Transient Analysis
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
Transient response
MPLAB Mindi simulations and lab results correlate well.
Impact of Ripple Injection Resistor, RINJ
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.
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
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.
Impact of Feed forward Capacitor, 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