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TEA1501 Datasheet(PDF) 5 Page - NXP Semiconductors |
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TEA1501 Datasheet(HTML) 5 Page - NXP Semiconductors |
5 / 20 page 1998 Aug 19 5 Philips Semiconductors Preliminary specification Greeny; GreenChip ™ TEA1501 FUNCTIONAL DESCRIPTION The TEA1501 contains a high voltage power switch, a high voltage startup circuit and low voltage control circuitry on the same IC. Together with a transformer and a few external components a low power, isolated, flyback converter can be built. The Greeny system operates in a burst mode. During each burst period the output voltage is regulated to a desired voltage level. System operation ON/OFF The Greeny system can be switched on and off by means of a low cost, low voltage switch. In the Off mode the startup current source and power switch are disabled. In the On mode, Greeny delivers the startup current for the supply capacitor and after the supply voltage reaches the startup level Greeny activates the power switch. STARTUP The startup is realized with a high voltage startup current source instead of a dissipative bleeder resistor which is commonly used by low voltage control ICs. When Greeny is switched on, the startup current source is enabled and starts charging the Vaux capacitor. The startup current level is high and accurate (typical 1.8 mA) which results in a well-defined and short startup time, within 0.25 s. After the supply voltage reaches the startup level the current source is switched off and the Vaux capacitor supplies the chip. Reducing the power dissipation in the current source to zero after startup is one of the green features of Greeny. OPERATION After startup the flyback converter starts delivering energy to the secondary and auxiliary winding. The Greeny system works with fixed switching frequency and fixed peak current. As all the windings of the flyback transformer have the same flux variation, the secondary voltage and the auxiliary voltage are related via the turns-ratio (ns/na). Therefore, the isolated secondary voltage is controlled by the non-isolated auxiliary voltage. The burst mode operates by switching at high frequency until the Vaux voltage reaches its regulation level of 20 V. Greeny stops switching until the time period set by the burst oscillator has expired. At the start of the next burst period Greeny starts switching at high frequency and repeats the cycle again. To guarantee a stable operation in a burst mode controlled system a Vaux slope compensation circuit is integrated in Greeny. The Greeny system delivers a constant voltage to the secondary load until a burst duty cycle of 40%. DATA TRANSFER The TEA1501 has a data transfer function which makes communication from the isolated secondary side to the non-isolated primary side of the transformer possible, without using an opto-coupler. This communication function is activated by increasing the secondary load. With this data transfer function a main power supply can be switched on and off by the Greeny system. The power delivered to the secondary and auxiliary winding is proportional to the number of primary current pulses per burst period, provided that the converter operates in discontinuous conduction mode. During each burst period the number of primary current pulses is counted. A threshold (Ndata) of 56 pulses is integrated. The clamp level on the OOD pin is set to data-on level from data-off level in case the Ndata threshold is passed. This data-on clamp level can be sensed by the on/off input of a main supply control IC of the GreenChip ™ family. The data-on clamp level is maintained until a burst appears with a number of pulses below the Ndata threshold. |
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