ADVANCE
CYW43570
5.5.3 BBC Power Management
The following are low-power operations for the BBC:
■ Physical layer packet-handling turns the RF on and off dynamically within transmit/receive packets.
■ Bluetooth-specified low-power connection modes: sniff, hold, and park. While in these modes, the CYW43570 runs on the low-
power oscillator and wakes up after a predefined time period.
■ A low-power shutdown feature allows the device to be turned off while the host and any other devices in the system remain
operational. When the CYW43570 is not needed in the system, the RF and core supplies are shut down while the I/O remains
powered. This allows the CYW43570 to effectively be off while keeping the I/O pins powered so they do not draw extra current
from any other devices connected to the I/O.
During the low-power shut-down state, provided VDDIO remains applied to the CYW43570, all outputs are tristated, and most
input signals are disabled. Input voltages must remain within the limits defined for normal operation. This is done to prevent
current paths or create loading on any digital signals in the system and enables the CYW43570 to be fully integrated in an
embedded device to take full advantage of the lowest power-saving modes.
Two CYW43570 input signals are designed to be high-impedance inputs that do not load the driving signal even if the chip does
not have VDDIO power supplied to it: the frequency reference input (WRF_TCXO_IN) and the 32.768 kHz input (LPO). When the
CYW43570 is powered on from this state, it is the same as a normal power-up, and the device does not contain any information
about its state from the time before it was powered down.
5.5.4 Wideband Speech
The CYW43570 provides support for wideband speech (WBS) using on-chip SmartAudio technology. The CYW43570 can perform
subband codec (SBC), as well as mSBC, encoding, and decoding of linear 16 bits at 16 kHz (256 kbps rate) transferred over the PCM
bus.
5.5.5 Packet Loss Concealment
Packet loss concealment (PLC) improves apparent audio quality for systems with marginal link performance. Bluetooth messages
are sent in packets. When a packet is lost, it creates a gap in the received audio bit-stream. Packet loss can be mitigated in several
ways:
■ Fill in zeros.
■ Ramp down the output audio signal toward zero (this is the method used in current Bluetooth headsets).
■ Repeat the last frame (or packet) of the received bit-stream and decode it as usual (frame repeat).
These techniques cause distortion and popping in the audio stream. The CYW43570 uses a proprietary waveform extension algorithm
to provide dramatic improvement in the audio quality. Figure 6 and Figure 7 show audio waveforms with and without Packet Loss
Concealment. Cypress PLC/BEC algorithms also support wideband speech.
Figure 6. CVSD Decoder Output Waveform Without PLC
Packet Loss Causes Ramp-down
Document Number: 002-15054 Rev. *I
Page 21 of 94
CYPRESS [ CYPRESS ]
