SNVA991A October 2022 – October 2025 LM5123-Q1
- 1
- How to Design a Boost Converter Using LM5123
- Trademarks
- 1Design Example
-
2Calculations and Component Selection
- 2.1 Switching Frequency
- 2.2 Initial Inductor Calculation
- 2.3 Current Sense Resistor Selection
- 2.4 Inductor Selection
- 2.5 Output Capacitor Selection
- 2.6 Input Capacitor Selection
- 2.7 Feedback Resistor Selection
- 2.8 UVLO Resistor Selection
- 2.9 Soft-Start Capacitor Selection
- 2.10 Control Loop Compensation
- 2.11 MOSFET selection
- 3Implementation Results
- 4Small Signal Frequency Modeling
- 5Resources
- 6Revision History
4.1 Boost Regulator Modulator Modeling
Table 4-1 includes equations model the plant (control-to-output) of a peak current mode boost regulator in continuous conduction mode.
Figure 4-1 Modulator transfer functionTable 4-1 Power Plant Equations
| Simplified Formula | Comprehensive Formula | |
|---|---|---|
| Modulator Equations | ||
| Modulator Transfer Function | ||
| Modulator DC Gain | ((1)) | ((1))((3)) |
| RHP Zero | ||
| ESR Zero | ||
| Low Frequency Pole | ((3)) | |
| Sub-Harmonic Double Pole | Not Considered | |
| Quality Factor | Not Considered | |
| Slope Compensation | Not Considered | ((1)) |
| Sensed Rising Inductor Slope | Not Considered | ((2)) |
| Not Considered | ((2)) | |
| Not Considered | ((1))((2)) | |
| Not Considered | ((2))((3)) | |
(1) VSL is the peak voltage of the
internal slope compensation 45mV
(2) ACS is the gain of the current sense amplifier, 10 V/V.
(3) KD is approximately equal to 2. This estimation simplifies the equation while still providing accurate high frequency modeling