Tripath Technology, Inc. - Technical Information
Protection Circuits
The TA2022 is guarded against over-current, over / under-voltage and over-temperature conditions.
If the device goes into an over-current or over / under-voltage condition, the HMUTE goes to a logic
HIGH indicating a fault condition. When this occurs, the amplifier is muted, all outputs are TRI-
STATED, and will float to approximately 2.5VDC.
Over-Current Protection
An over-current fault occurs if more than approximately 8 amps of current flows from any of the
amplifier output pins. This can occur if the speaker wires are shorted together or if one side of the
speaker is shorted to ground. An over-current fault sets an internal latch that can only be cleared if
the MUTE pin is toggled or if the part is powered down. See the over-current curves in the Typical
Characteristics section for more information.
Over/Under Voltage Protection
The TA2022 has built-in over and under voltage protection for both the VPP and VNN supply rails.
The nominal operating voltage will typically be chosen as the supply “center point.” This allows the
supply voltage to fluctuate, both above and below, the nominal supply voltage.
VPPSENSE (pin 19) performs the over and undervoltage sensing for the positive supply, VPP.
VNNSENSE (pin 18) performs the same function for the negative rail, VNN. In the simplest
implementation, the supply is done via a single, external resistor per sense pin. This scheme is
referred to as the “single resistor” sense circuit. Figure 9 shows the single resistor sense circuit.
VNN
TA2022
RVNNSENSE
18
VNNSENSE
VPP
RVPPSENSE
19
VPPSENSE
Figure 9: Single Resistor Sense Circuit
When the current through RVPPSENSE (or RVNNSENSE) goes below or above the values shown in the
Electrical Characteristics section (caused by changing the power supply voltage), the TA2022 will be
muted. VPPSENSE is internally biased at 2.5V and VNNSENSE is biased at 1.25V. For the “single
resistor” sense case (as shown in the Application / Test Diagram), these bias points must be taken
into consideration when calculating the RVPPSENSE or RVNNSENSE resistor.
Once the supply comes back into the supply voltage operating range (as defined by the supply sense
resistors), the TA2022 will automatically be unmuted and will begin to amplify. There is a hysteresis
range on both the VPPSENSE and VNNSENSE pins. If the amplifier is powered up in the hysteresis
band the TA2022 will be muted. Thus, the usable supply range is the difference between the over-
voltage turn-off and under-voltage turn-off for both the VPP and VNN supplies. It should be noted that
there is a timer of approximately 200mS with respect to the over and under voltage sensing circuit.
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TA2022 – KLI/1.2/07-04
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
