INA219 Current Measurement Audit
Task unable to complete.
2:13
Thought for 16 sec — Identifying necessary skills
Looking up PCB routing cleanup stale traces Q2 reverse polari....
Checking 5 design areas.
Reading schematic details for J1, F2, Q2 and 7 more.
Completed 5 design checks — found 39 issues.
Checking 5 design areas... (28 sec)
Reading layout details for Q2, F2, D3 and 5 more.
Thought for 10 sec
Work done
- Audited the scoped Q2 input-protection area and verified the corrected schematic connectivity.
- DRC still reports scoped layout problems: VIN_FUSED airwire between
F2:P2andQ2:D, VIN_PROTECTED airwires involvingQ2:S,D6:K, andR6:P2, plus stale/dangling trace remnants and an overlap atQ2:D. - Created the detailed status file: Q2 Input Protection Routing Remediation Status.
- ❌ Stale traces were identified but not removed in this run.
- ❌ The physical path is not yet fully routed as
J1 P1 -> F2 -> VIN_FUSED -> Q2 -> VIN_PROTECTED -> D3/C7/FB2 -> VIN_FILTERED. - ❌ DRC is not clean in the scoped area; airwires/dangling/overlap issues remain.
- ✅ The corrected schematic topology still supports reverse-polarity blocking, but the PCB must be cleaned/rerouted before fabrication.
Perform the physical trace cleanup/reroute in the PCB editor for the listed scoped items, then rerun DRC to confirm the Q2 input-protection area is clear.
Locate routing issues
Fix Q2 remnants
Route VIN_PROTECTED
Run targeted DRC
Refine this doc
Ask about this doc
LM2596 Buck Converter Stage Audit
Scope: Audit only. No project modifications were made.
Date: 2026-05-11
Verdict
FAIL — do not fabricate before layout and BOM corrections.
The schematic implements a recognizable LM2596 fixed-5V buck topology, but the physical PCB routing/placement is not acceptable for a switching regulator and the catch diode is under-rated and ambiguously documented. The highest-risk issues are D2 being a 1A SS14 while the LM2596 datasheet calls for a catch diode current rating at least 1.3× maximum load current, long/narrow switch-node and power-loop routing, input/output bulk capacitors far from U1, and no evident large thermal copper strategy for U1 GND_TAB.
Evidence Reviewed
- Schematic components/nets: U1, D2, L1, C1, C2, C3, C4.
- PCB placement/routing data around U1 and first-hop connected nets.
- DRC subset: airwires, dangling traces, overlapping copper, floating copper, trace corner radius, capacitor voltage rating, parts availability.
- Datasheet data for LM2596S-5.0/NOPB, SRR1260-680M, and SS14.
Schematic Connectivity
U1 LM2596S-5.0/NOPB
Pins:
Table
| U1 pin | Net | Assessment |
|---|---|---|
| VIN | VIN_FILTERED | Correct functional input net after protection/filter stage. |
| OUTPUT | BUCK_SW | Correct switch-node net. |
| GROUND | GND | Correct. |
| FEEDBACK | 5V | Correct for fixed 5V part: feedback senses regulated output. |
~ON~/OFF | GND | Correct for always-on operation. LM2596 datasheet says pulling ON/OFF below about 1.3V turns the regulator on, and tying it to ground or leaving it open keeps it ON. |
| GND_TAB | GND | Correct net assignment, but layout thermal copper is a concern. |
Buck power path in schematic
- Input:
VIN_FILTERED-> U1 VIN, C1 pin 1, C3 pin 1, FB2 pin 2. - Switch node: U1 OUTPUT -> D2 cathode -> L1 pin 1 on
BUCK_SW. - Catch diode: D2 anode ->
GND; D2 cathode ->BUCK_SW. - Output: L1 pin 2 ->
5V; C2 pin 1 ->5V; C4 pin 1 ->5V; U1 FEEDBACK ->5V. - Grounds: C1 pin 2, C2 pin 2, C3 pin 2, C4 pin 2, D2 anode, U1 GROUND, U1 GND_TAB, and U1 ON/OFF are on
GND.
Requested Checks
1. D2 role: catch diode vs back-power protection diode
FAIL.
