WM8945 datasheet(13/169 Pages) WOLFSON

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Production Data

WM8945

PD, May 2011, Rev 4.1

PARAMETER

SYMBOL

TEST CONDITIONS

MIN

TYP

MAX

UNIT

SYNC tip offset above

GND

VB_PD = 0

VB_GAIN = 1

Third order Low Pass

Filter response

(referenced to 100kHz)

RREF=187, RLOAD=75,

RSOURCE=75, 0dB gain

2.4MHz

-0.5

0.5

5.13MHz

-0.5

-0.2

0.5

9.04MHz

-3.0

-1.6

13.32MHz

-11.0

-7.0

-3.0

PSRR (with respect to

LDOVOUT)

100kHz

Clocking

MCLK frequency

30Hz

27MHz

FLL output frequency

2.045

MHz

FLL lock time

MICBIAS

Bias voltage (changes in

proportion to LDOVOUT)

MICBIAS

MICB_LVL = 0

2.7

MICB_LVL = 1

1.95

Bias Current source

Output noise spectral

density

1kHz to 20kHz

nV/

Hz

PSRR (with respect to

LDOVDD)

217Hz

1kHz

Analogue Reference Levels

Midrail Reference

Voltage (changes in

proportion to LDOVOUT)

VMID

VMID_REF_SEL = 1

VMID_CTRL=1

1.5

Bandgap Reference

BG_VSEL=01010

-10%

1.5

+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

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).

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.

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.

Mute Attenuation – This is a measure of the difference in level between the full scale output signal and the output with

mute applied.

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.

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.

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