Datasheet AK5370 Datasheet (AKM)

ASAHI KASEI

Encoder

r

[AK5370]

AK5370

Features:

n Incorporates USB Audio Controller

USB Serial Interface Engine
Audio Class Encoder/Decoder
2 Endpoints (FIFO)
USB transceiver

n 16 bit A/D Converter

1 channel
Mute/Volume Control
AGC pin for external control
A/D S/N: 84dBA (44.1kHz, Gain = 0dB)

n On-chip PLL

5 Sampling Frequencies support

8kHz, 11.025kHz

n Programmable Gain Amplifier

n Single Power Supply, Low Power

n Package

22.05kHz, 44.1kHz, 48kHz

+20dB to –58dB

+3.3Volts±10%

24pin VSOP

USB I/F A/D Converte

General Description

The AK5370 is AD converter for USB audio, especially
USB microphone . The AK5370 integrates USB serial
interface engine, USB transceiver, audio class decoder,
endpoints, and high quality AD converter into t he chip.

As the AK5370 incorporates PLL, it can support several
sampling frequencies, 8kHz, 11.025kHz, 22.05kHz, 44.1kHz,
and 48kHz with only one crystal. Moreover, the AK5370
integrates volume control, and mute function.

It is possible to make USB microphone with a few external
components

This device is good for not only business application such
as conferencing but also games, voice recognition, and
Karaoke.

Related Documents

For the detail of USB specification, and Audio Class, please
refer to the following documents.

Universal Serial Bus Specification Revision 1.1
Universal Serial Bus Device Class Definition for Audio
Devices, Revision 1.0

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MIC_BIAS

MIC_IN

VA

Power

Management

­+

AMP1O

VCOM

Common Voltage

­+

AMP2OAMP2I

AGC

Mute

&

Volume

control

16bit
ADC

VREF

LFLT1

AGCEN

Audio Class
Decoder

Audio Class

EndPoint1
IN_FIFO

adCLK

PLL

XTLIN XTLOUT

LFLT2

AGND VD

1

DGND

String ROM

EndPoint0
OUT_FIFO

EndPoint0
IN_FIFO

CRYSTAL

Config ROM

System
CLK

USB
Transceiver

RST

Serial
Interface
Engine

Testmode1,2

TEST1,2,3

DP
DN

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Pin/Function

No. Signal Name I/O Ana / Dig Description

1 DGND P D Digital Ground
2 VD P D Digital Power Supply, 3.3V
3 DP I/O D USB bus Non-Inverting pin.

Because AK5370 is full speed mode device, 1.5kΩ resistor will

be connected between D+ node to VD.
4 DN I/O D USB bus Inverting Pin.
5 TESTMODE3 I D Please tie down to AGND for normal operation.

6 XTALOUT O A Crystal Oscillator Output, Connect Crystal Resonator
7 XTALIN I A Crystal Oscillator Input, Connect Crystal Resonator
8 TESTMODE2 I A Please tie down to AGND for normal operation.
9 LFLT2 O A

10 LFLT1 O A

11 VCOM O A Analog Common Voltage Reference Pin
12 MICIN I A Microphone Input
13 AMP1O O A 1st Amplifier Output Pin
14 AMP2I I A 2nd Amplifier Input Pin
15 VA P A Analog Power Supply, 3.3V
16 AGND P A Analog Ground
17 VREF O A ADC Common Voltage Reference Pin.
18 AMP2O O A 2nd Amplifier Output Pin
19 TESTMODE1 I A Please tie down to AGND for normal oper ation.
20 MICBIAS O A Voltage Reference Output for the Microphones bias voltage

21 TEST I D Please tie down to AGND for normal operation.
22 AGCE I D AGC Enable Control Input Pin.

23 AGC O D AGC Control Pin

24 RSTN I D Reset Pin, Low input makes the chip reset sate.

System clock PLL loop filter Pin. Connect 18kΩ resistor and

6800pF capacitor in series externally.

adPLL loop filter Pin. Connect 51kΩ resistor and 8200pF

capacitor in series externally.

When this chip goes into Suspend mode, this pin goes to Hi -Z.

When the external AGC is used, High level should be applied

to this pin. When Low input is applied, AGC configuration

ROM data is set FALSE. Then AGC output is set to Low.

When the host requests set AGC_CONTROL request, this pin

goes to H.

L level AGCE input prevents this AGC_CONTROL request.

Low level output at SUSPEND. Default output at Reset is

Low.

Schmitt Trigger input.

[AK5370]

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Absolute Maximum Rating

AGND, DGND=0V

Parameter Symbol Min Max Units

Power Supplies

Analog
Digital

|DGND-AGND|
Input Current (any pins except for supplies) IIN ­Analog Input Voltage VINA -0.3 VA+0.3 V
Digital Input Voltage VIND -0.3 VD+0.3 V
Ambient Temperature Ta 0 70
Storage Temperature Tstg -40 125
Note 1. All voltages with respect to ground

Warning: Operation at or beyond these limits may results in permanent damage to the device. N ormal operation is
not guaranteed at these extremes.

