PP3V3_S3
3.3V sleep state power supply
What it is
PP3V3_S3 is the 3.3V power supply rail that remains active during the S3 (sleep) power state. The "S3" suffix indicates this rail is gated to the SLEEP power domain and should drop to zero or near-zero only during deeper sleep states (S4, S5) or mechanical shutdown (G3).
This rail is sourced from the primary PP3V3_S5 rail through one or more voltage regulators—typically an ISL6259, NCP81239, or similar buck converter with an integrated power MOSFET gate driver. The regulator enables/disables PP3V3_S3 based on the S3 state signal from the system controller, usually routed through an SMC or power management microcontroller.
Critical loads on this rail include the real-time clock circuit, wake-source control logic, memory retention circuits, and low-power debug interfaces. Unlike PPVCORE_S0, which is dynamic and fluctuates with CPU load, PP3V3_S3 carries minimal current during sleep and does not require high transient response.
In practice
During board-level troubleshooting, PP3V3_S3 faults typically manifest as:
- No wake from sleep: System refuses to wake on RTC alarm or keyboard input; PP3V3_S3 rail may be absent or collapsed to 0V.
- Lost RTC clock: Date/time resets on reboot even with CMOS battery present; indicates PP3V3_S3 starvation of the RTC circuit.
- Memory retention failures: System cannot exit sleep cleanly; memory corruption or loss of wake vectors.
- Thermal runaway in S3: System consumes excessive current during sleep; suspect a shorted load or regulator stuck in a high-dissipation mode.
To probe PP3V3_S3, locate test point TP_S3 or probe the output cap of the S3 buck converter (typically a large ceramic capacitor bank near the regulator). With the system in S3 sleep, measure steady-state voltage. If the rail is missing or sagging below 3.15V, check the regulator enable signal, switching frequency, and output stage for shorts to GND.
Use a INA3221 rail monitor if present on the board; it logs current draw on PP3V3_S3 and can reveal whether wake failures are due to regulator shutdown vs. load short. Typical sleep-state current draw is 2–50 mA depending on active RTC and retention circuits.
| Condition | Expected Voltage | Typical Current (Sleep) | Fault Indication |
|---|---|---|---|
| S0 (Active) | 3.25–3.45V | 100–500 mA | None; normal operation |
| S3 (Sleep) | 3.25–3.45V | 5–50 mA | Below 3.15V = regulator fault or load short |
| S5 (Soft Off) | 0.0V (off) or 3.3V (always-on variant) | < 1 mA | Stuck at 3.3V in S5 = enable control stuck high |
| G3 (Mech. Off) | 0.0V | 0 mA | Present voltage = main regulator failure |
See also
Related terms in this glossary:
- PPBUS_G3H — Main always-on power bus — Parent 3.3V rail (always-on, gates to S3)