253P IC
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Product Details
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SECTION 1: FUNCTIONAL ARCHITECTURE & CIRCUIT ROLE
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1. Circuit Position & Connectivity:
- Schematic Designation: Labeled as Q_CHG, U_CHG, or MOSFET switch in Infinix and Tecno schematics.
- Placement: Positioned directly between the sub-board charging flex connector (VBUS input line) and the main charging management IC / PMIC.
- Circuit Operation:
* Receives regulated +5.0V to +5.25V DC from the USB port across the motherboard charging flex line.
* Acts as an electronic power gate controlled by the charging control logic to pass full current into the battery charging stage.
* In several Transsion board designs (such as Tecno Spark 7 / Infinix Hot series), two 253P switches or dual internal channels are linked in parallel/tandem to share charging current and minimize thermal dissipation.
2. Electrical Characteristics:
- Input Operating Voltage: 3.5V to 6.5V DC (designed for 5V USB standard charging).
- Maximum Current Rating: 2.0A to 3.0A continuous throughput.
- Low Internal On-Resistance (Rds_on): Minimizes voltage drop across the switch to ensure efficient power transfer into the battery.
- Integrated Reverse Current Blocking: Prevents battery discharge back through the charging port when the charger is unplugged.
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SECTION 2: BOARD-LEVEL FAULT SYMPTOMS
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1. Fake Charging (Charging Animation Visible, Battery Percentage Does Not Rise):
- The device displays the charging lightning bolt icon and charging animation, but the battery percentage never increases, remains frozen, or even drains while connected to the charger.
- Root Cause: 253P internal junction degraded or partially damaged, causing a severe voltage drop where 5.2V input outputs only ~1.2V to 1.8V to the battery charging circuit instead of the required ~4.2V - 4.7V.
2. Complete Charging Failure (Dead USB Detection):
- Connecting a certified USB charger and cable yields 0.00A current consumption on the USB power meter; the phone fails to acknowledge the charger completely.
- Root Cause: Open-circuit failure of the internal pass transistor in 253P, blocking VBUS from reaching the PMIC.
3. Extremely Slow Charging:
- The phone requires 8 to 12 hours to achieve full charge.
- Root Cause: Increased internal drain-to-source resistance (Rds_on) restricting charging current to negligible levels (e.g., 0.10A - 0.25A).
4. Motherboard Heating Around Charging Section:
- When plugged into the charger, the area around the 253P IC becomes excessively hot to the touch or under a thermal camera, often leading to auto-shutdown or battery temperature warning prompts.
5. Off-State Battery Self-Discharge:
- The phone loses battery charge rapidly overnight when switched off due to reverse leakage across the damaged MOSFET switch.
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SECTION 3: STEP-BY-STEP MULTIMETER TESTING & DIAGNOSTICS
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1. Cold Testing (Diode Mode Drop Readings in mV):
- Multimeter in Diode Mode: Place RED probe on motherboard ground shield (GND); use BLACK probe to probe the pins and adjacent bypass capacitors:
* Input Capacitors (VBUS Rail): ~450 mV to 600 mV. A reading of 0.000V indicates a shorted input capacitor or punctured IC.
* Output Capacitors (Charging Rail to PMIC/VBAT): ~350 mV to 480 mV.
* Gate Control Line: ~500 mV to 700 mV.
* If output capacitors read dead short (0.000V with continuity beep), isolate 253P by desoldering to verify if the short clears.
2. Hot Testing (Live Voltage Checks With Charger Connected):
- Plug a 5V USB charger into the phone assembly:
* Measure Input Voltage at 253P Input Pin: Must read steady 5.0V to 5.25V DC.
* Measure Output Voltage at 253P Output Pin:
- Normal Condition: Must read 4.3V to 4.7V DC (without battery connected) or matches battery terminal voltage under load.
- Defective 253P: Input reads 5.2V, but output drops to 1.0V - 1.8V DC. This confirms the 253P switch has failed and requires immediate replacement.
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SECTION 4: SOLDERING, REBALLING & REWORK SPECIFICATIONS
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1. IC Desoldering Protocols:
- Rework Station: Quick 861DW, Atten ST-862D, or Sugon 8620DX.
- Temperature Setting: 320°C - 330°C.
- Airflow: 25% - 30% with a 3.0mm or 3.5mm straight nozzle.
- Thermal Protection: Mask nearby processor, flash storage (eMMC/UFS), and fragile plastic FPC connectors using polyimide (Kapton) tape and aluminum heat-shielding tape.
- Removal: Apply a drop of tacky no-clean flux (Amtech NC-559 or Relife RL-422). Heat the IC in gentle circular motions for 10-14 seconds until the bottom solder pads liquefy, then lift vertically with high-precision ESD micro-tweezers.
2. Motherboard Pad Leveling & Prep:
- Apply a small bead of leaded solder alloy (Sn63/Pb37, 183°C melting point) with a soldering iron tip set to 320°C to dissolve the factory high-melt lead-free alloy.
- Run a fine 0.8mm desoldering copper wick smoothly over the motherboard footprint to achieve completely flat, uniform pads.
- Clean the area thoroughly with 99.9% pure Isopropyl Alcohol (IPA) and inspect under microscope for pad bridging or torn traces.
3. Replacement IC Preparation (DFN Leadless Package):
- DFN packages utilize flat bottom surface pads rather than BGA spheres.
- Pre-tin the bottom contact pads of the new 253P chip with a very thin, uniform layer of leaded solder using a fine conical or micro-knife iron tip.
- Ensure pads have flat, micro-cushion profiles without excessive solder doming.
4. Alignment & Final Installation:
- Apply a micro-thin, translucent film of tacky flux across the motherboard footprint.
- Position the new 253P IC matching the Pin 1 orientation marker (dot/notch on chip surface aligned with motherboard silkscreen).
- Reflow at 320°C with 25% airflow. As solder melts, the component will self-align via surface tension.
- Give an ultra-gentle micro-nudge with fine tweezers to verify proper elastic rebound.
- Allow the PCB to cool naturally for 3 minutes, clean off flux residue, connect battery and charger, and confirm full charging current draw (typically 1.0A to 2.0A on USB tester).
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