TA0104A Tripath Technology Inc., TA0104A Datasheet - Page 13

• Manufacturer Part Number: TA0104A
• Manufacturer: Tripath Technology Inc.

Gate Resistor Selection
The gate resistors, R
voltage overshoots. They also dissipate a portion of the power resulting from moving the gate charge
each time the MOSFET is switched. If R
Large gate resistors lead to slower MOSFET switching, which requires a larger break-before-make
(BBM) delay. Tripath recommends using an R
70nC and 5.6: 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.
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, C
Test/Application Circuit to damp voltage ringing at these nodes due to the high currents flowing
through the parasitic (circuit board trace) inductance. C
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.
13
B B M 1
G
BY
, are used to control MOSFET switching rise/fall times and thereby minimize
, are necessary for each output MOSFET at the nodes shown in the
0
0
1
1
B B M 0
0
1
0
1
G
is too small, excessive heat can be generated in the driver.
G
145nS
105nS
Delay
65nS
25nS
of 10: when the Qg of the MOSFET is less than
BY
should be 0.1uF and have the appropriate
T r i p a t h T e c h n o l o g y , I n c . - T e c h n i c a l I n f o r m a t i o n
TA104A – Rev. 3.1/06.00