Recommended Operating Condition

AGND, DGND=0V

Parameter Symbol Min typ Max Units

Power Supplies

All voltages with respect to ground.

* AKM assumes no responsibility for the usage beyond the condition in this datasheet.

Analog
Digital

VA
VD

∆GND

VA
VD

3.0

3.0

-0.3

-0.3

3.3

3.3

4.5

4.5

0.3

±10

3.6

3.6

V
V
V

mA

°C
°C

V
V

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Analog Characteristics

Ta=25°C, VA=VD=3.3V, Signal Frequency=1kHz, Sampling Frequency Fs=44.1kHz

Parameter Min typ Max Units
Mono ADC (1 channel)

Resolution 16 bits
S/N (A weight)

st

and 2nd MIC amplifier are set to 0dB)

(1
S/(N+D) (-0.5dB analog input)

st

and 2nd MIC amplifier are set to 0dB)

(1

76 84 dBA

62 70 dB

MIC Amplifier (2nd Stage) <IPGA> Characteristics

Input Voltage 1.6 Vp-p
Gain Control Range -58 20 dB
Step Size 0 1.0 2.0 dB
Input Impedance @AMP2I pin 20

KΩ

MIC amplifier(1st Stage)

Gain range(defined by external resistors) 0 +20 dB
External Feedback Impedance 20

KΩ

MIC Bias

Output Voltage when 4.7KΩ resistor connected
Output Impedance 200 500

0.9VA Vdc

Ω

Output Current 3 mA

Power Supplies

Analog
Digital

Total

Power Down(Suspend Mode)

10.5

8.5

4.7

30

mA
mA
mA
mA

FILTER CHARACTERISTICS

(Ta=25°C VA, VD =3.0 - 3.6 V ; fs = 44.1 kHz)
Parameter Symbol Min typ Max Units
A/D Digital Filter

(Decimation LPF)
Passband +/- 0.2 dB PB 0 17.64 KHz
Stopband SB 26.5 KHz
Passband Ripple PR +/- 0.2 dB
Stopband Attenuation SA 68 dB
Group Delay GD 0.5 ms
A/Ddigital Filter (HPF)
Frequency Response -3 dB

-0.5 dB

-0.1 dB

FR 6.85

19.2

44.9

Hz

Hz
Hz

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Digital DC Characteristics

Ta=0 - 70°C; VD=3.0 - 3.6V; DGND=0V Measurement under static state
All digital pins except DP, DN. Schmitt hysteresis level of RST pin and levels of all test pins will not be tested.

Parameter Symbol Min Typ Max Units

AGCE pin H level input voltage VIH 70%VA V
AGCE pin L level input voltage VIL 30%VA V
RSTN pin H level voltage VIHR 2.0 V
RSTN pin L level voltage VILR 0.8 V
H level output voltage IOH= 2mA VOH 2.4 V
L level output voltage IOL= -2mA VOL 0.6 V
Input Leakage Current Iin

±10 µA

Switching Characteristics

Ta=25°C, VA=VD=3.3V

Parameter Symbol Min Typ Max Units

Master Clock Frequency MCLK - 11.2896 - MHz
Reset input width @RSTN pin(low active) Wrst 1.0 us
Singe Ended Receiver Threshold

Vse 0.8 2.0 V

Main Clock Stable Time

Tostb 100 ms
Vse(max) of D+ to stabilized MCLK
( Xtal oscillator start up + PLL lock-in )
Reset Signal Recognition

Both D+ and D- < Vse(min) to Reset mode
Device Ready
Ready for transaction after reset
Suspend Recognition

Trst_rec 2.5 5.5

µs

Tdrr 10 ms

Tsus_rec 3.0 ms
Idle state ( D+ > Vse(max) & D- < Vse(min) )
to Suspend mode
Resume Time

Tresm 30 ms
First flip of D+/D- from Idle sate
To Device Ready*)

Device Ready: VREF, Xtal oscillator, and PLL get stable and bus trans action with normal rate is ready.

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VD

D+

D- "L"

RST

Master

Clock

Device
Connected

Reset Mode

Tostb

Tdrr

T

Reset Mode

rst_rec

Figure 1. Mode change with respect to BUS States 1 (Power on and device connected)

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Tsus_rec

VDH

D+

D-

RSTH

Master

Clock

Tresm

Figure 2. Mode Change with respect to Bus States 2 (Bus transactions)

Transmitter Characteristics

Ta=25°C; VD=3.3V; DGND=0V; CL=50pF

Parameter Symbol Pins Conditions Min Typ Max Units

Data Rate DR DP,DN 11.97 12 12.03 MHz

Output Impedance (Hi) Roh DP, DN DP, DN=H 30

Output Impedance (Lo) Rol DP, DP DP, DN=L 30

Ω
Ω

H level Output Voltage Vohd DP, DN IOH=-200uA 2.8 V
L level Output Voltage Vold DP, DN IOH=2.2mA 0.3 V
Tri-state Leakage Current Iolk DP, DN 0 < DP, DN< 3.3V -10 10

µA

Rise/Fall Time Trf/Tff DP, DN 4 12 20 ns
Rise/Fall Time Matching Trfm DP, DN 100 %
Crossover Point Vcrs DP, DN 1.6 V

