ZXCD50STEVAL CIRCUIT DESCRIPTION.

Propriety circuit design and high quality magnetics are

necessary to yield the excellent THD performance of

the solution. At the heart of the circuit is the Zetex

ZXCD1000 class D audio IC.

The ZXCD50STEVAL circuit diagram is shown in figure

4. The board features two class D channels, one master

and one slave. These channels are essentially the same

other than the triangle synchronisation facilitated by

Q1 on the master channel.

Each audio channel consists of an input phase splitter,

the ZXCD1000, an output bridge to drive the load - via

L-C filters, and an over-current protection circuit. Each

channel also features its own dropper voltage

regulator.

The voltage regulator (Q5/105, ZD1/101 etc.) is

necessary to drop higher supply voltages (25V on the

bridge for 50W) to a level suitable for the ZXCD1000

and input phase splitter (12V on the board).

The input phase splitter per channel, built around the

NE5532 dual op amp, is necessary to drive the Audio A

and Audio B channels on each ZXCD1000.

Each channel phase splitter features a mute transistor

(Q11/111) which is controlled via the circuit built

around Q12. This circuit provides a mute function with

an active low input. The mute function reduces the

effective output signal by 54dB.

The Output Bridges are built around the Zetex

ZXM64P035G and ZXM64N035G PMOS and NMOS

SOT223 transistors.

The circuit built around Q10 facilitates a slow start for

the bridge supply voltage This circuit performs

anti-pop for the solution.

R20/120 are over current sense resistors. The circuit

built around these (Q2/102, Q3/103 etc) enables an

over-current protection for the solution. In fault

conditions the circuit disables the triangle modulation

waveform to the channel and thus disables the output

bridge. Protection is given for speaker shorts and

speaker to ground shorts.

The ZXCD1000 outputs drive Output Bridge MOSFET’s,

with the PWM signal, which subsequently drives the

load via L-C filters. The purpose of the filters is to low

pass filter the high frequency switching PWM signal

from the bridge. Thus the lower frequency audio signal

is recovered and is available at the speaker outputs.

ZXCD50STEVAL CIRCUIT PERFORMANCE

The graph shown in fig 5 indicates the typical THD

performance of the solution. THD is shown from zero

up to full power.

Distortion is sub 1% all the way up to full power,

typically at 1W 1kHz distortion is 0.1%.

ZXCD50STEVAL

ISSUE 1 - JULY 2002

4

WARNING - Appropriate safety precautions should be taken by

a competent person if the ZXCD100MOEVAL is to be connected

to any potentially hazardous equipment.

Figure 5.