CS35L01 Datasheet, PDF (19/34 Pages) Cirrus Logic – 2.9 W Mono Class-D Audio Amplifier with Low Idle Current

CS35L01/03
Static signals (i.e. sine waves at a fixed amplitude) are easier to consider than are dynamic signals (i.e.
musical content), as they are governed by the same equation as that listed in Section 5.3.3.1 and Section
5.3.3.2 on page 18. Modifications to that equation are limited to the voltage term (V) and the frequency
term (f), depending on whether the static input signal amplitude is causing the output devices to switch at
76 kHz or 192 kHz, and to operate off of the VBATT supply or off of the internally generated LDO.
It is important to note that the HD and FHD modes offer significant improvement over traditional Class-D
in idle power dissipation when an external output filter is necessary. This is because the voltage term (V)
is significantly reduced in HD and FHD mode. As can be seen in the equation, this is notable because
reduction in the operating voltage reduces power losses not linearly, but instead exponentially- due to the
voltage squared term (V²). It is also notable that when operated at high output levels, FHD modes also
offers unique improvement in output filter losses, due to reducing the switching frequency (f) at higher out-
put levels.
5.4 Power-Up and Power-Down
When pulled to a logic low state, the SD pin tristates the outputs and shuts down the CS35L01/03 device,
putting it into a low power mode.
5.4.1
Recommended Power-Up Sequence
1. With the SD pin pulled low, apply power to the CS35L01/03 and wait for the power supply to be stable.
2. Set the SD pin high to begin normal operation.
5.4.1.1 Zero-Crossing on Power-Up Functionality
The CS35L01/03 implements an input-signal zero-crossing detection function that is enabled during pow-
er-up. This function is designed to prevent audible artifacts and eliminate any need to mute the amplifier’s
input audio signal during the power-up process.
After a minimum start-up time of t_start, the CS35L01/03 will begin to detect input-signal zero-crossings.
The amplifier will then enable its switching outputs at the time of the first detected input-signal zero-cross-
ing transition. If no input-signal zero-crossing is detected before t_timeout, the zero-crossing function will tim-
eout and the outputs will begin switching immediately.
Both t_start and t_timeout are specified in “Power-Up & Power-Down Characteristics” on page 14.
IN+/-
SD
VIH
VIL
tstart
ttimeout
VBATT or VLDO
OUT+/-
Shut-Down /
Low Power
Mode
Internal
Start-Up
Device Ready:
Waiting for Zero
Crossing Input
Signal or ttimeout
PWM OUT+/-
Active
Figure 6. Power-Up Timing with Input
Zero-Crossing
IN+/-
SD
VIH
VIL
tstart
ttimeout
VBATT or VLDO
OUT+/-
Shut-Down /
Low Power
Mode
Internal
Start-Up
Device Ready: Waiting for Zero
Crossing Input Signal or ttimeout
PWM OUT+/-
Active
Figure 7. Power Up Timing without Input
Zero-Crossing
DS909A2
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