SNVSB12B November   2017  – May 2021 LM73605-Q1 , LM73606-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Characteristics
    7. 7.7 Switching Characteristics
    8. 7.8 System Characteristics
    9. 7.9 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Synchronous Step-Down Regulator
      2. 8.3.2  Auto Mode and FPWM Mode
      3. 8.3.3  Fixed-Frequency Peak Current-Mode Control
      4. 8.3.4  Adjustable Output Voltage
      5. 8.3.5  Enable and UVLO
      6. 8.3.6  Internal LDO, VCC_UVLO, and BIAS Input
      7. 8.3.7  Soft Start and Voltage Tracking
      8. 8.3.8  Adjustable Switching Frequency
      9. 8.3.9  Frequency Synchronization and Mode Setting
      10. 8.3.10 Internal Compensation and CFF
      11. 8.3.11 Bootstrap Capacitor and VBOOT-UVLO
      12. 8.3.12 Power-Good and Overvoltage Protection
      13. 8.3.13 Overcurrent and Short-Circuit Protection
      14. 8.3.14 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
        1. 8.4.3.1 CCM Mode
        2. 8.4.3.2 DCM Mode
        3. 8.4.3.3 PFM Mode
        4. 8.4.3.4 Fault Protection Mode
  9. 9 Layout
    1. 9.1 Layout Guidelines
      1. 9.1.1 Layout For EMI Reduction
      2. 9.1.2 Ground Plane
      3. 9.1.3 Optimize Thermal Performance
    2. 9.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Third-Party Products Disclaimer
      2. 10.1.2 Development Support
        1. 10.1.2.1 Custom Design With WEBENCH® Tools
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Receiving Notification of Documentation Updates
    5. 10.5 Support Resources
    6. 10.6 Support Resources
    7. 10.7 Trademarks
    8. 10.8 Electrostatic Discharge Caution
    9. 10.9 Glossary

Package Options

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

8.3.9 Frequency Synchronization and Mode Setting

The LM73605-Q1/6-Q1 switching action can synchronize to an external clock from 350 kHz to 2.2 MHz. TI recommends connecting the external clock to the SYNC/MODE pin with an appropriate termination resistor. Ground the SYNC/MODE pin if not used.

GUID-EE311FDD-7DD6-464C-9A0F-FD8BC05C20BE-low.gifFigure 8-13 Frequency Synchronization

Recommendations for the external clock include a high level no lower than 2 V, low level no higher than 0.4 V, duty cycle between 10% and 90%, and both positive and negative pulse width no shorter than 80 ns. When the external clock fails at logic high or low, the LM73605-Q1/6-Q1 at the frequency programmed by the RT resistor after a time-out period. TI recommends connecting a resistor to the RT pin such that the internal oscillator frequency is the same as the external clock frequency. This allows the regulator to continue operating at approximately the same switching frequency if the external clock fails with the same control loop behavior.

The SYNC/MODE pin is also used as an operation mode control input.

  • To set the operation in auto mode, connect SYNC/MODE pin to ground, or a logic signal lower than 0.3 V.
  • To set the operation in FPWM mode, connect SYNC/MODE pin to a bias voltage or logic signal greater than 0.6 V.
  • When the LM73605-Q1/6-Q1 synchronized to an external clock, the operation mode is FPWM.

Table 8-2 summarizes the operation mode and features according to the SYNC/MODE input signal. For more details, see the Section 8.4.3 and Section 8.3.2 sections.

Table 8-2 SYNC/MODE Pin Settings and Operation Modes
SYNC/MODE INPUTSWITCHING FREQUENCYOPERATING MODELIGHT LOAD BEHAVIOR
Logic lowSet by RT resistorAuto mode
  • No negative inductor current, device operates in discontinuous conduction mode (DCM) when current valley reaches 0 A.
  • Minimum peak inductor current is limited at IPEAK_MIN; device operates in pulse frequency modulation (PFM) mode when peak current reaches IPEAK_MIN.
  • Switching frequency reduces in PFM mode.
Logic highSet by RT resistorFPWM mode
  • Fixed frequency continuous conduction mode (CCM) regardless of load
  • Inductor current have negative portion at light loads
  • No IPEAK_MIN
External clockSet by external clock