SLVSHO3 April 2024 DRV8235
PRODUCTION DATA
The DRV8235 integrates current regulation using either a fixed off-time or a cycle-by-cycle PWM current regulation scheme. This allows the device to limit the output current in case of a motor stall, high torque, or other high current load events autonomously. The current regulation scheme is selectable by the REG_CTRL bit in I2C.
The internal current regulation can be disabled by tying IPROPI to GND and setting the VREF pin voltage greater than GND if current feedback is not required. Additionally, current regulation can also be disabled by setting IMODE to 00b as explained below. 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 voltage specified in the Recommended Operating Conditions table.
Bit* | Current Regulation Mode |
---|---|
00b | Fixed Off-Time |
01b | Cycle-By-Cycle |
*Additional REG_CTRL options 10b and 11b allow selection between motor voltage or speed regulation described in Section 7.3.6.2.1.
The current regulation 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.
For example, if VVREF = 3.3 V, RIPROPI = 1100 Ω and AIPROPI = 1500 μA/A, then ITRIP will be approximately 2 A.
VVREF must be lower than VVM by at least 1.25 V. The maximum recommended value of VVREF is 3.3 V. If INT_VREF bit is set to 1b, VVREF is internally selected with a fixed value of 3 V.
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 affecting the current regulation. These transients may be caused by a capacitor inside the motor or 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, helps filter the transients on IPROPI output so current regulation does not prematurely trigger. The capacitor value can be modified as needed, however large capacitor values may slow down the response time of the current regulation circuit.
The IMODE bits determine the behavior of current regulation for the motor driver.
When IMODE is 00b, current regulation is disabled.
When IMODE is 01b, the device performs current regulation only during the tINRUSH time when stall detection is enabled.
When IMODE is 10b, current regulation is enabled at all times.
The following table summarizes the IMODE bit settings.
IMODE | EN_STALL | Description |
---|---|---|
00b | X | No current regulation at any time |
01b | 0b | Current regulation at all times |
1b | Current regulation during tINRUSH only | |
1Xb | X | Current regulation at all times |