Description The ZXCD50 Steval evaluation board is based on the ZXCD1000 ClassDaudioAmplifiersolutionFromZetex. This board allows users to evaluate the high-fidelity audio performance offered by Zetex solutions with output powers up to 50W and music power up to 4.
Introduction ZXCD50Steval is a high performance class D amplifier with 50W music power (4 loads). The circuit contains MOSFET devices and should therefore be handled appropriately.
The board requires at least 13 volts and a maximum of 25 volts single rail power supply. Voltages in excess of 25 volts may cause permanent damage to the board.
At the heart of the solution is the ZXCD1000 Class D controller, which the user should convert to the ZXCD1000 datasheet for further technical information. The circuit has anti-jump, over-current protection and mute functions.
Features Stereo class D architecture Single power output power (VSupply=25V) 50W music conversion to 4 25W music conversion to 8 THD+N<0.5%@90% power>90% efficiency Flat frequency response 20Hz–20 kHz on/off pop suppression Overcurrent Protection Silent Device 8226 ; Noise Floor – 115dB
Note: The ZXCD50 Stevalisin provides an evaluation platform for Zetex Class D solutions. Zetex is not responsible for external equipment related to the ZXCD500Steval or any other form of consequential damage or loss.

Connections and Operation The following PCB diagram shows the connections required for proper operation of the ZXCD50 Steval board. Simple connector locks are provided for easy connection of mains voltage, audio input and speaker output.
Power Connections The ZXCD50 Steval requires a positive power supply voltage:
25V @ about 2.3a, 50 watts music converted to 4 notes: 8 speakers are available for this application. In this case, a 25 volt ridgeline power supply would produce 25 volts of musical output power. If this is required, C2/102 should be removed to maintain a flat frequency response. The power supply should not exceed 25 volts and should not drop below 13 volts to ensure proper operation of the amplifier. Make sure the polarity of the power supply is correct.
Audio Inputs The ZXCD50 Steval requires a single-ended audio input per channel, as follows:
The input impedance is 18K.
The input signal amplitude required for full output power is approximately 2.5 V peak-to-peak.
Speaker Connections 4 Speakers can be connected to the board as shown. Correct polarity connection of speakers is essential to avoid phase errors. Note: 8 speakers can be used in this application. If desired, C2/102 should be removed to maintain a flat frequency response. There is overcurrent protection on the board to prevent damage to the circuit from a short circuit between speakers or speakers.
Description and operation of the evaluation board The top copper, bottom copper, and silkscreen ID overlays are shown in Figures 1, 2, and 3.
The ZXCD1000 has a 16-pin exposed pad QSOP package. The exposed pad on the bottom of the package is soldered to a copper area on the printed circuit board for heat dissipation. To further treat heat dissipation, the printed circuit board is plated through the holes connecting the copper plate below the board.
The required MOSFETs on the motherboard are sub-parts of the Zetexzxm64 family. These SOT223 parts need to handle the power dissipation in an amplifier with a 50W music load.
The steady current transistor on the board is ZTX692B, an electronic circuit device. These devices require the 12V rail to be supplied to the channel from the 25V bridge power board input voltage.
The cardboard mounted conduit was chosen for its good linearity and low loss. These components sense minimal distortion and introduce audio signals at full powerband.
The speakers are connected as bridged loads (BTL). This means that both sides of the speaker are driven by the output bridge, so neither side of the speaker is grounded. This allows maximum power to be delivered to the load from a given supply voltage.

If you wish to view or measure the signal on the load, you must use a floating monitor - such as a differential probe. Alternatively, this can be accomplished by monitoring the outputs of Speaker A and Speaker B with a two-channel oscilloscope and using the invert and add functions. For diagnostic purposes, an oscilloscope (or other instrument) can be used for single-ended ground monitoring of the speaker output if desired. However, any results saved in this way are not suitable for evaluating performance. The real performance depends on some kind of differential offset on the speaker load.
The panel requires a 2.5vpeaktopeak input signal to produce full output power. The input impedance of the board is nominally 18K. This may attenuate the supply voltage, which may need to be distributed according to the output impedance of the supply.
The ZXCD50 Steval evaluation board has a maximum supply voltage of 25V, rated. A 25V supply voltage will achieve 50W of music into 4 loads.

ZXCD50 Steval circuit description. Proper circuit design and high-quality magnetic properties are necessary to obtain good properties of the solution. The heart of the circuit is the Zetex ZXCD1000 Class D audio IC.
The ZXCD50 StevalCircuit diagram is shown in Figure 4. The board features two classes of data channels, a master channel and a slave channel. These channels are essential in addition to the triangle synchronization facilitated by Q1 on the main channel.
Each audio channel includes an input phase splitter, the ZXCD1000, an output bridge that drives the load through an LC filter, and an overcurrent protection circuit. Each channel also has its own voltage regulator.
The voltage regulators (Q5/105, ZD1/101, etc.) need to step down the higher supply voltage (25V on the bridge, 50W) to a level suitable for the ZXCD1000 and the input phase splitter (12V on the board).
The input splitter for each channel is built around the NE5532Dualopamp, audio and audio B channels are required on each ZXCD1000.
Each channel splitter has a mute transistor (Q11/111) which is controlled by a circuit built around Q12. This circuit provides the same functionality as a low-level active input. The mute function reduces the effective output signal by 54dB. The output bridge is built around zetex zxm64p035g and zxm64n035g PMOS and nmos sot223 transistors.
The circuit built around Q10 facilitates the slow start of the bridge supply voltage. This circuit performs the anti-bump function for the solution.
R20 /120 are overcurrent detection resistors. Circuits built around these (Q2/102, Q3/103, etc.) can provide overcurrent protection for the solution. In a fault condition, the circuit disables the channel's triangular modulation waveform, thereby disabling the output bridge. Protects against speaker shorts and speaker shorts to ground.
The ZXCD1000 outputs an output bridge field effect transistor with a pulse width modulated signal, which then drives the load through an LC filter. The function of the filter is to low-pass filter the high frequency switching PWM signal from the bridge, thereby recovering the low frequency audio signal and making it available at the speaker output.

ZXCD50 Steval Circuit Performance The graph shown in Figure 5 shows the typical THD performance of the solution. THD shows zero to full power.
Distortion is below 1% up to full power, typically 0.1% at 1W 1KHz.