SLOSE71 April 2020 – December 2020 DRV8955
PRODUCTION DATA
When an output load is connected to the VM supply, and MODE pin is 0, 1 or Hi-Z; the load current can be regulated to the ITRIP level. Table 7-2 describes how the VREF pins control the output current in various modes of operation.
With MODE = 0, the ITRIP current (ITRIP) can be calculated as ITRIP (A) = VREF (V) / 1.32 (V/A).
For MODE = 1, ITRIP (A) = VREF (V) / 0.66 (V/A).
For MODE = Hi-Z, ITRIP (A) = VREF (V) / 0.33 (V/A).
The VREF voltage can be programmed by connecting resistor dividers from DVDD pin to ground. Both VREF pins can be tied together to program the same ITRIP current for all output channels.
With INx = 0, the low side FET is turned ON till the current increases and hits the ITRIP level. Once the load current equals ITRIP, the low-side FET is turned OFF and the high-side FET is turned on for a period of off-time determined by the TOFF pin. After the off-time expires, the low-side FET is again turned ON and the cycle repeats.
For resistive loads connected to VM, if the ITRIP is higher than the (VM / RLOAD), the load current is regulated at VM / RLOAD level while INx = 0. For inductive loads connected to VM, it should be ensured that the current decays enough every cycle to prevent runaway and triggering overcurrent protection. The different scenarios are shown below -
Another way of controlling the load current is the cycle-by-cycle control mode, where PWM pulse width of the INx input pins are controlled. This allows for additional control of the current chopping scheme by the external controller. For loads connected to VM, when INx = 0, the current through the load builds up; and when INx = 1, 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 below -
Similarly, current through loads connected to ground can be controlled by controlling the INx pin pulse width - INx = 1 builds up the current, and INx = 0 decays the current. Two such scenarios are shown below -
TOFF | OFF-TIME tOFF |
---|---|
0 | 7 µs |
1 | 16 µs |
Hi-Z | 24 µs |
330kΩ to GND | 32 µs |