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2004 May 05 6
Philips Semiconductors Preliminary specification
Power stage 2 x 10 or 1 x 20 W class-D
audio amplifier
TDA8928J
8 FUNCTIONAL DESCRIPTION
The TDA8928J is a two-channel audio power amplifier
system using class-D technology.
The power stage TDA8928J 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 high-power DMOS switches,
drivers, timing and handshaking between the power
switches and some control logic (see Fig.1).
The following functions are available:
• Switch (pins SW1 and SW2): digital inputs; switching
from V
SS
to V
SS
+ 12 V and driving the power DMOS
switches
• Release (pins REL1 and REL2): digital outputs;
switching from V
SS
to V
SS
+ 12 V; follow pin SW1 and
SW2 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
SS
+ 5 V with
respect to V
SS
• Enable (pins EN1 and EN2): digital inputs; at a level of
V
SS
the power DMOS switches are open and the PWM
outputs are floating; at a level of V
SS
+ 12 V the power
stage is operational
• Diagnostics (pin DIAG): digital open-drain output; pulled
down to V
SS
if the maximum temperature or maximum
current is exceeded.
8.2 Protection
Temperature and short-circuit protection sensors are
included in the TDA8928J. The diagnostic output is pulled
down to V
SS
in the event that the maximum current or
maximum temperature is exceeded. The system shuts
itself down when pin DIAG is connected to pins EN1 and
EN2.
8.2.1 MAXIMUM TEMPERATURE
Pin DIAG becomes LOW if the junction temperature (T
j
)
exceeds 150 °C. Pin DIAG becomes HIGH again if T
j
is
dropped to approximately 130 °C, so there is a hysteresis
of approximately 20 °C.
8.2.2 MAXIMUM CURRENT
When the loudspeaker terminals are short-circuited this
will be detected by the current protection. Pin DIAG
becomes LOW if the output current exceeds the maximum
output current of 2 A. Pin DIAG becomes HIGH again if the
output current drops below 2 A. The output current is
limited at the maximum current detection level when pin
DIAG is connected to pins EN1 and EN2.