TDA8926 Datasheet, PDF (6/32 Pages) NXP Semiconductors – Power stage 2 x 50 W class-D audio amplifier

Philips Semiconductors
Power stage 2 × 50 W class-D audio
amplifier
Preliminary specification
TDA8926
8 FUNCTIONAL DESCRIPTION
The combination of the TDA8926J and the TDA8929T
controller produces a two-channel audio power amplifier
system using the class-D technology (see Fig.3). In the
TDA8929T controller the analog audio input signal is
converted into a digital Pulse Width Modulation (PWM)
signal.
The power stage TDA8926 is used for driving the low-pass
filter and 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.
For a description of the controller, see data sheet
“TDA8929T, Controller class-D audio amplifier”.
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. For protection, a
temperature sensor and a maximum current detector are
built-in on the chip.
For interfacing with the controller chip the following
connections are used:
• 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 SW1 and SW2
with a small delay
• 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 and controlled by the switch pin if
pin POWERUP is at V_SS + 12 V
• Power-up (pin POWERUP): must be connected to a
continuous supply voltage of at least V_SS + 5 V with
respect to V_SS
• Diagnostics (pin DIAG): digital open-drain output; pulled
to V_SS if the temperature or maximum current is
exceeded.
8.2 Protection
Temperature and short-circuit protection sensors are
included in the TDA8926. The protection circuits are
operational only in combination with the controller
TDA8929T. In the event that the maximum current or
maximum temperature is exceeded the diagnostic output
is activated. The controller has to take appropriate
measures by shutting down the system.
8.2.1 OVERTEMPERATURE
If the junction temperature (T_j) exceeds 150 °C, then
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
SHORT-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 5 A, then
pin DIAG becomes LOW. The controller should shut down
the system to prevent damage. Using the controller
TDA8929T the system is shut down within 1 µs, and after
220 ms it will attempt to restart the system again. During
this time the dissipation is very low, therefore the average
dissipation during a short circuit is practically zero.
2002 Oct 10
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