the OCP retry period (tRETRY) has passed. nFAULT

becomes high again at this time and normal operation resumes. If the fault condition is still present, the cycle

repeats as shown in Figure 9-6. Please note that only the H-bridge where an overcurrent condition is detected

will be disabled while the other bridge will function normally.

DRV8411A

SLVSGI9A – OCTOBER 2022 – REVISED JULY 2023

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