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TDA4853 Datasheet(PDF) 13 Page - NXP Semiconductors |
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TDA4853 Datasheet(HTML) 13 Page - NXP Semiconductors |
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13 / 60 page  1999 Jul 13 13 Philips Semiconductors Product specification I2C-bus autosync deflection controllers for PC/TV monitors TDA4853; TDA4854 TDA4854: dynamic focus section [FOCUS (pin 32)] This section generates a complete drive signal for dynamic focus applications. The amplitude of the horizontal parabola is internally stabilized, thus it is independent of the horizontal frequency. The amplitude can be adjusted via register HFOCUS. Changing horizontal size may require a correction of HFOCUS. To compensate for the delay in external focus amplifiers a ‘pre-correction’ for the phase of the horizontal parabola has been implemented. The amplitude of the vertical parabola is independent of frequency and tracks with all vertical adjustments. The amplitude can be adjusted via register VFOCUS. FOCUS (pin 32) is designed as a voltage output for the superimposed vertical and horizontal parabolas. B+ control function block The B+ control function block of the TDA4853; TDA4854 consists of an Operational Transconductance Amplifier (OTA), a voltage comparator, a flip-flop and a discharge circuit. This configuration allows easy applications for different B+ control concepts. See also Application Note AN96052: “B+ converter Topologies for Horizontal Deflection and EHT with TDA4855/58”. GENERAL DESCRIPTION The non-inverting input of the OTA is connected internally to a high precision reference voltage. The inverting input is connected to BIN (pin 5). An internal clamping circuit limits the maximum positive output voltage of the OTA. The output itself is connected to BOP (pin 3) and to the inverting input of the voltage comparator. The non-inverting input of the voltage comparator can be accessed via BSENS (pin 4). B+ drive pulses are generated by an internal flip-flop and fed to BDRV (pin 6) via an open-collector output stage. This flip-flop is set at the rising edge of the signal at HDRV (pin 8). The falling edge of the output signal at BDRV has a defined delay of td(BDRV) to the rising edge of the HDRV pulse (see Fig.23). When the voltage at BSENS exceeds the voltage at BOP, the voltage comparator output resets the flip-flop and, therefore, the open-collector stage at BDRV is floating again. An internal discharge circuit allows a well defined discharge of capacitors at BSENS. BDRV is active at a LOW-level output voltage (see Figs 23 and 24), thus it requires an external inverting driver stage. The B+ function block can be used for B+ deflection modulators in many different ways. Two popular application combinations are as follows: • Boost converter in feedback mode (see Fig.23) In this application the OTA is used as an error amplifier with a limited output voltage range. The flip-flop is set on the rising edge of the signal at HDRV. A reset will be generated when the voltage at BSENS, taken from the current sense resistor, exceeds the voltage at BOP. If no reset is generated within a line period. The rising edge of the next HDRV pulse forces the flip-flop to reset. The flip-flop is set immediately after the voltage at BSENS has dropped below the threshold voltage VRESTART(BSENS). • Buck converter in feed forward mode (see Fig.24) This application uses an external RC combination at BSENS to provide a pulse width which is independent from the horizontal frequency. The capacitor is charged via an external resistor and discharged by the internal discharge circuit. For normal operation the discharge circuit is activated when the flip-flop is reset by the internal voltage comparator. The capacitor will now be discharged with a constant current until the internally controlled stop level VSTOP(BSENS) is reached. This level will be maintained until the rising edge of the next HDRV pulse sets the flip-flop again and disables the discharge circuit. If no reset is generated within a line period, the rising edge of the next HDRV pulse automatically starts the discharge sequence and resets the flip-flop. When the voltage at BSENS reaches the threshold voltage VRESTART(BSENS), the discharge circuit will be disabled automatically and the flip-flop will be set immediately. This behaviour allows a definition of the maximum duty cycle of the B+ control drive pulse by the relationship of charge current to discharge current. Supply voltage stabilizer, references, start-up procedures and protection functions The TDA4853; TDA4854 provides an internal supply voltage stabilizer for excellent stabilization of all internal references. An internal gap reference, especially designed for low-noise, is the reference for the internal horizontal and vertical supply voltages. All internal reference currents and drive current for the vertical output stage are derived from this voltage via external resistors. If either the supply voltage is below 8.3 V or no data from the I2C-bus has been received after power-up, the internal soft start and protection functions do not allow any of those outputs [HDRV, BDRV, VOUT1, VOUT2 and HUNLOCK (see Fig.25)] to be active. |
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