TDA8596_15 Datasheet, PDF (18/48 Pages) NXP Semiconductors – I2C-bus controlled 4 ´ 45 W power amplifier with symmetrical inputs

NXP Semiconductors
TDA8596
I²C-bus controlled 4 × 45 W power amplifier with symmetrical inputs
7.13 DC load detection
When the DC load detection is enabled (IB1[D1] = 1), a DC offset is slowly applied at the
outputs of the amplifiers during the start-up sequence (see Figure 4 and Figure 5) and the
load currents as a result of the applied offset are measured. Based on this measurement
the load impedance can be determined to differentiate between normal, line driver and no
load (see Figure 12).
LOAD
NORMAL
LINE DRIVER MODE
OPEN-CIRCUIT
DETECTION
LEVEL
20 Ω 100 Ω
800 Ω 5 kΩ
001aad176
Fig 12. DC load detection levels
When the amplifier is used in line driver mode and the external booster has an input
impedance between 100 Ω and 800 Ω (DC-coupled), the DC load bits will be set at
DBx[D5:D4] = 10 independent of the selected gain setting (see Table 5).
Table 5. DC load detection translation table
DC load bits
DBx[D5]
DBx[D4]
0
0
1
0
1
1
0
1
Load indication^[1]
normal load
line driver load
open load
not valid
[1] Only when IB1[D2] = 0.
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 and initiate the proper
selection of the amplifier gain, i.e. 26 dB for normal mode or 16 dB for line driver mode.
Gain selection will occur without audible pop noise when the amplifier is in mute.
The DC load bit DBx[D4] is shared with the AC load detection. This implies that Table 5 is
only valid when AC load detection is disabled (IB1[D2] = 0). When the AC load detection is
enabled (IB1[D2] = 1) the bits DBx[D4] will show the result of the AC load detection. After
disabling the AC load detection data bit DBx[D4] will show the result of the DC load
measurement, which was stored during the AC load measurement.
7.14 AC load detection
When AC load detection is enabled (IB1[D2] = 1), AC coupled speakers (e.g. tweeters)
can be detected during the assembly process. The detection is performed by means of
applying an audible input sine wave (e.g. 19 kHz) to the inputs of the amplifier. The AC
current into the load is measured with a 460 mA peak current detector to detect the
presence of an AC load. In order to prevent spurious AC load detection (e.g. due to
amplifier on/off switching), the AC load detection bit will only be set when the peak current
threshold is triggered at least three times. Besides the 460 mA peak current threshold, a
secondary threshold level at 230 mA is present. In case this level is not triggered, a high
ohmic DC load (e.g. line driver) is assumed (also refer to Figure 13).
TDA8596_2
Product data sheet
Rev. 02 — 8 November 2007
© NXP B.V. 2007. All rights reserved.
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