SPRS956H March   2016  – November 2019 DRA722 , DRA724 , DRA725 , DRA726

PRODUCTION DATA.  

  1. 1 Device Overview
    1. 1.1 Features
    2. 1.2 Applications
    3. 1.3 Description
    4. 1.4 Functional Block Diagram
  2. 2 Revision History
  3. 3 Device Comparison
    1. 3.1 Related Products
  4. 4 Terminal Configuration and Functions
    1. 4.1 Terminal Assignment
      1. 4.1.1 Unused Balls Connection Requirements
    2. 4.2 Ball Characteristics
    3. 4.3 Multiplexing Characteristics
    4. 4.4 Signal Descriptions
      1. 4.4.1  Video Input Ports (VIP)
      2. 4.4.2  Display Subsystem – Video Output Ports
      3. 4.4.3  Display Subsystem – High-Definition Multimedia Interface (HDMI)
      4. 4.4.4  Camera Serial Interface 2 CAL bridge (CSI2)
      5. 4.4.5  External Memory Interface (EMIF)
      6. 4.4.6  General-Purpose Memory Controller (GPMC)
      7. 4.4.7  Timers
      8. 4.4.8  Inter-Integrated Circuit Interface (I2C)
      9. 4.4.9  HDQ / 1-Wire Interface (HDQ1W)
      10. 4.4.10 Universal Asynchronous Receiver Transmitter (UART)
      11. 4.4.11 Multichannel Serial Peripheral Interface (McSPI)
      12. 4.4.12 Quad Serial Peripheral Interface (QSPI)
      13. 4.4.13 Multicannel Audio Serial Port (McASP)
      14. 4.4.14 Universal Serial Bus (USB)
      15. 4.4.15 SATA
      16. 4.4.16 Peripheral Component Interconnect Express (PCIe)
      17. 4.4.17 Controller Area Network Interface (DCAN)
      18. 4.4.18 Ethernet Interface (GMAC_SW)
      19. 4.4.19 Media Local Bus (MLB) Interface
      20. 4.4.20 eMMC/SD/SDIO
      21. 4.4.21 General-Purpose Interface (GPIO)
      22. 4.4.22 Keyboard controller (KBD)
      23. 4.4.23 Pulse Width Modulation (PWM) Interface
      24. 4.4.24 Audio Tracking Logic (ATL)
      25. 4.4.25 Test Interfaces
      26. 4.4.26 System and Miscellaneous
        1. 4.4.26.1 Sysboot
        2. 4.4.26.2 Power, Reset, and Clock Management (PRCM)
        3. 4.4.26.3 Real-Time Clock (RTC) Interface
        4. 4.4.26.4 System Direct Memory Access (SDMA)
        5. 4.4.26.5 Interrupt Controllers (INTC)
        6. 4.4.26.6 Observability
      27. 4.4.27 Power Supplies
  5. 5 Specifications
    1. 5.1  Absolute Maximum Ratings
    2. 5.2  ESD Ratings
    3. 5.3  Power-On-Hour (POH) Limits
    4. 5.4  Recommended Operating Conditions
    5. 5.5  Operating Performance Points
      1. 5.5.1 AVS and ABB Requirements
      2. 5.5.2 Voltage And Core Clock Specifications
      3. 5.5.3 Maximum Supported Frequency
    6. 5.6  Power Consumption Summary
    7. 5.7  Electrical Characteristics
      1. 5.7.1  LVCMOS DDR DC Electrical Characteristics
      2. 5.7.2  HDMIPHY DC Electrical Characteristics
      3. 5.7.3  Dual Voltage LVCMOS I2C DC Electrical Characteristics
      4. 5.7.4  IQ1833 Buffers DC Electrical Characteristics
      5. 5.7.5  IHHV1833 Buffers DC Electrical Characteristics
      6. 5.7.6  LVCMOS OSC Buffers DC Electrical Characteristics
      7. 5.7.7  LVCMOS CSI2 DC Electrical Characteristics
      8. 5.7.8  BMLB18 Buffers DC Electrical Characteristics
      9. 5.7.9  BC1833IHHV Buffers DC Electrical Characteristics
      10. 5.7.10 USBPHY DC Electrical Characteristics
      11. 5.7.11 Dual Voltage SDIO1833 DC Electrical Characteristics
      12. 5.7.12 Dual Voltage LVCMOS DC Electrical Characteristics
      13. 5.7.13 SATAPHY DC Electrical Characteristics
      14. 5.7.14 PCIEPHY DC Electrical Characteristics