T

DP, DN

T

rs

rf

T

T

fs

ff

90%VDD

10%VDD

Figure 3. Rise/Fall Time

DP, DN

Vcrs

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Figure 4. Crossover Point

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Receiver Characteristics

Ta=25°C; VD=3.3V; DGND=0V

Parameter Symbol Pins Conditions Min Typ Max Units

Schmitt High Level Voltage Vihs DP, DN 2.0 V
Schmitt Low Level Voltage Vils DP, DN 0.8 V

DP, DN

Vihs
Vils

Figure 5. Schmitt Level Voltage

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n

Overview of AK5370

The AK5370 is the advanced A/D converter, which converts analog signal of condenser microphone into USB audio class formats. This
device is suitable for USB microphone. The AK5370 includes the following blocks:

1. AD converter

2. Pre-Amplifier with variable gain/attenuation

3. Serial Interface Engine

4. Control block of Audio Device Class
Support Mute, Gain/Attenuation, Sampling Frequency Control, and AGC (only decode the request)

5. USB transceiver
AK4170 compliant

6. FIFO memory for bus synchronization
Memory Size (16bit wide x 100 depth)

7. PLL
Synchronize Audio Stream data with USB bus I/F

The AK5370 supports 5 sampling frequencies (8kHz, 11.025kHz, 22.05kHz, 44.1kHz, 48kHz) mute control, volume control of Feature
Unit in Audio Device Class. In addition to this, as the AK5370 decodes the AGC request, and puts “H” or “L” level to the external pin,
AGC pin, it is easy to implement AGC with external circuit.
In order to support these frequencies, the AK5370 incorporates PLL. In addition to this, as the AK5370 consumes low power, it is
possible to operate as bus-powered device.

n

Class & Descriptor Overview

USB peripheral usually belongs to a group, “Class”. The AK5370 belongs to Audio Device Class. The Class consists of four
Descriptors, Device Descriptor, Configuration Descriptor, Interface Descriptor, and Endpoint Descriptor. The AK5370 has Audio
Specific Interface Descriptor and Endpoint Descriptor.

(1) Device Descriptor
Device Descriptor describes the product information; product name, manufacturer, etc. In addition to this, Device Descriptor has
Endpoint0 fifo-buffer size. At enumeration phase, host reads 8 bytes from the top of Device Descriptor at first. The host knows by
reading bMaxPacketSize0 in the Device Descriptor, and uses this value for the following transactions, and does not send the bigger data
at once.

(2) Configuration Descriptor
Configuration Descriptor informs the host of the number of Interface, Bus-powered/Self-Powered device, etc.
This descriptor is the same as Standard Interface Descriptor.

(3) Interface Descriptor
There are two Interfaces in Audio Class; Audio Control (AC) Interface, and Audio Streaming (AS) Interface.
Each Audio Interface includes Standard Interface Descriptor and Class-Specific Interface.

Standard AC Interface Descriptor describes interface’s class.
Class-Specific AC Interface Descriptor is a concatenation of all the descriptors that are used to fully describe the audio function.

As the AK5370 has three logical audio functions; Input Terminal, Output Terminal, and Feature Unit (mute, volume, AGC), each
terminal and unit has their own Descriptor.
Not only each descriptor has their own information, but also has connection information between the blocks.

For example, bSourceID field in Output Terminal Descriptor is 0x03, which is ID of Feature Unit. This means that Feature Unit is
connected to Output Terminal.
Standard AS Interface has the interface class name (AUDIO) and sub-class name (AUDIO_STREAMING), the related Endpoint number,
etc.

Class-Specific AS Interface Descriptor mainly shows Audio Data Format information that follows as Descriptor.

There is a note for Alternate Setting:

Alternate setting 0 is a zero-bandwidth setting, used to relinquish the claimed bandwidth on the bus when the microphone is not in use. It
is the default setting after power-up. The zero bandwidth is implemented by specifying that this alternate setting of the interface has no
endpoints associated with it (bNumEndpoints=0).

(4) Endpoint Descriptor

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Endpoint Descriptor is a pipe for the data. The AK5370 has two Endpoints. One is Endpoint0 for Control Transfer. Another is
Endpoint 1, whose direction is IN, is used for Isochronous Transfer. Standard AS Isochronous Endpoint tells Endpoint type like
In/OUT, maximum packet size, synchronization type, etc. to the host.
Main information of Class-Specific AS Endpoint Descriptor is sampling frequency.

Figure 6 shows Descriptor’s hierarchy.

Device

Device

Descriptor

Interface

Class-Specific Descriptor

Configuration

Standard Audio Control

Interface Descriptor

Class-Specific Audio Control

Interface Descriptor

Configuration

Descriptor

Standard AS Interface

Descriptor Alt. Setting 0

Standard AS Interface

Descriptor Alt. Setting 1

Class-Specific Audio Streaming

Interface Descriptor

Class-Specific AS Format Type

Standard AS Isochronous
Endpoint Descriptor

Class-Specific AS Isochronous
Endpoint Descriptor

Descriptor

Endpoint

(IN)

StandardInterface Descriptor

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Figure 6. Descriptor Hierarchy

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N Frame

[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+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.

