TCL M28 Schematic

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SERVICE MANUAL FOR M28 ONE-CHIP CHASSIS

PART I. Servicing Precautions

When working, the unit is with high voltage about 25KV inside. So, to avoid the risk of electric shock, be careful to adjust the chassis!

1. Only qualified personnel should perform service procedures.

2. All specification must be met over line voltage ranger of 110V AC to 240V AC 50Hz/60Hz.

3. Do not operate in WET/DAMP conditions.

4. Portions of the power supply board are hot ground. The remaining boards are cold ground.

5. Discharge of CRT anode should be done only to CRT ground strap.

6. When fuse blow, ensure to replace a fuse with the same type and specification.

7. Keep the wires away from the components with high temperature or high voltage.

8. When replacing the resister with high power, keep it over the PCB about 10mm.

9. The CRT anode high voltage has been adjusted and set in the factory. When repairing the chassis, do not make the high voltage exceed 27.5KV (The beam current is 0uA). Generally, the high voltage is set on 25.5KV±1.5KV (The beam current is 700uA). * The values of parameters above are for information only.

10. Before return the fixed unit, do check all the covering of wires to ensure that not fold or not short with any metal components. Check the entire protection units, such as control knobs, rear cabinet & front panel, insulation resister & capacitor, mechanical insulators and so on.

11. There are some mechanical and electrical parts associating with safety (EMC) features (Generally related to high voltage or high temperature or electric shock), these features cannot be found out from the outside. When replace these components, perhaps the voltage and power suit the requirements, but efficient X-ray protection may not be provided. All these components are marked with Ì in the schematic diagram. When replace these, you’d better look up the components listed in this manual. If the component you replaced not has the same safety (EMC) performance, harmful X-ray may be produced.

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PART II -Product Specification

1. Ambient Conditions:

1.1 Ambient Temperatures: a. Operating: -10 ~ +40ćć b. Storage: -15 ~ +45ćć

1.2 Humidity a. Operation: <80% b. Storage: <90%

1.3 Air Pressure: 86kpa ~ 106kpa

2. GENERAL SPECIFICATION

2.1 MPU & Chroma IC: TMPA8803CSN (One-Chip)

2.2 TV Broadcasting System PAL DK/BG SECAM DK/BG NTSC 3.579/4.43 AV MODE

2.3 Scanning Lines & Frequencies 525/625 lines

15.625KHz/15.75KHz 50/60Hz

2.4 Color Sub-Carrier: 4.433MHz/3.579MHz

2.5 IF: Picture 38.9MHz Sound 5.5/6.5MHz

2.6 Power Consumption: 80W

2.7 Power Supply: AC 220V 50Hz±10%

2.8 Audio Output Power (7%THD): 4W + 4W

2.9 Aerial Input Impedance: 75 Unbalanced Din Jack Ant.Input

2.10 Product Safety Requirement: VDE Approval

2.11 Product EMC/EMI Requirement: FTZ Approval

3. Basic Features of Controller

3.1 Channel Tuning Method: Voltage Synthesizer

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3.2 Presettable Program: 100 Programs

3.3 Tuning for VHF and UHF Bands: Auto/Manual/Fine Tuning

3.4 Picture and Sound Adjustment Bright, Contrast, Color and Volume Control TINT Control (NTSC) Sharpness Control

3.5 OSD General Features (Volume, Brightness, Contrast, Color, Program, Band, Auto Search, Manual, Tune, Muting, AV and Sleep Timer) NICAM and Dual Language German Stereo Indicator

3.6 Sleep Timer: 10-120 Minutes with 10Min.Increment

3.7 Auto Off When No Broadcasting Signal: 15 min

3.8 Full Function Infrared Remote Control

3.9 Remote Effective Distance: 8m

4. Construction of Front Panel Main Power Switch Remote Sensor Standby Indicator Menu Select TV/AV Select Program and Volume Up/Down

5. Construction of Real Panel

75 Aerial Terminal RCA Socket –Audio-R+L In/Out, Video- In/Out Y/U/V Input

6. Other Information

6.1 Colour Temperature: 9300K X=284 Y=299

6.2 Magnetic Field: Bv=0.2~0.5Gs

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PART III. Brief Introduction on Chassis

AV INPUT/

OUTPUT

RF IN

XTAL

OSC

INFRARED

REMOTE

CONTROL

TUNER SAW

TMPA8803CPN(M28)