    8. 5.8  VPP Specifications for One-Time Programmable (OTP) eFuses
      1. Table 5-20 Recommended Operating Conditions for OTP eFuse Programming
      2. 5.8.1      Hardware Requirements
      3. 5.8.2      Programming Sequence
      4. 5.8.3      Impact to Your Hardware Warranty
    9. 5.9  Thermal Characteristics
      1. 5.9.1 Package Thermal Characteristics
    10. 5.10 Power Supply Sequences
  6. 6 Clock Specifications
    1. 6.1 Input Clock Specifications
      1. 6.1.1 Input Clock Requirements
      2. 6.1.2 System Oscillator OSC0 Input Clock
        1. 6.1.2.1 OSC0 External Crystal
        2. 6.1.2.2 OSC0 Input Clock
      3. 6.1.3 Auxiliary Oscillator OSC1 Input Clock
        1. 6.1.3.1 OSC1 External Crystal
        2. 6.1.3.2 OSC1 Input Clock
      4. 6.1.4 RTC Oscillator Input Clock
        1. 6.1.4.1 RTC Oscillator External Crystal
        2. 6.1.4.2 RTC Oscillator Input Clock
        3. 6.1.4.3 RC On-die Oscillator Clock
    2. 6.2 DPLLs, DLLs Specifications
      1. 6.2.1 DPLL Characteristics
      2. 6.2.2 DLL Characteristics
      3. 6.2.3 DPLL and DLL Noise Isolation
  7. 7 Timing Requirements and Switching Characteristics
    1. 7.1  Timing Test Conditions
    2. 7.2  Interface Clock Specifications
      1. 7.2.1 Interface Clock Terminology
      2. 7.2.2 Interface Clock Frequency
    3. 7.3  Timing Parameters and Information
      1. 7.3.1 Parameter Information
        1. 7.3.1.1 1.8V and 3.3V Signal Transition Levels
        2. 7.3.1.2 1.8V and 3.3V Signal Transition Rates
        3. 7.3.1.3 Timing Parameters and Board Routing Analysis
    4. 7.4  Recommended Clock and Control Signal Transition Behavior
    5. 7.5  Virtual and Manual I/O Timing Modes
    6. 7.6  Video Input Ports (VIP)
    7. 7.7  Display Subsystem - Video Output Ports
    8. 7.8  Display Subsystem - High-Definition Multimedia Interface (HDMI)
    9. 7.9  Camera Serial Interface 2 CAL bridge (CSI2)
      1. 7.9.1 CSI-2 MIPI D-PHY
    10. 7.10 External Memory Interface (EMIF)
    11. 7.11 General-Purpose Memory Controller (GPMC)
      1. 7.11.1 GPMC/NOR Flash Interface Synchronous Timing
      2. 7.11.2 GPMC/NOR Flash Interface Asynchronous Timing
      3. 7.11.3 GPMC/NAND Flash Interface Asynchronous Timing
    12. 7.12 Timers
    13. 7.13 Inter-Integrated Circuit Interface (I2C)
      1. Table 7-33 Timing Requirements for I2C Input Timings
      2. Table 7-34 Timing Requirements for I2C HS-Mode (I2C3/4/5/6 Only)
      3. Table 7-35 Switching Characteristics Over Recommended Operating Conditions for I2C Output Timings
    14. 7.14 HDQ / 1-Wire Interface (HDQ1W)
      1. 7.14.1 HDQ / 1-Wire - HDQ Mode
      2. 7.14.2 HDQ/1-Wire-1-Wire Mode
    15. 7.15 Universal Asynchronous Receiver Transmitter (UART)
      1. Table 7-40 Timing Requirements for UART
      2. Table 7-41 Switching Characteristics Over Recommended Operating Conditions for UART
    16. 7.16 Multichannel Serial Peripheral Interface (McSPI)
    17. 7.17 Quad Serial Peripheral Interface (QSPI)
    18. 7.18 Multichannel Audio Serial Port (McASP)
      1. Table 7-48 Timing Requirements for McASP1
      2. Table 7-49 Timing Requirements for McASP2
      3. Table 7-50 Timing Requirements for McASP3/4/5/6/7/8
    19. 7.19 Universal Serial Bus (USB)
      1. 7.19.1 USB1 DRD PHY
      2. 7.19.2 USB2 PHY
      3. 7.19.3 USB3 DRD ULPI-SDR-Slave Mode-12-pin Mode
    20. 7.20 Serial Advanced Technology Attachment (SATA)
