SLAA899 December   2019 TAS2110 , TAS2555 , TAS2557 , TAS2559 , TAS2560 , TAS2562 , TAS2563 , TAS2564 , TAS2770

 

  1.   Battery Voltage Tracking Limiter and Brown-Out Protection
    1.     Trademarks
    2. 1 Introduction
    3. 2 Benefits
    4. 3 Brown Out Protection and Limiter Design
    5. 4 VBAT tracking limiter
      1. 4.1 Threshold
      2. 4.2 Inflection Point and Slope
      3. 4.3 Attack
      4. 4.4 Hold Time
      5. 4.5 Release
    6. 5 Brown Out Protection (BOP)
    7. 6 System Testing
      1. 6.1 BOP (1)
      2. 6.2 BOP Release (2)
      3. 6.3 Limiter Release (3)
      4. 6.4 Maximum Output (4)
      5. 6.5 Limiter Attack (5)
      6. 6.6 BOP Attack (6)
    8. 7 Design Consideration
    9. 8 References

4.3 Attack

The AGC will adjust the gain gradually based on user settings when it is necessary to limit the maximum output voltage. The speed of this attack can be set through the step size and attack rate. The step size may vary from a minimum step of 0.25 dB to a maximum step of 2.5 dB.

The attack rate determines how quickly these steps occur. Attack rate ranges 1 sample per step all the way to 128 samples per step. The samples are a function of the frame clock frequency. Fewer samples per step will result in a faster overall attack.

MinAttenRate.gifFigure 4. Minimum Attack Rate

The attack example in Figure 4 is set to 128 samples per step, 0.5 dB per step, and 16.5 dB maximum attenuation. However, the signal is already somewhat attenuated by the limiter. In effect the amplifier only needs to attenuate an additional 13.5 dB. With a sample rate of 48 kHz the attack lasts over a total of 72 ms.

MaxAttenRate.gifFigure 5. Maximum Attack Rate

The Figure 5 uses 1 sample per step, 2 dB per step, and a total of 13.5 dB maximum attenuation. With a sample rate of 48 kHz the attack takes only 140 us.