Datasheet TDA8920CTH (NXP) - 9

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NXP Semiconductors TDA8920C 2
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110 W class-D power amplifier 8.3.1.2 OverTemperature Protection (OTP)
If TFB fails to stabilize the temperature and the junction temperature continues to rise, the amplifier will shut down as soon as the temperature reaches the thermal protection activation threshold, Tact(th_prot). The amplifier will resume switching approximately 100 ms after the temperature drops below Tact(th_prot). The thermal behavior is illustrated in Figure 6. Gain (dB) 30 dB 24 dB 0 dB (Tact(th_fold) − 5°C) T T act(th_prot) j (°C) Tact(th_fold) 1 2 3 001aah656 (1) Duty cycle of PWM output modulated according to the audio input signal. (2) Duty cycle of PWM output reduced due to TFB. (3) Amplifier is switched off due to OTP.
Fig 6. Behavior of TFB and OTP 8.3.2 OverCurrent Protection (OCP)
In order to guarantee the robustness of the TDA8920C, the maximum output current that can be delivered at the output stages is limited. OCP is built in for each output power switch. OCP is activated when the current in one of the power transistors exceeds the OCP threshold (IORM = 9.2 A) due, for example, to a short-circuit to a supply line or across the load. The TDA8920C amplifier distinguishes between low-ohmic short-circuit conditions and other overcurrent conditions such as a dynamic impedance drop at the loudspeaker. The impedance threshold (Zth) depends on the supply voltage. How the amplifier reacts to a short circuit depends on the short-circuit impedance:
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Short-circuit impedance > Zth: the amplifier limits the maximum output current to IORM but the amplifier does not shut down the PWM outputs. Effectively, this results in a clipped output signal across the load (behavior very similar to voltage clipping).
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Short-circuit impedance < Zth: the amplifier limits the maximum output current to IORM and at the same time discharges the capacitor on pin PROT. When CPROT is fully discharged, the amplifier shuts down completely and an internal timer is started. The value of the protection capacitor (CPROT) connected to pin PROT can be between 10 pF and 220 pF (typically 47 pF). While OCP is activated, an internal current source is enabled that will discharge CPROT. TDA8920C_2 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 02 — 11 June 2009 9 of 39
Document Outline 1. General description 2. Features 3. Applications 4. Quick reference data 5. Ordering information 6. Block diagram 7. Pinning information 7.1 Pinning 7.2 Pin description 8. Functional description 8.1 General 8.2 Pulse-width modulation frequency 8.3 Protection 8.3.1 Thermal protection 8.3.1.1 Thermal FoldBack (TFB) 8.3.1.2 OverTemperature Protection (OTP) 8.3.2 OverCurrent Protection (OCP) 8.3.3 Window Protection (WP) 8.3.4 Supply voltage protection 8.4 Differential audio inputs 9. Limiting values 10. Thermal characteristics 11. Static characteristics 12. Dynamic characteristics 12.1 Switching characteristics 12.2 Stereo SE configuration characteristics 12.3 Mono BTL application characteristics 13. Application information 13.1 Mono BTL application 13.2 Pin MODE 13.3 Estimating the output power 13.3.1 Single-Ended (SE) 13.3.2 Bridge-Tied Load (BTL) 13.4 External clock 13.5 Heatsink requirements 13.6 Pumping effects 13.7 Application schematic 13.8 Curves measured in reference design 14. Package outline 15. Soldering of SMD packages 15.1 Introduction to soldering 15.2 Wave and reflow soldering 15.3 Wave soldering 15.4 Reflow soldering 16. Soldering of through-hole mount packages 16.1 Introduction to soldering through-hole mount packages 16.2 Soldering by dipping or by solder wave 16.3 Manual soldering 16.4 Package related soldering information 17. Revision history 18. Legal information 18.1 Data sheet status 18.2 Definitions 18.3 Disclaimers 18.4 Trademarks 19. Contact information 20. Contents