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TEA1507P データシート(PDF) 9 Page - NXP Semiconductors |
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TEA1507P データシート(HTML) 9 Page - NXP Semiconductors |
9 / 20 page 2000 Dec 05 9 Philips Semiconductors Preliminary specification GreenChip ™II SMPS control IC TEA1507 Burst mode standby Pin CTRL (pin 3) is also used to implement the burst mode standby. In burst mode standby, the power supply enters a special low dissipation state, where it typically consumes less than 1 W of input power (Po < 100 mW), but is still able to supply a microprocessor, for example. Figure 12 shows a flyback converter using the burst mode standby function. The system enters burst mode standby when the microprocessor closes switches S2 and S3 on the secondary side. Switch S2 connects the high voltage output secondary winding to the low voltage microprocessor capacitor (CµC), bypassing Co. When the voltage on CµC exceeds the Zener voltage, the opto-coupler is activated, sending a large current signal to CTRL. In response to this signal, the IC stops switching and enters a ‘hiccup’ mode. This burst activation signal should be present for longer than the ‘burst blank’ period (typically 30 µs): the blanking time prevents false burst triggering due to spikes. Figure 11 shows the burst-mode standby signals. The hiccup mode during burst mode standby operation does not differ from the hiccup mode in safe-restart mode during a system fault condition (e.g. OVP or output short circuit). The power is reduced during soft-restart mode. Burst mode standby operation continues until the microcontroller opens switches S2 and S3. The system then enters the start-up sequence and begins normal switching behaviour. (For burst mode specification, see Figs 11 and 12.) Soft start-up (pin Isense) To prevent transformer rattle during hiccup, the transformer peak current is slowly increased by the soft start function. This can be achieved by inserting a resistor and a capacitor between pin Isense (pin 5) and the sense resistor. An internal current source charges the capacitor to V = Iss × Rss, with a maximum of about 0.5 V. The start level and the time constant of the increasing primary current level can be adjusted externally by changing the values of Rss and Css. The charging current Iss will flow as long as the voltage on pin Isense is below approximately 0.5 V. If the voltage on pin Isense exceeds the 0.5 V, the soft start current source will start limiting the current Iss. At the VCC(start) level, the Iss current source is completely switched off (see Fig.9). Since the soft start current Iss is subtracted from pin VCC charging current, the Rss value will affect the VCC charging current level by a maximum of 60 µA (typical value). Driver The driver circuit to the gate of the power MOSFET has a current sourcing capability of typically 125 mA and a current sink capability of typical 540 mA. This permits fast turn-on and turn-off of the power MOSFET for efficient operation. A low driver source current has been chosen to limit the ∆V/∆t at switch-on. This reduces Electro Magnetic Interference (EMI) and also limits the current spikes across Rsense. I burstmode V th R CTRL ----------------- I th on () + = I primary(max) V ocp I ss R ss × () – R sense -------------------------------------------- = τ R ss C ss × = handbook, halfpage CSS RSS Isense Rsense ISS Vocp start-up MGU237 pin 5 0.5 V Fig.9 Soft start-up. |
同様の部品番号 - TEA1507P |
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同様の説明 - TEA1507P |
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