    21. 7.21 Peripheral Component Interconnect Express (PCIe)
    22. 7.22 Controller Area Network Interface (DCAN)
      1. Table 7-68 Timing Requirements for DCANx Receive
      2. Table 7-69 Switching Characteristics Over Recommended Operating Conditions for DCANx Transmit
    23. 7.23 Ethernet Interface (GMAC_SW)
      1. 7.23.1 GMAC MII Timings
        1. Table 7-70 Timing Requirements for miin_rxclk - MII Operation
        2. Table 7-71 Timing Requirements for miin_txclk - MII Operation
        3. Table 7-72 Timing Requirements for GMAC MIIn Receive 10/100 Mbit/s
        4. Table 7-73 Switching Characteristics Over Recommended Operating Conditions for GMAC MIIn Transmit 10/100 Mbits/s
      2. 7.23.2 GMAC MDIO Interface Timings
      3. 7.23.3 GMAC RMII Timings
        1. Table 7-78 Timing Requirements for GMAC REF_CLK - RMII Operation
        2. Table 7-79 Timing Requirements for GMAC RMIIn Receive
        3. Table 7-80 Switching Characteristics Over Recommended Operating Conditions for GMAC REF_CLK - RMII Operation
        4. Table 7-81 Switching Characteristics Over Recommended Operating Conditions for GMAC RMIIn Transmit 10/100 Mbits/s
      4. 7.23.4 GMAC RGMII Timings
        1. Table 7-85 Timing Requirements for rgmiin_rxc - RGMIIn Operation
        2. Table 7-86 Timing Requirements for GMAC RGMIIn Input Receive for 10/100/1000 Mbps
        3. Table 7-87 Switching Characteristics Over Recommended Operating Conditions for rgmiin_txctl - RGMIIn Operation for 10/100/1000 Mbit/s
        4. Table 7-88 Switching Characteristics for GMAC RGMIIn Output Transmit for 10/100/1000 Mbps
    24. 7.24 Media Local Bus (MLB) interface
    25. 7.25 eMMC/SD/SDIO
      1. 7.25.1 MMC1-SD Card Interface
        1. 7.25.1.1 Default speed, 4-bit data, SDR, half-cycle
        2. 7.25.1.2 High speed, 4-bit data, SDR, half-cycle
        3. 7.25.1.3 SDR12, 4-bit data, half-cycle
        4. 7.25.1.4 SDR25, 4-bit data, half-cycle
        5. 7.25.1.5 UHS-I SDR50, 4-bit data, half-cycle
        6. 7.25.1.6 UHS-I SDR104, 4-bit data, half-cycle
        7. 7.25.1.7 UHS-I DDR50, 4-bit data
      2. 7.25.2 MMC2 - eMMC
        1. 7.25.2.1 Standard JC64 SDR, 8-bit data, half cycle
        2. 7.25.2.2 High Speed JC64 SDR, 8-bit data, half cycle
        3. 7.25.2.3 High Speed HS200 JEDS84 SDR, 8-bit data, half cycle
        4. 7.25.2.4 High Speed JC64 DDR, 8-bit data
          1. Table 7-119 Switching Characteristics for MMC2 - JC64 High Speed DDR Mode
      3. 7.25.3 MMC3 and MMC4-SDIO/SD
        1. 7.25.3.1 MMC3 and MMC4, SD Default Speed
        2. 7.25.3.2 MMC3 and MMC4, SD High Speed
        3. 7.25.3.3 MMC3 and MMC4, SD and SDIO SDR12 Mode
        4. 7.25.3.4 MMC3 and MMC4, SD SDR25 Mode
        5. 7.25.3.5 MMC3 SDIO High Speed UHS-I SDR50 Mode, Half Cycle
    26. 7.26 General-Purpose Interface (GPIO)
    27. 7.27 Audio Tracking Logic (ATL)
      1. 7.27.1 ATL Electrical Data/Timing
        1. Table 7-141 Switching Characteristics Over Recommended Operating Conditions for ATL_CLKOUTx
    28. 7.28 System and Miscellaneous interfaces
    29. 7.29 Test Interfaces
      1. 7.29.1 IEEE 1149.1 Standard-Test-Access Port (JTAG)
        1. 7.29.1.1 JTAG Electrical Data/Timing
          1. Table 7-142 Timing Requirements for IEEE 1149.1 JTAG
          2. Table 7-143 Switching Characteristics Over Recommended Operating Conditions for IEEE 1149.1 JTAG
          3. Table 7-144 Timing Requirements for IEEE 1149.1 JTAG With RTCK