I2C BUS

E2PROM

REMOTE

CONTROL

RECEIVER

SWITCH POWER

MC44608

NICAM BD

H DRIVE

R/G/B

V OUTPUT

DPC

H OUTPUT

AUDIO AMP

CRT

DRIVE

FBT

The TV signal is amplified by the frequency mixing circuit of the tuner. Then the tuner output PIF and SIF signals. The IF signals are amplified about 20dB by the pre IF amplifier (Q101). Having passed the SAW, the IF signals go into the TMP8803CPN from pin ƻ

, ƻ41. The IF signal pass the video detect circuit to generate CVBS signal. Then the processor deals the signal with luminance and chroma separation. The processor deals the luminance signal with Y-Delay, Y-Gamma correction, Y-hf compensation and black strength, all which ensure that there are enough bandwidth and gain with Y signal, so that the resolution of picture detail is improved and the Y signal is well timed with chroma signal. The processor also deals the chroma signal with chroma sub-carrier recovery, color system recognition and color signal decoding, then outputs B-Y and R-Y color difference signal. A matrix circuit converts the color difference signal (Y, B-Y and R-Y) into primary color signal (R/G/B). On the other hand, the processor separated the horizontal and vertical sync signal from the CVBS signal which was generated by video detect circuit. Having passed the horizontal (or vertical) frequency dividing circuit, the H (or V) OSC signal, which be generated by H-AFC (or V-AFC), is changed to H (or V) drive signal. The H/V drive signal make the horizontal/vertical circuits and scan output circuit to generate H/V saw tooth wave

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1.Channel Section

The RF signal is converted into IF signal by the tuner. Then the IF signal cross the IF amplifier circuit (pre IF amplifier) to get a gain about 15dB. By the coupling capacitance (c110) and the match resistance (R114 56), the input resistance of the pre-IF amplifier match with the tuner. The si gnals pass a parallel connection circuit with voltage NFB, which combines the advantages of low output impedance, of wide dynamic range and of less components. R116 is a voltage NFB component, which is used to adjust the gain in the pass band. Having been amplified by the IF amplifier, the IF signal pass a SAW, and then come into TMPA8803CSN from pin41 and pin42 with balance. The processor deal the IF signal with IF detection, PLL demodulation, IF AGC, AFC, video peak detection, and color system recognition etc., then output a AGC signal from pin 43 to the tuner to adjust the input amplitude of IF signal. R217, C218 and C219 make up of picture IF PLL circuit, which is used to control IF detection. IC201 output a sound IF signal from pin 31 and a video signal, which will be amplified by Q209, from pin30. The processor output a sound system control signal to Q208. If the processor output a high level from pin59 (sound detection), Q208 is on, and a video signal is separated from the IF signal by a trap. With capacitance coupling, the video signal comes into IC201 from pin26, and then it is selected by inner switches and output from pin45. Having come out, the video signal will be amplified by Q210, and a sync signal will be separated by a sync separate circuit which is made up by C208, Q202 and Q203. Then the video come into inner 870X CPU module from IC201 pin62 to detect whether the signal is live signal.

Tuning control and band switch control circuits The processor output a tuning control signal from pin60. The control signal will pass Q103 common emitter amplifying circuit, then an integrating circuit. Finally, it is added to the VT terminal to provide all channels’ tuning voltage for the tuner to stabilize the channels.

2.Vertical Output Section

TMPA8803CSN outputs vertical saw-tooth wave from pin 16. It come to pin5 of LA7840 with DC coupling, and is amplified by inner difference amplifier. Pin4 of LA7840 is the same phase input terminal. R307 and R308 are DC offset resistances. C305 is a filter capacitor. In application to M28, pin4 of la7840 is fixed as the DC amplify ref terminal. The amplified saw tooth wave come out la7840 from pin2 and make the deflect coil to generate the deflect current. R314 and C301 filtrate the inductive interference from the horizontal deflect coil. R317 and C309 are used to eliminate spurious oscillation generated by the deflect coil and distributed capacitance resonance. C308, R313, C307 and accessory circuit are in charge of draw AC saw tooth wave out at the deflect coil terminal connected with R315 & R316, and feedback to the input terminal of la7840 (pin5) to correct the linearity of horizontal scan. C306 is a high frequency decoupling capacitor. D301 and C303 make up of a voltage pump up circuit. La7840 output a vertical kickback impulse from pin7 to locate the OSD characters.

