reaches 750mA, the internal switch of RT9284 turns off, and supplies power for the rear circuit through
external diode D3 at the same time when switch is off until feedback voltage is lower than reference
voltage again. As for this PFM peak current control scheme adopted by convertor and discontinuous
conduction means (DCM), the frequency depends on output current and makes the frequency of entire
load very high. Pin 4 of RT9284 is working enable pin and connected with pin 56 of RK2608 to control
level change through software and control RT9284 to realize screen-save function.
When machine power on, display screen perform data communication through rear CPU and
restores the drive current signals sent from CPU on display screen. Signals sent from CPU are different
and display screen makes different displays, so we may see different displays and CPU also controls
screen-save function through software setup.
3.2.6 USB jack circuit
1. USB jack circuit is shown in the picture 3.2.6.1.
T1
SDCW2012-2-900T
1
3
2
4
R12
1M
R8
10K
R3
12K
L6
680
J1
3DU05S-32T-10
+5V
1
D-
2
NC
3
D+
4
GND
5
IN_L
6
IN_R
7
GND
8
C3
104
C4
104
C9
SFI0402-050E100NP*
C8
SFI0402-050E100NP*
R5
470R
R11
1M
Q2
SS8550LT
C6
SFI0402-050E100NP
D_GND
D_GND
D_GND
D_GND
D_GND
D_GND
D_GND D_GND
+5V
D_GND
USB_DM
USB_VBUS
2
USB_DP
USB_DET
USB_DET
L2
601 DCR<350m
L4
601 DCR<350m
SPEAKER_OUTL
SPEAKER_OUTR
Figure 3.2.6.1USB jack circuit diagram
2. Working principle: USB data jack is composed of USB_DM, USB_DP and GND (ground wire).
When the player is connected with computer or is charging through USB line, USB_VBUS is power
supply pin of USB jack, and also power input pin of USB jack charge at the same time. When he player is
charging through USB, the internal 5V power of PC charges Li battery through USB.
Meanwhile, IN_L and IN_R pin of USB jack is also audio output pin of the player. One channel of
audio signals after being processed by Wm8750 outputs to headphone through HP_OUT and one
channel performs external output through SPEAKER_OUT of USB jack.
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