SLUSFM1 December   2024 TPS4812-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 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 Switching Characteristics
    7. 6.7 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Charge Pump and Gate Driver Output (VS, GATE, BST, SRC)
      2. 8.3.2 Capacitive Load Driving
        1. 8.3.2.1 Using Low-Power Bypass FET (G Drive) for Load Capacitor Charging
        2. 8.3.2.2 Using Main FET (GATE Drive) Gate Slew Rate Control
      3. 8.3.3 Overcurrent and Short-Circuit Protection
        1. 8.3.3.1 I2t-Based Overcurrent Protection
          1. 8.3.3.1.1 I2t-Based Overcurrent Protection With Auto-Retry
          2. 8.3.3.1.2 I2t-Based Overcurrent Protection With Latch-Off
        2. 8.3.3.2 Short-Circuit Protection
      4. 8.3.4 Analog Current Monitor Output (IMON)
      5. 8.3.5 NTC-Based Temperature Sensing (TMP) and Analog Monitor Output (ITMPO)
      6. 8.3.6 Fault Indication and Diagnosis (FLT)
      7. 8.3.7 Reverse Polarity Protection
      8. 8.3.8 Undervoltage Protection (UVLO)
    4. 8.4 Device Functional Modes
      1. 8.4.1 State Diagram
      2. 8.4.2 State Transition Timing Diagram
      3. 8.4.3 Power Down
      4. 8.4.4 Shutdown Mode
      5. 8.4.5 Low Power Mode (LPM)
      6. 8.4.6 Active Mode (AM)
  10. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application 1: Driving Power at all times (PAAT) Loads With Automatic Load Wakeup
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
    3. 9.3 Typical Application 2: Driving Power at all times (PAAT) Loads With Automatic Load Wakeup and Output Bulk Capacitor Charging
      1. 9.3.1 Design Requirements
      2. 9.3.2 External Component Selection
      3. 9.3.3 Application Curves
    4. 9.4 Power Supply Recommendations
    5. 9.5 Layout
      1. 9.5.1 Layout Guidelines
      2. 9.5.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • RGE|23
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.3.2 External Component Selection

By following similar design procedure as outlined in , the external component values are calculated as below:

  • RSNS = 0.5mΩ
  • RSET = 300Ω
  • RIMON = 18.2kΩ
  • RIOC = 23kΩ to set 40A as I2t protection start threshold
  • CI2t = 1µF to set 3000A2s as I2T factor
  • CBST = 220nF
  • RISCP = 2.55kΩ to set 130A as short-circuit protection threshold
  • CTMR = 47nF to set 1000ms auto-retry time
  • R3 and R4 are selected as 470kΩ and 24.9kΩ respectively to set VIN undervoltage lockout threshold at 24V

Programming the Load Wakeup Threshold, RBYPASS and Q3 Selection

During normal operation, the series resistor RBYPASS is used to set load wakeup current threshold. After VG_GOOD threshold is reached, the voltage between DRN and CS2– is compared against V(LWU) threshold (200mV typ) for load wakeup event. For selecting the MOSFET Q3, important electrical parameters are the maximum continuous drain current ID, the maximum drain-to-source voltage VDS(MAX), the maximum drain-to-source voltage VGS(MAX), and the drain-to-source ON resistance RDSON.

Based on the design requirements, IAUS200N08S5N023 is selected and its ratings are:

  • 80V VDS(MAX) and ±20V VGS(MAX)

  • RDS(ON) is 2.3mΩ typical at 10V VGS

RBYPASS resistor value can be selected using below equation:

Equation 36. RBYPASS = V(LWU)ILWU

To set 200mA load wakeup current, RBYPASS resistor is calculated to be 1Ω.

The average power rating of the bypass resistor can be calculated by following equation:

Equation 37. PAVG= ILWU2× RBYPASS

The average power dissipation of RBYPASS is calculated to be 0.04W.

The peak power dissipation in the bypass resistor is given by following equation:

Equation 38. PPEAK= VBATT_MAX2RBYPASS

The peak power dissipation of RBYPASS is calculated to be ~3600W. The peak power dissipation time for power-up with short into LPM can be derived from t(LPM_SC) parameter (5μs) in electrical characteristics table.

Based on PPEAK and t(LPM_SC), Two of 2Ω, 1%, 1.5W CRCW25122R00JNEGHP resistor are used in parallel to support both average and peak power dissipation for > t(LPM_SC) time. TI suggests the designer to share the entire power dissipation profile of bypass resistor with the resistor manufacturer and get their recommendation.

The peak short-circuit current in bypass path can be calculated based on following equation:

Equation 39. IPEAK_BYPASS= VBATT_MAXRBYPASS

IPEAK_BYPASS is calculated to be 60A based on RBYPASS selected in Equation 36. TI suggest the designer to ensure that operating point (VBATT_MAX, IPEAK_BYPASS) for bypass path (Q3) is within the SOA curve for > t(LPM_SC) time.

Programming the Inrush Current, Rg and Cg Selection

Use following equation to calculate the IINRUSH:

Equation 40. IINRUSH= CLOAD× VBATT_MAXTcharge

IINRUSH calculated in Equation 40 should be always less than wakeup in short in low power mode (ILPM_SC) current which can be calculated using following equation:

Equation 41. ILPM_SC= 2 VRBYPASS

For 1Ω RBYPASS, ILPM_SC is calculated to be 2A which is less than IINRUSH.

Use following equation to calculate the required Cg based on IINRUSH calculated in Equation 40.

Equation 42. Cg = CLOAD × I(G)IINRUSH

Where, I(G) is 100µA (typical)

To set IINRUSH at 1.5A, Cg value is calculated to be ~50nF.

A series resistor Rg must be used in conjunction with Cg to limit the discharge current from Cg during turn-off .

The chosen value of Rg is 100Ω and Cg is 68nF.