Tripath Technology, Inc. - Preliminary Information
Mute
When a logic high signal is supplied to MUTE, both amplifier channels are muted (complementary
MOSFETs are turned off). When a logic level low is supplied to MUTE, both amplifiers are fully
operational. There is a delay of approximately 240 milliseconds between the de-assertion of MUTE and
the un-muting of the TDA1400.
Turn-on & Turn-off Noise
If turn-on or turn-off noise is present in a TDA1400 amplifier, the cause is frequently due to other circuitry
external to the TDA1400. While the TDA1400 has circuitry to suppress turn-on and turn-off transients,
the combination of the power supply and other audio circuitry with the TDA1400 in a particular application
may exhibit audible transients. It is recommended that MUTE is active (pulled high) during power up and
power down to minimize any audible transients.
DC Offset
While the DC offset voltages that appear at the speaker terminals of a TDA1400 amplifier are typically
small, Tripath recommends that all offsets be removed with the circuit shown in Figure 4. It should be
noted that the DC voltage on the output of a muted TDA1400 with no load is approximately 2.5V. This
offset does not need to be nulled. The output impedance of the amplifier in mute mode is approximately
20KΩ thus explaining why the DC voltage drops to essentially zero when a typical load is connected.
2.2uF, 25V
20.0kΩ
+
Input to TDA1400
(DC Bias ~2.5V)
R I
C I
V5
Ω
470k
470kΩ
10kΩ
0.1uF, 50V
Figure 4: Offset Adjustment
Over-current Protection
The TDA1400 has over-current protection circuitry to protect itself and the output transistors from short-
circuit conditions. The TDA1400 senses the voltage across resistor RS to detect an over-current
condition. Resistor RS is in series with the load just after the low pass filter. The voltage is measured via
OCSP1 and OCSN1 for channel 1 and OCSP2 and OCSN2 for channel 2. The OCS* pins must be Kelvin
connected for proper operation. See “Circuit Board Layout” in Application Information for details.
When the voltage across RS becomes greater than VTOC (typically 0.5V), the TDA1400 will shut off the
output stages of its amplifiers. The occurrence of an over-current condition also causes the TDA1400
Fault pin (pin 27) to go high. It is recommended that the Fault pin be connected externally to the mute pin
to mute the processor during an over-current condition. The Fault circuitry is an open drain configuration
and requires a pull-down resistor. The removal of the over-current condition returns the amplifier to
normal operation.
Setting Over-current Threshold
RS determines the value of the over-current threshold, ISC:
ISC = VTOC/RS where RS is in Ω’s
V
TOC = Over-current sense threshold voltage (See Electrical Characteristics Table)
= 0.55V typically
For example, to set an ISC of 11A, RS will be 50mΩ.
19
TDA1400 – Rev. 0.65/KLi/02.06
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
