Datasheet

TPA2028D1
www.ti.com SLOS660B –JANUARY 2010–REVISED SEPTEMBER 2012
TPA2028D1 AGC AND START-UP OPERATION
The TPA2028D1 is controlled by the I
2
C interface. The correct start-up sequence is:
1. Apply the supply voltage to the PV
DD
pin.
2. Apply a voltage above V
IH
to the EN pin. The TPA2028D1 powers up the I
2
C interface and the control logic.
I
2
C registers are reset to default value. By default, the device is in active mode (SWS = 0). After 5 ms the
amplifier will enable the class-D output stage and become fully operational.
CAUTION
Do not interrupt the start-up sequence after changing EN from V
IL
to V
IH.
CAUTION
Do not interrupt the start-up sequence after changing SWS from 1 to 0.
AGC STARTUP CONDITION
The amplifier gain at start-up depends on the following conditions:
1. Start-up from hardware reset (EN from 0 to 1): The amplifier starts up immediately at default fixed gain. AGC
starts controlling gain once the input audio signal exceeds noise gate threshold.
2. Start-up from software shutdown (SWS from 1 to 0): The amplifier starts up immediately at the latest fixed
gain during software shutdown, regardless the attack/ release time. For example:
– Audio is playing at fixed gain 6dB
– Devices goes to software shutdown (SWS = 1)
– Set fixed gain from 6 dB to 12 dB
– Remove software shutdown (SWS = 0)
– Amplifier starts up immediately at 12 dB
3. During audio playback with AGC on, gain changes according to attack/ release time. For example:
– Audio is playing at fixed gain 6 dB and 1:1 compression ratio
– Set fixed gain from 6 dB to 12 dB, at release time 500 ms / 6 dB
– Amplifier will take 500 ms to ramp from 6 dB to 12 dB
4. When EN = 0 and SWS = 0, the amplifier is set at fixed gain. The amplifier starts up at fixed gain when EN
transitions from 0 to 1.
The default conditions of TPA2028D1 allows audio playback without I2C control. Refer to Table 4 for entire
default conditions.
There are several options to disable the amplifier:
• Write EN = 0 to the register (0x01, 6). This write disables the amplifier, but leaves all other circuits operating.
• Write SWS = 1 to the register (0x01, 5). This action disables most of the amplifier functions.
• Apply V
IL
to EN. This action shuts down all the circuits and has very low quiescent current consumption. This
action resets the register to its default values.
CAUTION
Do not interrupt the shutdown sequence after changing EN from V
IH
to V
IL
.
Do not interrupt the shutdown sequence after changing SWS from 0 to 1.
Copyright © 2010–2012, Texas Instruments Incorporated 21
Product Folder Links: TPA2028D1