3.Horizontal Output Section

The processor outputs horizontal drive impulse from pin 13. The drive impulse is done with voltage division by R238 and R401, and then comes to the base of the drive triode (Q401). C401 is used to eliminate the noise in the H drive impulse. T401 is a horizontal drive transformer. Q402 is a horizontal output triode with a damper inside. L402 is connected with the emitter of the horizontal output diode to eliminate the radiation and to improve the distortions at the cross of vertical and horizontal white

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lines. C406 and C402 are retrace capacitors and C421 is an s-correct capacitor. L441 and L442 are horizontal linear inductors. R441 is used to eliminate the parasitic oscillation caused by horizontal linear inductors. C420, R413 and D411 are used to correct the M-distortion in horizontal direction. C422, R415 and R415A are coupling components for the horizontal retrace impulse, which are feed back to pin 12 of TMPA8803CSN. D404 is a negative peak-killer diode.

Horizontal scanning distortion and the method to compensate it The deflect coil and the horizontal output triode have some resistance R while they are ducting. The resistance R will cause the non-linear distortion, which means that the right direction scanning speed of the electron beam becomes slower, and the right of the raster is compressed to generate distortion. We use a horizontal linear adjuster to compensate this kind of distortion. We use L412 and L411 as the H linear adjusters in H scanning section of M28 chassis. R411, which is parallel connected with L411 and L412, is a despiking resistance for preventing the oscillation by compensating inductor and the stray capacitance. The lin ear adjuster is a transductor coi l with a magnetic core inside. If the curren t, which pass the linear adjuster coil, increase to a certain value, the magnetic core becomes saturated to decrease the inductance of the linear adjustment inductor. If the +B is steady, the increase speed of Iy is faster to compensate the reducing of deflecting current by the resistance R mention above. We can adjust the magnetic core to chang the inductance of the linear compensate inductor to adjust the H linearity.

The EHT generation circuit The FBT supply the anode high voltage, focus voltage and screen voltage for M28 chassis. D401 and C408 are in charge of regulating the primary impulse of the transformer to output a voltage of 190V for the video amplifiers. The ( 10 ) ~ ( 8 ) coils of the FBT supply the heater with power. Having passed the divider and clipping circuits, whi ch are maded up by R415, R415A, C422 and D404, the H retrace impulses getting out from ( 3 ) ~ ( 10 ) coils are inputed to pin12 of TMPA8803CSN to generate sand castle impulse. To limit the beam current in a safe range, we add a ABL circuit in M28 chassis. We add two sampling resistances (R414, R415) between +24V power supply and pin7 of the FBT. The voltage at the joint of the two resistances is feed back to pin27 of TMPA8803CSN to control bright and contrast to limit the beam current. It is also in charge of regulating EHT. C410 is a fliter capacitor for ABL voltage.

The impulses, which are induced by secondary coil 5, are changed to 12V once passed the regulating and fliting circuit made up by D402 and C413. IC401 change 12V power supply to 9V for many circuits, such as R/G/B output circuit of TMPA8803CSN, IC4053, pre IF-amplifier circuit, bright dots killer circuit and S terminal circuit. IC402 outputs a 5V power supply for the keyboard circuit. C418, C417, C423 and C425 are fliter capacitors. D402 and C413 are incharge of regulating and flitering for the output of coil6 to supply the V scanning output section with 24V power. The 24V is added to the upper terminal of the V deflecting yoke as the DC bias for the movement of V center.

Extension distortion and compensation This kind of distortion is mainly caused by the structure of CRT. Due to the srcreen of SF CRT is not a ture flat screen, the distances from the deflecting center to the screen are not the same. The scanning speed of the electron beam is uniform. If the electron beam scannning the screen equally with the

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effect of ture linear sawtooth current, the E-W sides of the picture are stretched. That is the extension distortion. Usually, we add a S-correct capacitor in series with the deflecting coil to compensate this kind of distortion. The integral character of S-correct capacitor make the current waveform S shape. So the scanning speed of electron beam at the center of screen is faster than the one at the side. So this action can correct the extension distortion. C421 is a S-correct capacitor. The capacitance is inverse ratio with the correcting effect.

