When MP3 player switches in FM tuning state, antenna is sent to the R
F
band-pass filter
(87.6MHz~108MHz and 76MHz
87.5MHz) composed of Li6, C57 and C59 through C56 coupling and
then to pin 35, 37 of TEA5767 for amplifying through TEA5767 inside. Pin 2, 3, 4 of TEA5767 is
connected with the internal VCO and with variant diode D10, D11 externally. Pin 2 id tuning voltage
output pin and voltage changes within 1V when in auto search. VCO power supply is sent to pin 5 of
TEA5767 by FM 3V3 through 69 limit and C68 filtering. The built-in I2C jack is controlled through pin 8, 9
of TEA5767 and CPU performs operation of channel search and selection through I2C bus. Digital power
is sent to pin 7 of TEA5767 by FM 3V3 through R73 limit and C76 filtering. XT1 (32.768) produces basic
clock of 32.768 and inputs to TEA5767 from pin 17. Analog audio signals after being processed by
TEA5767 output to rear stage power amplifying circuit from 23 (right channel), 22 (left channel) for
amplifying and then output through headphone jack.
3.2.5 Display screen boost circuit
1. Display screen boost circuit diagram is shown in the picture 3.2.5.1:
Figure 3.2.5.1 Display screen boost circuit
C5
102
LED-
R61
0R*
R63
0R*
C36
106/16V/1206
L10
CDRH3D16-100
U3
RT9284B
GND
2
EN
4
FB
3
OVP
5
LX
1
VCC
6
BACK_EN
D3
MBR0520/SOD123
C35
106/X5R
LED+
LEDP
R30
12R¡À1%
L9
601/0603
L11
601/0603
VB
D_GND
R59
1K
BACK_L
R60
10K
2. Working principle: 12V high voltage is needed for lightening display screen, so the boost circuit
must be matched to fulfill. This circuit includes two parts: boost circuit and display screen jack circuit.
Boost circuit is composed of DC-DC control IC Rt9284 and peripheral circuit; VIN is power input; EN is
enable end of Rt9284, effective when in high level; SW is high voltage output pin and FB is feedback pin.
After power on, the internal boost circuit of L10 and Rt9284 begins to boost and storage energy.
When current of L10 reaches 750mA, RT9284 internal switch turns off, and supplies power for the rear
circuit through external diode D3 at the same time when the switch is off. Voltage divide detect circuit
sends the detected voltage in pin 3 of RT9284. When detect voltage of pin 3 is lower than 1.235V
reference voltage (this IC has a 1.235V reference voltage comparator inside), the internal switch is on,
the internal boost circuit of L10 and RT9284 begins to boost and store energy. When current of L10
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