Transient Analysis

Last modified by Microchip on 2025/01/22 10:08

Solid, Stable Design - But Is It Optimized?

Solid, Stable Design - But Is It Optimized?

Back to our design example, configured for VFB ~ 100 mV. MPLAB® Mindi™ simulations on top, lab results on bottom. They correlate well.

  • SW node
  • Inductor current
  • Vout
  • VFB

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Transient response

Solid, Stable Design - But Is It Optimized? (cont.)

MPLAB Mindi simulations and lab results correlate well.

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Impact of Ripple Injection Resistor, RINJ

Impact of Ripple Injection Resistor

Let's re-examine the impact of Rinj on this design. Some Microchip datasheets define a Kdiv term and show the VFB equation with this term. It is equivalent to the equation we derived earlier.

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ΔVFB(p-p) vs. RINJ

ΔVFB (p-p) vs. RINJ

Transient response: MPLAB Mindi simulations and lab results correlate well, to a point.Rinj = 160k Ω → Simulations show stable operation with VFB=25 mV, while lab results are unstable. MPLAB Mindi plot highlights a nice aspect in simulation: multivariable simulations plotted together.

MPLAB Mindi:

  • Vout

  • VFB

  • Inductor current

Lab:

  • SW node

  • Inductor current

  • Vout

  • VFB 

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Load Transient Response vs. RINJ

Load Transient Response vs. RINJ

Transient response: MPLAB Mindi simulations and lab results correlate well, to a point. Rinj = 160k Ω → Simulations show stable operation with VFB = 25 mV, while lab results are unstable.

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Impact of Feed forward Capacitor, CFF

Impact of Feedforward Capacitor

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ΔVFB(p-p) vs. CFF

ΔVFB(p-p) vs. CFF

Transient response: MPLAB Mindi simulations & lab results correlate well, to a point. Cff = 15n, 22n → Simulations show stable operation with VFB= 34 mV, 21 mV while lab results are unstable.

MPLAB Mindi:

  • Vout
  • VFB
  • Inductor current

Lab:

  • SW node
  • VFB

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Summary of RINJ & CFF Impact

Summary of RINJ & CFF Impact

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Impact of Input Voltage Variation

Impact of Input Voltage Variation

ΔVFB(p-p) vs. Vin

ΔVFB(p-p) vs. Vin

ΔVFB(p-p) vs. Vin Cont

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