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We have below transimpedance amplifier, I have below issues, would like to know if this is even fixable or could be reduced:

  1. When a large load turn on in main power supply of TLE2426 turns on cause output to change.(I have Dedicated LDO before TLE2426)
  2. Due to 10uF feedback capacitor it take 20s to output recover to original state.

I would like to know how I can reduce spike or reduce spike duration without changing the 10uF, since if I reduce the capacitor the output will be noisy.

schematic

simulate this circuit – Schematic created using CircuitLab

Show spike due turning on the load enter image description here

Zoom in on of spikes showing how long it take to settle enter image description here

Layout

Please let me know if you need any other information. [u35:LTC1461, U7: TLE2426,U13: MCP6V01, U9: ADC] enter image description here

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  • \$\begingroup\$ What does your board layout and decoupling look like? \$\endgroup\$ – user1850479 Mar 4 at 18:17
  • \$\begingroup\$ @user1850479 I added the layout. I have decoupling capacitor on each device. \$\endgroup\$ – Shahreza Mar 4 at 18:39
  • \$\begingroup\$ How much current is the LTC1461 sourcing? C133 is an 0805 with a relatively large voltage across it, so its effective capacitance will be greatly reduced, although that may not matter if you are not pulling much current. The layout is also not ideal with the ferrite bead forcing decoupled current to flow in a larger loop. Quick thing to test: stick a 100uF electrolytic across C133 and see if the situation improves. \$\endgroup\$ – user1850479 Mar 4 at 19:02
  • \$\begingroup\$ Is this a 4 layer board (I see orange, red and blue so I think)? Do you have a power plane? The 4.096v line dipping ominously out of frame towards the load worries me, shouldn't that just connect to your power plane? \$\endgroup\$ – user1850479 Mar 4 at 19:04
  • \$\begingroup\$ @user1850479 The LTC1461 is only powering the VGND and Opamp which is less than 30mA. I have tried large capacitor but no lock, the voltage swing is on micro second and then it fix it self. The board is 4 layer dedicated ground and VGND plane, no plane for 4.096V. The most interesting is when I connect the external supply to earth ground cause the voltage to dip too. (External supply is AC DC convertor) please let me know if you need any thing else. \$\endgroup\$ – Shahreza Mar 4 at 20:12

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