SLVAF95 april   2023 TPS7H5001-SP

 

  1.   Abstract
  2.   Trademarks
  3.   Description
  4.   Features
  5.   Applications
  6. 1System Overview
    1. 1.1 Block Diagram
    2. 1.2 Design Considerations
    3. 1.3 System Design Theory
      1. 1.3.1 Switching Frequency
      2. 1.3.2 Transformer
      3. 1.3.3 RCD and Diode Clamp
      4. 1.3.4 Output Diode and MOSFET
      5. 1.3.5 Output Filter and Capacitance
      6. 1.3.6 Compensation
      7. 1.3.7 Controller Passives
  7. 2Test Results
    1. 2.1 Testing and Results
      1. 2.1.1 Test Setup
      2. 2.1.2 Test Results
        1. 2.1.2.1 Efficiency
        2. 2.1.2.2 Frequency Response
        3. 2.1.2.3 Thermal Characteristics
        4. 2.1.2.4 Output Voltage Ripple
        5. 2.1.2.5 Load Step
        6. 2.1.2.6 Start-Up
        7. 2.1.2.7 Shutdown
        8. 2.1.2.8 Component Stresses
  8. 3Design Files
    1. 3.1 Schematics
    2. 3.2 Bill of Materials
    3. 3.3 Assembly Drawings
  9. 4Related Documentation

1.3.7 Controller Passives

The sense resistor is used to sense the ripple current from the transformer as well as shutdown the switching cycle if the peak current of the converter is allowed to get too high. The voltage threshold of the CS pin is around 1 V and the gain of the current sense transformer is 100 due to the 1:100 turns ratio, thus the equation to find the sense resistor from the peak current is shown in Equation 39 and Equation 40.

Equation 39. R c s = V C S   T h r e s h o l d × G C S T r a n s f o r m e r I l i m i t
Equation 40. R c s = 1 V × 100 V 10 A = 10.0 Ω

Ilimit needs to be greater than IPriPeak.

The output voltage of the power converter is set by using a resister divider from the converter to the VSENSE pin. For a selected value of 10 kΩ, the value is found using Equation 41.

Equation 41. R b o t t o m =   V r e f   V o u t -   V r e f ×   R t o p = 0.613   V   5   V   -   0.613   V ×   10   k Ω =   1.37   k Ω

The TPS7H5001-SP allows programming of two independent dead times. This allows for the dead times to be optimized to prevent shoot-through between the primary and synchronous switches while attaining the best possible converter efficiency. Use Equation 42 to determine the values of and for a desired dead time.

Equation 42. R P S = R S P =   1.207   ×   D T - 8.858 = 1 . 207   ×   24   n s - 8.858 = 20.11   k Ω

Using a capacitor between the soft start (SS) pin and AVSS, the soft start of the device is programmed. Equation 43 shows the calculation of the SS capacitor:

Equation 43. C s s =   t s s   ×   I s s V r e f =   7   m s   ×   2.7   μ A 0.613   V =   30.8   n F

Leading edge blank time is utilized to remove any transient noise from the current-sensing loop after the primary switching outputs, OUTA or OUTB, go high. The leading-edge blank time was selected to be 100 ns. Equation 44 shows the calculation to program the LEB resistor for a chosen LEB time.

Equation 44. R L E B = 1.212   ×   L E B - 9.484 = 1 . 212   ×   50   n s - 9.484 =   51   k Ω