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Power Management

ISL9239

The ISL9239 is a high-efficiency, single-cell lithium-ion/lithium-polymer battery charger IC manufactured by Intersil. It integrates a synchronous buck converter, charger control logic, and protection circuitry in a compact package. On Apple logic boards, the ISL9239 manages charge current delivery from AC mains through the system's power delivery subsystem to the internal battery. It is critical for power delivery diagnostics: failures here manifest as slow or absent charging, thermal shutdown loops, or complete power delivery failure. Technicians must distinguish ISL9239 faults from upstream issues (charger adapter, USB-PD controller) or downstream battery problems.

Role on the Board

The ISL9239 operates as the primary battery charger controller on T2 and Apple Silicon MacBook logic boards. It regulates charging current and voltage according to battery chemistry and system state, communicates charging status to the SMC (T2) over SMBus, and implements thermal throttling and charge termination algorithms.

Power States: The ISL9239 is active in S5 (Soft Off), sleep, and S0 (Active) states. It remains partially powered during G3 (Mechanical Off) to support trickle charging and SMBus communication. Its input is sourced from PP5V_S5 and its output drives PPBAT (the battery rail).

Key Input/Output Signals:

Key Signals & Pins

Pin/Net Direction Description Typical Value
CHG_IN Input Adapter voltage input; regulated by upstream charger IC 5–20 V DC (depends on USB-PD or fixed adapter)
PPBAT (output) Output Regulated battery rail; primary charger output to pack 7.6–8.4 V DC (2S Li-ion)
IADP Input Adapter current limit sense; SMBus-controlled via I²C register 0–5 A (software-configurable)
ICHG Sense Charge current feedback; compared against register limit 0–5 A (battery-dependent)
CHG_EN Input (control) Charger enable; driven by SMC GPIO; low disables output 0 V (disabled) or 3.3 V (enabled)
CHG_TEMP Input (analog) Thermistor voltage divider; used for temperature-gated charging 0.5–2.5 V (depends on thermistor R, temperature)
SMBus (SDA/SCL) Bi-directional Communication with SMC for charge status, current limit, and fault reporting 0–3.3 V logic, ~100 kHz clock
VSS Reference Ground; critical return path for sense circuits 0 V (reference)

Measurement Reference

Test Point / Net Expected (Meter) Expected (Scope) Notes
PPBAT 7.6–8.4 V DC (2S cell) or 0 V (if disabled) ±50 mV ripple (during charging) Measure battery voltage directly; no ripple = IC disabled or shorted FET. If stuck at ~3.3 V, check for bootstrap cap failure.
CHG_IN 5–20 V DC (adapter/USB-PD) Clean DC ±100 mV; reject supplies with >300 mV ripple If absent, upstream charger IC or adapter fault. Confirm adapter rated power with user history.
IADP_CTRL (register via SMBus) N/A (read via SMBus host or scope I²C decode) SMBus writes from SMC at boot and on thermal events; typical values 0x00–0xA0 (0–5 A in steps) SMBus communication failure = SMC cannot adjust charge current. Check SCL/SDA pull-ups and termination.
ICHG (sense pin analog voltage) 0–2 V DC (proportional to charge current; ~200 mV per ampere typical) Smooth ramp during CC phase; flattens at CV (constant voltage) Meter reading during active charge; should increase from 0 V within 100 ms of CHG_EN rising. No rise = FET shorted or dead IC.
CHG_EN 0 V (disabled) or 3.3 V (enabled) Logic high at power-on; pulses or stays high during charging cycles Check SMC firmware health. If stuck low, SMC may have fault code; retrieve via Apple Service Toolkit or diagnostic mode.
PP5V_S5 (IC supply) 5.0–5.2 V DC ±50 mV during transients Low supply voltage starves the IC; may trigger brownout reset. Verify PPBUS_G3H regulator feeding PP5V_S5.

