Cirrus Logic CS42L51 - Manual (Page 38)

38 DS679F1
CS42L51
4.4.8 On-Chip Charge Pump
An on-chip charge pump derives a negative supply voltage from the VA_HP supply. This provides dual
rail supplies allowing a full-scale output swing centered around ground and eliminates the need for large,
DC-blocking capacitors. Added benefits include greater pop suppression and improved low frequency
(bass) response.
Note: Series resistance in the path of the power supplies must be avoided. Any voltage
drop on the VA_HP supply will directly impact the derived negative voltage on the charge pump supply,
VSS_HP, and may result in clipping.
The FLYN and FLYP pins connect to internal switches that charges and discharges the external capacitor
attached, at a default switching frequency. This frequency may be adjusted in the control port registers.
Increasing the charge-pumping capacitor will slightly decease the pumping frequency. The capacitor con-
nected to VSS_HP acts as a charge reservoir for the negative supply as well as a filter for the ripple in-
duced by the charge pump. Increasing this capacitor will decrease the ripple on VSS_HP. Refer to the
typical connection diagrams in
Figure 1 on page 10 or Figure 2 on page 11 for the recommended capacitor
values for the charge pump circuitry.
4.5 Serial Port Clocking
The CODEC serial audio interface port operates either as a slave or master. It accepts externally generated
clocks in slave mode and will generate synchronous clocks derived from an input master clock (MCLK) in
master mode.
The frequency of the MCLK must be an integer multiple of, and synchronous with, the system sample rate,
Fs. The LRCK frequency is equal to Fs, the frequency at which audio samples for each channel are clocked
into or out of the device.
The SPEED and MCLKDIV2 software control bits or the SDOUT/(M/S) and MCLKDIV2 stand-alone control
pins, configure the device to generate the proper clocks in Master Mode and receive the proper clocks in
Slave Mode. The value on the SDOUT pin is latched immediately after powering up in Hardware Mode.
Software
Controls:
“Charge Pump Frequency (Address 21h)” on page 74 .
Software
Control:
“MIC Power Control & Speed Control (Address 03h)” on page 50 , “DAC Control
(Address 09h)” on page 58 .
Hardware
Control:
Pin Setting Selection
“SDOUT, M/S” pin 29
47 k Ω Pull-down
Slave
47 k Ω Pull-up
Master
“MCLKDIV2” pin 2
LO No Divide
HI
MCLK is divided by 2 prior
to all internal circuitry.