Tool/software:
Hi team,
This is a follow up of previous post LM5088MH-2EVAL: LM5088-2 Based DC-DC Buck Converter stuck in Hiccup mode with no load condition - Power management forum - Power management - TI E2E support forums. issue.
I’m encountering persistent problems related to output voltage fluctuations, load transients, and unexpected shutdowns.
To summarize System Specifications:
- Vin = 36V
- Vout = 32V (±1V)
- Iout = 1.3A
- Fsw = 250KHz
- Cin, Cout = 390uF (Al-Electrolytic) + 22uF (Al-Electrolytic) + 10uF,0.47uF (ceramic x2)
- L = 47uH
I’ve attached the latest modified schematic with test setup images for reference.
Latest 36V Sch.zipTest Setup.zip
Observed Issues & Troubleshooting Attempts:
- Continuous Voltage Swing (~143Hz) with 3V-6V Fluctuation
-
This fluctuation persists until the device is turned off completely (Power Cycling)
- Occurs when:
- The load relay is switched ON.
- Sometimes randomly when the device is powered ON.
-
Troubleshooting so far:
- Changed current sense resistor to 10mΩ → No improvement.
- Removed bulk 390uF capacitor and TVS diode → No improvement.
- Increased boot capacitor from 62nF to 109nF → No improvement
-
- Large Voltage Dip (~11.2V for 240µs) During Load Transient
- Momentary Shutdown (0V) When Load is Disconnected
- When the relay disconnects the load, the output voltage drops to 0V before recovering.
- Initially, the device recovered after 2 seconds.
- After reducing hiccup capacitor (Cres) from 2.2uF to 0.1uF, the device now recovers in ~100ms, but the momentary 0V shutdown still persists.
- Additional attempts:
- Reduced soft-start capacitor from 33nF to 10nF → No improvement.
- Swapped relay to rule out mechanical issues → No improvement.
Additional Observations:
- Other LM5088-based converters (16V & 28V of same design) work fine in the same test setup.
- To rule out test setup issues, we tested using a lab bench power supply (for 32V), and the setup worked fine.
- The issue occurs only when using the LM5088-based 32V converter.
I would appreciate any insights or suggestions on Current Condition of these Issues:
- Load Transient issue, too much voltage dip need to minimize
- Scope Images Atached2.Load Transient.zip
- How to prevent Momentary device shutdown (0V) when load is disconnected,
- How to eliminate Random Hiccups when power cycling (10V swings at output with ~143Hz rate)
- scope Images Atached1. Continios Voltage Swing at 143Hz.zip
Kindly let me know any suggestions, to improve these issues.
Thank you in Advance!!