In the schematic, D2 is electrically the LM2596 catch/freewheel diode because it connects from
BUCK_SW to GND with cathode at BUCK_SW and anode at GND.However, D2 properties say:
Role Details: Prevents harmful back-power interaction between rails while allowing simple prototype power OR-ing
That description is not the LM2596 catch-diode role and conflicts with the actual schematic function. D2’s BOM/documentation must be corrected so it is not described as a back-power protection / OR-ing diode.
Required documentation correction: D2 should be described as the LM2596 catch/freewheel Schottky diode from switch node to ground.
2. D2 polarity for LM2596 catch diode
PASS for polarity.
D2 is connected:
- Cathode ->
BUCK_SW/ U1 OUTPUT / L1 pin 1 - Anode ->
GND
That is the correct polarity for a non-synchronous buck catch diode: it conducts when the switch node swings below ground during the off interval.
3. L1 value and current rating
PARTIAL / LIKELY FAIL for full 3A LM2596 use.
L1 is Bourns
SRR1260-680M:- Inductance: 68uH
- Tolerance: ±20%
- DCR max: 110mΩ
- Irms max: 2.10A
- Isat typ: 2.10A
The LM2596 datasheet quick-selection table supports 68uH for some 5V cases, especially lower current / high input combinations such as 5V, 2A, 20V–40V max input. But this inductor is not suitable for using the LM2596 as a 3A converter, because both Irms and Isat are 2.10A.
Assessment: acceptable only if the board’s 5V load is intentionally limited below the inductor’s thermal and saturation limits with margin. If this design expects relay + ESP32 only, it may be electrically adequate after load-current validation, but it should not be documented as a 3A-capable LM2596 stage.
4. C1/C2 voltage rating and ESR suitability
C1 input bulk: FAIL for 24V nominal input margin.
C1 is
RZW101M1VBK-0811, 100uF, 35V. The LM2596 datasheet states aluminum electrolytic input capacitor voltage rating should be approximately 1.5× maximum input voltage. For a 24V nominal system, that gives 36V minimum before considering automotive/industrial surges or adapter tolerance. Therefore 35V is below the datasheet derating guidance for a 24V nominal input.Also, C1 is only 100uF while the LM2596 datasheet typical fixed-output example uses 470uF/50V, and the input capacitor RMS ripple current must be checked against approximately 1/2 of DC load current. The C1 datasheet ripple/ESR data was not available from the parsed source, so ESR/ripple suitability remains ambiguous.
C2 output bulk: PARTIAL.
C2 is also 100uF, 35V. Voltage rating is more than adequate for 5V output. Capacitance is within the LM2596 datasheet’s broad output capacitor range of low-ESR electrolytics between 82uF and 820uF, but the datasheet emphasizes ESR as the key stability parameter. Since the C2 ESR/ripple data was not available from the parsed source, output stability/ripple suitability is not fully verified.
Required before fabrication: confirm C1/C2 ESR and ripple current from the exact capacitor datasheet, or use capacitor series explicitly recommended/validated for LM2596 switching service.
5. C3/C4 100nF placement and voltage rating
FAIL / AMBIGUOUS.
C3 and C4 are generic 100nF capacitors and have no voltage rating property recorded.
Placement:
- C3 center: approximately (-7.19mm, -26.94mm)
- U1 center: approximately (-9.02mm, 4.82mm)
- Approximate center-to-center distance: about 31.8mm
C3 is therefore not physically close to U1 VIN/GND, despite being documented as high-frequency VIN bypass near the LM2596.
- C4 center: approximately (-34.90mm, -9.62mm)
- U1 center: approximately (-9.02mm, 4.82mm)
- Approximate center-to-center distance: about 29.6mm
C4 is also far from U1 and appears near the diode/output area rather than tightly across the output capacitor/load return loop.
Required before fabrication: add/relocate high-frequency bypassing so the VIN-to-GND loop is tight at U1 VIN/GND, and ensure C3/C4 have explicit voltage ratings. For a VIN-side 100nF capacitor on a 12V–24V input, use a voltage rating appropriate for the protected VIN rail, not a generic/unrated part.
6. U1 thermal copper area and GND_TAB connection
NET PASS, LAYOUT FAIL / NOT VERIFIED SUFFICIENT.
U1 GND_TAB is connected to
GND, which is correct. But the layout data shows the U1 GND_TAB pad with no evident large dedicated copper heat-spreading area or via stitching details in the inspected data.The LM2596S TO-263 datasheet states the tab is intended to be soldered to PCB copper, with at least 0.4in² copper and ideally two or more square inches of 2oz copper for good thermal behavior. The current inspected layout does not demonstrate that level of thermal copper.
