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This lesson talks about the touch circuit of the OLED screen

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First look at the power line

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There are two power supplies for the touch circuit of the OLED screen, 3.3 V and 1.8 V

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In the drawing, they are TP_3P3 and TP_1P8

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Some are described like this, this is 1.8V power supply,

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this is 3.3V power supply

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Let's open a drawing of Xiaomi 9 to have a look

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First find the display and touch connector

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Mi 9 Pro uses an OLED screen

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We enter the power supply of the display circuit, ELVSS and ELVDD

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We can use this code to find the display circuit

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ELVSS refers to the negative voltage supply of the display

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display and touch are together, we can indirectly find the touch

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TP means touch

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Of course, we can also find the touch circuit by looking for TP_3P3

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First find the touch connector

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TP is touch, 3P3 means 3.3 V power supply of the touch

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Look at another power supply of touch

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TP_L1C_1P8, this is the 1.8 volt power supply for the touch

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Let's first look at the 3.3 V power supply

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The power supply leads to the second pin of the touch connector J6400

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Which chip does this power supply come from?

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We are going back

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Double click it, click down to find

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As you can see here, it comes from the chip U6400

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This chip has four pins,

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VIN is power supply input, VOUT is power supply output,

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EN is an open signal, GND is ground

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Pin A1 is the input power supply

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Pin A2 is the power supply output after step-down

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This module is usually an LDO step-down module, which is a linear voltage regulator

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It needs an input power supply, it can step down this voltage, the output is 3.3 V

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Under the control of the turn-on signal of pin B1,

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it steps down the 5V voltage of VDD_BOOST_5V and outputs 3.3 V

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This is the channel for the 3.3 V power supply

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Next, let's take a look at the 1.8 V power supply channel of the touch connector

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This 1.8 volt power supply is supplied to the fourth pin of the touch connector J6400

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Let's see where this power comes from

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Double-click it, of course, the power supply here is to provide pull-up for other circuits,

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we don鈥檛 look at it here

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We continue to find the roots of this touch power supply

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Here is a chip U4700

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The model of the chip is PM8150A, which is a small power supply

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It outputs 1.8 V to power the touch

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After pressing the power button, it will output these power supplies one after another

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The 1.8 V power supply of the touch comes from the pin 118 of U4700,

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and it is supplied to the fourth pin of the touch connector

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This is the 3.3 V and 1.8 V power supply lines of the OLED screen touch circuit

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That's all for this lesson