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USB-C / Thunderbolt

ANX7411

The ANX7411 is a USB-C DisplayPort Alt Mode multiplexer and signal redriver found on Apple logic boards that support USB-C video output and external display connectivity. It manages lane switching between USB 3.1 data paths and DisplayPort Alt Mode video lanes, while simultaneously amplifying weak high-speed signals to maintain signal integrity across the USB-C connector and external cable runs. In diagnostics, ANX7411 failures present as missing or degraded video output over USB-C despite successful data enumeration, or intermittent display dropout—making it critical to isolate from SMC power sequencing and USB controller issues.

Role on the Board

The ANX7411 operates as a transparent multiplexer and active redriver in the USB-C signal path. It receives differential RX and TX pairs from the main PS5169 (USB 3.1 hub) and host SoC, then switches between two operational modes:

The ANX7411 is powered by PP3V3 (core logic) and PP5V (output drivers). Mode selection is controlled via I²C commands from the SMC or embedded controller. The IC remains active whenever USB-C device is connected, even in low-power states, to monitor for Alt Mode plug/unplug events. This IC is found on boards with Thunderbolt 3 / USB 4 support and external video capability.

Key Signals & Pins

Pin / Net Name Direction Description Typical Value
DP_RX1_P / DP_RX1_N Input (differential) DisplayPort RX lane 1 from host SoC; high-speed pair routed directly from SoC via length-matched traces. AC coupled, ~400 mV p-p eye diagram at 8.1 Gbps
DP_TX1_P / DP_TX1_N Output (differential) DisplayPort TX lane 1 to USB-C connector; redriven signal with boosted amplitude and equalization. AC coupled, ~600–800 mV p-p after redriver gain
DP_RX2_P / DP_RX2_N Input (differential) DisplayPort RX lane 2; second receive pair for 4-lane DP configurations. AC coupled, ~400 mV p-p eye diagram
DP_TX2_P / DP_TX2_N Output (differential) DisplayPort TX lane 2; redriven to USB-C port. AC coupled, ~600–800 mV p-p after redriver
MUX_SEL Input (GPIO) Mode select signal from SMC; controls USB 3.1 vs. DisplayPort Alt Mode routing. 0 V = USB 3.1 mode, 3.3 V = DP Alt Mode
PP3V3 Power input Core logic and I²C termination supply; derived from PPBUS_G3H via local LDO or regulator. 3.25–3.45 V DC, <10 mA quiescent
PP5V Power input Output driver supply; powers redriver amplifiers and output stages. 4.75–5.5 V DC, <50 mA typical under DP traffic
I2C_SDA / I2C_SCL Bi-directional I²C bus for register access; SMC writes mode, gain, and equalization settings during boot and Alt Mode negotiation. 3.3 V open-drain, 100 kHz clock
INT_N Output (open-drain) Interrupt flag for cable fault, ESD event, or thermal shutdown; optionally monitored by SMC. Pulled high to 3.3 V via 10 kΩ resistor; asserts low on fault

Measurement Reference

Test Point / Net Expected (Meter) Expected (Oscilloscope) Notes
PP3V3_USB (near ANX7411 pin 1) 3.25–3.45 V DC ±50 mV AC ripple, <100 kHz noise floor If <3.2 V, suspect LDO dropout or upstream PPBUS_G3H loss. If oscillating, reflow or reballing likely needed.
PP5V (ANX7411 pin 2 or nearby) 4.75–5.5 V DC ±100 mV AC ripple, stable under DP Alt Mode load Sag below 4.75 V during Alt Mode indicates weak source or fault in ANX7411 output stage. Measure DC under video traffic for load-line verification.
DP_TX1_P (to USB-C CC pin) ~0 V DC (AC coupled) 600–800 mV p-p differential eye at 8.1 Gbps DP 1.4 rate; clean zero-crossings; <−3 dB peaking Measure AC directly at ANX7411 output pad. If <400 mV p-p, suspect redriver disable or ESD damage. Use 13 GHz passive probe, 1:1 coupling. Compare TX1 and TX2 symmetry.
MUX_SEL (GPIO input) 0 V (USB 3.1) or 3.3 V (DP Alt Mode) Digital logic level; transitions clean within 1 µs of Alt Mode entry Verify transition timing via SMC I²C log. If stuck at mid-rail (~1.6 V), check SMC GPIO driver or ANX7411 pin integrity. Use logic analyzer if available.
I2C_SDA (ANX7411 address 0x54) 3.3 V DC (at rest) Clock: 100 kHz square wave, duty cycle 40/60; data transitions synchronized to clock edges Probe at ANX7411 pin, not at SMC. Confirm ACK from ANX7411 (SDA pulled low during clock low). If no I²C traffic, suspect SMC firmware issue or ANX7411 I²C interface failure. Use bus analyzer if clock is present but no data transactions.
INT_N (interrupt flag) 3.3 V DC (idle) or 0 V (asserted) Runt pulses <100 ns may indicate intermittent fault; stable low state >100 ms suggests thermal shutdown or persistent ESD latch. Monitor during USB-C plug/unplug and DP Alt Mode entry. If INT_N asserts and latches, force SMC reset via power cycle. Repeated assertions point to redriver over-temperature or signal integrity collapse.