Required before fabrication: provide a large GND copper pour/heat spreader tied to U1 GND_TAB, with thermal vias to inner/bottom GND copper if using the 4-layer board.
7. Switch-node copper length and area
FAIL.
The switch node
BUCK_SW is routed as a long trace:- U1 OUTPUT around (-15.42mm, 6.52mm)
- Routed through approximately (-20.18mm, 6.52mm), (-23.76mm, 10.10mm), (-35.56mm, 10.10mm), down near (-36.90mm, -5.23mm), and to D2/L1 pads.
- D2 is at approximately (-34.85mm, -5.34mm).
- L1 is at approximately (-30.75mm, 5.51mm).
This is a large switch-node geometry for a 150kHz buck regulator. The LM2596 datasheet explicitly says the OUTPUT/switch-node copper area must be kept to a minimum to reduce coupling to sensitive circuitry.
Required before fabrication: place D2 and L1 adjacent to U1 OUTPUT so the switch-node copper is short and compact.
8. Loop area: U1 switch pin -> D2 -> GND -> U1 GND
FAIL.
D2 is far from U1, and the
BUCK_SW trace from U1 OUTPUT to D2 cathode is long. The GND return path from D2 anode back to U1 GROUND/GND_TAB is not shown as a tight local loop in the inspected routing. This violates the LM2596 layout requirement to keep high di/dt loop traces wide and short.Required before fabrication: move D2 next to U1 OUTPUT and U1 GND/GND_TAB; route cathode directly to U1 OUTPUT and anode directly into the local U1 ground/thermal copper.
9. Loop area: U1 switch pin -> L1 -> COUT -> GND -> U1 GND
FAIL.
L1 and C2 are not placed/routed as a tight output power loop:
- U1 center: (-9.02mm, 4.82mm)
- L1 center: (-30.75mm, 5.51mm)
- C2 center: (-34.36mm, -16.08mm)
The output path is physically spread over roughly 20–30mm scale distances. C2 is not close to L1/U1 ground return. This increases output ripple, EMI, and transient impedance.
Required before fabrication: move L1 and C2 close to U1, with C2 ground returning directly to the same low-impedance ground region as U1 GND_TAB and D2 anode.
10. Relay switching / ESP32 Wi-Fi current pulse droop/reset risk
FAIL / HIGH RISK without layout changes and load validation.
Schematic connectivity alone does not prove droop/reset immunity. Current design risks:
- Long/narrow 5V output routing and distributed output capacitor placement.
- C2 is only 100uF and ESR/ripple specs are not verified.
- L1 is limited to about 2.10A Irms/Isat typical, not a full 3A LM2596 inductor.
- ESP32 Wi-Fi bursts can create fast load transients on 5V/3.3V rails; relay coil switching creates supply disturbance and ground bounce risk.
- If the LM2596 layout stays spread out, transient response and EMI will be worse, increasing reset risk.
Recommendation: after layout correction, validate with bench testing under relay switching while ESP32 Wi-Fi transmits; monitor 5V and 3.3V rails at the ESP32 module with an oscilloscope.
DRC / Layout Check Results
The selected review checks reported 4 dangling trace warnings:
- Trace 1855
- Trace 45f1
- Trace 4f4c
- Trace 8aa5
No airwire errors were returned in the selected review subset, but dangling traces must be resolved before routing signoff because they may indicate stale copper or unintended antennas/stubs.
