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TDA8927ST Fiches technique(PDF) 8 Page - NXP Semiconductors |
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TDA8927ST Fiches technique(HTML) 8 Page - NXP Semiconductors |
8 / 36 page 2001 Dec 11 8 Philips Semiconductors Objective specification Power stage 2 × 80 W class-D audio amplifier 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 +12V • 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: Example 1: with Rext =27kΩ 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. I O(max) 2.1 10 5 × R ext 28 k Ω + --------------------------------- = |
Numéro de pièce similaire - TDA8927ST |
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Description similaire - TDA8927ST |
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