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PART IV. IC Pin Description

1. MC44608-High Voltage PWM Controller

Pin Name Description

The Demag pin offers 3 different functions: Zero voltage crossing detection

1 Demag

sense

Control Input

4 Ground This pin is the ground of the primary side of the SMPS.

5Driver

7 This pin is to provide isolation between the Vi pin 8 and the VCC pin 6.

(50mV), 24 A current detectionǂ and 120 A current detection. The 24 Aǂǂ level is used to detect the secondary reconfiguration status and the 120 A level ǂ to detect an Over Voltage status called Quick OVP. The Current Sense pin senses the voltage developed on the series resistor inserted in the source of the power MOSFET. When Isense reaches 1V, the Driver output (pin 5) is disabled. This is known as the Over Current Protection function. A 200 A current source is flowing out of the pin 3 during theǂ start–up phase and during the switching phase in case of the Pulsed Mode of operation. A resistor can be inserted between the sense resistor and the pin 3, thus a programmable peak current detection can be performed during the SMPS stand–by mode. A feedback current from the secondary side of the SMPS via the opto–coupler is injected into this pin. A resistor can be connected between this pin and GND to allow the programming of the Burst duty cycle during the Stand–by mode.

The current and slew rate capability of this pin are suited to drive Power MOSFETs. This pin is the positive supply of the IC. The driver output gets disabled when the voltage becomes higher than 15V and the operating range is between 6.6V and 13V. An intermediate voltage level of 10V creates a disabling condition called Latched Off phase.

This pin can be directly connected to a 500V voltage source for start–up function of the IC. During the Start–up phase a 9 mA current source is internally delivered to the VCC pin 6 allowing a rapid charge of the VCC capacitor. As soon as the IC starts–up, this current source is disabled.

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OPERATING DESCRIPTION

Regulation

The pin 3 senses the feedback current provided by the opto-coupler. During the switching phase the switch S2 is closed and the shunt regulator is accessible by the pin 3. The shunt regulator voltage is typically 5V. The dynamic resistance of the shunt regulator represented by the zener diode is 20:. The gain of the Control input is given on Figure 10 which shows the duty cycle as a function of the current injected into the pin 3.

A 4KHz filter network is inserted between the shunt regulator and the PWM comparator to cancel the high frequency residual noise.

The switch S3 is closed in Stand–by mode during the Latched Off Phase while the switch S2 remains open. (See section PULSED MODE DUTY CYCLE CONTROL).

The resistor Rdpulsed (Rduty cycle burst) has no effect on the regulation process. This resistor is used to

determine the burst duty cycle described in the chapter “Pulsed Duty Cycle Control” on page 8.

PWM Latch

The MC44608 works in voltage mode. The on–time is controlled by the PWM comparator that compares the oscillator sawtooth with the regulation block output.

The PWM latch is initialized by the oscillator and is reset by the PWM comparator or by the current sense comparator in case of an over current. This configuration ensures that only a single pulse appears at the circuit output during an oscillator cycle.

Current Sense

The inductor current is converted to a positive voltage by inserting a ground reference sense resistor R

Sense

in series

with the power switch.

The maximum current sense threshold is fixed at 1V. The peak

current is given by the following

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equation:

Ipk

max

= 1/R

(:) (A)

sense

In stand–by mode, this current can be lowered as due to the activation of a 200PA current source: Ipk

MAX-STBY

The current sense input consists of a filter (6k:, 4pF) and of a leading edge blanking. Thanks to that, this pin is not sensitive to the power switch turn on noise and spikes and practically in most applications, no filtering network is required to sense the current.

Finally, this pin is used: – as a protection against over currents (I

sense

> I)

– as a reduction of the peak current during a Pulsed Mode switching phase.

The overcurrent propagation delay is reduced by producing a sharp output turn off (high slew rate). This results in an abrupt output turn off in the event of an over current and in the majority of the pulsed mode switching sequence.

Demagnetization Section

The MC44608 demagnetization detection consists of a comparator designed to compare the V

winding voltage to a

reference that is typically equal to 50mV.

This reference is chosen low to increase effectiveness of the demagnetization detection even during start–up.

A latch is incorporated to turn

the demagnetization block output into a low level as soon as a voltage less than 50 mV is detected, and to keep it in this state until a new pulse is generated on the output. This avoids any ringing on the input signal which may alter the demagnetization detection.

