Philips TDA8928J - Manual (Page 6)

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 M AXIMUM 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 M AXIMUM 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.