SLRS063C September   2013  – February 2016 DRV8816

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Bridge Control
      2. 7.3.2 Charge Pump
      3. 7.3.3 VPROPI
      4. 7.3.4 Protection Circuits
        1. 7.3.4.1 VBB UVLO
        2. 7.3.4.2 VCP UVLO (CPUV)
        3. 7.3.4.3 OCP
        4. 7.3.4.4 OTW
        5. 7.3.4.5 OTS
    4. 7.4 Device Functional Modes
      1. 7.4.1 SENSE
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Motor Voltage
        2. 8.2.2.2 Power Dissipation
        3. 8.2.2.3 Motor Current Trip Point
        4. 8.2.2.4 Sense Resistor Selection
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Bulk Capacitance
    2. 9.2 Power Supervisor
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Ground
    2. 10.2 Layout Example
    3. 10.3 Thermal Protection
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resource
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The DRV8816 is typically used to drive a brushed DC motor.

8.2 Typical Application

DRV8816 sch.gif Figure 7. Typical Application

8.2.1 Design Requirements

Table 5 shows parameters to consider when designing.

Table 5. Design Parameters

DESIGN PARAMETER REFERENCE EXAMPLE VALUE
Motor voltage VBB 24 V
Motor RMS current IRMS 0.8 A
Motor startup current ISTART 2 A
Motor current trip point ITRIP 2.5 A

8.2.2 Detailed Design Procedure

8.2.2.1 Motor Voltage

The motor voltage to use will depend on the ratings of the motor selected and the desired RPM. A higher voltage spins a brushed DC motor faster with the same PWM duty cycle applied to the power FETs. A higher voltage also increases the rate of current change through the inductive motor windings.

8.2.2.2 Power Dissipation

The power dissipation of the DRV8816 is a function of RMS motor current and the each output’s FET resistance (RDS(ON)).

Equation 1. DRV8816 eq_2_lrs063.gif

For this example, the ambient temperature is 35°C, and the junction temperature reaches 65°C. At 65°C, the sum of RDS(ON) is about 1Ω. With an example motor current of 0.8A, the dissipated power in the form of heat will be 0.8A² x 1Ω = 0.64W.

The temperature that the DRV8816 reaches will depend on the thermal resistance to the air and PCB. It is important to solder the device PowerPAD to the PCB ground plane, with vias to the top and bottom board layers, in order dissipate heat into the PCB and reduce the device temperature. In the example used here, the DRV8816 had an effective thermal resistance RθJA of 47°C/W, and:

Equation 2. DRV8816 eq_3_1_lrs063.gif

8.2.2.3 Motor Current Trip Point

When the voltage on pin SENSE exceeds VTRIP (0.5V), overcurrent is detected. The RSENSE resistor should be sized to set the desired ITRIP level.

Equation 3. DRV8816 eq_4_1_lrs063.gif

To set ITRIP to 2A, RSENSE = 0.5V / 2A = 0.25Ω.

To prevent false trips, ITRIP must be higher than regular operating current. Motor current during startup is typically much higher than steady-state spinning, because the initial load torque is higher, and the absence of back-EMF causes a higher voltage and extra current across the motor windings.

It can be beneficial to limit startup current by using series inductors on the DRV8816 output, as that allows ITRIP to be lower, and it may decrease the system’s required bulk capacitance. Startup current can also be limited by ramping the forward drive duty cycle.

8.2.2.4 Sense Resistor Selection

For optimal performance, it is important for the sense resistor to be:

  • Surface-mount
  • Low inductance
  • Rated for high enough power
  • Placed closely to the motor driver

The power dissipated by the sense resistor equals IRMS² x R. For example, if peak motor current is 3A, RMS motor current is 2A, and a 0.05Ω sense resistor is used, the resistor will dissipate 2A² x 0.05Ω = 0.2W. The power quickly increases with higher current levels.

Resistors typically have a rated power within some ambient temperature range, along with a de-rated power curve for high ambient temperatures. When a PCB is shared with other components generating heat, margin should be added. It is always best to measure the actual sense resistor temperature in a final system, along with the power MOSFETs, as those are often the hottest components.

Because power resistors are larger and more expensive than standard resistors, it is common practice to use multiple standard resistors in parallel, between the sense node and ground. This distributes the current and heat dissipation.

8.2.3 Application Curves

DRV8816 Fwd_fast_slrs063.png
Figure 8. Forward Drive, Fast Decay
DRV8816 Fwd_slow_slrs063.png
Figure 10. Forward Drive, Slow Decay
DRV8816 Rvs_fast_slrs063.png
Figure 9. Reverse Drive, Fast Decay
DRV8816 Rvs_slow_slrs063.png
Figure 11. Reverse Drive, Slow Decay