Cirrus Logic CS42L42 Manual page 43

4.6.2 Power-Supply Transitions
Charge-pump transitions from the lower to the higher set of rail voltages occur on the next FLYN/FLYP clock cycle. Despite
the system's fast response time, the VCP_FILT pin's capacitive elements prevent rail voltages from changing instantly.
Instead, the rail voltages ramp from the lower to the higher supply, based on the time constant created by the output
impedance of the charge pump and the capacitor on the VCP_FILT pin (the transition time is approximately 20 µs).
Fig. 4-15 shows Class H supply switching. During this transition, a high dV/dt transient on the inputs may briefly clip the
outputs before the rail voltages charge to the full higher supply level. This transitory clipping has been found to be inaudible
in listening tests.
+2.5 V
+VCP
+VCP
2
+VCP
3
-VCP
3
-VCP
2
-VCP
-2.5 V
When the charge pump transitions from the higher to the lower set of rail voltages, there is a 5.5-s delay before the charge
pump supplies the lower rail voltages to the amplifiers. This hysteresis ensures that the charge pump does not toggle
between the two rail voltages as signals approach the clip threshold. It also prevents clipping in the instance of repetitive
high-level transients in the input signal.
DS1083F2
Ideal Transition
Figure 4-15. VCP_FILT Transitions—Headphone Output
Fig. 4-16 shows this transitional behavior.
Actual Transition caused
by +VCP_FILT Capacitor
CS42L42
4.6 Class H Amplifier
Time
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