TDA8933 Datasheet, PDF (10/47 Pages) NXP Semiconductors – Class-D audio amplifier

NXP Semiconductors
TDA8933
Class-D audio amplifier
8.4.1 Thermal Foldback (TF)
If the junction temperature of the TDA8933 exceeds the threshold level (T_j > 140 °C), the
gain of the amplifier is decreased gradually to a level where the combination of
dissipation (P) and the thermal resistance from junction to ambient (R_th(j-a)) results in a
junction temperature around the threshold level.
This means that the device will not switch off completely, but remains operational at lower
output power levels. With music output signals, this feature enables high peak output
powers while still operating without any external heat sink other than the printed-circuit
board area.
If the junction temperature still increases due to external causes, the OverTemperature
Protection (OTP) shuts down the amplifier completely.
8.4.2 OverTemperature Protection (OTP)
If the junction temperature T_j > 155 °C, the power stage will shut down immediately.
8.4.3 OverCurrent Protection (OCP)
When the output current of the device exceeds 2 A due to a short-circuit across the load
or an impedance drop, the cycle-by-cycle current limitation becomes active. This means
the device will not switch off, but continue to operate while limiting the current without
causing audio holes (interruptions). The maximum output current will not go beyond the
absolute maximum current.
If the current exceeds 2 A due to a low ohmic short from the demodulated output (after the
inductor) to either V_SS or V_DD both power stages become floating. The DIAG is set low for
50 ms and the internal timer of 100 ms is started. The timer will keep both power stages
disabled for 100 ms. As long as the short remains, this cycle will repeat. The average
power dissipation in the TDA8933 will be low because the short-circuit current will flow
only during a very small part of the timer cycle of 100 ms.
8.4.4 Window Protection (WP)
WP checks the PWM output voltage before switching from Sleep mode to Mute mode
(outputs switching) and is activated:
• During the start-up sequence, when pin POWERUP is switched from Sleep mode to
Mute mode.
In the event of a short-circuit at one of the output terminals to V_DDP1, V_SSP1, V_DDP2 or
V_SSP2 the start-up procedure is interrupted and the TDA8933 waits for open-circuit
outputs. Because the check is done before enabling the power stages, no large
currents will flow in the event of a short-circuit.
• When the amplifier is shut down completely, due to activation of the OCP because a
short to one of the supply lines is made, then during restart (after 100 ms) the window
protection will be activated. As a result, the amplifier will not start up until the short to
the supply lines is removed.
8.4.5 Supply voltage protections
If the supply voltage drops below 10 V, the UVP circuit is activated and the system will
shut down directly. This switch-off will be silent and without pop noise. When the supply
voltage rises above the threshold level, the system is restarted again after 100 ms.
TDA8933_1
Preliminary data sheet
Rev. 01 — 15 May 2007
© NXP B.V. 2007. All rights reserved.
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