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Hello everyone, today we continue to study the circuit timing of the Wistron 15221 motherboard,

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mainly learning how the EC standby condition is generated

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EC position number is U2407

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Directly search for "U2407" in the circuit diagram to find the EC

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Its model is IT8226E, which is consistent with the actual model

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The standby power supply of EC is usually AVCC or VSTBY

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These are the standby supply pins of the EC

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In addition to the pins AVCC and VSTBY.

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There are some other power supply pins next to it

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For example, VSTBY0 is also provided by 3D3V_ AUX_S5_EC

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Track down this power source

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Found it from 3D3V_AUX_S5

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Through the block diagram, it is found that it is output by RT6575D

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After searching, we found RT6575D

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Its position number is PU45011

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The LDO3 pin of this chip is a linear output pin, and the external name is 3D3V_ AUX_S5, which is its source

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Therefore, we can find through the timing diagram

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The external name of VSTBY0 pin of EC is 3D3V_ AUX_S5

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Provided by LDO3 of this PU4501 (standby chip)

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PU4501 is in the actual product, its actual model is "5X="

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This is a chip produced by Richtek

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Because the chip is relatively small

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It cannot print all the chip models on the chip surface

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Therefore, it uses this code to indicate the model of the chip

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When we encounter this kind of code in the maintenance process, but don't know its actual model

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In this case, you can find the actual model corresponding to it by querying the code name in this search bar

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Select "Signal original pass and search", input "5X="

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You can find that the actual model of "5X=" is RT6575D

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In the future, we will encounter codes on the surface of this chip in the maintenance process

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You can find the actual model of the chip by searching its code name in Xinzhizao

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Ok, let's take a look at the workflow of RT6575D

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Through the chip data sheet can be found

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For RT6575D to output LDO, it only needs to satisfy VIN

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After the main power supply of VIN, the LDO3 output will be generated

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When the output of LDO3 exceeds 2.5V, LDO5 will also start to output

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Ok, this is the LDO3 output condition

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We find "VIN" in the circuit diagram

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Its power supply comes from 19V_DCBATOUT, which is the common point voltage

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When the chip meets the VIN power supply, it will automatically output LDO3 (3D3V_ AUX_S5)

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Therefore, we can find from this timing diagram that when the common point of the small current is normal,

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it can provide the main power supply to the standby chip

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Then the standby chip will output the external name of LDO3

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as 3D3V_AUX_S5 to provide power to the VSTBY pin of the EC

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Then, after the VSTBY pin of the EC is powered, it will output a high-frequency XLP_OUT to

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control the generation of AVCC power supply

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Let's take a look at the source of AVCC

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The external name of the AVCC pin is also AVCC

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It comes from this 33 ohm resistor, which is renamed AVCC by 3D3V_AUX_KBC through the resistor,

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and then goes to provide standby power to EC

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3D3V_AUX_KBC also provides standby power to the VSTBY pin of the EC

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Let's take a look at the power generation source of 3D3V_AUX_KBC

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This power supply can be generated in two ways

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The first is to connect directly through a resistor, and rename 3D3V_AUX_S5 to 3D3V_AUX_KBC

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The second is to conduct through the MOS tube

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These two generation methods, the circuit will only use one of them

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We find Q2412, R2496, and R2493 by searching the component position number

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to see which method is used in the actual circuit

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It can be found from the actual object that the two resistors are not installed,

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that is to say, the two resistors 2496 and 2493 are empty.

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The resistor is not installed, indicating that the second method is used

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After being turned on by Q2412, the AVCC power supply and VSTBY of EC are generated

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This is a P-channel mode tube

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To make this 3D3V_AUX_S5 conduction, the G pole voltage must be less than the S pole voltage

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The G pole is connected to the 6th pin of Q2410

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If pin 6 is connected to ground, it can pull the G pole of Q2412 to low level

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The conduction condition of Q2410 is: the XLP_OUT signal must be greater than 2.5V (must be a high level)

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This high level comes from the EC

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After the EC receives power from VSTBY0, it sends a high-level control signal

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Control pins 1 and 6 of Q2410 to turn on, pull down the G pole of Q2412,

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make 3D3V_AUX_S5 flow to 3D3V_AUX_KBC,

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and provide standby power supply for VSTBY and AVCC pins of EC

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Ok, this is the EC's standby power generation process