🔋 Redmi 5A Charging Solution – Full Guide

• Redmi 5A Charging Solution – Full Guide Step By Steps

1. Battery & Connector Check

• Minimum Battery Voltage must be 3.6V.

• If battery is below 3.6V → pre-charge using a regulated power supply.

• If still not detected: check BSI line (Battery Sense) & TH line (Temperature).

• Clean/replace battery connector if loose or oxidized.

2. Charging Connector & Sub PCB to Mainboard Lines

• Inspect USB connector for physical damage.

• Verify continuity from Sub PCB to Mainboard:

  • Vbus (+5V) → must reach OVP IC input.

  • GND (Ground) → proper ground return.

  • DP, DM (USB Data Lines) → must connect correctly to Charging IC for handshake.

  • VBAT line → direct connection to Battery Connector.

3. OVP IC (Over Voltage Protection IC)

• Protects the phone from >5.5V input.

• Check:

  • Input Pin → 5V from charger.

  • Output Pin → regulated 5V to Charging IC (BQ).

• If input is present but no output → replace OVP IC.

4. BQ Charging IC (PMIC Charging Controller)

The BQ IC (Texas Instruments family, commonly used in Redmi 5A) is the main charging controller.

🔄 Charging Sequence of LDOs (BQ IC Working Steps):

1. Adapter Detection

   • Vbus (5V) detected → BQ IC activates.

   • DP/DM handshake with charger decides charging current (Normal USB: 500mA, Fast Charger: up to 2A).

2. LDO Power-up

   • BQ IC generates internal LDO voltages (1.8V, 3.3V) to activate charging logic.

3. Battery Pre-Charge

   • If VBAT < 3.6V → BQ IC sends a small pre-charge current (~100–200mA).

4. Fast Charge Mode

   • Once VBAT > 3.6V → full charging current (up to 1.5A).

   • DP/DM confirm charger capability.

5. Constant Voltage Phase

   • At VBAT ~4.2V, current reduces gradually to protect the battery.

6. Charge Complete

   • Charging stops when current drops below threshold.

5. Role of DP & DM Lines

• DP/DM lines are not just for data – they are used for charger handshake (DCP/CDP/Apple/Samsung protocol).

• If DP/DM are open/short:

  • Phone may show “Charging” icon but no current flows (Fake Charging).

  • Only 0.1A–0.2A drawn on power supply.

6. Common Problems & Fixes

⚡ Fake Charging Issue

• Symptom: Phone shows charging symbol, but battery percentage doesn’t increase.

• Causes:

  • DP/DM line open.

  • OVP IC output faulty.

  • BQ IC malfunction.

• Fix: Check DP/DM continuity → Replace OVP → Reball/Replace BQ IC.

🌡 Temperature Issues

• Symptom: Phone stops charging / error “Battery temperature too high/low”.

• Causes:

  • TH line open or short.

  • Faulty thermistor inside battery.

  • Damaged PMIC sensor circuit.

• Fix: Replace battery → Check TH line to mainboard → Replace PMIC if needed.

🔄 Restart / Auto Reboot Issue While Charging

• Symptom: Phone restarts randomly during charging.

• Causes:

  • Weak battery (high internal resistance).

  • Bad BSI line connection.

  • Overheating of Charging IC (BQ).

• Fix: Replace battery → Reball BQ IC → Reflow PMIC.

7. Quick Current Reading Reference (On DC Power Supply)

• Connect phone without battery → should boot with ~0.05A idle draw.

• Connect with battery and charger:

  • Pre-charge: 0.15A–0.3A

  • Normal charge: 0.8A–1.5A

  • Fake charging: <0.1A (symbol shows but no charge).

🔧 Final Technician Notes

• Always test with original cable & charger.

• If water damage suspected, clean charging section before repair.

• If all above checks are fine → last suspect is PMIC main power IC.

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Thanks From All GSM FILE

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