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AK5370 Descriptors Specification

1. Product description

This device is one channel 16-bit ADC with USB I/F for monaural microphone, and operates as IN
device.

2. Descriptor structure

This device includes one configuration, two interfaces, which are an audio control interface (0) and
an audio streaming interface (1), two endpoints, which are endpoint 0 for default pipe, and endpoint
1 for audio streaming.
The descriptor is partly fixed and partly programmable by means of selectable test pin map. The
programmable descriptors are marked with a star.

3. Device descriptor

Offset Field Size Value Description

0 bLength 1 0x12 Size of this descriptor in bytes
1 bDescriptorType 1 0x01 DEVICE descriptor
2 bcdUSB 2 0x0110 1.10  current revision of USB spec.
4 bDeviceClass 1 0x00 Device defined at Interface level
5 bDeviceSubClass 1 0x00 Unused
6 bDeviceProtocol 1 0x00 Unused
7 bMaxPacketSize0 1 0x08 8 bytes
8 idVendor 2 0x0556 AKMs Vendor ID
10 idProduct 2 0x0001 00 means Audio Product, 01 is AKMproduct ID ,
12 bcdDevice 2 0x0001 Device release code
14 iManufacturer 1 0x01 AKM
15 iProduct 1 0x02 AK5370
16 iSerialNumber 1 0x00 Unused
17 bNumConfigurations 1 0x01 One configuration

4. Configuration block

The configuration block consists of a confi guration descriptor followed by interface, endpoint, and
class-specific descriptors.

4.1 Configuration descriptor

Offset Field Size Value Description

0 bLength 1 0x09 Size of this descriptor
1 bDescriptorType 1 0x02 CONFIGURATION descriptor
2 wTotalLength 2 0x0076 Length of entire configuration block

Total 118 bytes including this interface

descriptor.
4 bNumInterfaces 1 0x02
5 bConfigurationValue 1 0x01 Index of this configuration
6 iConfiguration 1 0x00 Null string
7 bmAttributes 1 0x80 Bus Powered Device
8 MaxPower 1 0x2D Power consumption:90mA

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4.2 Audio control interface

The audio control interface describes the device structure and is used to manipulate the audio
controls.

4.2.1 Interface descriptor

This descriptor describes a standard interface which includes USB class code and the index to
class-specific information.

Offset Field Size Value Description

0 bLength 1 0x09 Size of this descriptor
1 bDescriptorType 1 0x04 INTERFACE descriptor
2 bInterfaceNumber 1 0x00 Index of this interface
3 bAlternateSetting 1 0x00 Index of this setting
4 bNumEndpoints 1 0x00 Endpoint 0
5 bInterfaceClass 1 0x01 AUDIO
6 bInterfaceSubclass 1 0x01 AUDIO_CONTROL
7 bInterfaceProtocol 1 0x00 Unused
8 iInterface 1 0x00 null string

4.2.2 Class-specific interface header descriptor

Contains general information about the audio device.

Offset Field Size Value Description

0 bLength 1 0x09 Size of this descriptor
1 bDescriptorType 1 0x24 CS_INTERFACE
2 bDescriptorSubtype 1 0x01 HEADER subtype
3 bcdADC 2 0x0100 Revision of class specification  1.0
5 wTotalLength 2 0x0026 Total size of class-specific Audio Control

Interface descriptors (includes this

descriptor)
7 bInCollection 1 0x01 Number of streaming interfaces
8 baInterfaceNr(1) 1 0x01 Streaming interface number 1 belongs to

this audio control interface.

4.2.3 Input terminal descriptor

This descriptor describes the signal coming through the input port NumChannels is 1(monaural)
and ChannelConfig is set no position. Terminal type is Microphone.

Offset Field Size Value Description

0 bLength 1 0x0C Size of this descriptor
1 bDescriptorType 1 0x24 CS_INTERFACE
2 bDescriptorSubtype 1 0x02 INPUT_TERMINAL subtype
3 bTerminalID 1 0x01 ID of this terminal
4 wTerminalType 2 0x0201 Terminal is Microphone
6 bAssocTerminal 1 0x02 ID of associated Output Terminal is

0x02
7 bNrChannels 1 0x01 One channel (Monaural)
8 wChannelConfig 2 0x0000 Mono sets no position bits

10 iChannelNames 1 0x00 Unused
11 iTerminal 1 0x00 Unused

4.2.4 Output terminal descriptor

This descriptor describes the USB stream to host.

Offset Field Size Value Description

0 bLength 1 0x09 Size of this descriptor
1 bDescriptorType 1 0x24 CS_INTERFACE
2 bDescriptorSubtype 1 0x03 OUTPUT_TERMINAL subtype
3 bTerminalID 1 0x02 ID of this terminal
4 wTerminalType 2 0x0101 USB Streamer
6 bAssocTerminal 1 0x01 ID of associate Input Terminal is 0x01
7 bSourceID 1 0x03 From Feature Unit
8 iTerminal 1 0x00 Unused

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4.2.5 Feature Unit descriptor

This descriptor describes Mute Control, Volume Control and Automatic Gain Control(AGC) .

