TDA8927 View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
TDA8927 Datasheet PDF : 36 Pages
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Philips Semiconductors
Power stage 2 × 80 W class-D
audio ampliï¬er
Objective speciï¬cation
TDA8927
8 FUNCTIONAL DESCRIPTION
The combination of the TDA8927J and the TDA8929T
produces a two-channel audio power amplifier system
using the class-D technology (see Fig.5). In the TDA8929T
controller device the analog audio input signal is converted
into a digital Pulse Width Modulation (PWM) signal.
The power stage TDA8927 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 switchs between the main
supply lines. A second-order low-pass filter converts the
PWM signal into an analog audio signal across the
loudspeaker.
See the specification of the TDA8929T for a description of
the controller.
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 VSS to VSS + 12 V and driving the power DMOS
switches
• Release (pins REL1 and REL2): digital outputs to
indicate switching from VSS to VSS + 12 V, follows
pins SW1 and SW2 with a small delay
• Enable (pins EN1 and EN2): digital inputs; at a level of
VSS the power DMOS switches are open and the PWM
output is floating; at a level of VSS + 12 V the power
stage is operational and controlled by the switch pin if
pin POWERUP is at VSS + 12 V
• Power-up (pin POWERUP): must be connected to a
continuous supply voltage of at least VSS + 5 V with
respect to VSS
• Diagnostics (pin DIAG): digital open-drain output; pulled
to VSS if temperature or maximum current is exceeded.
8.2 Protections
Temperature and short-circuit protection sensors are
included in the TDA8927 power stage. These protections
are only operational in combination with the 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 (Tj) 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 it will
be detected by the current protection. If the output current
exceeds the maximum output current of 7.5 A, then
pin DIAG becomes LOW. The controller should shut down
the system to prevent damage. Using the 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, so the average dissipation during a
short-circuit is practically zero.
For the TDA8927TH the limit value can be externally
adjusted using a resistor. For the maximum value of 7.5 A
pin LIM should be connected to VSS. When a resistor Rext
is connected between pin LIM and VSS the maximum
output current can be set at a lower value, using:
IO(max) = R-----e2---x-.-t1---+--×---2--1-8--0---k-5--Ω---
Example 1: with Rext = 27 kΩ the current is limited at
3.8 A.
Example 2: with Rext = 0 Ω the current is limited at 7.5 A.
In the TDA8927J and the TDA8927ST pin LIM is internally
connected to VSS, so IO(max) = 7.5 A.
2001 Dec 11
8
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