          4. Table 7-145 Switching Characteristics Over Recommended Operating Conditions for IEEE 1149.1 JTAG With RTCK
      2. 7.29.2 Trace Port Interface Unit (TPIU)
        1. 7.29.2.1 TPIU PLL DDR Mode
  8. 8 Applications, Implementation, and Layout
    1. 8.1 Introduction
      1. 8.1.1 Initial Requirements and Guidelines
    2. 8.2 Power Optimizations
      1. 8.2.1 Step 1: PCB Stack-up
      2. 8.2.2 Step 2: Physical Placement
      3. 8.2.3 Step 3: Static Analysis
        1. 8.2.3.1 PDN Resistance and IR Drop
      4. 8.2.4 Step 4: Frequency Analysis
      5. 8.2.5 System ESD Generic Guidelines
        1. 8.2.5.1 System ESD Generic PCB Guideline
        2. 8.2.5.2 Miscellaneous EMC Guidelines to Mitigate ESD Immunity
        3. 8.2.5.3 ESD Protection System Design Consideration
      6. 8.2.6 EMI / EMC Issues Prevention
        1. 8.2.6.1 Signal Bandwidth
        2. 8.2.6.2 Signal Routing
          1. 8.2.6.2.1 Signal Routing—Sensitive Signals and Shielding
          2. 8.2.6.2.2 Signal Routing—Outer Layer Routing
        3. 8.2.6.3 Ground Guidelines
          1. 8.2.6.3.1 PCB Outer Layers
          2. 8.2.6.3.2 Metallic Frames
          3. 8.2.6.3.3 Connectors
          4. 8.2.6.3.4 Guard Ring on PCB Edges
          5. 8.2.6.3.5 Analog and Digital Ground
    3. 8.3 Core Power Domains
      1. 8.3.1 General Constraints and Theory
      2. 8.3.2 Voltage Decoupling
      3. 8.3.3 Static PDN Analysis
      4. 8.3.4 Dynamic PDN Analysis
      5. 8.3.5 Power Supply Mapping
      6. 8.3.6 DPLL Voltage Requirement
      7. 8.3.7 Loss of Input Power Event
      8. 8.3.8 Example PCB Design
        1. 8.3.8.1 Example Stack-up
        2. 8.3.8.2 vdd Example Analysis
    4. 8.4 Single-Ended Interfaces
      1. 8.4.1 General Routing Guidelines
      2. 8.4.2 QSPI Board Design and Layout Guidelines
    5. 8.5 Differential Interfaces
      1. 8.5.1 General Routing Guidelines
      2. 8.5.2 USB 2.0 Board Design and Layout Guidelines
        1. 8.5.2.1 Background
        2. 8.5.2.2 USB PHY Layout Guide
          1. 8.5.2.2.1 General Routing and Placement
          2. 8.5.2.2.2 Specific Guidelines for USB PHY Layout
            1. 8.5.2.2.2.1  Analog, PLL, and Digital Power Supply Filtering
            2. 8.5.2.2.2.2  Analog, Digital, and PLL Partitioning
            3. 8.5.2.2.2.3  Board Stackup
            4. 8.5.2.2.2.4  Cable Connector Socket
            5. 8.5.2.2.2.5  Clock Routings
            6. 8.5.2.2.2.6  Crystals/Oscillator
            7. 8.5.2.2.2.7  DP/DM Trace
            8. 8.5.2.2.2.8  DP/DM Vias
            9. 8.5.2.2.2.9  Image Planes
            10. 8.5.2.2.2.10 Power Regulators
        3. 8.5.2.3 References
      3. 8.5.3 USB 3.0 Board Design and Layout Guidelines
        1. 8.5.3.1 USB 3.0 interface introduction
        2. 8.5.3.2 USB 3.0 General routing rules
      4. 8.5.4 HDMI Board Design and Layout Guidelines
        1. 8.5.4.1 HDMI Interface Schematic
        2. 8.5.4.2 TMDS General Routing Guidelines
        3. 8.5.4.3 TPD5S115
        4. 8.5.4.4 HDMI ESD Protection Device (Required)
        5. 8.5.4.5 PCB Stackup Specifications
        6. 8.5.4.6 Grounding
      5. 8.5.5 SATA Board Design and Layout Guidelines
        1. 8.5.5.1 SATA Interface Schematic
        2. 8.5.5.2 Compatible SATA Components and Modes
        3. 8.5.5.3 PCB Stackup Specifications
        4. 8.5.5.4 Routing Specifications