Offset Field Size Value Description

0 bLength 1 0x08 Size of this descriptor
1 bDescriptorType 1 0x24 CS_INTERFACE
2 bDescriptorSubtype 1 0x06 FEATURE_UNIT descriptor subtype
3 bUnitID 1 0x03 ID of this feature Unit
4 bSourceID 1 0x01 ID to Terminal to which this is connected.
5 bControlSize 1 0x01 Size in bytes of an element of the

bmaControl()
6 bmaControls(0) 1 0x43* D0(Mute), and D1(Volume), D6(AGC) is

enable
7 iFeature 1 0x00 Unused

*) When “L” level is applied to AGCE pin, bmaControl (0) data is modified to 0x03 to state AGC is not
enable.

Note that there is never endpoint descriptor for endpoint 0.

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4.3 Audio streaming interface

4.3.1 Zero bandwidth interface descriptor

Offset Field Size Value Description

0 bLength 1 0x09 Length of this descriptor
1 bDescriptorType 1 0x04 INTERFACE descriptor
2 bInterfaceNumber 1 0x01 Index of this interface
3 bAlternateSetting 1 0x00 Index of this setting
4 bNumEndpoints 1 0x00 Endpoints 0
5 bInterfaceClass 1 0x01 AUDIO
6 bInterfaceSubclass 1 0x02 AUDIO_STREAMING
7 bInterfaceProtocol 1 0x00 Unused
8 iInterface 1 0x00 null string

4.3.2 Interface descriptor

Offset Field Size Value Description

0 bLength 1 0x09 Length of this descriptor
1 bDescriptorType 1 0x04 INTERFACE descriptor
2 bInterfaceNumber 1 0x01 Index of this interface
3 bAlternateSetting 1 0x01 Index of this setting
4 bNumEndpoints 1 0x01 Endpoint 1
5 bInterfaceClass 1 0x01 AUDIO
6 bInterfaceSubclass 1 0x02 AUDIO_STREAMING
7 bInterfaceProtocol 1 0x00 Unused
8 iInterface 1 0x00 null string

4.3.3 Class-specific audio streaming interface descriptor

Offset Field Size Value Description

0 bLength 1 0x07 Length of this descriptor
1 bDescriptorType 1 0x24 CS_INTERFACE descrip tor
2 bDescriptorSubtype 1 0x01 AS_GENERAL
3 bTerminalLink 1 0x02 Unit ID of terminal(Output Terminal ID)
4 bDelay 1 0x01 Interface delay
5 wFormatTag 2 0x0001 PCM

4.3.4 Type I format type descriptor

Offset Field Size Value Description

0 blength 1 0x17 Size of this descriptor
1 bDescriptorType 1 0x24 CS_INTERFACE

2 bdescriptorSubtype 1 0x02 FORMAT_TYPE
3 bformatType 1 0x01 FORMAT_TYPE_I
4 bNrChannels 1 0x01 One channel
5 bSubFrameSize 1 0x02 Two bytes per slot
6 bBitResolution 1 0x10 16 bits
7 bSamFreqType 1 0x05 Five frequencies
8 tSamFreq[0] 3 0x001F40 8000Hz

11 tSamFreq[1] 3 0x002B11 11025Hz
14 tSamFreq[2] 3 0x005622 22050Hz
17 tSamFreq[3] 3 0x00AC44 44100Hz
20 tSamFreq[4] 3 0x00BB80 48000Hz

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4.4 Endpoint descriptor

4.4.1 Standard Endpoint Descriptor

Offset Field Size Value Description

0 bLength 1 0x07 Length of this descriptor
1 bDescriptorType 1 0x05 ENDPOINT descriptor
2 bendpointAddress 1 0x81 Endpoint 1, IN direction
3 bmAttributes 1 0x01 Isochronous, asynchronous, not shared
4 wMaxPacketSize 2 0x0064 2byte*50sample*1ch=100 byte/frame
6 wInterval 1 0x01 One packet every frame (Must be set to 1)

4.4.2 Class-specific isochronous audio data endpoint descriptor

Offset Field Size Value Description

0 bLength 1 0x07 Size of this descriptor
1 bDescriptorType 1 0x25 CS_ENDPOINT
2 bDescriptorSubtype 1 0x01 GENERAL
3 bmAttributes 1 0x01 Sample rate control
4 bLockDelayUnits 1 0x00 Unused
5 wLockDelay 2 0x0000

4.5 String descriptor 1

String descriptors use UNICODE. except for LANGID.

4.5.1 LANGID (0x00) Field

Offset Field Size Value Description

0 bLength 1 0x04 Length of this descriptor
1 bDescriptorType 1 0x03 STRING descriptor
2 bString 2 0x0409 English(US)

4.5.2.1 iManufacterer (0x01) Field in Device Descriptor

Offset Field Size Value Description

0 bLength 1 0x022 Length of this descriptor
1 bdescriptorType 1 0x03 STRING descriptor
2 bString 6 0x0041

0x004B
0x004D
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020
0x0020

AKM 

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4.5.3.1iProduct (0x02) Field in Device Descriptor

Offset Field Size Value Description

0 bLength 1 0x22 Length of this descriptor
1 bDescriptorType 1 0x03 STRING descriptor
2 bString 12 0x0041

0x004B
0x0035
0x0033
0x0037
0x0030
0x0020
0x0020
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AK5370 

[AK5370]

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[AK5370]

5. Standard requests

5.1 Clear Feature

The AK5370 accepts Clear Feature request without stall. Though this request does not influence
to the operation of the device, the AK5370 does not support this request.

