TDA8358J Full bridge vertical deflection output circuit in ... - Laro

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Philips SemiconductorsFull bridge vertical deflection output circuitin LVDMOS with east-west amplifierProduct specificationTDA8358JR M calculationBefore calculating the measuring resistor (R M ), thedifferential input voltage [V i(dif) ] has to be known. Thisvoltage can be measured between pins INA and INB. TheVcalculation is as follows: R M= i(dif)(p-p)---------------------I o(p-p)Most of the TV signal processors from Philips have acurrent output. This current has to be converted byresistors at the input of the TDA8358J (R CV1 and R CV2 ).The voltage across these resistors can be calculated. Thedifferential input voltage is given in the following equation(see also Fig 5):V i(dif)(p-p) =I i1(p-p) × R CV1 − [−I i2(p-p) ] × R CV2I I(bias)0TV SIGNALPROCESSORI I(bias)0I i1(p-p)I i2(p-p)C52.2 nFC62.2 nFR CV12.2 kΩR CV22.2 kΩFig.5 Differential input voltage.Values for these currents are, for instance:I i(bias) = 400 µA; I i1(p-p) =I i2(p-p) = 475 µA.Therefore the differential input voltage be as follows:V i(dif)(p-p) = 475 µA × 2.2 kΩ −(−475 µA × 2.2 kΩ)= 2.09 V12MBL520Supply voltage calculationFor calculating the minimum required supply voltage,several specific application parameter values have to beknown. These parameters are the required maximum(peak) deflection coil current I coil(peak) , the coil impedanceR coil and L coil and the measuring resistance of R M . Therequired maximum (peak) deflection coil current shouldalso include the overscan.The deflection coil resistance has to be multiplied by 1.2 inorder to take account of hot conditions.Chapter “Characteristics” supplies values for the voltagelosses of the vertical output stage. For the first part of thescan the voltage loss is given by V loss(1) . For the secondpart of the scan the voltage loss is given by V loss(2) .The voltage drop across the deflection coil during scan isdetermined by the coil impedance. For the first part of thescan the inductive contribution and the ohmic contributionto the total coil voltage drop are of opposite sign, while forthe second part of the scan the inductive part and theohmic part have the same sign.For the vertical frequency the maximum frequencyoccurring must be applied to the calculations.The required power supply voltage V P for the first part ofthe scan is given by:V P1 ( ) I coil( peak)( R coil + R M )– L coil × 2I coil( peak)× f vert( max)+ V loss( 1)The required power supply voltage V P for the second partof the scan is given by:The minimum required supply voltage V P shall be thehighest of the two values V P(1) and V P(2) . Spread in supplyvoltage and component values also has to be taken intoaccount.Flyback supply voltage calculationIf the flyback time is known, the required flyback supplyvoltage can be calculated by the simplified formula:where:=×V P2 ( ) = I coil( peak)×( R coil + R M )+ L coil × 2I coil( peak)× f vert( max)+ V loss( 2)V FB=× R -------------------------- coil + R M( )1 e – t FB–⁄ xI coil p–pL coilR coilR Mx = --------------------------+2002 Sep 25 12
Philips SemiconductorsFull bridge vertical deflection output circuitin LVDMOS with east-west amplifierProduct specificationTDA8358JThe flyback supply voltage calculated this way isapproximately 5% to 10% higher than required.Calculation of the power dissipation of the verticaloutput stageThe power dissipation of the vertical output stage is givenby the formula:P V =P sup − P LThe power to be supplied is given by the formula:IP sup = V coil( peak)P × ----------------------- + V2 P × 0.015 [A] + 0.3 [W]In this formula 0.3 [W] represents the average value of thelosses in the flyback supply.The average external load power dissipation in thedeflection coil and the measuring resistor is given by theformula:P L( I coil( peak)) 2= ------------------------------- × ( R3coil + R M )ExampleTable 1Table 2Application valuesSYMBOL VALUE UNITI coil(peak) 1.2 AI coil(p-p) 2.4 AL coil 5 mHR coil 6 ΩR M 0.6 Ωf vert 50 Hzt FB 640 µsCalculated valuesSYMBOL VALUE UNITV P 14 VR M +R coil (hot) 7.8 Ωt vert 0.02 sx 0.000641V FB 30 VP sup 8.91 WP L 3.74 WP V 5.17 WPower dissipation calculation for the east-west stageIn general the shape of the east-west output wave form isa parabola. The output voltage will be higher at thebeginning and end of the vertical scan compared to thevoltage at the scan middle, while the output current will behigher at the scan middle. This results in an almost uniformpower dissipation distribution during scan. Therefore thepower dissipation can be calculated by multiplying theaverage values of the output voltage and the outputcurrent of pin OUTEW.When verifying the dissipation the switch-on and switch-offdissipation should also be taken into account. Powerdissipation during start-up can be 3 to 5 times higher thanduring normal operation.Heatsink calculationThe value of the heatsink can be calculated in a standardway with a method based on average temperatures. Therequired thermal resistance of the heatsink is determinedby the maximum die temperature of 150 °C. In general werecommend a design for an average die temperaturenot exceeding 130 °C. It should be noted that theheatsink thermal resistance R th(h-a) found by performing astandard calculation will be lower then normally found fora vertical deflection stand alone device, due to thecontribution of the EW power dissipation to this value.EXAMPLEMeasured or known values:P EW = 3 W; P V = 6 W; T amb =40°C; T j = 130 °C;R th(j-c) = 4 K/W; R th(c-h) = 1 K/W.The required heatsink thermal resistance is given by:T j – T amb( ) = ------------------------ –( R+th( j – c)+ R th c – hR th h – aP EWP VWhen we use the values known we find:130 – 40( ) = --------------------- – (3+64 + 1 ) = 5 K/WR th h – aThe heatsink temperature will be:( ) )T h =T amb +R th(h-a) × P tot =40+5×9=85°C2002 Sep 25 13
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