Introduction

Today we will learn in detail about the MediaTek (MTK) charging section. We will understand how it differs from Qualcomm's charging section and how it works. After completing this chapter, you will be able to easily identify and fix charging-related problems in MediaTek phones.

It is important to understand that in a MediaTek charging circuit, the Power IC plays a crucial role because some critical charging-related components are located inside the Power IC.

Key Differences Between Qualcomm and MediaTek Charging

Before working on any MediaTek phone, it is essential to know how its charging circuit differs from Qualcomm's. There are four main differences:

1. Position of the Current Sense Resistor (Code Resistor):
   • Qualcomm: The current sense resistor is placed in the positive (VBAT) line of the battery.
   • MediaTek: The current sense resistor is placed in the negative (Ground) line of the battery. This is the first and most significant difference.
2. Location of the Fuel Gauge:
   • Qualcomm: The fuel gauge can be inside the charging IC or installed as a separate IC.
   • MediaTek: The fuel gauge section is integrated inside the Power IC. Its lines are known as CSN (Current Sense Negative) and CSP (Current Sense Positive).
3. VCDT (Voltage Charging Detection) Line:
   • Qualcomm: There is no special detection line of this kind.
   • MediaTek: It has a VCDT line that directly informs the Power IC that a charger has been connected. This line is not found in Qualcomm circuits.
4. Charging LDO Line:
   • Qualcomm: This line is not present.
   • MediaTek: There is another line to activate the Power IC, called the Charging LDO.

How the MediaTek Charging Circuit Works

Now we will understand step-by-step how voltage travels in a MediaTek phone when a charger is plugged in.

Step 1: 5V Input and VPH Power Generation

1. When you plug in the charging jack (Type-C or other), a 5-volt supply is initiated.
2. This 5V supply passes through an OVP (Over Voltage Protection) IC to reach the charging IC. This process is nearly identical in both Qualcomm and MediaTek.
3. After the 5V is input into the charging IC, switching begins inside the IC, and VPH power is generated. In MediaTek, VPH is also known as VSYS.
4. This VPH/VSYS voltage powers the entire phone's circuit. After this, the output from the charging IC charges the battery.

Step 2: Power IC Activation (VCDT and Charging LDO)

In Qualcomm, the 5V only goes to the charging IC, but this is not the case in MediaTek. In MediaTek, it is necessary to trigger both the charging IC and the Power IC simultaneously to start the charging process. Two new lines are created for this purpose:

A. VCDT (Voltage Charging Detection) Line

• Purpose: This line's purpose is to inform the Power IC that a charger has been connected.
• Circuit: It originates from the 5V input line and goes to the Power IC through a voltage divider circuit.
• Components: This circuit uses two resistors:
  • R1: 330 Kilo Ohm (kΩ)
  • R2: 39 Kilo Ohm (kΩ)
• Voltage: When 5V is input at R1, R1 and R2 together reduce the voltage, and the Power IC receives approximately 0.5V. This range can be from 0.5V to 1.2V.
• Importance: If this line breaks or a resistor fails, the Power IC will not receive the signal, and the phone will not detect charging.

B. Charging LDO Line

• Purpose: This is another detection line that goes from the 5V input to the Power IC.
• Circuit: A resistor is placed in the middle of this line.
• Component: It uses a 7.5 Kilo Ohm (kΩ) resistor.
• Voltage: On one side of the resistor, there is a 5V input, and on the other side (at the output), approximately 2.8V is available, which goes to the Power IC.
• Importance: If there is any fault in this line or if this resistor breaks, the phone will still not detect charging.

Important Note: Where This Rule Does Not Apply

This VCDT and Charging LDO concept applies only to specific MediaTek Power ICs, such as:

• MT6357
• MT6358
• MT6359

This circuit does not work in newer 5G phones that have the MT6365 Power IC and MT6360 charging IC. Their charging detection concept is different.

Troubleshooting Charging Problems in MediaTek Phones

If a MediaTek phone comes to you with a charging problem, follow these steps:

1. First Check (PMID): Plug in the charger and check for 5V at the PMID test point near the charging IC. This will confirm that the input voltage is reaching the charging IC.
2. Second Check (VCDT): Locate the voltage divider circuit for the VCDT line near the Power IC.
   • Check for 5V at the input of R1 (330 kΩ).
   • Check for 0.5V at the junction (output) of R1 and R2. If this voltage is not present, check these resistors.
3. Third Check (Charging LDO): Find the 7.5 kΩ resistor on the Charging LDO line.
   • Check for 5V on the input side of the resistor.
   • Check for 2.8V on the output side of the resistor.
4. Fourth Check (For Fake Charging): If the phone is fake charging or the battery percentage is stuck, then:
   • Check the Current Sense Resistor (Code Resistor) on the negative line of the battery connector.
   • Check the continuity of the CSN and CSP lines going from this resistor to the Power IC. If any of the balls for these lines are missing, it can cause fake charging or battery percentage issues.

Summary (Conclusion)

To fix the charging circuit of a MediaTek phone, working only on the charging IC is not enough. We must also understand the role of the Power IC, as it controls charging detection and the fuel gauge. Whenever you repair a MediaTek phone, always prioritize these three voltages:

• 5V at PMID
• 0.5V at VCDT
• 2.8V at Charging LDO

By checking these three lines, you can easily solve 90% of charging problems.