TA0105A View Datasheet(PDF) - Tripath Technology Inc.
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TA0105A
Tripath Technology Inc.
TA0105A Datasheet PDF : 29 Pages
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Tripath Technology, Inc. - Technical Information
As stated in the Mute section above, a common cause of turn off pops can be attributed to the 5V supply
collapsing while the other supply rails are still present. On power down, mute should be activated (pulled
high) before the power supplies, especially the 5V, begin to collapse. A microcontroller supervisor, now
available from multiple manufacturers, is a good way to insure proper control of the mute during power
supply sequencing.
DC OFFSET
While the DC offset voltages that appear at the speaker terminals of a TA0105A amplifier are typically
small, Tripath recommends that any offsets during operation be nulled out of the amplifier with a circuit
like the one shown connected to IN1 and IN2 in the Application/Test Circuit. It should be noted that the
DC voltage on the output of a TA0105A amplifier with no load in mute will not be zero. This offset does
not need to be nulled. The output impedance of the amplifier in mute mode is approximately 40KΩ(RFB +
1.0kΩ). This means that the DC voltage drops to essentially zero when a typical load is connected.
OVER-CURRENT PROTECTION
The TA0105A has over-current protection circuitry to protect itself and the output transistors from short-
circuit conditions. The TA0105A measures the voltage across a resistor, RS (via OCSxHP, OCSxHN,
OCSxLP and OCSxLN) that is in series with each output MOSFET to detect an over-current condition. RS
and ROCR are used to set the over-current threshold. The OCS pins must be Kelvin connected for proper
operation. This implies connecting a trace directly from the resistor lead to the respective sense pin. No
other current or power supply connections should be made to the OCS pins of the TA0105A. Doing so
will result in false overcurrent events due to the IR losses of the PCB trace. See “Circuit Board Layout” in
Application Information for additional details.
When the voltage across ROCR becomes greater than VTOC (typically 0.97) the TA0105A will shut off the
output stages of its amplifiers. The occurrence of an over-current condition is latched in the TA0105A and
can be cleared by toggling the MUTE input or cycling power.
SETTING OVER-CURRENT THRESHOLD
RS and ROCR determine the value of the over-current threshold, IOC:
IOC = 4990 x (VTOC – IBIAS * (9100+ROCR))/((9100+R OCR) * RS)
ROCR = ((4990 x VTOC)/(IOC * RS+ 4990 * IBIAS)) - 9100
where:
RS and ROCR are in Ω
VTOC = Over-current sense threshold voltage (See Electrical Characteristics Table)
= 0.97V typically
IBIAS = 15uA
For example, to set an IOC of 10A, ROCR = 18.58KΩ (use 20KΩ, 1%) and RS will be 10mΩ.
As high-wattage resistors are usually only available in a few low-resistance values (10mΩ, 25mΩ and
50mΩ), ROCR can be used to adjust for a particular over-current threshold using one of these values for
RS.
It should be noted that the overcurrent trip level has a “duty cycle” dependence of roughly 2:1. This is due
to the peak current detection (with some filtering) nature of the protection circuit implemented on the
TA0105A. Thus, a current limit into a “short” will produce a peak current level roughly twice that of an
over-current into a 12.5 (or higher) load. Most mosfets can withstand 3-4 times the rated continuous
current for short durations (less than 100uS).
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TA0105A – RW/ Rev. 2.2/05.05
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