SLVAFH6 November   2023 LM25066 , LM5066 , LM5066I , TPS25984 , TPS25985 , TPS25990 , TPS536C9T

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2What are PSYS™ and PSYS_CRIT#™?
  6. 3Implementation of PSYS Monitor
    1. 3.1 Existing Designs
    2. 3.2 Proposed Designs
  7. 4ISYS Resistor (RISYS) and Gain (ISYS_IN_GAIN) Selection in TPS536C9T VR14 Controller
    1. 4.1 Steps to Calculate the Value of RIMON or RISYS and ISYS_IN_GAIN
    2. 4.2 Design Example
  8. 5Functional Verification of PSYS and PSYS_CRIT# in TPS536C9T VR14 Controller Using TPS25984, TPS25985, or TPS25990 eFuses as PSYS Monitor
  9. 6Extraction of Platform Current Information With Multiple PSYS Monitors Connected to the Same PSU
    1. 6.1 Designing the Non-Inverting Summing Amplifier
    2. 6.2 Design Guideline and Example
  10. 7Summary
  11. 8References

4 ISYS Resistor (RISYS) and Gain (ISYS_IN_GAIN) Selection in TPS536C9T VR14 Controller

The IMON pin in TPS25984, TPS25985, or TPS25990 eFuses serves two purposes:

  • sets the over-current protection threshold and the scalable fast-trip threshold during steady-state.
  • provides a fast and accurate analog output load current monitor signal during steady-state.

Therefore, the same resistance, either called RIMON or RISYS, is determined by considering the required over-current protection threshold for the eFuses as well as the full-scale analog voltage range of the ISYS_IN pin in the VR14 controller.

The analog current monitoring output (IIMON), sourced on the IMON pin in TPS25984, TPS25985, or TPS25990 eFuses, is defined as Equation 1.

Equation 1. IIMON=IIN×GIMON

GIMON is the current monitor gain (IIMON : IIN) in TPS25984, TPS25985, or TPS25990 eFuses, whose typical value is 18.18 µA/A. IIN is the total input current to the platform. The over-current condition is detected by comparing the voltage at the IMON pin (VIMON) by dropping the IIMON across the RIMON resistance against a reference threshold of VIREF. VIMON is obtained using Equation 2.

Equation 2. VIMON=IIMON×RIMON=IIN×GIMON×RIMON

The circuit-breaker threshold during steady-state (IOCP) can be calculated using Equation 3. For more details, see the Steady-State Over-current Protection (Circuit-Breaker) section in TPS25984, TPS25985, or TPS25990 eFuses data sheets.

Equation 3. IOCP=VIREFGIMON×RIMON

In TPS25990 eFuse, VIREF is set through PMBus® using E0h register.

In TPS25984 and TPS25985 eFuses, VIREF is specified by placing a resistor (RIREF) at the IREF pin. Equation 4 is used to calculate the value of RIREF.

Equation 4. RIREF=VIREFIIREF

IIREF = 25 µA (typical).

The total platform input current drawn from the PSU, as sensed by the VR14 controller at the ISYS_IN pin, is given by Equation 5.

Equation 5. ISYSA=IINA×RISYSΩ×GISYSμAA×ISYS_IN_GAINAμA×Ω

IIN is the platform current drawn from the PSU. Essentially, GISYS and GIMON are the same parameter with identical values. RISYS and RIMON are the same parameter with identical values.

ISYS_IN_GAIN: A scaling factor internal to the VR14 controller to account for the external gain factors GISYS and RISYS.