Datasheet

PSU
VPP
GND
INPWM
TAS5086
OUT
S0270-01
PowerStage
TAS5086
SLES131C – FEBRUARY 2005 – REVISED JUNE 2008 ................................................................................................................................................... www.ti.com
Figure 9. SE Filter Configuration
The TAS5086 supports two mechanisms for controlling the split-capacitor midpoint.
In the extra half-bridge scheme (the TAS5186 power stage is an example of this) an additional half-bridge is
started and brought to a 50-percent duty cycle, i.e., a situation where the average voltage of the half-bridge is
equal to the voltage which must be applied to the split-capacitor midpoint to start up without clicks in the speaker.
A resistor per channel is connected between the extra half-bridge and each midpoint for the split capacitors. The
split capacitors are charged through this resistor. This approach requires an extra VALID pin on the modulator to
control the extra half-bridge, therefore the 1N+2 interface. Figure 10 shows the topology of the extra half-bridge.
In some situations, a channel configured in BTL can be used to charge the split capacitor instead of the extra
half-bridge. This is shown in Figure 11 .
The mid-Z scheme charges the split capacitor through the loudspeaker. In order to do this without audible
artifacts the charge current must be limited. This is done by applying a start sequence which charges the output
state between low, high and high-Z. Because the ouput stage is in high-Z in a part of the sequence, the resulting
output impedance can be brought to a level suitable for charging the split capacitors without audible artifacts.
This solution does not require external components, as shown in Figure 9 . Not all power stages are compatible
with the mid-Z scheme, double-check the power-stage data sheet for compabitility. The PWM start register
(0x18) programs the TAS5086 for mid-Z or the standard low-Z start sequence.
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