¶ Board Bring-Up Guide: Renesas CN274 Buck-Boost Last Gasp Power Supply
To guide customers through the board bring-up process after shipment
¶ ℹ️ Introduction
This document outlines the bring-up procedure for the Renesas CN274 evaluation board, designed as a buck-boost DC/DC converter optimized for last-gasp power delivery in energy metering applications. It guides engineers through setup, validation, and testing of critical components and interfaces.
¶ 💡 Key Specifications
- Board Model: CN274
- Controller IC: ISL85413 Buck-Boost Controller
- Input Voltage Range: 3.6 V to 27 V
- Output Voltage: 3.3 V typical (regulated)
- Output Current: Up to 2 A
- Efficiency: ~90%
- Key Components:
- ISL85413 Buck-Boost controller
- MLCCs for high-efficiency filtering
- Current-sense resistors and inductor
- Connectors:
- VIN and GND test points
- VOUT and GND test points
- ENABLE pin
- PG (Power Good) pin
¶ 📋 Pre-Build Preparations
¶ 3.1 Tools and Equipment
- DC Power Supply (up to 30 V, 2 A)
- Multimeter
- Oscilloscope (≥100 MHz recommended)
- Electronic Load (optional, for full-load testing)
- Thermal camera or infrared thermometer (optional for thermals)
¶ 3.2 Software Requirements
- No firmware is involved. Purely hardware analog/power management bring-up.
¶ ♾️ Functional Description
The CN274 board is a last-gasp energy storage and conversion circuit, meant to sustain critical operations during power failures in smart meters. The ISL85413 chip provides seamless buck-boost conversion to maintain output regulation during falling input voltage conditions.
¶ 📢 Lab Setup
- Place the board on an ESD-safe surface.
- Connect power supply leads to VIN and GND test points.
- Connect a load or monitoring circuit to the VOUT and GND test points.
- Use probes on the ENABLE and PG pins to monitor logic behavior.
¶ 🧩 Connecting the Evaluation Board
- Connect VIN to a programmable power supply. Start at 3.6 V and ramp to 27 V.
- Connect the oscilloscope to:
- VOUT for ripple analysis
- PG for monitoring regulation
- If desired, enable the board via the ENABLE pin (pull high to enable).
¶ 📙 Bring-Up Procedure
¶ 7.1 Power-On Verification
- Turn on VIN and verify that VOUT stabilizes around 3.3 V.
- Check PG output—should go high when output is in regulation.
- Use a multimeter to verify input/output voltages.
¶ 7.2 Load Testing
- Connect a resistive load or electronic load.
- Sweep the load from light (100 mA) to full load (2 A).
- Monitor for voltage droop, excessive heating, and stability.
¶ 7.3 Fault Condition Testing
- Test undervoltage lockout by lowering VIN below threshold (3.6 V).
- Observe VOUT cutoff and PG de-assertion.
- Check recovery when VIN is ramped up again.
¶ 7.4 Enable/Disable Behavior
- Toggle ENABLE pin and verify output response.
- Ensure clean transitions and no overshoot/undershoot.
¶ 8. Performance Tests
- Efficiency Measurement: Measure input/output power across different loads.
- Thermal Performance: Measure inductor and controller temperature at full load.
- Ripple & Noise: Capture output ripple with oscilloscope at full load.
- Transient Response: Step load from 0.5 A to 2 A and record recovery behavior.
¶ 🛠️ Troubleshooting
| Issue | Suggested Fixes |
|---|---|
| No output voltage | Check ENABLE pin status and VIN polarity. |
| PG pin remains low | Verify output is in regulation and no overload present. |
| Output voltage too low/high | Inspect feedback resistors and load condition. |
| Excessive ripple | Check output capacitor ESR and solder joints. |
¶ ⌛ Conclusion
The Renesas CN274 evaluation board successfully demonstrated stable operation of the ISL85413 buck-boost controller over the full input voltage range (3.6 V to 27 V), with regulated 3.3 V output under varying load conditions. Key functions such as PG (Power Good), ENABLE, and fault protections were validated. Thermal and ripple performance were within expected tolerances for energy metering applications.
No major issues were observed during bring-up. Minor recommendations include:
- Add optional bulk capacitance on VOUT if high transient loads are expected.
- Use low-ESR capacitors to minimize output ripple in final product integration.