      6. 8.5.6 PCIe Board Design and Layout Guidelines
        1. 8.5.6.1 PCIe Connections and Interface Compliance
          1. 8.5.6.1.1 Coupling Capacitors
          2. 8.5.6.1.2 Polarity Inversion
        2. 8.5.6.2 Non-standard PCIe connections
          1. 8.5.6.2.1 PCB Stackup Specifications
          2. 8.5.6.2.2 Routing Specifications
            1. 8.5.6.2.2.1 Impedance
            2. 8.5.6.2.2.2 Differential Coupling
            3. 8.5.6.2.2.3 Pair Length Matching
        3. 8.5.6.3 LJCB_REFN/P Connections
      7. 8.5.7 CSI2 Board Design and Routing Guidelines
        1. 8.5.7.1 CSI2_0 and CSI2_1 MIPI CSI-2 (1.5 Gbps)
          1. 8.5.7.1.1 General Guidelines
          2. 8.5.7.1.2 Length Mismatch Guidelines
            1. 8.5.7.1.2.1 CSI2_0 and CSI2_1 MIPI CSI-2 (1.5 Gbps)
          3. 8.5.7.1.3 Frequency-domain Specification Guidelines
    6. 8.6 Clock Routing Guidelines
      1. 8.6.1 32-kHz Oscillator Routing
      2. 8.6.2 Oscillator Ground Connection
    7. 8.7 DDR3 Board Design and Layout Guidelines
      1. 8.7.1 DDR3 General Board Layout Guidelines
      2. 8.7.2 DDR3 Board Design and Layout Guidelines
        1. 8.7.2.1  Board Designs
        2. 8.7.2.2  DDR3 EMIF
        3. 8.7.2.3  DDR3 Device Combinations
        4. 8.7.2.4  DDR3 Interface Schematic
          1. 8.7.2.4.1 32-Bit DDR3 Interface
          2. 8.7.2.4.2 16-Bit DDR3 Interface
        5. 8.7.2.5  Compatible JEDEC DDR3 Devices
        6. 8.7.2.6  PCB Stackup
        7. 8.7.2.7  Placement
        8. 8.7.2.8  DDR3 Keepout Region
        9. 8.7.2.9  Bulk Bypass Capacitors
        10. 8.7.2.10 High Speed Bypass Capacitors
          1. 8.7.2.10.1 Return Current Bypass Capacitors
        11. 8.7.2.11 Net Classes
        12. 8.7.2.12 DDR3 Signal Termination
        13. 8.7.2.13 VREF_DDR Routing
        14. 8.7.2.14 VTT
        15. 8.7.2.15 CK and ADDR_CTRL Topologies and Routing Definition
          1. 8.7.2.15.1 Four DDR3 Devices
            1. 8.7.2.15.1.1 CK and ADDR_CTRL Topologies, Four DDR3 Devices
            2. 8.7.2.15.1.2 CK and ADDR_CTRL Routing, Four DDR3 Devices
          2. 8.7.2.15.2 Two DDR3 Devices
            1. 8.7.2.15.2.1 CK and ADDR_CTRL Topologies, Two DDR3 Devices
            2. 8.7.2.15.2.2 CK and ADDR_CTRL Routing, Two DDR3 Devices
          3. 8.7.2.15.3 One DDR3 Device
            1. 8.7.2.15.3.1 CK and ADDR_CTRL Topologies, One DDR3 Device
            2. 8.7.2.15.3.2 CK and ADDR/CTRL Routing, One DDR3 Device
        16. 8.7.2.16 Data Topologies and Routing Definition
          1. 8.7.2.16.1 DQS and DQ/DM Topologies, Any Number of Allowed DDR3 Devices
          2. 8.7.2.16.2 DQS and DQ/DM Routing, Any Number of Allowed DDR3 Devices
        17. 8.7.2.17 Routing Specification
          1. 8.7.2.17.1 CK and ADDR_CTRL Routing Specification
          2. 8.7.2.17.2 DQS and DQ Routing Specification
  9. 9 Device and Documentation Support
    1. 9.1 Device Nomenclature
      1. 9.1.1 Standard Package Symbolization
      2. 9.1.2 Device Naming Convention
    2. 9.2 Tools and Software
    3. 9.3 Documentation Support
    4. 9.4 Related Links
    5. 9.5 Support Resources
    6. 9.6 Trademarks
    7. 9.7 Electrostatic Discharge Caution
    8. 9.8 Glossary
  10. 10Mechanical, Packaging, and Orderable Information
    1. 10.1 Packaging Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • ABC|760
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.4 Step 4: Frequency Analysis

