OUT

GND

LS

Integrated

Current Sense

AIPROPI

ILOAD

IPROPI

RIPROPI

IPROPI

MCU

ADC

+

±

VPROPI

+

±

Control

Inputs

VREF

IPROPI

Clamp

Copyright © 2017, Texas Instruments Incorporated

12

DRV8874

SLVSF66A – AUGUST 2019 – REVISED DECEMBER 2019

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Copyright © 2019, Texas Instruments Incorporated

7.3.3 Current Sense and Regulation

The DRV887x family of devices integrate current sensing, regulation, and feedback. These features allow for the

device to sense the output current without an external sense resistor or sense circuitry reducing system size,

cost, and complexity. This also allows for the devices to limit the output current in the case of motor stall or high

torque events and give detailed feedback to the controller about the load current through a current proportional

output.

7.3.3.1 Current Sensing

The IPROPI pin outputs an analog current proportional to the current flowing through the low-side power

MOSFETs in the H-bridge scaled by AIPROPI. The IPROPI output current can be calculated by Equation 1. The

ILSx in Equation 1 is only valid when the current flows from drain to source in the low-side MOSFET. If current

flows from source to drain, the value of ILSx for that channel is zero. For instance, if the bridge is in the brake,

slow-decay state, then the current out of IPROPI is only proportional to the current in one of the low-side

MOSFETs.

IPROPI (μA) = (ILS1 + ILS2) (A) x AIPROPI (μA/A)

(1)

The current is measured by an internal current mirror architecture that removes the needs for an external power

sense resistor. Additionally, the current mirror architecture allows for the motor winding current to be sensed in

both the drive and brake low-side slow-decay periods allowing for continuous current monitoring in typical

bidirectional brushed DC motor applications. In coast mode, the current is freewheeling and cannot be sensed

because it flows from source to drain. However, the current can be sampled by briefly reenabling the driver in

either drive or slow-decay modes and measuring the current before switching back to coast mode again. In the

case of independent PWM mode and both low-side MOSFETs are carrying current, the IPROPI output will be the

sum of the two low-side MOSFET currents.

The IPROPI pin should be connected to an external resistor (RIPROPI) to ground in order to generate a

proportional voltage (VIPROPI) on the IPROPI pin with the IIPROPI analog current output. This allows for the load

current to be measured as the voltage drop across the RIPROPI resistor with a standard analog to digital converter

(ADC). The RIPROPI resistor can be sized based on the expected load current in the application so that the full

range of the controller ADC is utilized. Additionally, the DRV887x devices implement an internal IPROPI voltage

clamp circuit to limit VIPROPI with respect to VVREF on the VREF pin and protect the external ADC in case of

output overcurrent or unexpected high current events.

The corresponding IPROPI voltage to the output current can be calculated by Equation 2.

VIPROPI (V) = IPROPI (A) x RIPROPI (Ω)

(2)

Figure 11. Integrated Current Sensing