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TEA1566 データシート(PDF) 6 Page - NXP Semiconductors |
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TEA1566 データシート(HTML) 6 Page - NXP Semiconductors |
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6 / 24 page  1999 Apr 20 6 Philips Semiconductors Preliminary specification GreenChip ™; SMPS module TEA1566 Reference All reference voltages are derived from a temperature compensated, on-chip, band gap. The band gap reference voltage is also used, together with an external resistor connected at pin Iref, to generate accurate, temperature independent, bias currents in the chip: [A] The frequency of the controller is also set by the reference resistor Rref (also see Section “Oscillator”). Sample and hold GreenChip ™ ICs employ voltage mode feedback for regulating the output voltage. In primary feedback mode, a novel sample and hold circuit is used. The sample and hold circuit works by sampling the current into pin Dem, which is related to the output voltage via Rdem, during the time that the secondary current is flowing: a × V out =Iref × Rdem +Vdem+ where: Vdem+ is specified in chapter “Characteristics” a = a constant determined by turn ratio of the transformer. This sampled current information is stored on the external capacitor connected to pin Vctrl. The pulse width modulator uses this voltage information to set the duty cycle of operation for the power MOSFET. In secondary feedback, the feedback voltage is provided by an opto-coupler. Pulse width modulator The pulse width modulator, which is made up of an inverting error amplifier and a comparator (see Fig.2), drives the power MOSFET with a duty cycle which is inversely proportional to the voltage on pin Vctrl. In primary feedback mode, this is the voltage on the sample and hold capacitor and in secondary feedback mode, this voltage is provided by an opto-coupler. A signal from the oscillator sets a latch that turns on the power MOSFET. The latch is reset by the signal from the pulse width modulator or by the duty cycle limiting circuit. The latching PWM mode of operation prevents multiple switching of the power switch. The maximum duty cycle is set internally at 80%. Figure 7 shows the normal switching operation of the IC. I REF V REF R REF -------------- = Oscillator The oscillator is used to set the switching duty cycle by comparing the oscillator ramp to the output of the error amplifier in the pulse width modulator circuit.The oscillator is fully integrated and works by charging and discharging an internal capacitor between two voltage levels to create a sawtooth waveform with a rising edge which is 80% of the oscillator cycle. This ratio is used to set a maximum switching duty cycle of 80% for the IC. The oscillator is internally trimmed to 5% accuracy. The oscillator frequency can be adjusted between 50 to 100 kHz (see symbol fosc-h-range in Chapter “Characteristics”) by changing the external reference resistor (see symbol Rref in Chapter “Characteristics”) that sets the chip bias currents. This gives additional flexibility to the power supply designer in the choice of his system components.The frequency is correlated with the value of the reference resistor Rref (see Fig.6). In Chapter “Characteristics” fosc-typical, fosc-l and fosc-h and the Rref operating resistor range are specified. Fig.6 Frequency as function of the RREF value. handbook, halfpage 10 20 30 40 110 90 50 30 70 MGR936 RREF (kΩ) high frequency (kHz) 55 45 25 15 35 low frequency (kHz) (2) (1) (1) High frequency mode. (2) Low frequency mode. |
同様の部品番号 - TEA1566 |
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同様の説明 - TEA1566 |
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