SLVSI23A September   2025  – December 2025 DRV81646

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specification
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements
    7.     13
    8. 5.7 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Control Interface and Slew Rate (RSLEW/CNTL)
      2. 6.3.2 Current Sensing With FET Source Terminals
      3. 6.3.3 Integrated Clamp Diode, VCLAMP
      4. 6.3.4 Protection Circuits
        1. 6.3.4.1 ILIM Analog Current Limit
          1. 6.3.4.1.1 Effect of Load Resistance on Power Dissipation Before TSD
        2. 6.3.4.2 Cut-Off Delay (COD)
        3. 6.3.4.3 INRUSH Mode
        4. 6.3.4.4 Thermal Shutdown (TSD)
        5. 6.3.4.5 Undervoltage Lockout (UVLO)
      5. 6.3.5 Fault Conditions Summary
    4. 6.4 Device Functional Modes
      1. 6.4.1 Hardware Interface Operation
      2. 6.4.2 Parallel Outputs
      3. 6.4.3 SPI Mode
        1. 6.4.3.1 Parity Bit Calculation
        2. 6.4.3.2 SPI Input Packet
        3. 6.4.3.3 SPI Response Packet
        4. 6.4.3.4 SPI Error Reporting
        5. 6.4.3.5 SPI Daisy Chain
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 External Components
      2. 7.2.2 Continuous Current Capability
      3. 7.2.3 Power Dissipation
      4. 7.2.4 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Bulk Capacitance
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

6.3.4.2 Cut-Off Delay (COD)

Since the analog current limit condition results in very high power dissipation, the DRV81646 offers a cut-off delay feature that controls the maximum length of an ILIM or overcurrent condition. tCOD can be adjusted with a pull-down resistor on the COD/INRUSH pin as shown in Table 6-5.

Table 6-5 Cut-Off Delay (COD) Settings
RCOD RESISTOR BETWEEN COD/INRUSH AND GND FUNCTION BEHAVIOR nFAULT PIN FAULT BIT (SPI)
0 ≤ RCOD< 20kΩ Cut-off delay function is disabled, output stage and IC are protected by thermal shutdown only Pulled low when a channel hits thermal shutdown. Released when channel temperature returns to safe level The FAULT bit of the corresponding channel is set if the channel hits thermal shutdown. The bit is cleared automatically at the end of valid SPI transaction
60kΩ ≤ RCOD ≤ 240kΩ Current limit allowed to persist for tCOD = RCOD(kΩ)/120ms typical, before power stage shuts off Pulled low when tCOD elapses. Released when tRETRY elapses. The FAULT bit of the corresponding channel is set when tCOD elapses. The bit is cleared automatically at the end of valid SPI transaction
240kΩ ≤ RCOD ≤ 470kΩ tCOD = RCOD(kΩ)/120ms, but linearity is not specified.
RCOD ≥ 1MΩ INRUSH mode enabled. tINRUSH = 10ms typical. Masked during inrush period tINRUSH, then pulled low if a power stage hits thermal shutdown. The FAULT bit of the corresponding channel is masked during inrush period tINRUSH, then pulled low if a power stage hits thermal shutdown.

For 60kΩ ≤ RCOD ≤ 240kΩ, the device lasts in current limit condition for duration tCOD = RCOD(kΩ)/120ms. After the channel shuts off, the channel retries only after an interval of tRETRY = (tCOD × 32) ms typical. If the user changes channel state during a current limit condition, the controller responds to the input state change. During tRETRY, however, the controller does not respond to an input state change.

For RCOD ≥ 240kΩ the same equation holds true, tCOD (ms) = RCOD(kΩ)/120, but linearity is not specified.

If a thermal shutdown occurs during the COD interval, the channel turns off and retries once the temperature reaches safe level. The COD timer is paused for the duration the output turns off due to thermal shutdown.

DRV81646 Current Limit Circuit Response to Short with COD Enabled Figure 6-10 Current Limit Circuit Response to Short with COD Enabled

The cut-off delay-based timing of tCOD and tRETRY feature reduces the average power dissipation compared to thermal-shutdown based retry. Without COD, the device recovers from thermal shutdown in 1-5ms at room temperature with one channel on. With COD, the device waits the full tRETRY period before re-enabling the output. For example, let's calculate the average power dissipation per cycle with versus without COD for RILIM=100kΩ, VVM = VLOAD = 24V, RLOAD = 1Ω

Equation 10. I L I M = 60 R I L I M = 60 100 = 0.6 A
Equation 11. P O U T x _ I L I M = V O U T x × I L I M = V L O A D - I L I M × R L O A D × I L I M = 24 V - 1 Ω × 0.6 A = 0.6 A = 14.0 W

With cut-off delay enabled (60kΩ ≤ RCOD ≤ 240kΩ) the average current depends on the tCOD and the tRETRY = tCOD × 32ms. For RCOD = 120kΩ

Equation 12. t C O D = R C O D k Ω 120 = 120 120 = 1 m s
Equation 13. t R E T R Y = t C O D × 32 = 1 m s × 32 = 32 m s
Equation 14. P C O D _ A V E R A G E = P O U T x _ I L I M × t C O D t C O D + t R E T R Y = 14.0 W × 1 m s 1 m s + 32 m s = 0.43 W

Without cut-off delay (COD pin connected to GND, or RCOD < 20kΩ) the device automatically retries after thermal hysteresis (TJ < (tTSD – tTSD_HYS). Calculate the average power dissipation using a retry time of tTSD_HYS_RETRY = 2.5ms and the same 1ms on-time as if the device thermal shutdown after tTSD = 1ms:

Equation 15. P I L I M _ A V E R A G E = P O U T x _ I L I M × t T S D t T S D + t T S D _ H Y S _ R E T R Y = 14.0 W × 1 m s 1 m s + 2.5 m s = 4 W

Cut-off delay results in a significantly lower average power dissipation (0.43W in this example) than thermal-shutdown based protection (4W in this example). This result leads to lower overall system heating and better performance on adjacent device channels.