5.2 Get Configuration

AKM USB Microphone should return the value, one, to the host.

Offset

0 bmRequestType 1 0x80
1 bRequest 1 0x08 GET_CONFIGURATION
2 wValue 2 0x0000
4 wIndex 2 0x0000
6 wLength 2 0x0001 AKM USB Mic. has one configuration.

5.3 Get Descriptor

Offset Field Size Value Description

0 bmRequestType 1 0x80
1 bRequest 1 0x06 GET_DESCRIPTOR
2 wValue 2 0xZZZZ ZZZZ is assigned by host:

4 wIndex 2 0x0000

6 wLength 2 0xZZZZ Descriptor Length (ZZZZ is assigned by host)

Field Size Value Description

High Byte is Descriptor Type, Low Byte is Index.
DEVICE : 0x0100 : (Index is 0 only)
CONFIGURATION : 0x0200
STRING: 0x03??(?? is 00, 01, 02)

if wValue is DEVICE or CONFIGURATION, wIndex is
zero. If wValue is 0x0300(LANGID), wIndex is zero.
If wValue is 0x0301 or 0x0302, wIndex is 0x0409.

5.4 Get Interface

AKM USB Microphone has alternate Audio Streaming Interface, ;zero bandwidth, and normal.
So, the device returns the current selected bAlternateSetting v alue, 0x00(zero bandwidth Audio
Streaming Interface) or 0x01(normal Audio Streaming Interface). If wIndex is 0 (Audio Control
Interface), the device returns the value, 0x00.

Offset Field Size Value Description

0 bmRequestType 1 0x81
1 bRequest 1 0x0A GET_INTERFACE
2 wValue 2 0x0000 ZERO
4 wIndex 2 0x0000

0x0001

6 wLength 2 0x0001 AKM USB Mic. Has zero bandwidth Audio

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Audio Control Interface
Audio Streaming Interface

Streaming Interface and normal Audio Streaming
Interface.

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[AK5370]

5.5 Get Status

Offset Field Size Value Description

0 bmRequestType 1 0x80

0x81

0x82
1 bRequest 1 0x00 GET_STATUS
2 wValue 2 0x0000 ZERO
4 wIndex 2
6 wLength 2 0x0002

The AKM USB MIC returns the following status.

DEVICE
INTERFACE
ENDPOINT

a)Device : 0x00 ( AKM USB MIC is bus-powered device)
b)Interface: 0x00 (All Zero)
c)Endpoint : 0x00

5.6 Set Address

AKM USB MIC stores the wValue in the internal memory as Device Address. In addition to this,
the device returns ACK.

Offset Field Size Value Description

0 bmRequestType 1 0x00 Zero
1 bRequest 1 0x05 SET_ADDRESS
2 wValue 2 0xZZZZ Device Address : ZZZZ is assigned by host
4 wIndex 2 0x0000 Zero
6 wLength 2 0x0000 Zero

5.7 Set Configuration

AKM USB MIC is placed to configured state only wValue of this request is 0x00 01. In addition to
this, the device returns ACK.

Offset Field Size Value Description

0 bmRequestType 1 0x00 Zero
1 bRequest 1 0x09 SET_CONFIGURATION
2 wValue 2 0x0000

0x0001

others
4 wIndex 2 0x0000 Zero
6 wLength 2 0x0000 Zero

Unconfigured State
AKM USB MIC is set to configured state
Unconfigured State

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[AK5370]

5.8 Set Feature

The AK5370 accepts Set Feature request without stall. However note that the AK5370 does not
support this request.

5.9 Set Interface

This request selects the alternate setting on interface 1 to control bandwidth allocation. Only
0x0000 is selected if wIndex is 0x0000 (Audio Control Interface) as current Interface.

Offset Field Size Value Description

0 bmRequestType 1 0x01 ONE

D7 0 = Host to device
D6..5 0 = Standard request

D4..0 1 = Recipient is interface
1 bRequest 1 0x0B SET_INTERFACE
2 wValue 2

0x0000
0x0001

4 wIndex 2 0x0000

0x0001

6 wLength 2 0x0000 Zero

Alternate Setting

Control Interface or Zero Bandwidth of

Streaming Interface

Normal Streaming

Audio Control Interface

Audio Streaming Interface

5.10 Synch Frame

As AKM USB Microphone does not support this request , pipe is stalled.

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[AK5370]

6. Device specific requests

AKM USB Microphone supports ONLY SET_CUR as bRequest field in Set Request Values.

