AK5371A Datasheet, PDF (12/32 Pages) Asahi Kasei Microsystems – 2ch A/D Converter with USB I/F

ASAHI KASEI
[AK5371A]
„ Audio Format of the AK5371A
The AK5371A supports two audio formats: 16bit/mono and 16bit/stereo. This feature can avoid the unnecessary occupation of USB
bandwidth. 16bit/mono is assigned to <Interlace 1, Alt1>, 16bit/stereo is assigned to <Interface 1, Alt2>. The A/D data on USB bus
is LSB first, Left channel first. When 16bit/mono audio format is selected, the AK5371A outputs left channel data on the USB bus.
Audio format is changed by “Set Interface” Request.
„ Synchronization
The AK5371A operates as Asynchronous Device. A/D converter in the AK5371A operates asynchronously with USB SOF timing.
The data from A/D converter are sent continuously to a buffer memory while the data are burstly transferred at the interval of SOF on
the USB. In order to arbitrate the difference of timing, AK5371A has a FIFO memory with a capacity of 2-frame depth .The average
sampling rate calculating from USB frame should be in accordance with A/D sampling rate (fs).
The AK5371A sends all A/D samples that were stored in the last frame to avoid overflow or underflow of FIFO. The following
figure shows an example. When sampling frequency is set to 44.1kHz, the AK5371A sends 45 samples once per ten times, and sends
44 samples in other frames. Average frequency is 44.1kHz. See Figure 7.
N Frame
44 samples
(N+1) Frame
44 samples
(N+9) Frame
45 samples
(N+10) Frame
44 samples
Figure 7. Synchronization
„ Power Management Control
When idle state continues for 3ms, the AK5371A goes to suspend state and forces almost all blocks including PLL, ADC block and
mic bias into stopping in order to observe 500μA, which is USB suspend current requirement.
The device resumes the normal operation within 30ms after the device receives resume signal.
In the normal operation, MICBIAS outputs the voltage to supply the microphone’s bias voltage.
SUSN pin shows USB bus status; suspend mode (“L") or normal operation (“H").
SUSN pin can be used for external power control.
The AK5371A is very low power device at both normal state and suspend state. However, note that USB suspend current
requirement, 500μA, specifies the current which is totally consumed by not only the AK5371A, by also regulator(s), and resistors.
Therefore, low power regulator should be selected to design USB microphone.
„ Feature Unit Control & Frequency Control
When the AK5371A receives “SET_FEATURE_UNIT_CONTROL” request, the device decodes the request and sets the value.
Note that only CUR value is valid for “SET_FEATURE_UNIT_CONTROL” request, and that MIN/MAX/RES value is invalid.
When the AK5371A receives “GET_FEATURE_UNIT_CONTROL” request, the device decodes the request and returns the value
to the host. CUR/MAX/MIN/RES value is valid for "Get Volume Request", but only CUR value is meaningful for "Get Mute
Request".
When the AK5371A receives “SET_ENDPOINT_CONTROL” request, it changes sampling frequency(fs). If fs is not supported,
the device forces to set the appropriate fs which it supports. When the AK5371A receives “GET_ENDPOINT_CONTROL”
request, it sends back the current value to the host.
MS0546-E-00
MS0103-E-00
12
2007/02