Common Failure Modes

  1. No charging current despite valid input adapter
    Symptom: Charger adapter detected, USB-PD negotiated correctly, but PPBAT does not rise and ICHG remains at 0 V.
    Likely Cause: Output FET shorted to ground (low-side pass element failure), or IC stuck in disable state due to SMBus communication loss.
    Diagnostic Step: Check CHG_EN signal and SMBus traffic (scope I²C decode or SMC logs). Measure DC resistance from PPBAT to ground with power off (~500 Ω nominal; <10 Ω indicates shorted FET). If SMBus is dead, check SCL/SDA continuity and pull-up supply.
  2. Rapid thermal shutdown, charging stops after 30–60 seconds
    Symptom: Charging begins, then ICHG ramps down to zero; SMC reports thermal throttling in logs; system remains cool to touch.
    Likely Cause: CHG_TEMP thermistor circuit open or shorted, or NTC Thermistor failed (high resistance). IC falsely detects over-temperature and throttles current to zero by firmware.
    Diagnostic Step: Measure CHG_TEMP voltage: should be 0.5–2.5 V at room temperature. If outside range or non-responsive to ambient heat, check thermistor continuity (typically 10 kΩ @ 25 °C). Confirm divider pull-up voltage and IC supply. Read SMC temperature sensor data via diagnostic tools.
  3. Charging current stuck at maximum, battery not entering constant-voltage phase
    Symptom: ICHG ramps to max (typically 5 A) and stays there indefinitely; battery voltage climbs beyond 8.4 V; SMC may issue over-voltage warning or force shutdown.
    Likely Cause: ISL9239 internal charge-pump or feedback divider failure; IC cannot properly sense battery voltage. Or ICHG sense pin shorted to ground, causing false low-current indication.
    Diagnostic Step: Monitor PPBAT voltage and ICHG signal simultaneously. If PPBAT exceeds 8.6 V and ICHG does not decrease, the IC's internal CV feedback is broken. Check for corrosion or liquid damage near sense pins. Probe the ICHG pin with multimeter in diode mode to check for shorted capacitors.
  4. SMBus communication errors, SMC cannot read/write charger registers
    Symptom: SMC logs "ISL9239 SMBUS ERROR" or similar; charge current is fixed at a default value; thermal throttling does not work; adapter current cannot be adjusted.
    Likely Cause: SMBus pull-up resistors unpopulated, shorted, or dead; SDA/SCL pins shorted to power or ground; level-shifter failure if IC operates at different logic voltage than SMC.
    Diagnostic Step: Scope the I²C lines at the ISL9239 pins and SMC pins. Check for clock stretching (hold low by slave). Measure DC resistance of SDA and SCL to ground (should be 10–50 kΩ). Verify pull-up supply (PP3V3 typical) is present and stable. Use I²C bus analyzer or SMC firmware log to identify address conflicts or CRC errors.
  5. Intermittent charging: works for several minutes, then stops with no error code
    Symptom: Charging works briefly after cold boot, then mysteriously halts; reboot restores charge for a short period; happens at room temperature with no visible fault.
    Likely Cause: PP5V_S5 supply rail intermittently sags below IC minimum operating voltage (~4.5 V), causing brownout and IC latch-off. Or capacitor on CHG_IN or PPBAT decoupling is failing.
    Diagnostic Step: Scope PP5V_S5 for dips below 4.5 V during charging transients. Check all decoupling caps near the ISL9239 with an ESR meter (should be <100 mΩ). Measure cold resistance of PPBAT output capacitors. If PP5V_S5 sags, trace the fault upstream to the regulator feeding it (often PPBUS_G3H regulator).
  6. Charger IC draws excessive quiescent current in S5/sleep, draining battery
    Symptom: Battery drains in sleep mode even with charger disconnected; PPBAT current is >50 mA, no SMBus traffic observed.
    Likely Cause: Internal leakage in IC due to manufacturing defect, or external pull-down resistor always active (not gated by sleep control). Or CHG_TEMP input floating, causing ADC to oscillate and burn power.
    Diagnostic Step: Disconnect the battery and charger. Measure current draw into PP5V_S5 pin and CHG_IN pin individually. Confirm CHG_EN is pulled to ground in sleep mode. Check CHG_TEMP is properly biased (not floating). If only the ISL9239 draws excessive current when isolated, the IC is internally damaged and must be replaced.