6.1 Audio Control Request

AKM USB microphone support ONLY Feature Unit Control Request, not support other requests.
Addition to this, it only supports SET_CUR value as bRequest field in Set Feature Unit Control
Request Values. All Audio Control Requests are applied to channel 0, which means master
channel.

6.1.1 Set Feature Unit Control Request

AKM USB Microphone supports only one form of parameter block.
a) Mute Control

Offset Field Size Value Description

0 bmRequestType 1 0x21
1 bRequest 1 0x01 SET_CUR
2 wValue 2 0x0100 MUTE_CONTROL | CHANNEL_ 0
4 wIndex 2 0x0300 Upper Byte : bUnit ID field in Feature Unit

Descriptor.(0x03)

Lower Byte : Audio Control Interface(0x00)
6 wLength 2 0x0001 The Length of Mute Control Parameter Block

The parameter block of mute control is the following.

Offset Field Size Value Description

0 bMute 1 0x01

0x00

b) Volume Control

Offset Field Size Value Description

0 bmRequestType 1 0x21
1 bRequest 1 0x01 SET_CUR
2 wValue 2 0x0200 VOLUME_CONTROL | CHANNEL_0
4 wIndex 2 0x0300 Upper Byte : bUnit ID field in Feature Unit

6 wLength 2 0x0002 Volume Control

The parameter block of mute control is the following.

Offset Field Size Value Description

0 wVolume 2 0xZZZZ The value is mapped to the volume register value.

If the wVolume exceeds the range, the AK5370 forces the value into the range. Please see the
conversion table in the Get Feature Unit Control Request.

c) Automatic Gain Control

Offset Field Size Value Description

0 bmRequestType 1 0x21
1 bRequest 1 0x01 SET_CUR
2 wValue 2 0x0700 AUTOMATIC_GAIN_CONTROL | CHANNEL_0
4 wIndex 2 0x0300 Upper Byte : bUnit ID field in Feature Unit

6 wLength 2 0x0001 The Length of Mute Control Parameter Block

The parameter block of mute control is the following.

Offset Field Size Value Description

0 bAGC 1 0x01

0x00

TRUE

FALSE

Descriptor.(0x03)

Lower Byte : Audio Control Interface(0x00)

(refer to Figure 3 conversion table )

ZZZZ is assigned by the host

Descriptor.(0x03)

Lower Byte : Audio Control Interface(0x00)

TRUE (AGC pin is H)

FALSE (AGC pin is L: Default)

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[AK5370]

6.1.2 Get Feature Unit Control Request

AKM USB Microphone supports only one form of parameter block.
a) Mute Control

Offset Field Size Value Description

0 bmRequestType 1 0xA1
1 bRequest 1 0x81 GET_CUR
2 wValue 2 0x0100 MUTE_CONTROL | CHANNEL_0
4 wIndex 2 0x0300 Upper Byte : bUnit ID field in Feature Unit

Descriptor.(0x03)

Lower Byte : Audio Control Interface(0x00)
6 wLength 2 0x0001 The Length of Mute Control Parameter Block

The device outputs the current setting of mute status.

Offset Field Size Value Description

0 bMute 1 0x01

0x00

b) Volume Control

Offset Field Size Value Description

0 bmRequestType 1 0xA1
1 bRequest 1 0x81

0x82
0x83

0x84
2 wValue 2 0x0200 VOLUME_CONTROL | CHANNEL_0
4 wIndex 2 0x0300 Upper Byte : bUnit ID field in Feature Unit

6 wLength 2 0x0002 Volume Control

The parameter block of Volume Control is the following.

Offset Field Size Value Description

0 wVolume 2 0xZZYY

0xC600

0x1400

0x0100

Table 1 is the conversion map of USB class and internal volume register.
When host requests the volume value which is larger than the MAX value in the device, the device
sets the MAX value to the volume. When host requests the volume value which is smaller than
the MIN value in the device, the device sets the MIN value to the volume. RES value is 1.0dB.

TRUE
FALSE

GET_CUR
GET_MIN
GET_MAX
GET_RES

Descriptor.(0x03)
Lower Byte : Audio Control Interface(0x00)

bRequest = GET_CUR : returns current volume.
YY must be 00h
bRequest = GET_MIN : -58dB
bRequest = GET_MAX : +20dB
bRequest = GET_RES : 1.0dB

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Field

wVolume

0x7FFF 20.0000

-------- ---------

0x1400 20.0000

0x13FF 19.0000

--------- --------
0x1301 19.0000
0x1300 19.0000

0x12FF 18.0000

--------- --------
0x1201 18.0000
0x1200 18.0000

--------- --------

--------- --------

0x02FF 2.0000

--------- --------
0x0201 2.0000
0x0200 2.0000

0x01FF 1.0000

--------- ---------
0x0101 1.0000
0x0100 1.0000

0x00FF 0.0000

--------- ---------
0x0001 0.0000
0x0000 0.0000 1.0dB

0xFFFF -1.0000

-------- --------
0xFF01 -1.0000
0xFF00 -1.0000

0xFEFF -2.0000

-------- --------
0xFE01 -2.0000
0xFE00 -2.0000

--------- ---------

--------- ---------

0xC700 -57.0000

0xC6FF -58.0000

--------- ---------
0xC601 -58.0000
0xC600 -58.0000

0xC5FF -58.0000

--------- ---------

0x8000 -58.0000

Table 1 Conversion Table of Volume Control

value Step

[AK5370]

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c) Automatic Gain Control

Offset Field Size Value Description

0 bmRequestType 1 0xA1
1 bRequest 1 0x81 GET_CUR
2 wValue 2 0x0700 AUTOMATIC_GAIN_CONTROL | CHANNEL_0
4 wIndex 2 0x0300 Upper Byte : bUnit ID field in Feature Unit

Descriptor.(0x03)
Lower Byte : Audio Control Interface(0x00)

6 wLength 2 0x0001 The Length of Mute Control Parameter Block

The device outputs the current setting of AGC.