Exact Buck Converter Paths
VIN path to U1
Protected/filtered input path into the buck:
VIN_PROTECTED -> FB2 -> VIN_FILTERED -> U1 VINOn
VIN_FILTERED:FB2:2, C1:1, C3:P1, U1:VINSwitch path
U1:OUTPUT -> BUCK_SW -> D2:Cathode and L1:1Catch diode path
BUCK_SW -> D2:Cathode -> D2 -> D2:Anode -> GNDOutput path
L1:2 -> 5V -> C2:1, C4:P1, U1:FEEDBACK, U2:EXT_5V, RSHUNT:P1, U6:IN+, D1:cathodeOutput return path
C2:2 / C4:P2 / load grounds -> GND -> U1 GROUND and U1 GND_TABMissing or Ambiguous Values / Ratings
Table
| Component | Issue |
|---|---|
| D2 SS14 | Electrically used as catch diode, but documented as back-power/OR-ing diode. Rated 1A, 40V; under-rated for LM2596 full-current catch-diode service. |
| L1 SRR1260-680M | 68uH is plausible for reduced-current conditions, but Irms/Isat are 2.10A, below full LM2596 3A capability. |
| C1 RZW101M1VBK-0811 | 100uF 35V input bulk; 35V is below LM2596 datasheet 1.5× guidance for 24V nominal input. ESR/ripple not verified from parsed datasheet. |
| C2 RZW101M1VBK-0811 | 100uF 35V output bulk; voltage OK for 5V, ESR/ripple not verified. |
| C3 generic 100nF | No voltage rating property; placed too far from U1 VIN/GND. |
| C4 generic 100nF | No voltage rating property; placed far from U1/output loop. |
| U1 thermal copper | GND_TAB net is correct, but sufficient thermal copper/via strategy not verified. |
Critical Layout Changes Required Before Fabrication
- Re-place U1, D2, L1, C1/CIN, C2/COUT, and C3/C4 as a compact buck cluster.
- Move D2 directly next to U1 OUTPUT and U1 GND/GND_TAB. Keep
U1 OUTPUT -> D2 cathode -> D2 anode -> U1 GNDloop extremely short. - Move L1 adjacent to U1 OUTPUT and 5V output node. Minimize
BUCK_SWcopper area. - Move C1/CIN close to U1 VIN and U1 GND. Current placement is far away and routed with narrow/long traces.
- Move C2/COUT close to L1 output and U1 GND return. Use wide copper for L1-to-COUT and COUT-to-GND return.
- Create a large GND copper heat spreader for U1 GND_TAB. Add thermal vias to internal/bottom GND copper.
- Increase widths for VIN, BUCK_SW, diode current path, inductor current path, 5V output, and GND returns. Current inspected routes include 0.254mm/0.3mm segments in power paths, which are not appropriate as the main buck current paths.
- Correct D2 BOM/role description. It must be documented as the LM2596 catch diode, not as back-power protection.
- Replace or re-rate D2 if the 5V rail can exceed roughly 0.77A load. For a full LM2596-capable design, use a Schottky diode meeting the datasheet current requirement and reverse voltage margin.
- Resolve dangling traces before signoff.
D2 BOM Description Requirement
Yes — D2 BOM description must be corrected.
D2 is the LM2596 buck catch/freewheel diode in the actual schematic. Its present role details describe back-power protection / OR-ing, which is incorrect and will confuse assembly/debug/review. Additionally, the selected SS14 is not an acceptable full-current LM2596 catch diode because the SS14 average rectified current is 1A while the LM2596 datasheet recommends catch diode current rating at least 1.3× maximum load current.
Final PASS/FAIL
FAIL.
The schematic buck topology is mostly correct, but the implementation is not fabrication-ready because of:
- D2 role documentation conflict.
- D2 current rating too low for full LM2596 catch-diode service.
- C1 input capacitor voltage rating below LM2596 1.5× guidance for 24V nominal input.
- Missing/ambiguous ESR/ripple data for C1/C2.
- Missing voltage ratings for generic C3/C4.
- Poor physical placement and routing for buck high-current/high-di/dt loops.
- Long switch-node copper.
- Insufficiently verified U1 thermal copper.
- Dangling traces reported by DRC.
Verdict
Evidence Reviewed
Schematic Connectivity
U1 LM2596S-5.0/NOPB
Buck power path in schematic
Requested Checks
1. D2 role: catch diode vs back-power protection diode
2. D2 polarity for LM2596 catch diode
3. L1 value and current rating
4. C1/C2 voltage rating and ESR suitability
5. C3/C4 100nF placement and voltage rating
6. U1 thermal copper area and GND_TAB connection
7. Switch-node copper length and area
8. Loop area: U1 switch pin -> D2 -> GND -> U1 GND
9. Loop area: U1 switch pin -> L1 -> COUT -> GND -> U1 GND
10. Relay switching / ESP32 Wi-Fi current pulse droop/reset risk
DRC / Layout Check Results
Exact Buck Converter Paths
VIN path to U1
Switch path
Catch diode path
Output path
Output return path
Missing or Ambiguous Values / Ratings
Critical Layout Changes Required Before Fabrication
D2 BOM Description Requirement
Final PASS/FAIL