For a higher safety, the demagnetization block output is also directly connected to the

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output, which is disabled during the demagnetization phase.

The demagnetization pin is also used for the quick, programmable OVP. In fact, the demagnetization input current is sensed so that the circuit output is latched off when this current is detected as higher than 120PA.

This function can be inhibited by grounding it but in this case, the quick and programmable OVP is also disabled.

Oscillator

The MC44608 contains a fixed frequency oscillator. It is built around a fixed value capacitor CT succesively charged and discharged by two distinct current sources ICH and IDCH. The window comparator senses the CT voltage value and activates the sources when the voltage is reaching the

2.4V/4V levels.

The complete demagnetization status DMG is used to inhibit the recharge of the CT capacitor. Thus in case of incomplete transformer demagnetization the next switching cycle is postpone until the DMG signal appears. The oscillator remains at 2.4V corresponding to the sawtooth valley voltage. In

this way the SMPS is working in the so called SOPS mode (Self Oscillating Power Supply). In that case the effective switching frequency is variable and no longer depends on the oscillator timing but on the external working conditions (Refer to DMG signal in the Figure 5). The OSC and Clock signals are provided according to the Figure 5. The Clock signals correspond to the CT capacitor discharge. The bottom curve represents the current flowing in the sense resistor Rcs. It starts from zero and stops when the sawtooth value is equal to the control voltage Vcont. In this way the SMPS is regulated with a voltage mode control.

Overvoltage Protection

The MC44608 offers two OVP functions: – a fixed function that detects when V

is higher than 15.4V

– a programmable function that uses the demag pin. The current flowing into the demag pin is mirrored and compared to the reference current Iovp (120PA). Thus this OVP is quicker as it is not impacted by the V

inertia and is called QOVP.

In both cases, once an OVP condition is detected, the output is latched off until a new circuit

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START–UP.

Start–up Management

The Vi pin 8 is directly connected to the HV DC rail Vin. This high voltage current source is

internally connected to the

pin and thus is used to

charge the V

capacitor. The

VCC capacitor charge period corresponds to the Start–up phase. When the V

voltage

reaches 13V, the high voltage 9mA current source is disabled and the device starts working. The device enters into the switching phase.

It is to be noticed that the maximum rating of the Vi pin 8 is 700V. ESD protection circuitry is not currently added to this pin due to size limitations and technology constraints. Protection is limited by the drain–substrate junction in avalanche breakdown. To help increase the application safety against high voltage spike on that pin it is possible to insert a small wattage 1k: series resistor between the Vin rail and pin 8.

The Figure 6 shows the V into the V

pin during the switching phase. This case can be encountered in SMPS when the self

voltage evolution in case of no external current source providing current

supply through an auxiliary winding is not present (strong overload on the SMPS output for example). The Figure 16 also depicts this working configuration.

In case of the hiccup mode, the duty cycle of the switching phase is in the range of 10%.

Mode Transition

The LW latch Figure 7 is the memory of the working status at the end of every switching sequence. Two different cases must be considered for the logic at the termination of the SWITCHING PHASE:

1. No Over Current

was observed

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2. An Over Current was observed

These 2 cases are corresponding to the signal labeled NOC in case of “No Over Current” and “OC” in case of Over Current. So the effective working status at the end of the ON time memorized in LW corresponds to Q=1 for no over current and Q=0 for over current. This sequence is repeated during the Switching phase.

Several events can occur:

1. SMPS switch OFF

2. SMPS output overload

3. Transition from Normal to Pulsed Mode

4. Transition from Pulsed Mode to Normal Mode



1. SMPS SWITCH OFF

When the mains is switched OFF, so long as the bulk electrolithic bulk capacitor provides energy to the SMPS, the controller remains in the switching phase. Then the peak current reaches its maximum peak value, the switching frequency decreases and all the secondary voltages are reduced. The V

voltage is also reduced. When VCC is equal to 10V, the SMPS stops working.

2. Overload

In the hiccup mode the 3 distinct phases are described as follows (refer to Figure 6): The SWITCHING PHASE: The SMPS output is low and the regulation block reacts by increasing the ON time (dmax = 80%). The OC is reached at the end of every switching cycle. The LW latch (Figure

7) is reset before the VPWM signal appears. The SMPS output voltage is low. The V

voltage cannot

be maintained at a normal level as the auxiliary winding provides a voltage which is also reduced in a ratio similar to the one on the output (i.e. Vout nominal / Vout short–circuit). Consequently the V

voltage is reduced at an operating rate given by the combination VCC capacitor value together with the I

working consumption (3.2mA) according to the equation 2. When VCC crosses 10V the

WORKING PHASE gets terminated. The LW latch remains in the reset status.

