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Texas Instruments DC Detect on TPA311xDx Devices Application notes
Application Report
SLOA261 – December 2017
DC Detect on TPA311xDx Devices
Shawn Zheng
ABSTRACT
The TPA311xDx device has circuitry which protects speakers from DC current on the input, or shorts on
the printed circuit board at the inputs. The minimum differential input voltages required to trigger the DC
detect are described in this application report. This document only applies for TPA311xDx devices.
1
2
3
4
Contents
General Overview ............................................................................................................
Effect of PVCC ...............................................................................................................
Effect of Gain .................................................................................................................
Conclusion ....................................................................................................................
2
2
3
3
List of Figures
............................................................................
1
DC Detect Threshold at Input Versus PVCC
2
DC detect threshold at output Versus PVCC ............................................................................ 2
2
3
DC Detect Threshold at Input Versus Gain .............................................................................. 3
4
DC Detect Threshold at Output Versus Gain ............................................................................ 3
List of Tables
......................................................................................
1
DC Detect Threshold Versus PVCC
2
DC Detect Threshold When PVCC = 12 V ............................................................................... 3
2
3
DC Detect Threshold When PVCC = 18 V ............................................................................... 3
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DC Detect on TPA311xDx Devices
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1
General Overview
1
www.ti.com
General Overview
The TPA311xD2 device has circuitry which protects the speakers from DC current, which may occur due
to defective capacitors on the input or shorts on the printed circuit board at the inputs. A DC detect fault is
reported on the FAULT pin as a low state. The DC Detect fault also causes the amplifier to shutdown, by
changing the state of the outputs to Hi-Z. To clear the DC Detect fault, it is necessary to cycle the PVCC
supply. Cycling SD does not clear a DC detect fault.
The minimum differential input voltages required to trigger the DC detect depend on the gain and PVCC.
This document shows some data collected on the TPA3113D2 device.
2
Effect of PVCC
The DC detect threshold increases as PVCC increases when Gain is fixed. There is a linear relationship
between the threshold and PVCC. Figure 1 shows the DC detect threshold at the input when gain = 26
dB.
140
Input Offset (mV)
120
100
80
60
40
20
0
6
8
10
12
14
16
18
PVCC (V)
20
22
24
26
D001
Figure 1. DC Detect Threshold at Input Versus PVCC
Figure 2 shows the DC detect threshold at the output when gain = 26 dB.
3000
Output Offset (mV)
2500
2000
1500
1000
500
0
6
8
10
12
14
16
18
PVCC (V)
20
22
24
26
D002
Figure 2. DC detect threshold at output Versus PVCC
Table 1 lists the raw data for Figure 1 and Figure 2.
Table 1. DC Detect Threshold Versus PVCC
2
PVCC (V)
Input DC Offset (mV)
Output DC Offset (mV)
8
45
882
10
55
1088
12
67
1322
14
79
1564
16
90
1783
18
100
1983
20
110
2204
22
120
2409
24
131
2609
DC Detect on TPA311xDx Devices
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Effect of Gain
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3
Effect of Gain
The DC detect threshold at the input decreases as the gain value increases when PVCC is fixed. There is
a linear relationship between the logarithm of the threshold and gain in dB. Figure 3 shows the DC detect
threshold at the input when PVCC = 12 V and 18 V.
250
PVCC = 12 V
PVCC = 18 V
Input DC Offset (mV)
200
150
100
50
0
20
22
24
26
28
30
Gain (dB)
32
34
36
D003
Figure 3. DC Detect Threshold at Input Versus Gain
Figure 4 shows the DC detect threshold at the output when PVCC = 12 V and 18 V.
2500
Output DC Offset (mV)
2000
1500
1000
500
0
20
22
24
26
28
30
Gain (dB)
32
34
36
D004
Figure 4. DC Detect Threshold at Output Versus Gain
Table 2 and Table 3 list the raw data for Figure 3 and Figure 4.
Table 2. DC Detect Threshold When PVCC = 12 V
Gain (dB)
Input DC Offset (mV)
Output DC Offset (mV)
20
133
1323
26
67
1322
32
33
1320
36
21
1309
Table 3. DC Detect Threshold When PVCC = 18 V
4
Gain (dB)
Input DC Offset (mV)
Output DC Offset (mV)
20
197
1979
26
100
1983
32
49
1960
36
31
1950
Conclusion
The DC detect threshold at the input depends on the PVCC and gain. While the DC detect threshold at
the output only depends on the PVCC.
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