ASAHI KASEI

[AK5370]

MS0027-E-00

10

2000/05

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.

44 samples

44 samples

45 samples

N Frame

(N+1) Frame

(N+9) Frame

44 samples

(N+10) Frame

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.