Push Button Controller Issue with LTC2950-1  - Page 1
Forum section: electronics / projects

author: madhu.wesly01
author_rank: Regular Contributor
timestamp: March 25, 2025, 12:45:07 pm
content: Hi,I'm working on a new application using nPM1100 PMIC for power management and LTC2950-1 as a push-button controller to try to implement device ON-OFF and SOS functionality using single Tactile/Push Button Switch.However, the push-button circuit is not working as expected. The board gets hot, and the VSYS voltage drops to around 1V when connected to a 5V USB supply. When I removed the push-button circuit block, everything works fine.I'm sharing the implemented circuit and the reference schematics I followed. Could anyone help debug the issue?Additionally, I'm looking for a better alternative to LTC2950-1 for my application to achieve Device Power ON-OFF and SOS functionality.Thanks in advance.

author: thm_w
author_rank: Super Contributor
timestamp: March 25, 2025, 11:31:51 pm
content: What if you remove R8 and R9 to try to isolate the IC?Are you sure the board does not get hot if EN_DCDC line is pulled high with LTC2950 removed?Sounds like either a problem with the design of the rest of the board, or soldering issue with this IC.

author: temperance
author_rank: Super Contributor
timestamp: March 26, 2025, 01:34:04 am
content: DFN or SOT package?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 26, 2025, 01:49:19 am
content: Hi,The reason temperance is asking DFN or SOT:The pin numbers are different for the two packages.Regards,Jay_Diddy_B

author: madhu.wesly01
author_rank: Regular Contributor
timestamp: March 26, 2025, 05:10:56 am
content: Hi,Thank you for your insights.Regarding your queries:> What if you remove R8 and R9 to try to isolate the IC?> Sounds like either a problem with the design of the rest of the board, or soldering issue with this IC.I have tested three initial boards, and all exhibit the same issue. Below are the debugging steps I have performed so far:- Soldering and Shorts Check – Verified for any shorts on the board; no issues found.- Resistance Values – Measured all resistor values; the 200K pull-up resistors were showing 200 ohms when no power supply was connected. I removed them and retested, but the VSYS supply drop persisted, and there was no 3.3V or 1.8V output.- Isolation Test (R8 & R9) – Removed R8 and R9 to isolate the circuit from the nRF MCU and retested, but the issue remained.I will revalidate these steps along with your suggested debugging ideas.> Are you sure the board does not get hot if EN_DCDC line is pulled high with LTC2950 removed?Based on the current hardware implementation, EN_DCDC is not pulled high externally. I will test this by enabling the pull-up in software and verify the behavior.> DFN or SOT package?I am using the DFN package.Additionally, I have concerns regarding the circuit correctness:1. Using the Same VSYS for Input and Pull-ups: In a recent reference design, I noticed the use of two different supplies. Would this impact performance?2. Pull-Up on PB Pin: The LTC2950 datasheet suggests adding a pull-up resistor on the PB pin, which differs from my implementation. Could this be a potential issue?Looking forward to your thoughts.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: March 26, 2025, 01:10:34 pm
content: Good Morning Madhu.wesly01, Is your push-button switch N.O. or N.C.

author: madhu.wesly01
author_rank: Regular Contributor
timestamp: March 26, 2025, 01:16:26 pm
content: Hi,It is a Normally Open (N.O.) switch. Part Number: B3U-1100P

author: xvr
author_rank: Frequent Contributor
timestamp: March 26, 2025, 01:59:38 pm
content: QuotePin numbers is your original schematics are for SOT package. If PCB was made from original schematic it will not work with DFN package