National Semiconductor LM49250, Руководство пользователя, Страница: 4 / 10

I 2 C Software Interface
The LM49250 evaluation board is controlled through an I 2 C
compatible USB interface. The LM49250 I 2 C interface soft-
ware provides a user friendly interface to easily evaluate the
functionality of the device. Each button corresponds to bits in
an I
2 C command byte. See LM49250 datasheet for detailed
I 2 C information.
30029111
FIGURE 2. LM49250 I 2 C Software Interface
Default
The DEFAULT button sets the LM49250 and the interface
software to its default state. In the default state all output am-
plifiers, spread spectrum, and 3D controls are off, all output
modes are set to 0, the fully differential input mode is selected,
all input gains are set to -64dB, right and left loudspeaker
output gain is 6dB, and headphone and earpiece output gain
are set to 0dB. Each time the power supply to the device is
cycled, the interface must be reset to its default state.
Chip Power
The Chip Power button enables or disables the entire device.
Even if an individual amplifier channel is enabled, the device
will not output any audio if the Chip Power button is set to
“OFF”.
LDOH
The LDOH button enables and disables the internal LDO. The
LDO is used to drive the ground referenced headphone am-
plifiers. This allows the speaker and headphone amplifiers to
operate from separate power supplies. The separate power
supplies allow the speaker amplifiers to operate from a higher
voltage for maximum headroom, while the headphone ampli-
fiers operate from a lower voltage, improving power dissipa-
tion.
If the LDO and the Chip Power is enabled, 2.25V will be seen
the VO(LDO) pin. However, if the LDO is disabled but either
headphone output is enabled, 2.25V will be seen at the VO
(LDO) pin (see Table 3).
TABLE 3. LDO Disabling Options
LDOH HPR_ON/HPL_ON PWR_ON
V
O(LDO)
(V)
0 0 X 0
0 1 1 2.25
1 X 0 VDD
1 1 0 2.25
0 1 0
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