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TA0105A View Datasheet(PDF) - Tripath Technology Inc.

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TA0105A Datasheet PDF : 29 Pages
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Tripath Technology, Inc. - Technical Information
OVER- AND UNDER-VOLTAGE PROTECTION
The TA0105A senses the power rails through the VPP and VNN pins on the module. These voltages are
converted to currents by internal resistor networks connected to VLOW and VHIGH. The over- and under-
voltage limits are determined by the internal bias currents, the values of the resistors in the networks,
along with process variations. If the supply voltage falls outside the upper and lower limits determined by
the resistor networks, the TA0105A shuts off the output stages of the amplifiers. The removal of the over-
voltage or under-voltage condition returns the TA0105A to normal operation. Please note that trip points
specified in the Electrical Characteristics table are at 25°C and may change over temperature.
Once the supply comes back into the supply voltage operating range (as defined by the power supply
sense resistors), the TA0105A will automatically be un-muted and will begin to amplify. There is a
hysteresis range on both the VPP and VNN supplies. If the amplifier is powered up in the hysteresis
band, the TA0105A will be muted. Thus, the usable supply range is the difference between the over-
voltage restart and under-voltage restart points 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.
Thus, the supply voltage must be outside of the user defined supply range for greater than 200mS for the
TA0105A to be muted.
The overvoltage and undervoltage resistor values were chosen for the maximum supply range possible
based on the internal hybrid components in conjunction with internal bias current settings. It is possible to
lower the supply range via an external “parallel” resistor connected from VPP (pin23) to VHIGH (pin 37)
and a second resistor connected from VNN (pin 24) to VLOW (pin 38). The delta between each of the trip
points is a fixed ratio and not externally controllable. The current flowing into VHIGH controls the supply
range for VPP while the current flowing out of VLOW controls the supply range for VNN.
The procedure for shifting the VPP range is as follows.
1) Choose the maximum VPP undervoltage turn on voltage point, VPPUVTONMAX
2) Use the following equation to calculate the external parallel resistor, RVPP1
R VPP1
= (VPP UVTONMAX 2.5V)
80 µA
-
(
VPP UVTONMAX
1.4M
)
3) Use the following equation to calculate the resulting minimum VPP overvoltage restart point,
VPPOVRSTMIN
VPP OVRSTMIN = 2.5 1.4M Ω + (1.4M * RVPP1 138 µA)
1.4M Ω + R VPP1
4) Use the following equation to calculate the resulting maximum VPP undervoltage restart
point, VPPUVRSTMAX
VPP UVRSTMAX = 2.5 1.4M Ω + (1.4M * RVPP1 86 µA)
1.4M Ω + R VPP1
The usable (inside the hysteresis band) positive supply range is defined by VPPOVRSTMIN minus
VPPUVRSTMAX.
A similar procedure for shifting the VNN range is as follows.
1) Choose the maximum VNN undervoltage turn on voltage point, VNNUVTONMAX.
2) Use the following equation to calculate the external parallel resistor, RVNN1.
R VNN1
= (1.25V + | VNN UVTONMAX | )
87 µA
-
|VNN UVTONMAX
1.27M
|
20
TA0105A – RW/ Rev. 2.2/05.05
 

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