ZXCD1000 datasheet(11/16 Pages) ZETEX

11 / 16 page

Class D 50W Mono Bridge Tied Load (BTL)

Solution with Feedback – Circuit Description

With the addition of feedback (hence closed loop

solution) it is possible to obtain even better THD

performance. A schematic diagram for this is shown in

Figure 9. Again proprietary circuit and special

magnetic design is necessary to yield the high THD

performance and deviation from this could

significantly reduce performance.

Much of the circuitry is the same as described for the

open loop solution. The main differences being a

consequence of using the feedback circuitry. The audio

input is ac coupled and applied to an op-amp (1/2 of U3)

configured as a non–inverting amplifier with a gain of

approximately 4. Feedback is applied differentially

from the bridge outputs via the other half of U3

op-amp. A portion of the single ended output from this

op-amp is subtracted from the output of the

non-inverting op-amp output above. Overall negative

feedback is applied due to the polarity and connection

of the signals involved.

The audio signal from the above circuitry is applied to a

phase splitter as was done for the open loop solution.

This is built around the other 5532 dual op-amp (U2).

One of these op-amps is configured as a voltage

follower and the other as a X1 inverting amplifier. This

produces in phase and inverted signals for application

to the ZXCD1000 Audio A and Audio B inputs

respectively.

The output circuitry downstream of the ZXCD1000 is as

described for the open loop solution. In order to

support the 50W output power of this solution a 25V

rail is required for a 4

load. The MOSFETs used are

SOT223 packaged (ZXM64N035G and ZXM64P035).

Further information on this design is available through

Zetex applications.

Higher Power Solutions

With some modifications the applications solutions

can be extended to give output power up to 100W. The

main differences being the supply voltage, the TO220

MOSFETs, and the output magnetics. The magnetics

for 100W are necessarily larger than required for

25/50W in order to handle the higher load currents. For

100W operation the supply voltage to the circuit is

nominally 35V with a 4

load. However the maximum

supply voltage to the ZXCD1000 class D controller IC is

18V, hence a voltage dropper is required. This could be

done, for example, as in the open loop solution

described previously. A 100W circuit is shown on

figure 10. This features a 35V bridge supply TO220

MOSFETs (ZXM64N035L3 and ZXM64P035L3) and

also proposed protection circuits for over current and

over temperature and an alternative anti pop circuit.

Further information on this 100W reference design can

be obtained through Zetex applications.

The ZXCD1000 class D controller IC is inherently

capable of driving even higher power solutions, with

the appropriate external circuitry. However as stated

above the maximum supply voltage to the ZXCD1000

class D controller IC is 18V and the higher supply

voltages must therefore be dropped. Also due

consideration must be given to the ZXCD1000 output

drive levels and the characteristics of the bridge

MOSFET’s. The latter must be sufficiently enhanced by

the OutA and OutB outputs to ensure the filter and load

network is driven properly. If the gate drive of the

ZXCD1000 is too low for the chosen MOSFET then the

OUTA and OUTB signal must be buffered using an

appropriate MOSFET driver circuit. Additionally,

suitable magnetics are essential to achieve good THD

performance.

Package details

The ZXCD1000 is available in a 16 pin exposed pad

QSOP package. The exposed pad on the underside of

the package should be soldered down to an area of

copper on the PCB, to function as a heatsink. The PCB

should have plated through vias to the underside of the

board, again connecting to an area of copper.

ZXCD1000

ISSUE 2 - APRIL 2002

ZXCD1000 データシート(PDF) 11 Page - Zetex Semiconductors

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