Cirrus Logic CS35L03 - Manual (Page 19)

CS35L01/03
DS909F1 19
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 (V
2 ). 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 .
5.4.2 Recommended Power-Down Sequence
1. Mute the audio supplied to the CS35L01/03.
2. Pull the SD pin low in order to reset the device and put it into the low power mode.
3. The power supply to the CS35L01/03 can now be removed.
OUT+/-
Shut-Down /
Low Power
Mode
t
start
SD
V IH
Device Ready:
Waiting for Zero
Crossing Input
Signal or t timeout
Internal
Start-Up
V IL
PWM OUT+/-
Active
VBATT or VLDO
IN+/-
t
timeout
Figure 6. Power-Up Timing with Input
Zero-Crossing
Figure 7. Power Up Timing without Input
Zero-Crossing
OUT+/-
Shut-Down /
Low Power
Mode
t start
SD
V
IH
Device Ready: Waiting for Zero
Crossing Input Signal or t timeout
Internal
Start-Up
V
IL
PWM OUT+/-
Active
VBATT or VLDO
IN+/-
t timeout