T E C H N I C A L I N F O R M A T I O N
It should be noted that the DC voltage on the output of a TA3020 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 10KΩ. This means that the DC voltage drops to essentially zero when a
typical load is connected.
HMUTE
The HMUTE pin is a 5V logic output that indicates various fault conditions within the device. These
conditions include: over-current, overvoltage and undervoltage. The HMUTE output is capable of
directly driving an LED through a series 2kΩ resistor.
Over-current Protection
The TA3020 has over-current protection circuitry to protect itself and the output transistors from
short-circuit conditions. The TA3020 uses the voltage across a resistor RS (measured via OCS1HP,
OCS1HN, OCS1LP and OCS1LN) 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. See “Circuit Board Layout” in Application Information for
details.
When the voltage across ROCR becomes greater than VTOC (approximately 1.0V) the TA3020 will
shut off the output stages of its amplifiers. The occurrence of an over-current condition is latched in
the TA3020 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, ISC:
ISC = 3580 x (VTOC – IBIAS * ROCR)/(R OCR * RS)
R
OCR = (3580 x VTOC)/(ISC * RS+3580 * IBIAS
)
where:
RS and ROCR are in Ω
VTOC = Over-current sense threshold voltage (See Electrical Characteristics Table)
= 1.0V typically
IBIAS = 20uA
For example, to set an ISC of 30A, ROCR = 9.63KΩ 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.
Over- and Under-Voltage Protection
The TA3020 senses the power rails through external resistor networks connected to VNNSENSE
and VPPSENSE. The over- and under-voltage limits are determined by the values of the resistors in
the networks, as described in the table “Test/Application Circuit Component Values”. If the supply
voltage falls outside the upper and lower limits determined by the resistor networks, the TA3020
shuts off the output stages of the amplifiers. The removal of the over-voltage or under-voltage
TA3020, Rev 2.1, 01.01
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TRIPATH [ TRIPATH TECHNOLOGY INC. ]
