SNAS660D June   2015  – May 2021 LM53600-Q1 , LM53601-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 System Characteristics
    7. 7.7 Timing Requirements
    8. 7.8 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 Control Scheme
      2. 8.3.2 Soft-Start Function
      3. 8.3.3 Current Limit
      4. 8.3.4 Hiccup Mode
      5. 8.3.5 RESET Function
      6. 8.3.6 Forced PWM Operation
      7. 8.3.7 Auto Mode Operation and IQ_VIN
      8. 8.3.8 SYNC Operation
      9. 8.3.9 Spread Spectrum
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown
      2. 8.4.2 FPWM Operation
      3. 8.4.3 Auto Mode Operation
  9. 9 Applications and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Off-Battery 5-V, 1-A Output Automotive Converter with Spread Spectrum
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Inductor Selection
          2. 9.2.1.2.2 Output Capacitor Selection
          3. 9.2.1.2.3 Input Capacitor Selection
          4. 9.2.1.2.4 FB Voltage Divider for Adjustable Versions
          5. 9.2.1.2.5 RPU - RESET Pull Up Resistor
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Off-Battery 3.3 V, 1 A Output Automotive Converter with Spread Spectrum
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Design Procedure
        3. 9.2.2.3 Application Curves
    3. 9.3 Do's and Don't's
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Plane Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.3.5 RESET Function

While the reset function of the LM53600-Q1 and LM53601-Q1 devices resembles a standard power good function, its functionality is designed to replace a discrete reset IC, reducing BOM cost. There are three major differences between the reset function and the normal power good function seen in most regulators:

  • A delay has been added for release of reset. See waveforms below.
  • RESET output signals a fault (pulls its output to ground) while the part is disabled.
  • RESET continues to operate with input voltage as low as 1.5 V. Below this input voltage, RESET output may be high impedance.
GUID-5C841B6A-B03E-4ED4-87DC-E63EF703CEEE-low.gifFigure 8-5 Reset Output Function Operation

The following table summarizes conditions that cause a fault to be flagged by RESET . Once a fault is flagged, RESET will not be released (become high impedance) until either there is no fault for treset_act or VIN drops below Vreset_valid.

Table showing conditions that cause RESET to signal a fault (pull low).

FAULT CONDITION INITIATEDFAULT CONDITION ENDS (AFTER WHICH Treset_act MUST PASS BEFORE RESET OUTPUT IS RELEASED)
FB below Vreset_UV for longer than treset_filtFB above Vreset_UV + Vreset_hyst for longer than treset_filt
FB above Vreset_OV for longer than treset_filtFB below Vreset_OV - Vreset_hyst for longer than treset_filt
Junction temperature exceeds TSDJunction temperature falls below TSD – TSD_hyst
EN lowtEN passes after EN becomes high(1)
VIN falls below Vin_UVLO - Vin_UVLO _hyst or VCC pin falls below Vcc_UVLO - Vcc_UVLO_hystVoltage on VIN exceeds Vin_UVLO and VCC exceed Vcc_UVLO
(1) As an additional safety feature, RESET remains low until approximately 1ms after soft start ends even if all other conditions in this table are met and treset_act has passed. Lockout during soft start does not require treset_act to pass before RESET is released.

The threshold voltage for the RESET function is specified taking advantage of the availability of the LM53600-Q1 internal feedback threshold to the RESET circuit. This allows a maximum threshold of 97% of selected output voltage to be specified at the same time as 95.7% of actual operating point. The net result is a more accurate reset function while expanding the system allowance for transient response without the need for extremely accurate internal circuitry. See output voltage error stack up comparison, below.

GUID-1D65DF76-3676-4D9A-A3AD-0141814A781B-low.gifFigure 8-6 Reset Threshold Voltage Stack Up