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Hello everyone, today we will learn about the 4-switch buck and boost circuit in the Apple A2337 circuit

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Let鈥檚 take a look

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When the CD3217 converts the 5V power supply of the adapter,

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it will first provide power to the charging chip U5200

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U5200 is in this position in the circuit

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This is ISL9240, the charging chip

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The power supply of the adapter is called PPDCIN_AONSW,

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it passes through a current-sensing resistor,

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and from here it provides power to the P_IN pin of the charging chip

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After the charging chip is powered,

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it will output a 5V linear from the VDD pin to provide power to the VDDP pin,

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and at the same time pull up the CELL pin

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In the circuit, this is the VDDA pin

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In the circuit diagram, it outputs from the VDDA pin, and then supplies power to the VDDP pin,

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there is a 4.7 ohm resistor in the middle

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Then, this VDDA has to pull up the CELL pin

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CELL is the setting pin for the number of cells

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When the level is high, it means 3 cells,

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when it is low, it means 2 cells

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The voltage of 1 cell is about 4.2V,

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and the voltage of 3 cells is about 12.6V

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It is also the common point voltage setting pin, and also the charging voltage setting pin,

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It sets its charging voltage according to the number of battery cells

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When the charging chip meets the power supply, the output is linear, and the CELL pin is pulled up

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This chip will output GATE_Q1, GATE_Q2, GATE_Q3, GATE_Q4,

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It outputs these pins to drive two external composite tubes

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It can also be said that two pairs of upper and lower tubes jointly generate a common point voltage, PPBUS_AON

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Ok, let's look how these 4 MOS tubes work

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Let's learn through this sequence diagram

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When the adapter voltage comes in, it will supply power to the P_IN pin

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Then it will generate a linear output from the VDDA pin to supply power to VDDP,

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and at the same time pull up the CELL pin, which is the battery cells setting pin,

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or the charging voltage setting pin, or the common point voltage setting pin

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After the chip meets these conditions,

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it will work in boost mode and drive 4 MOS tubes to conduct in turn,

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and boost the 5V to get 12V power supply

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How did this 12V come from?

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The average voltage of one cell is about 4V

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When the CELL pin is grounded, it is set to two cells,

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and when it is connected to the power supply, it is set to three cells.

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We are based on three battery cells to calculate

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Each cell is about 4V, so three cells are 12V

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This 12V is the common point voltage, which is called PPBUS_AON

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At the same time, it is also the charging voltage,

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which can charge the battery after the charging current detection resistor

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and the battery isolation tube are turned on.

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It can also support batteries and adapters to provide power to the system at the same time,

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supporting mixed power supply

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Regarding the boost process, it usually uses inductor energy storage for boosting

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When the upper MOS tube is turned on, the lower MOS tube is turned off

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The MOS tube here is turned on, so that the inductor can charge and store energy

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Then, after the MOS tube is turned off, this side is turned on,

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and the incoming electricity and the stored electricity are released together,

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superimposed together to obtain a higher voltage

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The PWM waveform can be measured at the G poles of these 4 MOS tubes

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In the maintenance process, if there is no common point,

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we mainly check the condition of the charging chip, or replace the chip

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The boosted common point voltage will be returned to provide power

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to the PBUS and PBUS_PWR pins for detecting the common point voltage

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When it detects that the common point voltage is normal,

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it will output an EN signal to turn on the power supply of other circuits

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Ok, this is an introduction to the 4-switch buck and boost circuit