Common Failure Modes

  1. No DisplayPort over USB-C despite successful USB 3.1 enumeration
    Symptom: USB data works; external display not detected; USB-C AltMode negotiation hangs or fails.
    Likely cause: ANX7411 not switching to DP mode due to I²C communication failure, MUX_SEL GPIO stuck, or redriver output disabled by ESD latch.
    Diagnostic step: Confirm I²C clock and data presence at ANX7411 during AltMode entry (use bus analyzer or oscilloscope on SDA/SCL). Verify MUX_SEL transitions to 3.3 V. Measure DP_TX1/TX2 AC amplitude; if 0 mV p-p, IC is likely in ESD protect mode—force power cycle and retest.
  2. Video flicker or dropout under USB-C video output; USB data remains stable
    Symptom: DP Alt Mode connects intermittently; display flashes or goes black for 100–500 ms, then returns; no HDCP or audio over USB-C.
    Likely cause: ANX7411 redriver gain or equalization settings corrupted; weak PP5V supply causing output stage dropout; or high-speed trace impedance mismatch causing reflections that trigger ANX7411 ESD/thermal shutdown.
    Diagnostic step: Scope DP_TX lanes for eye closure, rising/falling edge jitter >100 ps, or asymmetric differential swing. Measure PP5V sag during DP traffic. Check I²C register reads via SMC diagnostic tool (if available); verify gain and equalization values match design spec. If INT_N pulses intermittently, overtemp is likely—inspect for nearby power losses or IC rework damage.
  3. ANX7411 appears dead; no I²C acknowledgment, INT_N stuck low
    Symptom: I²C address 0x54 does not respond; INT_N held at 0 V continuously; USB-C port may not enumerate at all if ANX7411 reset is gated with USB hub.
    Likely cause: ANX7411 internal ESD latch triggered by cable insertion surge; loss of PP3V3 or PP5V supply; or SMC not asserting ANX7411 reset (if applicable).
    Diagnostic step: Verify PP3V3 and PP5V are both present and stable. Attempt SMC reset via power cycle (disconnect battery, hold power button 10 s, reconnect). Probe ANX7411 GND pad to confirm 0 V reference. If I²C still unresponsive after reset, attempt reballing or microsoldering inspection for solder bridge on I²C pins; alternatively, check if ANX7411 is in a hard shutdown mode (datasheet Section 2.5 Thermal Shutdown Register).
  4. DP Alt Mode works, but only at lower lane counts (e.g., 2 lanes instead of 4); bandwidth-dependent apps fail
    Symptom: USB-C monitor connects at HBR2 (2 lanes, 17.28 Gbps) instead of HBR3 (4 lanes, 32.4 Gbps); Thunderbolt dock negotiates to lower speed tier.
    Likely cause: ANX7411 TX3/TX4 differential pair degraded by ESD, reflow crack, or high-speed trace impedance discontinuity; or redriver gain insufficient for lane 3/4 due to aging or manufacturing defect.
    Diagnostic step: Scope all four DP TX pairs (TX1–TX4) side-by-side; compare eye diagrams and amplitude. TX3/TX4 should match TX1/TX2 within 50 mV. If TX3/TX4 are significantly attenuated, probe the ANX7411 RX3/RX4 inputs from SoC to rule out upstream attenuation. Measure ANX7411 temperature under sustained DP traffic (thermal camera if available); high temp + low-lane mode points to redriver clipping output due to over-temperature.
  5. ANX7411 draws excessive quiescent current; battery drains rapidly in idle with USB-C connected
    Symptom: Overnight idle current >200 mA despite S5 state; PP3V3_USB and PP5V rails do not power-gate when USB-C device removed.
    Likely cause: ANX7411 output driver stage stuck in active mode; missing firmware command to gate redriver; or ANX7411 internal LDO regulator leaking to GND.
    Diagnostic step: Measure ANX7411 quiescent current by placing ammeter in series with PP5V supply to ANX7411. Nominal is <10 mA; >50 mA is abnormal. Verify via I²C that redriver is commanded to low-power mode when USB-C is idle. If current remains high despite shutdown command, suspect ANX7411 analog section failure (leaking bias network or shorted output stage)—thermal imaging may show hot spot on ANX7411 die. Board replacement is typically more cost-effective than IC rework.
  6. ESD event during USB-C hot-swap; ANX7411 latches and stops responding until power cycle
    Symptom: User unplugs USB-C cable with external monitor powered on (hot-disconnect); system detects ANX7411 fault via INT_N assertion; USB 3.1 enumeration fails; INT_N remains asserted for >5 s.
    Likely cause: ESD transient on USB-C TX/RX pairs exceeds ANX7411 clamping threshold (typically 6–8 kV); internal protection diodes or latch-up mechanism activated; firmware not executing ANX7411 reset sequence.
    Diagnostic step: Check INT_N assertion timing relative to USB-C removal (use oscilloscope trigger on CC pin or USB insertion detection). If INT_N asserts cleanly and releases within 100 ms on SMC-commanded reset, IC is functional but firmware may need tuning. If INT_N remains latched, ANX7411 ESD protection structure may be permanently damaged; reballing is required. For prevention, verify USB-C connector shell ground continuity and review external EMI shielding design with hardware team.

