AK5370VF Asahi Kasei Microsystems, AK5370VF Datasheet - Page 10

• Manufacturer Part Number: AK5370VF
• Description: USB I/F A/D CONVERTER
• Manufacturer: Asahi Kasei Microsystems

ASAHI KASEI
[AK5370]
n Synchronization
The AK5370 operates as Asynchronous Device. A/D converter in the AK5370 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 control the difference of timing, AK5370 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 following figure shows an example. When sampling frequency is set to 44.1kHz, the number of data is almost 44 samples in one
frame. But the AK5370 must send 45 samples in once per ten times. Please see Figure 7.
N Frame
(N+1) Frame
(N+9) Frame
(N+10) Frame
44 samples
44 samples
45 samples
44 samples
Figure 7. Synchronization
The data sampled by A/D converter in N Frame are output to the USB bus on somewhere the (N+1) frame by issuing IN transfer.
n Power Management Control
In the normal operation, MICBIAS outputs the voltage to supply the microphone’s bias voltage.
When idle state continues for 3ms, the AK5370 goes to suspend state and forces ADC block and other unnecessary block to power-down
mode. MICBIAS pin does not supply the bias voltage to save power consumption and is open state under suspend state.
The device resumes the normal operation within 30ms after the device receives resume signal
n Feature Unit Control & Frequency Control
The AK5370 has three feature unit function; mute, volume, and AGC.
The host issues “SET_FEATURE_UNIT_CONTROL” request to change the volume, the status of mute or AGC. The AK5370 responds
to the request for CUR value only, not respond for MIN, MAX, RES value. Note that the AK5370 doesn’t have AGC circuit itself and
that it decodes AGC request only.
The host can get the CUR/MAX/MIN/RES value of the volume by requesting “GET_FEATURE_CONTROL”. However, only CUR
value is supported for mute and AGC.
Volume Control Format of USB Audio Class is a) 16-bit integer, b) upper-bye is integer (-127 to 127), and lower-bye is fraction.
The AK5370 follows the conversion table described in Table 1 in page 22 for the volume control request
When the AK5370 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. The host can get fs by issuing “GET_ENDPOINT_CONTROL” request.
MS0027-E-00
10
2000/05