The current chopping threshold (I_TRIP) is set through a combination of the VREF voltage (V_VREF) and IPROPI output resistor (R_IPROPI). This is done by comparing the voltage drop across the external R_IPROPI resistor to V_VREF with an internal comparator.

For example, to set I_TRIP at 5 A with V_VREF at 3.3 V, R_IPROPI has to be -

R_IPROPI = V_VREF / (I_TRIP x A_IPROPI ) = 3.3 / (5 x 212 x 10^-6) = 3.09 kΩ

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). If current feedback is required and current regulation is not required, set V_VREF and R_IPROPI such that V_IPROPI never reaches the V_VREF threshold.

The DRV8962-Q1 can simultaneously drive up to four resistive or inductive loads. When an output load is connected to ground, the load current can be regulated to the I_TRIP level. The PWM off-time (t_OFF) is fixed at 17 μs. The fixed off-time mode allows for a simple current chopping scheme without involvement from the external controller. Fixed off-time mode will support 100% duty cycle current regulation.

Another way of controlling the load current is the cycle-by-cycle control mode, where PWM pulse width of the INx input pins have to be controlled. This allows for additional control of the current chopping scheme by the external controller.

Few scenarios of driving high-side and low-side loads are described below -

• Resistive loads connected to ground:

The regulated current will not exceed I_TRIP, as long as there is some load inductance to slow down the rate of increase of current during the blanking time. If I_TRIP is higher than the (VM / R_LOAD), the load current is regulated at VM / R_LOAD level while INx = 1 (shown in Figure 6-3).

Figure 6-3 Resistive Load Connected to ground, Cycle-by-cycle control

• Inductive loads connected to ground:

It should be ensured that the current decays enough every cycle to prevent runaway and triggering overcurrent protection.

• For the scenario shown in Figure 6-4, with INx = 1, the low-side MOSFET is turned on for t_OFF duration after I_OUT exceeds I_TRIP. After t_OFF, the high side MOSFET is again turned on till I_OUT exceeds I_TRIP again.

Figure 6-4 Inductive Load Connected to ground, fixed off-time current chopping

• Loads can also be controlled using the cycle-by-cycle method. When INx = 1, the current through the load builds up; and when INx = 0, the current through the load decays. By properly choosing the duty cycle of the INx pulse, current can be regulated to a target value. Various such scenarios are shown in Figure 6-5 and Figure 6-6.

Figure 6-5 Inductive Load Connected to ground, Cycle-by-cycle control

The next scenario requires INx pin duty cycle adjustment (T has to be less than T_OFF) to ensure that the current does not run away.

Figure 6-6 Inductive Load Connected to ground, Cycle-by-cycle control

• Loads connected to VM:

Such loads can be controlled by controlling the INx pin pulse width: INx = 0 builds up the current, and INx = 1 decays the current, as shown in Figure 6-7 and Figure 6-8.

Figure 6-7 Inductive Load Connected to VM, Cycle-by-cycle control

This scenario requires INx pin duty cycle adjustment to ensure that the current does not run away.

Figure 6-8 Resistive Load Connected to ground, Cycle-by-cycle control