TA0104A Ver la hoja de datos (PDF) - Tripath Technology Inc.

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Fabricante

TA0104A

STEREO 500W (4Ω) CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPPTM) TECHNOLOGY

Tripath Technology Inc. 

Tripath Technology, Inc. - Technical Information

Gate Resistor Selection

The gate resistors, RG, are used to control MOSFET switching rise/fall times and thereby minimize

voltage overshoots. They also dissipate a portion of the power resulting from moving the gate charge

each time the MOSFET is switched. If RG is too small, excessive heat can be generated in the driver.

Large gate resistors lead to slower MOSFET switching, which requires a larger break-before-make

(BBM) delay. Tripath recommends using an RG of 10Ω when the Qg of the MOSFET is less than

70nC and 5.6Ω when the Qg is greater than 70nC.

Break-Before-Make (BBM) Timing Control

The half-bridge power MOSFETs require a deadtime between when one transistor is turned off and

the other is turned on (break-before-make) in order to minimize shoot through currents. BBM0 and

BBM1 are logic inputs (connected to logic high or pulled down to logic low) that control the break-

before-make timing of the output transistors according to the following table. Note that if either BBM0

or BBM1 are left floating, they are pulled internally to a logic high level.

BBM1

0

0

1

1

BBM0

0

1

0

1

Delay

145nS

105nS

65nS

25nS

The tradeoff involved in making this setting is that as the delay is reduced, distortion levels improve

but shoot-through and power dissipation increase. Since the actual amount of BBM required is

dependent upon other component values and circuit board layout, the value selected should be

verified in the actual application circuit/board. It should also be verified under maximum temperature

and power conditions since shoot-through in the output MOSFETs can increase under these

conditions, possibly requiring a higher BBM setting than at room temperature.

Clamping Diodes

The purpose of the diode, D, across each of the output MOSFETs is to clamp the voltages the

MOSFET experiences to levels within its rating to prevent damage. Tripath recommends that fast-

recovery or schottky diodes be used for this purpose. The breakdown voltage rating of this diode

should be similar to that of the MOSFET. Also, the forward voltage drop of this diode should be less

than that of the internal body diode of the MOSFET.

MOSFET Bypass Capacitor

Bypass capacitors, CBY, are necessary for each output MOSFET at the nodes shown in the

Test/Application Circuit to damp voltage ringing at these nodes due to the high currents flowing

through the parasitic (circuit board trace) inductance. CBY should be 0.1uF and have the appropriate

voltage rating. They should be physically located as close to the MOSFET leads as possible.

Turn-on & Turn-off Noise

If turn-on or turn-off noise is present in a TA0104A amplifier, the cause is frequently due to other

circuitry external to the TA0104A. While the TA0104A has circuitry to suppress turn-on and turn-off

transients, the combination of the power supply and other audio circuitry with the TA0104A in a

particular application may exhibit audible transients. One solution that will completely eliminate turn-

on and turn-off pops and clicks is to use a relay to connect/disconnect the amplifier from the speakers

with the appropriate timing at power on/off. The relay can also be used to protect the speakers from

a component failure (e.g. shorted output MOSFET), which is a protection mechanism that some

amplifiers have. Circuitry external to the TA0104A would need to be implemented to detect these

failures.

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TA104A – Rev. 3.1/06.00

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