SLVSC86A January   2014  – March 2014 UCD9244-EP

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Description (Continued)
  6. Terminal Configuration and Functions
    1.     Terminal Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  Handling Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics
    6. 7.6  Electrical Characteristics (Continued)
    7. 7.7  ADC Monitoring Intervals And Response Times
    8. 7.8  Hardware Fault Detection Latency
    9. 7.9  PMBus/SMBus/I2C
    10. 7.10 I2C/SMBus/PMBus Timing Requirements
    11. 7.11 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  PMBus Interface
      2. 8.3.2  Resistor Programmed PMBus Address Decode
      3. 8.3.3  VID Interface
      4. 8.3.4  Jtag Interface
      5. 8.3.5  Bias Supply Generator (Shunt Regulator Controller)
      6. 8.3.6  Power-On Reset
      7. 8.3.7  External Reset
      8. 8.3.8  ON_OFF_CONFIG
      9. 8.3.9  Output Voltage Adjustment
      10. 8.3.10 Calibration
      11. 8.3.11 Analog Front End (AFE)
      12. 8.3.12 Voltage Sense Filtering
      13. 8.3.13 DPWM Engine
      14. 8.3.14 Rail/Power Stage Configuration
      15. 8.3.15 DPWM Phase Synchronization
      16. 8.3.16 Output Current Measurement
      17. 8.3.17 Current Sense Input Filtering
      18. 8.3.18 Over-Current Detection
      19. 8.3.19 Input Voltage Monitoring
      20. 8.3.20 Input UV Lockout
      21. 8.3.21 Temperature Monitoring
      22. 8.3.22 Auxiliary ADC Input Monitoring
      23. 8.3.23 Soft Start, Soft Stop Ramp Sequence
      24. 8.3.24 Non-Volatile Memory Error Correction Coding
      25. 8.3.25 Data Logging
    4. 8.4 Device Functional Modes
      1. 8.4.1 4-Bit VID Mode
      2. 8.4.2 6-Bit VID Mode
      3. 8.4.3 8-Bit VID Mode
      4. 8.4.4 Current Foldback Mode
  9. Applications and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Automatic System Identification (Auto-ID)
    2. 9.2 Typical Applications
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Digital Compensator
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Trademarks
    2. 12.2 Electrostatic Discharge Caution
    3. 12.3 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Current Sense Input Filtering

Each power stage current is monitored by the device at the CS terminals. The device monitors the current with a 12-bit ADC and also monitors the current with a digitally programmable analog comparator. The comparator can be disabled by writing a zero to the FAST_OC_FAULT_LIMIT.

Because the current sense signal is both digitally sampled and compared to the programmable over-current threshold, it should be conditioned with an RC network acting as an anti-alias filter. If the comparator is disabled, the CS input should be filtered at 35% of the sampling rate. An RC network with this characteristic can be calculated as

Equation 9. UCD9244-EP eq7_lvsal7.gif

where Nrails is the number of rails configured and TIout is the sample period for the current sense inputs. Therefore, when the comparator is not used, the recommended component values for the RC network are C = 10 nF and R = 35.7 kΩ.

When the fast over-current comparator is used, the filter corner frequency based on the ADC sample rate may be too slow and a corner frequency that is a compromise between the requirements of fast over-current detection and attenuating aliased content in the sampled current must be sought. In this case, the filter corner frequency can be calculated based on the time to cross the over-current threshold.

Equation 10. UCD9244-EP eq8_lvsal7.gif

where VOC_thres is the programmed OC comparator threshold, VCS_nom is the nominal CS voltage, ΔVImon is the change in CS voltage due to an over-current fault and τ is the filter time constant. Using the equation for the comparator voltage above, the RC network values can be calculated as

Equation 11. UCD9244-EP eq9_lvsal7.gif

where Tdet is the time to cross the over-current comparator threshold. For Tdet = 10 µs, ΔVImon = 1.5V, VOC_thres = 2.0V and VCS_nom = 1.5V, the corner frequency is 6.4 kHz and the recommended RC network component values are C = 10 nF and R = 2.49 kΩ.