Production Data
PARAMETER
WM8945
SYMBOL
TEST CONDITIONS
VB_PD = 0
VB_GAIN = 1
2.4MHz
MIN
TYP
MAX
UNIT
SYNC tip offset above
GND
0
40
75
mV
Third order Low Pass
Filter response
(referenced to 100kHz)
-0.5
-0.5
0
0.5
0.5
0
dB
dB
dB
dB
5.13MHz
-0.2
-1.6
-7.0
9.04MHz
-3.0
RREF=187, RLOAD=75,
13.32MHz
-11.0
-3.0
RSOURCE=75, 0dB gain
PSRR (with respect to
LDOVOUT)
100kHz
60
dB
Clocking
MCLK frequency
FLL output frequency
FLL lock time
30Hz
2.045
27MHz
50
Hz
MHz
ms
2
MICBIAS
Bias voltage (changes in
proportion to LDOVOUT)
MICBIAS
MICB_LVL = 0
MICB_LVL = 1
2.7
V
V
1.95
Bias Current source
3
mA
Output noise spectral
density
1kHz to 20kHz
15
nV/Hz
PSRR (with respect to
LDOVDD)
217Hz
1kHz
70
85
dB
Analogue Reference Levels
Midrail Reference
Voltage (changes in
proportion to LDOVOUT)
VMID
VMID_REF_SEL = 1
VMID_CTRL=1
1.5
1.5
V
V
Bandgap Reference
BG_VSEL=01010
-10%
+10%
Note:
The maximum LDO output current is the total internal and external load capability; internal circuits of the WM8945 will typically
account for 25mA of this capacity.
TERMINOLOGY
1. Signal-to-Noise Ratio (dB) – SNR is the difference in level between a full scale output signal and the device output
noise with no signal applied, measured over a bandwidth of 20Hz to 20kHz. This ratio is also called idle channel noise.
(No Auto-zero or Mute function is employed).
2. Total Harmonic Distortion (dB) – THD is the difference in level between a 1kHz reference sine wave output signal and
the first seven harmonics of the output signal. The amplitude of the fundamental frequency of the output signal is
compared to the RMS value of the next seven harmonics and expressed as a ratio.
3. Total Harmonic Distortion plus Noise (dB) – THD+N is the difference in level between a 1kHz reference sine wave
output signal and all noise and distortion products in the audio band. The amplitude of the fundamental reference
frequency of the output signal is compared to the RMS value of all other noise and distortion products and expressed
as a ratio.
4. Mute Attenuation – This is a measure of the difference in level between the full scale output signal and the output with
mute applied.
5. Power Supply Rejection Ratio (dB) – PSRR is a measure of ripple attenuation between a power supply rail and a
signal output path. With the signal path idle, a small sine wave ripple is applied to power supply rail. The amplitude of
the supply ripple is compared to the amplitude of the output signal generated and is expressed as a ratio.
6. All performance measurements are carried out with 20kHz AES17 low pass filter for distortion measurements, and an
A-weighted filter for noise measurement. Failure to use such a filter will result in higher THD and lower SNR and
Dynamic Range readings than are found in the Electrical Characteristics. The low pass filter removes out-of-band
noise; although it is not audible, it may affect dynamic specification values.
PD, May 2011, Rev 4.1
13
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