The LATCHED–OFF PHASE: The V

capacitor voltage continues to drop. When it reaches 6.5V

this phase is terminated. Its duration is governed by equation 3.

The START–UP PHASE is reinitiated. The high voltage start–up current source (–I activated and the MODE latch is reset. The V

voltage ramps up according to the equation 1. When it

= 9mA) is

CC1

reaches 13V, the IC enters into the SWITCHING PHASE.

The NEXT SWITCHING PHASE: The high voltage current source is inhibited, the MODE latch (Q=0) activates the NORMAL mode of operation. Figure 2 shows that no current is injected out pin 2. The over current sense level corresponds to 1V.

As long as the overload is present, this sequence repeats. The SWITCHING PHASE duty cycle is in the range of 10%.

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3. Transition from Normal to Pulsed Mode

In this sequence the secondary side is reconfigured (refer to the typical application schematic on page

13). The high voltage output value becomes lower than the NORMAL mode regulated value. The TL431 shunt regulator is fully OFF. In the SMPS stand–by mode all the SMPS outputs are lowered except for the low voltage output that supply the wake–up circuit located at the isolated side of the power supply. In that mode the secondary regulation is performed by the zener diode connected in parallel to the TL431.

The secondary reconfiguration status can be detected on the SMPS primary side by measuring the voltage level present on the auxiliary winding Laux. (Refer to the Demagnetization Section). In the reconfigured status, the Laux voltage is also reduced. The V

self–powering is no longer possible

thus the SMPS enters in a hiccup mode similar to the one described under the Overload condition.

In the SMPS stand–by mode the 3 distinct phases are: The SWITCHING PHASE: Similar to the Overload mode. The current sense clamping level is reduced according to the equation of the current sense section, page 5. The C.S. clamping level depends on the power to be delivered to the load during the SMPS stand–by mode. Every switching sequence ON/OFF is terminated by an OC as long as the secondary Zener diode voltage has not been reached. When the Zener voltage is reached the ON cycle is terminated by a true PWM action. The proper SWITCHING PHASE termination must correspond to a NOC condition. The LW latch stores this NOC status.

The LATCHED OFF PHASE: The MODE latch is set.

The START–UP PHASE is similar to the Overload Mode. The MODE latch remains in its set status (Q=1).

The SWITCHING PHASE: The Stand–by signal is validated and the 200PA is sourced out of the Current Sense pin 2.



4. Transition from Stand–by to Normal

The secondary reconfiguration is removed. The regulation on the low voltage secondary rail can no longer be achieved, thus at the end of the SWITCHING PHASE, no PWM condition can be encountered. The LW latch is reset.

At the next WORKING PHASE a NORMAL mode status takes place.

In order to become independent of the recovery time SWITCHING PHASE constant on the secondary side of the SMPS an additional reset input R2 is provided on the MODE latch. The condition I

<24PA corresponds to the activation of the secondary reconfiguration status. The R2 reset

demag

insures a return into the NORMAL mode following the first corresponds to 1V. START–UP PHASE.

Pulsed Mode Duty Cycle Control

During the sleep mode of the SMPS the switch S3 is closed and the control input pin 3 is connected to

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a 4.6V voltage source thru a 500: resistor. The discharge rate of the VCC capacitor is given by I

–latch (device consumption during the LATCHED OFF phase) in addition to the current drawn out

of the pin 3. Connecting a resistor between the Pin 3 and GND (R drawn from the V presence of the resistor R

through pin 3. The duration of the LATCHED OFF phase is impacted by the

DPULSED

. The equation 3 shows the relation to the pin 3 current.

DPULSED

) a programmable current is

Pulsed Mode Phases

Equations 1 through 8 define and predict the effective behavior during the PULSED MODE operation. The equations 6, 7, and 8 contain K, Y, and D factors. These factors are combinations of measured parameters. They appear in the parameter section “K factors for pulsed mode operation” page 4. In equations 3 through 8 the pin 3 current is the current defined in the above section “Pulsed Mode Duty Cycle Control”.