Boards Using This IC

Diagnostic Workflow

  1. Verify USB 3.1 enumeration. Connect USB-C hub or dock and confirm USB data ports (keyboard, mouse, storage) are recognized. This isolates the issue to video-specific circuitry. If USB 3.1 also fails, suspect PS5169 instead.
  2. Check power rails. Measure PP3V3 and PP5V at ANX7411 power pins with multimeter. Both must be within spec (3.25–3.45 V and 4.75–5.5 V respectively). If either rail is absent, trace upstream to regulator or SMC power sequencing.
  3. Probe I²C bus. Place oscilloscope on I²C_SDA and I²C_SCL near ANX7411. Command Alt Mode entry via system (e.g., macOS USB-C video output control panel). Observe clock and data transitions. Confirm ANX7411 acknowledges its address (0x54) by pulling SDA low during ACK phase. If no I²C activity, suspect SMC firmware or I²C pullup resistor failure.
  4. Monitor MUX_SEL and INT_N. Trigger oscilloscope on MUX_SEL GPIO rising edge (Alt Mode entry). Verify transition to 3.3 V within 10 ms. Simultaneously scope INT_N; it should remain high (3.3 V) unless an error condition is present. Repeated INT_N pulses indicate ESD, over-temperature, or signal integrity issue.
  5. Acquire high-speed differential eye diagrams. Using 13 GHz passive probe and high-bandwidth oscilloscope (≥4 GHz), capture DP_TX1_P/N waveform directly at ANX7411 output. Enable eye-diagram overlay (min. 1000 UI). Expected: clean eye opening ≥600 mV p-p, zero-crossings centered, <−3 dB peaking. Compare all four TX pairs (TX1–TX4). Asymmetry >100 mV suggests lane-specific damage.
  6. Test with known-good USB-C display. Connect a second USB-C monitor or dock with different cable to eliminate cable/display firmware variables. If this succeeds, previous failure was likely in external device negotiation. If it also fails, ANX7411 is the root cause.
  7. Thermal stress test (optional for intermittent failures). If video flickers under sustained DP traffic, use thermal camera to image ANX7411 and surrounding components. Operating temperature should not exceed 85 °C. If ANX7411 exceeds 90 °C with normal airflow, internal power dissipation is excessive (e.g., output driver stuck on), indicating analog failure.
  8. Decision point: Rework vs. Replace. If all power and I²C are confirmed good, but ANX7411 does not respond to reset or eye diagram is collapsed, reballing is warranted. If reballing fails, replace with new IC using reflow station and stencil. If power or I²C communication is absent, verify upstream control signals from SMC before proceeding with ANX7411 rework.

See Also

Last updated: 2026-05-01 · Browse all components