Delivering low noise voltage sources are very important to allowing a system to operate at the lowest possible Operational Performance Point (OPP) for any one Use Case. An OPP is a combination of the supply voltage level and clocking rate for key internal processor domains. A SCH and PCB designed to provide low noise voltage supplies will then enable the processor to enter optimal OPPs for each Use Case that in turn will minimize power dissipation and junction temperatures on-die. Therefore, it is a good engineering practice to perform a Frequency Analysis over the key power domains.

Frequency analysis and design methodology results in a PDN design that minimizes transient noise voltages at the processor’s input power balls. This allows the processor’s internal transistors to operate near the minimum specified operating supply voltage levels. To accomplish this one must evaluate how a voltage supply will change due to impedance variations over frequency. This analysis will focus on the decoupling capacitor network (VDD_xxx and VSS/Gnd rails) at the load. Sufficient capacitance with a distribution of self-resonant points will provide for an overall lower impedance vs frequency response for each power domain.

Decoupling components that are distant from their load’s input power are susceptible to encountering spreading loop inductance from the PCB design. Early analysis of each key power domain’s frequency response helps to determine basic decoupling capacitor placement, optimal footprint, layer assignment, and types needed for minimizing supply voltage noise/fluctuations due to switching and load current transients.

NOTE

Evaluation of loop inductance values for decoupling capacitors placed ~300mils closer to the load’s input power balls has shown an 18% reduction in loop inductance due to reduced distance.
  • Decoupling capacitors must be carefully placed in order to minimize loop inductance impact on supply voltage transients. A real capacitor has characteristics not only of capacitance but also inductance and resistance.

    • Figure 8-6 shows the parasitic model of a real capacitor. A real capacitor must be treated as an RLC circuit with effective series resistance (ESR) and effective series inductance (ESL).

