(No.MA511<Rev.001>)14/16
4.3
DC Offset error description
4.3.1 DC Offset detection circuit design
• Purpose:
To prevent breakdown, burning and emitting smoke from cus-
tomer's car speaker when occur DC offset between speaker
output "+" and "-".
• Target:
Detect DC offset, then stop the Power Amp operation and shift
to specified condition.
4.3.2 Possible causes of DC offset at speaker output lines
(1) Mis-connection for Speaker output for example touch to car
body or battery line.
(2) Current leak of coupling capacitor for Power IC input.
(3) Current leak of Ac-GND capacitor for Power IC Ac-GND.
(4) Capacitor shorted of above parts due to foreign object.
4.3.3 Type of checking
4.3.3.1
To detect DC Offset Error
• Mis-connection
- Short any one speaker out line to GND or Vcc
• Capacitor leak
- Parallel 330k
Ω
to either any one of coupling cap or Ac-GND
cap (to simulate current leakage of capacitor)
- Shorted either any one of coupling cap or Ac-GND cap.
4.3.3.2
To avoid mis-judge music as DC offset error
• Low frequency signal (17Hz or 20Hz) is more prone to cause
mis-detection.
- Play 17Hz (or 20Hz) signal and make sure micon will not de-
tect and judge this as happen DC offset error.
4.3.4 Detection Timing chart
4.3.5 Manipulate after detect DC Offset
• If detected error 10 consecutive times, and 10th error occurred
in "Mis-connect detection period", judge as "Mis-connect".
• If detected error 10 consecutive times, and 10th error occurred
in "Capacitor leak detection period", judge as "Capacitor leak ".
• If detected error 10 consecutive times, and 10th error occurred
in "Other detection period" and detected another 10 errors con-
secutively, then judge as "Other".
• If judge as "Mis-connect".
- turn off speaker output.
- display "MIS WIRING"
→
"CHK WIRING"
→
"THEN RESET"
→
"UNIT".
- key access disable except button of Eject, Reset and service
mode
- record error in EEPROM "DC1 ERR"
- Set is able to be recovered by Reset button.
• If judge as "Capacitor leak ".
- turn off speaker output.
- display "WIRING"
→
"CHK WIRING"
→
"THEN RESET"
→
"UNIT".
- key access disable except button of Eject, Reset and service
mode
- record error in EEPROM "DC2 #" (# means counter number)
- Set can be recovered by pressing the Reset button before
the capacitor leak error counter reach "DC2 4".
After that, only clear the counter back to "0" can recover the
set.
• If judge as "Other" (manipulation same as mis-connect)
4.3.6 How to clear the DC offset error recorded in EEPROM
Refer to "DC error information mode".
E-Vol
Audio Pwr Amp
Micon
In 1
In 2
In 3
In 4
AcGnd
Offset Detect
Out
ADC In
R4
C3
R3
R1
R2
Sw5V
C-ac2
C-ac1
C-tc
Win_TC
Win_In
DC Error
C-in
C-in
C-in
C-in
PWIC_STBY
PWIC_MUTE
AUD_MUTE
1.5sec or more
0.7sec or more
1.0sec
50ms
or more
Missconnect
detection period
Capacitor leak
detection period
Other (miss detection etc.)
detection period
2.0sec or more
0.8sec
