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Philips Semiconductors
Power stage 2 x 15 to 25 W class-D
audio amplifier
8
FUNCTIONAL DESCRIPTION
The TDA8925 is a two-channel audio power amplifier
system using the class-D technology (see Fig.1).
The power stage TDA8925S is used for driving the
loudspeaker load. It performs a level shift from the
low-power digital PWM signal, at logic levels, to a
high-power PWM signal that switches between the main
supply lines. A 2nd-order low-pass filter converts the PWM
signal into an analog audio signal across the loudspeaker.
8.1
Power stage
The power stage contains the high-power DMOS
switches, the drivers, timing and handshaking between the
power switches and some control logic (see Fig.1). For
protection, a temperature sensor and a maximum current
detector are built-in on the chip.
The following functions are available:
• Switch (pins SW1 and SW2): digital inputs; switching
from V
to V
+ 12 V and driving the power DMOS
SS
SS
switches
• Release (pins REL1 and REL2): digital outputs;
switching from V
to V
SS
with a small delay. Note: for self oscillating applications
this pin is not used.
• Power-up (pin POWERUP): must be connected to a
continuous supply voltage of at least V
respect to V
SS
• Enable (pins EN1 and EN2): digital inputs; at a level
of V
the power DMOS switches are open and the
SS
PWM outputs are floating; at a level of V
power stage is operational
• Diagnostics (pin DIAG): digital open-drain output; pulled
to V
if the temperature or maximum current is
SS
exceeded.
2004 May 06
+ 12 V; follow SW1 and SW2
SS
+ 5 V with
SS
+ 12 V the
SS
8.2
Protection
Temperature and short-circuit protection sensors are
included in the TDA8925. In the event that the maximum
current or maximum temperature is exceeded the
diagnostic output is pulled down to V
diagnostic is connected to the enable pins in the
application the system shuts down itself.
8.2.1
O
VERTEMPERATURE
If the junction temperature (T
pin DIAG becomes LOW. The diagnostic pin is released if
the temperature is dropped to approximately 130 °C, so
there is a hysteresis of approximately 20 °C.
8.2.2
S
-
HORT
CIRCUIT ACROSS THE LOUDSPEAKER
TERMINALS
When the loudspeaker terminals are short-circuited this
will be detected by the current protection. If the output
current exceeds the maximum output current of 3 A, then
pin DIAG becomes LOW. Using pin DIAG in combination
with the enable pins the system will shut down
immediately, and restart again. The result is that the output
current is limited at the overcurrent detection level.
6
Product specification
TDA8925
. Since the
SS
) exceeds 150 °C, then
j
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