Switching Power Supplies
Purpose
This dual switching power supplies convert wide-range input voltage to regulated 5V and 3.3V rails. The system achieves extreme efficiency for what it does, which is important for this device to be used as a battery monitor.
- VIN_2-60: 4.2V to 65V (recommended operating range)
- Absolute maximum: Up to 70V (stress rating)
- Typical operating voltage: 12V (automotive/industrial applications)
Output Rails
5V Rail Specifications
| Parameter |
Value |
| Output Voltage |
5.0V ±2% |
| Maximum Current |
1A |
| Input Range |
4.2V - 65V |
| Peak Efficiency |
94% @ 300-500mA |
| Full Load Efficiency |
92% @ 1A |
| Power Dissipation @ 1A |
0.43W |
3.3V Rail Specifications
| Parameter |
Value |
| Output Voltage |
3.3V ±2% |
| Maximum Current |
2A |
| Input Source |
5V rail |
| Peak Efficiency |
95.5% @ 500mA |
| Full Load Efficiency |
92% @ 2A |
| Power Dissipation @ 2A |
0.57W |
Main Components
5V Stage (LMR36510ADDA)
| Component |
Function |
| LMR36510ADDA |
Wide-input synchronous buck converter |
| L3 (SRP6540-220M) |
22µH switching inductor |
| R42/R48 |
Feedback network (10kΩ/24.9kΩ) |
| C55 (100nF) |
Bootstrap capacitor |
| C56-C58 |
Output filtering (22µF × 3) |
3.3V Stage (TLV62569DBV)
| Component |
Function |
| TLV62569DBV |
High-efficiency step-down converter |
| L1 (2.2µH) |
Switching inductor |
| R25 (100kΩ) |
Enable control resistor |
| C22/C23 |
Input filtering |
| C24 (22µF) |
Output filtering |
| Load Current |
Output Power |
Efficiency |
Power Loss |
| 1 mA |
5 mW |
80% |
1 mW |
| 10 mA |
50 mW |
89% |
6 mW |
| 100 mA |
0.5 W |
92% |
43 mW |
| 300 mA |
1.5 W |
94% |
96 mW |
| 500 mA |
2.5 W |
94% |
0.16 W |
| 1 A |
5.0 W |
92% |
0.43 W |
| Load Current |
Output Power |
Efficiency |
Power Loss |
| 1 mA |
3 mW |
90% |
0 mW |
| 10 mA |
33 mW |
94.5% |
2 mW |
| 100 mA |
0.33 W |
95% |
17 mW |
| 500 mA |
1.65 W |
95.5% |
78 mW |
| 1 A |
3.30 W |
95% |
0.17 W |
| 2 A |
6.60 W |
92% |
0.57 W |
Current Limitations
Maximum Continuous Current
| Rail |
Thermal Limit |
Safe Continuous |
Failure Point |
| 5V |
1A (datasheet) |
1A |
>1A (overcurrent protection) |
| 3.3V |
2A (datasheet) |
2A |
>2A (overcurrent protection) |
Practical Operating Limits
- 5V rail: Limited to 1A by LMR36510ADDA current capability
- 3.3V rail: Limited to 2A by TLV62569DBV current capability
- Combined power: 11.6W maximum (5W + 6.6W)
- Input current at 12V: ~1A maximum at full load
System Efficiency Analysis
Overall Efficiency (12V → 3.3V)
When both converters operate in series:
| 3.3V Load |
5V Stage |
3.3V Stage |
Overall |
| 100 mA |
92% |
95% |
87.4% |
| 500 mA |
94% |
95.5% |
89.8% |
| 1 A |
92% |
95% |
87.4% |
Power Budget at Maximum Load
- 3.3V rail: 6.6W @ 2A
- 5V rail power required: 7.17W (including 3.3V stage losses)
- 12V input power: 8.2W (including 5V stage losses)
- Total system efficiency: 80.5% at maximum 3.3V load
Control and Enable Logic
- 3.3V Enable: Controlled via 5V rail through R25 (100kΩ)
- Enable threshold: ~1.4V (typical for TLV62569)
- Soft-start: Integrated in both converters
- Shutdown current: <10µA when disabled
- High efficiency: >90% at typical operating loads
- Wide input range: Support 12V-48V automotive/industrial systems
- Clean regulation: <50mV ripple on both rails
- Fast transient response: <50µs settling time
- Low quiescent current: Minimize idle power consumption
Thermal Considerations
- 5V stage: 0.43W dissipation at 1A requires adequate copper area
- 3.3V stage: 0.57W dissipation at 2A may require thermal vias
- PCB design: 4-layer board recommended for thermal management
- Component spacing: Allow airflow around inductors and ICs
Notes
- Both converters include integrated synchronous rectification for high efficiency
- Output capacitor ESR affects stability and ripple performance
- Input filtering critical for EMI compliance
- Enable sequencing: 5V must be stable before 3.3V rail activates
Nominal Current Budget in our use case
| Component |
Active Mode |
Sleep Mode |
Rail |
| ESP32 (WiFi off) |
80 mA |
10 µA |
3.3V |
| ADS1115 ADC |
150 µA |
150 µA |
3.3V |
| INA228 Current Monitor |
1 mA |
1 mA |
3.3V |
| BMP390 Pressure Sensor |
3 µA |
3 µA |
3.3V |
| LM2907 Frequency Converter |
5 mA |
5 mA |
5V |
| Voltage Dividers |
20 mA |
20 mA |
Various |
| System Total |
106 mA |
26 mA |
Mixed |
Operating Point Efficiency
At typical load currents, the system operates in the high-efficiency region:
| Operating Mode |
Load Current |
5V Stage Efficiency |
3.3V Stage Efficiency |
Overall Efficiency |
| Active (ESP32 on) |
106 mA |
92% |
95% |
87.4% |
| Sleep (ESP32 off) |
26 mA |
90% |
95% |
85.5% |
Power Consumption Summary
| Mode |
3.3V Power |
5V Power |
12V Input Power |
Efficiency |
| Active |
350 mW |
25 mW |
430 mW |
87.4% |
| Sleep |
86 mW |
25 mW |
130 mW |
85.5% |
Design Margin
- Current headroom: 10-20× safety margin on both rails
- Thermal margin: Minimal power dissipation (<100mW total)
- Voltage regulation: Excellent for precision analog circuits
- EMI performance: Switching converters with integrated synchronous rectification
This load profile demonstrates optimal utilization of the switching supply's capabilities, operating in the peak efficiency region while maintaining substantial design margin for future expansion.