2. TDA9801-Single standard VIF-PLL demodulator and FM-PLL detector

FUNCTIONAL DESCRIPTION

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SYMBOL PIN DESCRIPTION

VIF1 VIF2 2 VIF differential input 2

TOP 3 tuner AGC TakeOver Point (TOP) connection ADJ 4 phase adjust connection MUTE 5 sound mute switch connection TPLL 6 PLL time constant connection CVBS 7 CVBS (positive) video output n.c. 8 not connected AF 9 AF output DAF 10 AF amplifier decoupling capacitor connection SI 11 sound intercarrier input TAGC 12 tuner AGC output VSO 13 video and sound intercarrier output VI 14 buffer amplifier video input AFC 15 AFC output VCO1 16 VCO1 reference circuit for 2fPC VCO2 17 VCO2 reference circuit for 2fPC GND 18 ground supply (0 V) AGC 19 AGC detector capacitor connection VP 20 supply voltage (+5 V)

VIF differential input 1

Stage IF amplifier

The VIF amplifier consists of three AC-coupled differential amplifier stages. Each differential stage comprises a feedback network controlled by emitter degeneration.

AGC detector, IF AGC and tuner AGC

The automatic control voltage to maintain the video output signal at a constant level is generated in accordance with the transmission standard. Since the TDA9801 is suitable for negative modulation only the peak sync pulse level is detected.

The AGC detector charges and discharges capacitor C voltage on capacitor C

AGC is transferred to an internal IF control signal, and is fed to the tuner AGC to

AGC to set the IF amplifier and tuner gain. The

generate the tuner AGC output current on pin TAGC (open-collector output). The tuner AGC takeover point level is set at pin TOP. This allows the tuner to be matched to the SAW filter in order to achieve the optimum IF input level.

Frequency detector and phase detector

The VIF amplifier output signal is fed into a frequency detector and into a phase detector. During acquisition the frequency detector produces a DC current proportional to the frequency difference between the input and the VCO signal. After frequency lock-in the phase detector produces a DC current proportional to the phase difference between the VCO and the input signal. The DC current of

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either frequency detector or phase detector is converted into a DC voltage via the loop filter which controls the VCO frequency.

Video demodulator

The true synchronous video demodulator is realized by a linear multiplier which is designed for low distortion and wide bandwidth. The vision IF input signal is multiplied with the ‘in phase’ component of the VCO output. The demodulator output signal is fed via an integrated low-pass filter (f

= 12

MHz) for suppression of the carrier harmonics to the video amplifier.

VCO, AFC detector and travelling wave divider

The VCO operates with a symmetrically connected reference LC circuit, operating at the double vision carrier frequency. Frequency control is performed by an internal variable capacitor diode.

The voltage to set the VCO frequency to the actual double vision carrier frequency is also amplified and converted for the AFC output current.

The VCO signal is divided-by-2 with a Travelling Wave Divider (TWD) which generates two differential output signals with a 90 degree phase difference independent of the frequency.

Video amplifier

The composite video amplifier is a wide bandwidth operational amplifier with internal feedback. A nominal positive video signal of 1 V (p-p) is present at pin VSO.

Buffer amplifier and noise clipper

The input impedance of the 7 dB wideband CVBS buffer amplifier (with internal feedback) is suitable for ceramic sound trap filters. Pin CVBS provides a positive video signal of 2 V (p-p). Noise clipping is provided internally.

Sound demodulation

IMITER AMPLIFIER

The FM sound intercarrier signal is fed to pin SI and through a limiter amplifier before it is demodulated. The result is high sensitivity and AM suppression. The limiter amplifier consists of 7 stages which areinternally AC-coupled in order to minimizing the DC offset.

FM-PLL DETECTOR

The FM-PLL demodulator consists of an RC oscillator, loop filter and phase detector. The oscillator frequency is locked on the FM intercarrier signal from the limiter amplifier. As a result of this locking, the RC oscillator is frequency modulated. The modulating voltage (AF signal) is used to control the oscillator frequency. By this, the FM-PLL operates as an FM demodulator.

AF AMPLIFIER

The audio frequency amplifier with internal feedback is designed for high gain and high common-mode rejection. The low-level AF signal output from the FM-PLL demodulator is amplified and buffered in a low-ohmic audio output stage. An external decoupling capacitor CDAF removes the

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