SBVA102 august   2023 TPS56837

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2D-CAP3 Control Architecture
    1. 2.1 Adaptive On-Time Control
    2. 2.2 D-CAP3 Control
  6. 3Large Duty Cycle Operation
    1. 3.1 Min Off-Time Performance of Buck Converters
    2. 3.2 On-Time Extension Function
  7. 4Bench Test and Comparison
    1. 4.1 Comparison Between TPS56837 and TPS56637
    2. 4.2 Comparison of On-Time Extension between TPS56837 and TPS568230
    3. 4.3 Load Transient Improvement by On-Time Extension
  8. 5Summary
  9. 6References
  10. 7Also From TI

2.1 Adaptive On-Time Control

Adaptive on-time control is a non-linear control architecture for buck regulators. At the beginning of each switching cycle, the high-side MOSFET is turned on. This MOSFET is turned off after an internal one shot timer expires. The ON time duration is set proportional to the output voltage, VOUT, and inversely proportional to the converter input voltage, VIN, to maintain a pseudo-fixed frequency over the input voltage operating range. The ON timer is reset and the high-side MOSFET is turned on again when the feedback voltage falls below the reference voltage.

GUID-20230822-SS0I-0FCD-J18V-KCWVJW7J52GK-low.svgFigure 2-1 Adaptive On-Time Control (AOT Control)

In ACOT control, the pseudo-fixed frequency is designed with the calculations in Equation 1 and Equation 2.

Equation 1. GUID-A7488443-D5FF-4FC1-BD72-7BDEF6F067AA-low.gif
Equation 2. GUID-F927D24C-D949-420F-8017-783DDB144E7C-low.gif

Based on Equation 1, if TON is adjusted with VOUT and VIN, the switching frequency FSW will be constant. For the TPS56837 device, the switching frequency FSW, is selectable at 500 kHz, 800 kHz , or 1.2 MHz.