    DRA722 DRA724 DRA725 DRA726 SPRS906_PCB_FREQ_01.gifFigure 8-6 Characteristics of a Real Capacitor With ESL and ESR

    The magnitude of the impedance of this series model is given as:

    DRA722 DRA724 DRA725 DRA726 SPRS906_PCB_FREQ_02.gifFigure 8-7 Series Model Impedance Equation

Figure 8-8 shows the resonant frequency response of a typical capacitor with a self-resonant frequency of 55 MHz. The impedance of the capacitor is a combination of its series resistance and reactive capacitance and inductance as shown in the equation above.

DRA722 DRA724 DRA725 DRA726 SPRS906_PCB_FREQ_03.gifFigure 8-8 Typical Impedance Profile of a Capacitor

Because a capacitor has series inductance and resistance that impacts its effectiveness, it is important that the following recommendations are adopted in placing capacitors on the PDN.

Wherever possible, mount the capacitor with the geometry that minimizes the mounting inductance and resistance. This was shown earlier in Figure 8-1. The capacitor mounting inductance and resistance values include the inductance and resistance of the pads, trace, and vias. Whenever possible, use footprints that have the lowest inductance configuration as shown in Figure 8-9

The length of a trace used to connect a capacitor has a big impact on parasitic inductance and resistance of the mounting. This trace must be as short and as wide as possible. wherever possible, minimize distance to supply and Gnd vias by locating vias nearby or within the capacitor’s solder pad landing. Further improvements can be made to the mounting by placing vias to the side of capacitor lands or doubling the number of vias as shown in Figure 8-9. If the PCB manufacturing processes allow it and if cost-effective, via-in-pad (VIP) geometries are strongly recommended.

In addition to mounting inductance and resistance associated with placing a capacitor on the PCB, the effectiveness of a decoupling capacitor also depends on the spreading inductance and resistance that the capacitor sees with respect to the load. The spreading inductance and resistance is strongly dependent on the layer assignment in the PCB stack-up. Therefore, try to minimize X, Y and Z dimensions where the Z is due to PCB thickness (as shown in Figure 8-9).

From left (highest inductance) to right (lowest inductance) the capacitor footprint types shown in Figure 8-9 are known as:

  • 2-via, Skinny End Exit (2vSEE)
  • 2-via, Wide End Exit (2vWEE)
  • 2-via, Wide Side Exit (2vWSE)
  • 4-via, Wide Side Exit (4vWSE)
  • 2-via, In-Pad (2vIP)
DRA722 DRA724 DRA725 DRA726 SPRS906_PCB_FREQ_04.gifFigure 8-9 Capacitor Placement Geometry for Improved Mounting Inductance

NOTE

Evaluation of loop inductance values for decoupling capacitor footprints 2vSEE (worst case) vs 4vWSE (2nd best) has shown a 30% reduction in inductance when 4vWSE footprint was used in place of 2vSEE.

Decoupling Capacitor (Dcap) Strategy:

  1. Use lowest inductance footprint and trace connection scheme possible for given PCB technology and layout area in order to minimize Dcap loop inductance to power pin as much as possible (see Figure 8-9).
  2. Place Dcaps on “same-side” as component within their power plane outline to minimize “decoupling loop inductance”. Target distance to power pin should be less than ~500mils depending upon PCB layout characteristics (plane's layer assignment and solid nature). Use PI modeling CAD tool to verify minimum inductance for top vs bottom-side placement.
  3. Place Dcaps on “opposite-side” as component within their power plane outline if “same-side” is not feasible or if distance to power pin is greater than ~500mils for top-side location. Use PI modeling CAD tool to verify minimum inductance for top vs bottom-side placement.
  4. Use minimum 10mil trace width for all voltage and gnd planes connections (that is, Dcap pads, component power pins, etc.).
  5. Place all voltage and gnd plane vias “as close as possible” to point of use (that is, Dcap pads, component power pins, etc.).
  6. Use a “Power/Gnd pad/pin to via” ratio of 1:1 whenever possible. Do not exceed 2:1 ratio for small number of vias within restricted PCB areas (that is, underneath BGA components).

Frequency analysis for the CORE power domain has yielded the vdd Impedance vs Frequency response shown in Section 8.3.8.2, vdd Example Analysis. As the example shows the overall CORE PDN Reff meets the maximum recommended PDN resistance of 10mΩ.