TDF8544
NXP Semiconductors
I2C-bus controlled 4 50 W power amplifier
COMPARATORS
OFFSET
GENERATOR
out +
SPIKE
FILTER
DOOR-SLAM
PROCESSOR
out −
2
I C-BUS BITS
LOAD CONDITION
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Fig 10. Principle of start-up diagnostics
The load detection values are shown in Figure 11.
SHORTED
NORMAL
LINE DRIVER
OPEN
high gain
low gain
0.5 Ω
1.5 Ω
1.5 Ω
3.2 Ω
20 Ω
20 Ω
80 Ω
80 Ω
200 Ω
200 Ω
400 Ω
400 Ω
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Fig 11. Start-up diagnostics load detection levels
If only 4 speakers are connected, the low gain mode can be selected during the start-up
diagnostics. A shorted load is indicated until an impedance of 1.5 is reached. Even ‘soft’
shorts in the wiring harness will be detected.
IB1[D1]
turn on diagnostic
enable
STB
t
d(sudiag-on)
amplifier
output
(1)
(2)
t
t
amp_on
sudiag
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(1) First stage: open load/load/line driver load; short across the load.
(2) Second stage: amplifier start plus short to ground/VP; speaker fault.
Fig 12. Start-up with start-up diagnostics
TDF8544
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© NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 2 — 29 August 2011
15 of 54
NXP [ NXP ]
