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TEA1771 数据表(PDF) 7 Page - NXP Semiconductors |
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TEA1771 数据表(HTML) 7 Page - NXP Semiconductors |
7 / 25 page TEA1771_1 © NXP B.V. 2009. All rights reserved. Product data sheet Rev. 01 — 6 February 2009 7 of 25 NXP Semiconductors TEA1771 GreenChip PC primary control IC The switch that is in series with the current source, charging LVIN via DM2, is opened when the IC is in System failure mode (see the SUPPLY block in Figure 1). The IC consumption slowly discharges the LVIN capacitor. When VLVIN has been discharged to the level of VDECVCC and VDECPVCC, these nodes are also discharged. Eventually the DECVCC voltage will drop below the UVLO level and the IC enters Charge mode. This is called a safe restart cycle. The period of this cycle depends on the capacitors at pins LVIN, DECVCC, and DECPVCC. 8.4 Oscillator In Figure 5 the OSCILLATOR block is shown together with the STANDBY block. The OSCILLATOR block shows the internal capacitor that is subsequently charged and discharged with the currents 0.3 × I osc and 0.7 × Iosc. The lower part of Figure 5 shows the oscillator signals. It points out that the Ich/Idch current ratio determines an internal clock with a duty cycle of 0.7. In Section 8.5 will be made clear that the clock duty cycle determines the max duty cycle that can be regulated. Together with the capacitor value the Iosc current level determines the frequency. The Iosc is not fixed and therefore the frequency varies also. Figure 5 shows that Iosc is generated by the STANDBY block and fed to the OSCILLATOR block. The curves in the STANDBY block show that Iosc is regulated by the current on pin OPTO, IOPTO. For IOPTO >2IIREF the Iosc current is set to the maximum level, Iosc =IIREF. As a result the frequency is set to the maximum level by putting IOPTO >2IIREF. (1) • fosc(max) (kHz) • IIREF (µA) IIREF is regulated by the external resistor to pin IREF. The voltage on this pin is set to 3.6 V. The current IIREF is set by choosing the resistor value. (2) Fig 4. State diagram 014aaa172 CHARGE RUNNING VDECVCC < VUVLO(DECVCC) SWP or OVP or IOPTO > Iprot(OPTO) SWP or OVP or IOPTO > Iprot(OPTO) VVRSTOK and VLVIN > Vstartup(LVIN) STATE DIAGRAM SYSTEM FAILURE f osc max () I IREF 2 ------------- = I IREF V IREF R IREF --------------- 3.6 R IREF -------------- == |
类似零件编号 - TEA1771 |
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类似说明 - TEA1771 |
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