SNVSBU3 March   2021 LP87702


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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 I2C Serial Bus Timing Parameters
    7. 6.7 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Descriptions
      1. 7.3.1  Step-Down DC/DC Converters
        1. Overview
        2. Transition Between PWM and PFM Modes
        3. Buck Converter Load Current Measurement
      2. 7.3.2  Boost Converter
      3. 7.3.3  Spread-Spectrum Mode
      4. 7.3.4  Sync Clock Functionality
      5. 7.3.5  Power-Up
      6. 7.3.6  Buck and Boost Control
        1. Enabling and Disabling Converters
        2. Changing Buck Output Voltage
      7. 7.3.7  Enable and Disable Sequences
      8. 7.3.8  Window Watchdog
      9. 7.3.9  Device Reset Scenarios
      10. 7.3.10 Diagnostics and Protection Features
        1. Voltage Monitorings
        2. Interrupts
        3. Power-Good Information to Interrupt, PG0, and PG1 Pins
          1. PGx Pin Gated (Unusual) Mode
          2. PGx Pin Operation in Continuous Mode
          3. Summary of PG0, PG1 Gated, and Continuous Operating Modes
        4. Warning Interrupts for System Level Diagnostics
          1. Output Power Limit
          2. Thermal Warning
        5. Protections Causing Converter Disable
          1. Short-Circuit and Overload Protection
          2. Overvoltage Protection
          3. Thermal Shutdown
        6. Protections Causing Device Power Down
          1. Undervoltage Lockout
      11. 7.3.11 OTP Error Correction
      12. 7.3.12 Operation of GPO Signals
      13. 7.3.13 Digital Signal Filtering
    4. 7.4 Device Functional Modes
      1. 7.4.1 Modes of Operation
    5. 7.5 Programming
      1. 7.5.1 I2C-Compatible Interface
        1. Data Validity
        2. Start and Stop Conditions
        3. Transferring Data
        4. I2C-Compatible Chip Address
        5. Auto Increment Feature
    6. 7.6 Register Maps
      1. 7.6.1 Register Descriptions
        1. LP8770_map Registers
  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. Application Components
          1. Inductor Selection
          2. Buck Input Capacitor Selection
          3. Buck Output Capacitor Selection
          4. Boost Input Capacitor Selection
          5. Boost Output Capacitor Selection
          6. Supply Filtering Components
      3. 8.2.3 Current Limit vs Maximum Output Current
      4. 8.2.4 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Third-Party Products Disclaimer
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

Layout Guidelines

The high frequency and large switching currents of the LP87702 make the choice of layout important. Good power supply results only occur when care is given to proper design and layout. Layout affects noise pickup and generation and can cause a good design to perform with less-than-expected results. With a range of output currents from milliamps to several amps, good power supply layout is much more difficult than most general PCB design. Use the following steps as a reference to ensure the device is stable and maintains proper voltage and current regulation across its intended operating voltage and current range.

  1. Place CIN as close as possible to the VIN_Bx pin and the PGND_Bx pin. Route the VIN trace wide and thick to avoid IR drops. The trace between the input capacitor's positive node and one or more of the device VIN_Bx pins, as well as the trace between the negative node of the input capacitor and one or more of the power PGND_Bx pins must be kept as short as possible. The input capacitance provides a low-impedance voltage source for the switching converter. The inductance of the connection is the most important parameter of a local decoupling capacitor – parasitic inductance on these traces must be kept as tiny as possible for proper device operation.
  2. The output filter, consisting of L and COUT, converts the switching signal at SW_Bx to the noiseless output voltage. It should be placed as close as possible to the device keeping the switch node small, for best EMI behavior. Route the traces between the LP87702 devices output capacitors and the load's input capacitors direct and wide to avoid losses due to the IR drop.
  3. Input for analog blocks (VANA and AGND) should be isolated from noisy signals. Connect VANA directly to a quiet system voltage node and AGND to a quiet ground point where no IR drop occurs. Place the decoupling capacitor as close as possible to the VANA pin.
  4. If remote voltage sensing can be used for the load, connect the device feedback pins FB_Bx to the respective sense pins on the load capacitor. The sense lines are susceptible to noise. They must be kept away from noisy signals such as PGND_Bx, VIN_Bx, and SW_Bx, as well as high bandwidth signals such as the I2C. Avoid capacitive and inductive coupling by keeping the sense lines short and direct. Run the lines in a quiet layer. Isolate them from noisy signals by a voltage or ground plane (if possible).
  5. PGND_Bx, VIN_Bx and SW_Bx should be routed on thick layers. They must not surround inner signal layers which are not able to withstand interference from noisy PGND_Bx, VIN_Bx and SW_Bx.

Due to the small package of this converter and the overall small solution size, the thermal performance of the PCB layout is important. Many system-dependent issues such as thermal coupling, airflow, added heat sinks, convection surfaces, and the presence of other heat-generating components affect the power dissipation limits of a given component. Proper PCB layout, focusing on thermal performance, results in lower die temperatures. Wide power traces come with the ability to sink dissipated heat. This can be improved further on multi-layer PCB designs with vias to different planes. This results in reduced junction-to-ambient (RθJA) and junction-to-board (RθJB) thermal resistances, which reduces the device junction temperature (TJ). TI strongly recommends performing a careful system-level 2D or full 3D dynamic thermal analysis at the beginning product design process, by using a thermal modeling analysis software.