Offset Field Size Value Description

0 bAGC 1 0x01

0x00

TRUE (AGC pin is H)
FALSE (AGC pin is L)

[AK5370]

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[AK5370]

6.2 Endpoint Control Request

The AK5370 supports five sampling frequencies. The sampling rate is changed when Set
Endpoint Control Request  is issued. SET_CUR, GET_CUR of bRequest is only supported.
GET_MIN, GET_ MAX, and GET_RES of bRequest are not supported.

6.2.1 Set Endpoint Control Request

Offset Field Size Value Description

0 bmRequestType 1 0x22
1 bRequest 1 0x01 SET_CUR
2 wValue 2 0x0100 Upper byte: SAMPLING_FREQ_CONTROL (0x01)

Lower byte : zero

4 wIndex 2 0x0081 Upper Byte : zero

Lower Byte : Endpoint Address (0x81)

6 wLength 2 0x0003 The Length of Sampling Frequency Parameter

Block

The parameter block of mute control is the following.

Offset Field Size Value Description

0 iSampleFreq 3 0xYYYYYY The following five values are valid. Others are

invalid.
0x001F40 : 8kHz
0x002B11 : 11.025kHz
0x005622 : 22.05kHz
0x00AC44 : 44.1kHz(default)
0x00BB80 : 48kHz

If the iSampleFreq is different from the above values, the AK5370 forces sampling frequency to the
appropriate value.

6.2.2 Get Endpoint Control Request

Offset Field Size Value Description

0 bmRequestType 1 0xA2
1 bRequest 1 0x81 GET_CUR
2 wValue 2 0x0100 Upper byte: SAMPLING_FREQ_CONTROL (0x01)

Lower byte : zero

4 wIndex 2 0x0081 Upper Byte : zero

Lower Byte : Endpoint Address (0x81)

6 wLength 2 0x0003 The Length of Sampling Frequency Parameter

Block

The parameter block of mute control is the following.

Offset Field Size Value Description

0 iSampleFreq 3 0xYYYYYY The following five values are valid. Others are

invalid.
0x001F40 : 8kHz
0x002B11 : 11.025kHz
0x005622 : 22.05kHz
0x00AC44 : 44.1kHz
0x00BB80 : 48kHz

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24pin VSOP (Unit: mm)

[AK5370]

Package

24

1

0.22 +0.10

-0.05

Seating Plane

*7.9±0.2

0.12

13

A

5.6

12

0.65

M

0.08

Detail A

0.15+0.10

-0.05

0.10±0.05

1.25±0.20

0.5±0.2

0.2

±

7.6

NOTE: Dimension "*" does not include mold flash.

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[AK5370]

Marking

AKM

AK5370VF
AAXXXX

1) Pin #1 indication

2) AA: LOT#

3) Date Code: XXXXX(4 digits)

4) Marketing Code: AK5370VF

5) Asahi Kasei Logo

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[AK5370]

IMPORTANT NOTICE

• These products and their specifications are subject to change without notice. Before
considering any use or application, consult the Asahi Kasei Microsystems Co., Ltd. (AKM)
sales office or authorized distributor concerning their current status.

• AKM assumes no liability for infringement of any patent, intellectual property, or other right in
the application or use of any information contained herein.

• Any export of these products, or devices or systems containing them, may require an export
license or other official approval under the law and regulations of the country of export
pertaining to customs and tariffs, currency exchange, or strategic materials.

• AKM products are neither intended nor authorized for use as critical components in any safety,
life support, or other hazard related device or system, and AKM assumes no responsibility
relating to any such use, except with the express written consent of the Representative
Director of AKM. As used here:

(a) A hazard related device or system is one designed or intended for life support or

maintenance of safety or for applications in medicine, aerospace, nuclear energy, or other
fields, in which its failure to function or perform may reasonably be expected to result in
loss of life or in significant injury or damage to person or property.

(b)A critical component is one whose failure to function or perform may reasonably be

expected to result, whether directly or indirectly, in the loss of the safety or effectiveness of
the device or system containing it, and which must therefore meet very high standards of
performance and reliability.

• It is the responsibility of the buyer or distributor of an AKM product who distributes, disposes
of, or otherwise places the product with a third party to notify that party in advance of the
above content and conditions, and the buyer or distributor agrees to assume any and all
responsibility and liability for and hold AKM harmless from any and all claims arising from the
use of said product in the absence of such notification.

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