AKM’s AK4955 is a 24-bit stereo CODEC integrating microphone amplifier, speaker amplifier, video amplifier, LCD and DSP, with recording function, playback function, power management and master-slave mode, mainly used in portable equipment with recording/playing function . This article introduces the AK4955 main features, block diagram, and AKD4955-A evaluation board block diagram, circuit diagram and PCB layout.
The AK4955 is a 24bit stereo CODEC with a microphone amplifier, speaker amplifier, video amplifier, LDO, and DSP. The input circuits include a microphone amplifier and the output circuits include a speaker amplifier. It is suitable for portable application with recording/playback function . A one channel composite In/Out video amplifier is also integrated. The internal charge pump generates a negative power eliminating the need for AC-coupling capacitors. The AK4955 is available in a small 36pin CSP (3.0mm 
Applications: DSCs, DVCs
AK4955 main features:
Recording Functions
· Stereo Single-ended input with two Selectors
MIC Amplifier (+24dB/+21dB/+18dB/+16dB/+14dB/+11dB/+8dB/+5dB/0dB)
· Digital ALC (Automatic Level Control) (Setting Range: +36dB ~ -54dB, 0.375dB Step)
ADC Performance: S/(N+D): 81dB, DR, S/N: 88dB (MIC-Amp=+18dB) S/(N+D): 82dB, DR, S/N: 96dB (MIC-Amp =0dB)
· 5 Band Notch Filters
· Digital MIC Interface
Playback Functions
· Digital De-emphasis Filter (tc=50/15
· Soft Mute
· Digital ALC (Automatic Level Control) (Setting Range: +36dB ~ -54dB, 0.375dB Step)
· Digital Volume Control (+12dB ~ -115dB, 0.5dB Step, Mute)
· Stereo Emphasis Circuit
· Stereo Line Output
Output Voltage: +2dBV(1.26Vrms) (LVDD = 4.8V)2.52Vpp (LVDD=3.3V)
-S/(N+D): 85dB, S/N: 92dB
· Mono Mixing Output
· Mono Speaker-Amplifier
SPK-Amp Performance: S/(N+D): 70dB@150mW, 60dB@250mW, S/N: 95dB
– BTL Output
– Output Power: 600mW@8
400mW@8
· Analog Mixing: Mono Input
· Beep Sound
Power Management
· Thermal Shut-down Function
Master Clock:
(1) PLL Mode
Frequencies: 11.2896MHz, 12MHz, 13.5MHz, 24MHz, 27MHz (MCKI pin) 32fs or 64fs (BICK pin)
(2) External Clock Mode
Frequencies: 256fs, 512fs or 1024fs (MCKI pin)
Output Master Clock Frequencies: 32fs/64fs/128fs/256fs
Sampling Frequency
PLL Slave Mode (BICK pin): 7.35kHz ~ 48kHz
PLL Slave Mode (MCKI pin): 8kHz, 11.025kHz, 12kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz
PLL Master Mode: 8kHz, 11.025kHz, 12kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz
EXT Master/Slave Mode: 7.35kHz ~ 48kHz (256fs, 512fs), 7.35kHz ~ 13kHz (1024fs)
Master/Slave mode
Audio Interface Format: MSB First, 2’s complement
ADC: 24bit MSB justified, 16/24bit I2S
DAC: 24bit MSB justified, 16bit LSB justified, 24bit LSB justified, 16/24bit I2S
Video Functions
· One Composite Signal Input
· Capacitor-less Video Amplifier for Composite Signal Output Gain: +6 / +9 / +12 / +16.5dB
· LPF
· Charge Pump Circuit for Negative Power Supply
Ta = -30 ~ 85℃
Power Supply:
· Analog Power Supply (AVDD): 2.7 ~ 3.6V
· Digital Power Supply (DVDD): 1.6 ~ 2.0V
· Line Output Power Supply (LVDD): 2.7 ~ 5.5V
· Speaker Power Supply (SVDD): 2.7 ~ 5.5V
· Digital I/O Power Supply (TVDD): -0.2 ~ 3.6V
Package: 36pin QFN (3.0
Evaluation Board: AKD4955
figure 1. AK4955 block diagram
AKD4955-A Evaluation Board
The AKD4955-A is an evaluation board for AK4955, 24bit stereo CODEC with a microphone/ speaker/ video amplifiers, DSP and LDO. The AKD4955-A has the Digital Audio I/F and can achieve the interface with digital audio systems via optical connector .
figure 2. AKD4955-A Evaluation Board Block Diagram
image 3. AKD4955-A Evaluation Board Circuit Diagram (1)
Figure 4. AKD4955-A Evaluation Board Circuit Diagram (2)
Figure 5. AKD4955-A Evaluation Board Circuit Diagram (3)
Image 6. AKD4955-A Evaluation Board Circuit Diagram (4)
Figure 7. AKD4955-A Evaluation Board Circuit Diagram (5)
Figure 8. AKD4955-A Evaluation Board Circuit Diagram (6)
Figure 9. AKD4955-A Evaluation Board Circuit Diagram (7)
Figure 10. AKD4955-A Evaluation Board PCB Layout
For details, see:
http://www.asahi-kasei.co.jp/akm/en/product/ak4950/ak4950_f00e.pdf
and
http://www.asahi-kasei.co.jp/akm/en/product/ak4955/akd4955-a1-03e.pdf
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