Boards Using This IC

Diagnostic Workflow

  1. Confirm charger adapter and USB-PD negotiation
    Connect known-good charger adapter rated for the system. Use multimeter to verify CHG_IN voltage is within expected range (5–20 V DC, typically 9 V or 15 V for USB-PD). If CHG_IN is absent or incorrect, the fault is upstream (ISL6259, ISL9239 charger, or FUSB302 USB-PD controller). Do not proceed until CHG_IN is valid.
  2. Verify ISL9239 supply and enable signal
    Measure PP5V_S5 (input supply to the charger IC); it should be 5.0–5.2 V. Verify CHG_EN signal is 3.3 V (charger enabled) or 0 V (disabled by SMC). If PP5V_S5 is low or absent, the fault is in the power distribution network (PPBUS_G3H regulator failure). If CHG_EN is stuck low or toggling abnormally, suspect SMC (T2) firmware or GPIO driver fault.
  3. Measure output voltage and current behavior
    With the charger connected and system powered on, measure PPBAT voltage. Should rise from 0 V to battery nominal (7.6–8.4 V for 2S cell) within 1–2 seconds of CHG_EN going high. Simultaneously observe ICHG signal: should ramp from 0 V smoothly toward 2–4 V (representing CC phase charging at 2–5 A). If PPBAT remains at 0 V or does not rise, the output FET is likely shorted or the IC is not toggling. If ICHG rises but then stalls or oscillates, suspect feedback network corruption or SMBus control loss.
  4. Check SMBus communication health
    Connect a logic analyzer or I²C sniffer to the SMBus SDA and SCL lines. Observe traffic during boot and during charging transitions. ISL9239 should respond to SMC read/write commands on I²C address 0x16 (typical, verify in schematic). Look for NAK responses, CRC errors, or clock stretching. If no traffic appears or SMC reports bus errors, check SDA/SCL pull-ups (typically 4.7–10 kΩ to PP3V3) and measure DC resistance to ground. If SMBus is stuck low, trace the short and identify the offending component (often a failed pull-up array IC or shorted capacitor).
  5. Validate thermal sensor and charge termination
    Measure CHG_TEMP voltage with a multimeter. At room temperature (~25 °C), expect 1.0–2.0 V (depends on NTC Thermistor value, typically 10 kΩ @ 25 °C). Gently warm the thermistor with your finger or a heat gun; voltage should decrease (thermistor resistance drops). Cool it with compressed air; voltage should rise. If CHG_TEMP is fixed (e.g., always 0 V or 3.3 V), the thermistor or its pull-up is open/shorted. If voltage does not respond to temperature, the thermistor is thermally decoupled (loose or repositioned). Verify the thermistor is mounted near the battery cell or on the charger output to detect real junction temperature.
  6. Inspect for liquid damage and solder defects
    Visually examine the ISL9239 and surrounding passives under bright light or magnification. Look for corrosion on pins, discolored solder joints, or lifted component leads. Check for liquid residue (white salt deposits, sticky residue) around the IC and sense networks. Use a Diode Mode multimeter to probe the sense pins and bootstrap pins for short circuits to power or ground. If you see signs of corrosion or poor solder quality, the IC may need reflowing or replacement. Confirm via X-ray if available.
  7. Test IC isolation and functional replacement
    If all upstream signals (charger input, SMBus, enable, supply) are valid but PPBAT remains dead and ICHG is zero, suspect internal IC failure or a shorted output FET. Measure DC resistance from PPBAT to ground with power isolated: should be 500 Ω to several kΩ (depends on battery equivalent impedance). If resistance is <10 Ω, the output pass FET is shorted. The IC must be reballed and replaced; micro-reballing repair is not recommended for charge-path components due to safety risk (fire hazard if FET shorts during operation).
  8. Correlate with SMC diagnostics and system logs
    After each test, check SMC fault codes via Apple Service Toolkit or diagnostic mode. Look for charger-related error codes (e.g., "ISL9239 SMBUS FAIL", "CHG_TEMP OOR", "PPBAT LOW"). Cross-reference against the board schematic and power delivery tree to rule out secondary failures upstream (e.g., if PP5V_S5 is low, fault the regulator feeding it, not the ISL9239 itself). Use system logs and thermal sensor data to confirm whether charge cycles are being throttled by SMC or by IC limit enforcement.

See Also

Last updated: 2026-04-07 · Browse all components