Demystifying the Power Up Cycle in Mobile Device Repair: Analyzing PMIC, CPU, and Energy Saving Mode.
When repairing mobile devices, understanding the power up cycle, including the roles of the power management integrated circuit (PMIC), central processing unit (CPU), and energy saving mode, is essential for diagnosing issues and providing effective solutions. This article will delve into the connections between the PMIC, CPU, and power button, as well as explain the significance of energy saving mode in identifying and resolving mobile device issues.

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Understanding the Power Button, PMIC, and CPU

A schematic diagram illustrating the design of the power button, PMIC, and CPU reveals crucial connections between these components. The back lines connecting the PMIC and CPU provide the current required to power the CPU, while the boost input lines supply the primary power current to the PMIC.

The capacitors on the boost line work in tandem with the V-BAT line, or VPH PWR. If there are seven boost input capacators, for instance, there must also be seven bobbins or seven back output inductors. It is important to note and understand these connections to properly diagnose mobile device issues.

The Power Up Cycle: Gradual Increases in Current

During the power up cycle, the current begins with a low level and gradually increases, resembling a staircase. Depending on the device's range, the current may reach 200-250 milliamps (mA) before the image appears on the screen, which is when the PMIC, CPU, and memory start to operate.

In a lab setting, by pressing the power button for half a second, the PMIC delivers a current of up to 70 mA. In the following second, the consumption may reach 200 mA without an image appearing on the screen, indicating that the PMIC, CPU, and memory are working together to initiate the power up cycle.

When the image is displayed, the peak current can reach 300-350 mA. At this point, the CPU sends information to the circuits via the I2C communication line, powering up the entire system. The current may then increase to 500 mA, allowing other circuits, such as the image, touch, camera, and audio, to start functioning.

The peak current should not exceed 10 seconds, as a longer duration may indicate a problem with the motherboard. After the peak, the current should gradually decrease.

Energy Saving Mode: An Essential Test for Mobile Device Repair

Energy saving mode is a critical test to perform after mobile device repair. This mode allows technicians to determine whether the issue lies with the motherboard or the battery. To perform the test, connect the device to a laboratory power supply and wait for it to enter energy saving mode.

In this mode, the device consumes a lower current, which gradually decreases to three, four, or five mA. This indicates that the motherboard has minimal consumption, which is important for diagnosing potential issues.

If a customer reports that their device's battery drains quickly, the energy saving mode test can help identify the problem. If the device consumes very little current (around four or five mA) in this mode, the issue is likely with the battery. Conversely, if the device consumes more than 50 mA, the problem is on the motherboard. The higher the current consumed, the faster the battery will discharge.

Case Study: Samsung A51

Consider a Samsung A51, for instance. By checking the power button three or four times for half a second, we observe a slightly high current of 200 mA. First, inspect the PMIC inputs and outputs, and then proceed with the complete power up cycle to diagnose the issue. Observe peak currents of up to 1.5 mA, followed by a gradual decrease in current

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