Tripath Technology, Inc. - Technical Information
VPPSENSE (pin 19) performs the over and undervoltage sensing for the positive supply, VPP.
VNNSENSE (pin 17) performs the same function for the negative rail, VNN. 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 TK2150 will be
muted. VPPSENSE is internally biased at 2.5V and VNNSENSE is biased at 1.25V.
Once the supply comes back into the supply voltage operating range (as defined by the supply
sense resistors), the TK2150 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 TK2150 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. Thus, the supply voltage must be outside of the user defined
supply range for greater than 200mS for the TK2150 to be muted.
Figure 5 shows the proper connection for the Over / Under voltage sense circuit for both the
VPPSENSE and VNNSENSE pins.
V5
VNN
TC2001
RVNN2
RVNN1
17
19
VNNSENSE
V5
VPP
RVPP1
RVPP1
VPPSENSE
Figure 5: Over / Under voltage sense circuit
The equation for calculating RVPP1 is as follows:
VPP
VPPSENSE
R
VPP1 =
I
Set RVPP2 = RVPP1 .
The equation for calculating RVNNSENSE is as follows:
VNN
R
VNN1 =
I
VNNSENSE
Set
.
R
VNN2 = 3 × RVNN1
IVPPSENSE or IVNNSENSE can be any of the currents shown in the Electrical Characteristics
table for VPPSENSE and VNNSENSE, respectively.
The two resistors, RVPP2 and RVNN2 compensate for the internal bias points. Thus, RVPP1 and
RVNN1 can be used for the direct calculation of the actual VPP and VNN trip voltages without
considering the effect of RVPP2 and RVNN2
.
23
TK2150 – Rev. 1.0/12.02
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
