Tripath Technology, Inc. – Preliminary Technical Information

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TPS4100 – KL/Rev. 2.5/02.05

FAULT PIN

The FAULT pin is a logic output that indicates various fault conditions within the device. These conditions

include: over-voltage, under-voltage, over-current at any output, low charge pump voltage, low 5V

regulator voltage, and over-temperature (junction temperature greater than approximately 160

°C).

The FAULT pin is an open drain output. The recommended pull-up to an external 3.3V or 5V supply is

51k

Ω. Alternatively, this pin can be pulled up to VPP through a 51kΩ resistor. A logic high on this pin

indicates a fault condition. This pin has a 1mA maximum sink current capability.

CIRCUIT BOARD LAYOUT

When used in conjunction with a Class T controller the TPS4100 is a power (high current) amplifier that

operates at relatively high switching frequencies. Therefore, amplifier outputs switch between the supply

voltage and ground at high speeds while driving high currents. This high-frequency digital signal is

passed through an LC low-pass filter to recover the amplified audio signal. Since the amplifier must drive

the inductive LC output filter and speaker loads, the amplifier outputs can be pulled above the supply

voltage and below ground by the energy in the output inductance. To avoid subjecting the TPS4100 to

potentially damaging voltage stress, it is critical to have a good printed circuit board layout. It is

recommended that Tripath’s layout and application circuit be used for all applications and only be

deviated from after careful analysis of the effects of any changes.

Please refer to the TPS4100

evaluation board document, EB-TPS4100, available on the Tripath website, at www.tripath.com.

The following components are important to place near either their associated TPS4100 pins. The

recommendations are ranked in order of layout importance, either for proper device operation or

performance considerations.

-

serve to reduce spikes and modulation of the power supply rails. Please note that bypassing

requires a combination of capacitors for adequate stabilization.

-

Improper routing of these diodes will render them useless due to PCB trace inductance. Thus,

these components must be located very close to the output pins with the “other side of the

diode” routed directly to the appropriate VPP or PGND pin.

bypassing requires a combination of capacitors for adequate stabilization.

OUTPUT FILTER DESIGN

One advantage of Tripath amplifiers over PWM solutions is the ability to use higher-cutoff-frequency

filters. This means any load-dependent peaking/droop in the 20kHz audio band potentially caused by the

filter can be made negligible. This is especially important for applications where the user may select a 4

Ω

or 8

Ω speaker. Furthermore, speakers are not purely resistive loads and the impedance they present

changes over frequency and from speaker model to speaker model.

The core material of the output filter inductor has an effect on the distortion levels produced by a

TPS4100 amplifier. Tripath recommends low-mu type-2 iron powder cores because of their low loss and

high linearity or high current capability bobbin types that will not saturate at peak currents below 9A.

Recently, there have been a number of dual inductors designed specifically for bridged output switching

amplifiers. These dual inductors are two inductors shielded by a common ferrite shield. They may be