TDA8929T Datasheet, PDF (9/36 Pages) NXP Semiconductors – Controller class-D audio amplifier

Philips Semiconductors
Controller class-D audio amplifier
Preliminary specification
TDA8929T
8.2 Pulse width modulation frequency
The output signal of the power stage is a PWM signal with
a carrier frequency of approximately 300 kHz. Using a
second-order LC demodulation filter in the application
results in an analog audio signal across the loudspeaker.
This switching frequency is fixed by an external resistor
R_OSC connected between pin OSC and V_SS. With the
resistor value given in the application diagram, the carrier
frequency is typical 317 kHz. The carrier frequency can be
calculated using: f_osc = ^9---R--×--_O---1-_S---0_C---⁹- [Hz]
If two or more class-D systems are used in the same audio
application, it is advised to have all devices working at the
same switching frequency. This can be realized by
connecting all OSC pins together and feed them from an
external oscillator. Using an external oscillator it is
necessary to force pin OSC to a DC-level above SGND for
switching from the internal to an external oscillator. In this
case the internal oscillator is disabled and the PWM will
switch on the external frequency. The frequency range of
the external oscillator must be in the range as specified in
the switching characteristics.
Application in a practical circuit:
• Internal oscillator: R_OSC connected between pin OSC
and V_SS
• External oscillator: connect oscillator signal between
pin OSC and pin SGND; delete R_OSC.
8.3.2 DIAGNOSTIC CURRENT
This input is intended to protect against short-circuits
across the loudspeaker load. In the event that the current
limit in the power stage is exceeded, pin DIAGCUR must
be pulled to a LOW level. A LOW level on the diagnostic
current input will immediately force the output pins EN1
and EN2 to a LOW level. The power stage will shut down
within less than 1 µs and the high current is switched off.
In this state the dissipation is very low. Every 220 ms the
controller will attempt to restart the system. If there is still
a short-circuit across the loudspeaker load, the system is
switched off again as soon as the maximum current is
exceeded. The average dissipation will be low because of
this low duty factor. The actual current limiting value is set
by the power stage.
Depending on the type of power stage which is used,
several values are possible:
• TDA8926TH: limit value can be externally adjusted with
a resistor; maximum is 5 A
• TDA8927TH: limit value can be externally adjusted with
a resistor; maximum is 7.5 A
• TDA8926J and TDA8926ST: limit value is fixed at 5 A
• TDA8927J and TDA8927ST: limit value is fixed at 7.5 A.
8.3 Protections
The controller is provided with two diagnostic inputs. One
or both pins can be connected to the diagnostic output of
one or more power stages.
8.3.1 DIAGNOSTIC TEMPERATURE
A LOW level on pin DIAGTMP will immediately force both
pins EN1 and EN2 to a LOW level. The power stage shuts
down and the temperature is expected to drop. If
pin DIAGTMP goes HIGH, pins EN1 and EN2 will
immediately go HIGH and normal operation will be
maintained.
Temperature hysteresis, a delay before enabling the
system again, is arranged in the power stage. Internally
there is a pull-up resistance to 5 V at the diagnostic input
of the controller. Because the diagnostic output of the
power stage is an open-drain output, diagnostic lines can
be connected together (wired-OR). It should be noted that
the TDA8929T itself has no temperature protection.
2001 Dec 11
9