TFA9881_15 Datasheet, PDF (11/32 Pages) NXP Semiconductors – 3.4 W PDM input class-D audio amplifier

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:
f_{high–3dB} = ^–----^f--^c--^l--^k---^---^l-₁-ⁿ--₆--^--⁸-_--¹-_k--⁹--_-¹--_---^--⁸---¹---⁹---²----^
(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.
TFA9881
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 23 April 2013
© NXP B.V. 2013. All rights reserved.
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