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 VBAT tracking limiter

The battery tracking voltage limiter can be customized to the end application power specifications. The limiter may also be configured to reduce gain gradually to avoid impacting the listening experience. Once VBAT recovers, the gain will be slowly restored to the programmed operating condition.

The advantage of this solution is that it dynamically configures the Automatic Gain Control (AGC) to help extend battery life, improve the end listening experience for the user, and does not require additional adjustments to the audio stream provided to by the host.

An example of the battery tracking limiter actively adjusting gain can be seen in the scope capture in Figure 2. In this example the battery voltage is provided by a bench top supply and is ramped down over time causing the limiter to engage.

Limiter-Ramp.gifFigure 2. Limiter Attack Response

Figure 2 shows that over a 20 second period that the amplitude is slowly reducing in response to the downward ramp of the VBAT supply voltage. Normally in a real scenario the battery voltage would decay much more slowly than what is demonstrated here. The attenuation settings may be set to produce a smaller overall shift in signal amplitude as well. Figure 2 was produced using the profile shown in Figure 3.

The voltage tracking limiter has several key parameters which control the behavior of the device as battery conditions change.

LimiterPPC3.gifFigure 3. Battery Tracking Limiter Profile