SLOA326 October   2022 TAS2781

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Hybrid-Pro Boost Controller
  5. 3Hardware, Software, and Test Results
    1. 3.1 Hardware Connections
      1. 3.1.1 Schematic Connections
      2. 3.1.2 Equations
    2. 3.2 Software Settings
      1. 3.2.1 Steps To Enable Class-H Using PPC3
      2. 3.2.2 Class-H Configuration Settings
    3. 3.3 Hybrid-Pro Feature Performance Results
      1. 3.3.1 Class-H Operation
        1. 3.3.1.1 PWM Steps
        2. 3.3.1.2 Lookahead Time
        3. 3.3.1.3 Margin
        4. 3.3.1.4 Inflation Factor
      2. 3.3.2 Battery Life
      3. 3.3.3 Thermal Performance
  6. 4References

3.1.2 Equations

Equation 1 and Equation 2 are derived assuming RO = 0 and PWM_CTRL voltage = 0 V (for duty cycle of 0%) or IOVDD (for duty cycle of 100%):

Equation 1. V B S T M = V F B × 1 + R F B 1 2 × R F + R P U + R F B 1 R F B 2
Equation 2. V B S T m = V F B × 1 + R F B 1 2 × R F + R P U + R F B 1 R F B 2 - I O V D D × R F B 1 2 × R F + R P U

where

  • IOVDD = Supply voltage of the digital interface of TAS278x
  • VFB = FB voltage of the boost converter (from boost converter data sheet)
  • VBSTM = Maximum output voltage of boost for duty cycle= 0%
  • VBSTm = Minimum output voltage of boost for duty cycle = 100%
  • RPU = External pullup resistor on PWM_CTRL pin to interface supply of TAS278x

For push-pull configuration of the PWM_CTRL pin, Equation 1 and Equation 2 are derived assuming RPU = 0.

With IOVDD, VFB, VBSTM, VBSTm derived from system requirements and resistor RFB1 selected (10 kΩ to 1000 kΩ), resistors RFB2 and RF result from solving Equation 1 and Equation 2.

With RF calculated as previously shown, the cutoff frequency fC of the low-pass filter can be selected as a few decades lower than the PWM frequency. The capacitor CF in the low-pass filter can be calculated using
Equation 3:

Equation 3. C F ≥ 1 2 × π × f C + R F

On the TAS278x EVM, the TPS61089 boost FB pin is connected to the TAS278x PWM_CTRL pin by installing jumper J14. The FB voltage of the TPS61089 boost converter is 1.212 V and RFB1 is chosen as 330 kΩ. Resistors RFB2 and RF are calculated using Equation 1 and Equation 2 for 1.8-V IOVDD operation, such that minimum and maximum boost output voltages are 4.5 V and 12.6 V, respectively. This is the default setting on the TAS278x EVM.