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TFA9881UK/N1,023

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TFA9881 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 23 April 2013 10 of 32
NXP Semiconductors
TFA9881
3.4 W PDM input class-D audio amplifier
corner frequency where the noise is increasing. The bandwidth in Figure 8 scales with the
clock input frequency. This bandwidth can be extended via the bandwidth extension
silence pattern (0xE4; see Section 8.4.1
). The PWM switching frequency also scales with
the bandwidth extension setting. The bandwidth and the PWM switching frequency when
bandwidth extension is on and off are given in Table 12
.
Remark: The Bandwidth extension should be switched off when f
clk
> 4.1 MHz.
8.4.7 Mute
Mute mode is activated when the mute silence pattern (at least 32 consecutive 0x66
bytes) is applied on the DATA input. The TFA9881 remains in Mute mode as long as the
0x66 pattern is repeated. It will return to Operating mode when a pattern other than 0x66
is received. Transitions to and from Mute mode occur as soon as the relevant pattern is
recognized by the TFA9881 (hard mute and hard unmute).
8.4.8 Power-down
Power-down mode is activated when the power-down silence pattern (at least 128
consecutive 0xAC bytes) is applied on the DATA input. The TFA9881 remains in
Power-down mode as long as the 0xAC pattern is repeated. It will return to Operating
mode when a pattern other than 0xAC is received.
Table 12. Bandwidth extension setting
Setting Bandwidth Switching frequency
bandwidth extension on
bandwidth extension off; default setting
Fig 8. Output power spectrum, f
clk
= 6.144 MHz
f
clk
8
--------
f
clk
256
---------
f
clk
16
--------
010aaa709
−120
−80
−40
output
(dBFS)
−160
f (Hz)
10 10
6
10
5
10
2
10
4
10
3
TFA9881 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 23 April 2013 11 of 32
NXP Semiconductors
TFA9881
3.4 W PDM input class-D audio amplifier
8.5 High-pass filter
The high-pass filter will block the DC components in the incoming audio stream. The
cut-off frequency, f
high(3dB)
, is determined by the clock frequency, and is defined in
Equation 1
:
(1)
where k depends on the bandwidth extension setting (see Section 8.4.6
):
• k = 2 if bandwidth extension is off
• k = 1 if bandwidth extension is on
f
high(3dB)
is about 7.5 Hz at a clock frequency of 6.144 MHz when bandwidth extension is
off. The high-pass filter is always enabled.
Remark: Care should be taken when DC dither is applied to the PDM audio input stream.
The PDM source should slowly increase this DC-dither to avoid pop noise.
8.6 Protection mechanisms
The following protection circuits are included in the TFA9881:
• Invalid Data Protection (IDP)
• OverTemperature Protection (OTP)
• OverVoltage Protection (OVP)
• UnderVoltage Protection (UVP)
• OverCurrent Protection (OCP)
The reaction of the device to fault conditions differs depending on the protection circuit
involved.
8.6.1 Invalid Data Protection (IDP)
IDP is designed to detect the absence of a data input signal. IDP is activated when 128
consecutive 0s or 1s are received on the DATA input.
IDP is disabled when a PDM stream that does not contain 128 consecutive 0s or 1s is
received. The output stages are set floating when IDP is active.
Remark: The maximum PDM input modulation depth should be limited to avoid false IDP
triggering.
8.6.2 OverTemperature Protection (OTP)
OTP prevents heat damage to the TFA9881. It is triggered when the junction temperature
exceeds 130 °C. When this happens, the output stages are set floating. OTP is cleared
automatically via an internal timer (100 ms with f
clk
= 6.144 MHz), after which the output
stages will start to operate normally again.
f
high 3dB–
f
clk
– 8191 8192ln
16 k 
------------------------------------------------------
=
TFA9881 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 23 April 2013 12 of 32
NXP Semiconductors
TFA9881
3.4 W PDM input class-D audio amplifier
8.6.3 Supply voltage protection mechanisms (UVP and OVP)
UVP is activated, setting the outputs floating, if V
DDP
drops below the undervoltage
protection threshold, V
P(uvp)
. This transition will be silent, without pop noise. When the
supply voltage rises above V
P(uvp)
again, the system will be restarted after 100 ms with
f
clk
= 6.144 MHz.
OVP is activated, setting the power stages floating, if the supply voltage rises above the
overvoltage protection threshold, V
P(ovp)
. The power stages are re-enabled as soon as the
supply voltage drops below V
P(ovp)
again. The system will be restarted after 100 ms with
f
clk
= 6.144 MHz.
Note that a supply voltage > 5.5 V may damage the TFA9881.
8.6.4 OverCurrent Protection (OCP)
OCP will detect a short circuit across the load or between one of the amplifier outputs and
one of the supply lines. If the output current exceeds the overcurrent protection threshold
(I
O(ocp)
), it will be limited to I
O(ocp)
while the amplifier outputs are switching (the amplifier is
not powered down completely). This is called current limiting. The amplifier can
distinguish between an impedance drop at the loudspeaker and a low-ohmic short circuit
across the load or to one of the supply lines. The impedance threshold depends on which
supply voltage is being used:
• In the event of a short circuit across the load or a short to one of the supply lines, the
audio amplifier is switched off completely. It will try to restart again after approximately
100 ms with f
clk
= 6.144 MHz. If the short-circuit condition is still present after this
time, this cycle will be repeated. Average dissipation will be low because of the short
duty cycle.
• In the event of an impedance drop (e.g. due to dynamic behavior of the loudspeaker),
the same protection mechanism will be activated. The maximum output current is
again limited to I
O(ocp)
, but the amplifier will not switch off completely (thus preventing
audio holes from occurring). This will result in a clipped output signal without artifacts.
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TFA9881UK/N1,023

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Buy TFA9881UK/N1,023
Manufacturer:
NXP Semiconductors
Description:
IC AMP AUDIO CLASSD 3.4W 9WLCSP
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