TDA8595 Datasheet, PDF (18/50 Pages) NXP Semiconductors – I2C-bus controlled 4 ´ 45 W power amplifier

NXP Semiconductors
TDA8595
I²C-bus controlled 4 × 45 W power amplifier
LOAD
NORMAL
LINE DRIVER MODE
OPEN-CIRCUIT
DETECTION
LEVEL
20 Ω 100 Ω
800 Ω 5 kΩ
001aad176
Fig 13. DC load detection levels
If the amplifier is used as line driver and the external booster has an input impedance of
more than 100 Ω and less than 800 Ω (DC-coupled), the DC load bits will contain
DBx[D5:D4] = 10, independent of the gain setting (see Table 5).
Table 5. DC load detection
DC load bits
DBx[D5]
DBx[D4]
0
0
1
0
1
1
0
1
Meaning (when IB1[D2] = 0)
normal load
line driver load
open load
not valid
By reading the I²C-bus bits the microprocessor can determine, after the start-up of the
amplifier, whether a speaker or an external booster is connected.
Depending on these bits, the amplifier gain can be selected, 26 dB for normal mode or
16 dB for line driver mode. If the gain select is performed when the amplifier is muted, the
gain select will be pop free.
The DC load bits are combined with the AC load bits and are only valid when the AC load
detection is disabled. When the AC load detection is enabled (IB1[D2] = 1), the bits
DBx[D4] will show the content of the AC load detection. When the AC load detection is
disabled again, bit DBx[D4] will show the content of the DC load measurement, which was
stored during the AC load measurement. The AC load detection can only be performed
after the amplifier has completed its start-up cycle and will not conflict with the DC load
detection.
7.16 AC load detection
The AC load detection, enabled with IB1[D2] = 1, is used to detect if AC coupled
speakers, for example tweeters, are connected correctly during assembly. The detection is
audible because a sine wave of a certain frequency (e.g. 19 kHz) needs to be applied to
the inputs of the amplifier. The output voltage over the load impedance will generate an
amplifier current. If the amplifier peak current triggers a 460 mA (peak) threshold detector
three times, the AC load detection bit will be set. A three ‘threshold cross’ counter is used
to prevent false AC load detection when switching the input signal on or off.
An AC coupled speaker will reduce the impedance at the output of the amplifier in a
certain frequency band. The presence of an AC coupled speaker can be determined
using 460 mA (peak) and 230 mA (peak) threshold current detection. For instance, at an
output voltage of 2 V (peak) the total impedance must be less than 4 Ω to detect the AC
coupled load, or more than 8 Ω to guarantee only a DC connection is detected.
TDA8595_2
Product data sheet
Rev. 02 — 21 November 2007
© NXP B.V. 2007. All rights reserved.
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