STAC9750 Datasheet, PDF (56/73 Pages) Integrated Device Technology – VALUE-LINE TWO-CHANNEL AC’97 CODECS

STAC9750/9751
VALUE-LINE TWO-CHANNEL AC’97 CODECS
PC AUDIO
7. LOW POWER MODES
The STAC9750/9751 is capable of operating at reduced power when no activity is required. The
state of power-down is controlled by the Powerdown Register (26h). There are 7 commands of sep-
arate power down. The power down options are listed in Table 40. The first three bits, PR0..PR2, can
be used individually or in combination with each other, and control power distribution to the ADCs,
DACs and Mixer. The last analog power control bit, PR3, affects analog bias and reference voltages,
and can only be used in combination with PR0, PR1, and PR2. PR3 essentially removes power from
all analog sections of the CODEC, and is generally only asserted when the CODEC will not be
needed for long periods. PR0 and PR1 control the PCM ADCs and DACs only. PR2 and PR3 do not
need to be “set” before a PR4, but PR0 and PR1 must be “set” before PR4. PR5 disables the internal
CODEC clock and requires an external cold reset for recovery. PR6 disables the headphone driver
amplifier for additional analog power saving.
GRP Bits
PR0
PR1
PR2
PR3
PR4
PR5
PR6
Table 40. Low Power Modes
Function
PCM in ADCs & Input Mux Powerdown
PCM out DACs Powerdown
Analog Mixer power down (VREF still on)
Analog Mixer power down (VREF off)
Digital Interface (AC-Link) power down (external clock off)
Internal Clock disable
Powerdown HEADPHONE_OUT
The Figure 19 illustrates one example procedure to do a complete power down of STAC9750/9751.
From normal operation, sequential writes to the Powerdown Register are performed to power down
STAC9750/9751 a piece at a time. After everything has been shut off, a final write (of PR4) can be
executed to shut down the AC-Link. The part will remain in sleep mode with all its registers holding
their static values. To wake up, the AC'97 controller will send an extended pulse on the sync line,
issuing a warm reset. This will restart the AC-Link (resetting PR4 to zero). The STAC9750/9751 can
also be woken up with a cold reset. A cold reset will reset all of the registers to their default states.
When a section is powered back on, the Powerdown Control/Status register (index 26h) should be
read to verify that the section is ready (stable) before attempting any operation that requires it.
Figure 19. Example of STAC9750/9751 Powerdown/Powerup Flow
PR0=1
PR1=1
PR2=1
PR4=1
Normal
ADCs off PR0 DACs off PR1
Analog off
PR2 or PR3
Digital I/F off
PR4
Shut off
AC-Link
PR0=0 & ADC=1 PR1=0 & DAC=1 PR2=0 & ANL=1
Warm Reset
Ready =1
Default
Cold Reset
IDT™
VALUE-LINE TWO-CHANNEL AC’97 CODECS
56
STAC9750/9751
V 5.8 103106