Datasheet TEA1501 (NXP) - 7

Philips Semiconductors TEA1501 GreenChip SMPS controller IC
operation IAUX 12 V 16 V 20 V UVLO Vstart VAUX(max) VAUX Istart start-up mgm824
Fig 5. IAUX as a function of VAUX 7.3.3 Start-up current source
The start-up sequence is carried out using an accurate start-up current source. The start-up current flows from the DRAIN pin to the AUX pin via the start-up current source and charges the AUX capacitor. When AUX reaches the start-up threshold the start-up current is switched off and the flyback converter starts operating and the output voltage rises. The AUX capacitor must be capable of supplying the entire supply current (IAUX(low)) until the output voltage is in regulation. From that moment the AUX capacitor is charged by the flyback converter via the auxiliary winding.
7.3.4 Reference block
The reference block contains a band gap circuit which determines all the accurate and temperature independent reference voltages and currents. It defines the voltage detection level for the primary current comparator and it defines the voltage at the REF pin. The value of the reference resistor determines the burst frequency, the switching frequency and the leading edge blanking time.
7.3.5 Temperature protection
The temperature protection circuit senses the chip temperature using a proportional to absolute temperature voltage (Vptat) generated in the reference block. If the chip temperature exceeds 140 °C the power switch and the start-up current source are disabled. When the chip cools down below 100 °C, the start-up circuit is enabled again.
7.3.6 Switch oscillator
The switch oscillator determines the switching frequency and the maximum on-time of the power switch. The maximum on-time is set at 66 % of the switching period. The switching frequency is determined by the reference resistor at the REF pin and an internal capacitor. The switching frequency can be adjusted in a range from 20 kHz to 50 kHz, thus above the audible spectrum.
7.3.7 Burst oscillator
The burst oscillator generates a triangular wave signal for determination of the burst frequency. The burst frequency is determined accurately and temperature independent by the externally connected reference resistor RREF and burst capacitor CBURST. TEA1501_2 © Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Product data sheet Rev. 02 — 31 March 2006 7 of 21
Document Outline 1. General description 2. Features 2.1 Distinctive features 2.2 Green features 2.3 Protection features 3. Quick reference data 4. Ordering information 5. Block diagram 6. Pinning information 6.1 Pinning 6.2 Pin description 7. Functional description 7.1 System operation 7.1.1 On/off 7.1.2 Start-up 7.1.3 Operation 7.1.4 Data transfer 7.2 Waveforms in the Off mode, Start-up mode and Operation mode 7.3 Circuit block description 7.3.1 On/off/data section 7.3.2 VAUX management 7.3.3 Start-up current source 7.3.4 Reference block 7.3.5 Temperature protection 7.3.6 Switch oscillator 7.3.7 Burst oscillator 7.3.8 Gate driver 7.3.9 Power switch 7.3.10 Primary current comparator 7.3.11 Leading edge blanking 7.3.12 Modulator 7.3.13 Counter 7.3.14 Supply current tracking 7.4 Design Equations 7.4.1 Primary peak current 7.4.1.1 Minimum value of RSOURCE 7.4.2 Switch oscillator 7.4.2.1 Range of RREF values 7.4.3 Leading edge blanking 7.4.4 Burst oscillator 7.4.4.1 Minimum value of CBURST 8. Limiting values 9. Thermal characteristics 10. Characteristics 11. Test information 11.1 Quality information 12. Package outline 13. Soldering 13.1 Introduction to soldering surface mount packages 13.2 Reflow soldering 13.3 Wave soldering 13.4 Manual soldering 13.5 Package related soldering information 14. Revision history 15. Legal information 15.1 Data sheet status 15.2 Definitions 15.3 Disclaimers 15.4 Trademarks 16. Contact information 17. Contents