TPA2080D1 Datasheet, PDF (12/20 Pages) Texas Instruments – 2.2 W Constant Output Power Class-D Audio Amplifier with Class-G Boost Converter

TPA2080D1
SLOS733 – JANUARY 2012
BOOST CONVERTER COMPONENT SECTION
The critical external components are summarized in the following table:
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PARAMETER
Boost converter inductor
Boost converter input
capacitor
Boost converter output
capacitor
TEST CONDITIONS
At 30% rated DC bias current of the inductor
MIN TYP MAX UNIT
1.5 2.2 4.7 µH
4.7
10 µF
Working capacitance biased at boost output voltage, if 4.7µH inductor is chosen,
then minimum capacitance is 10 µF
4.7
22 µF
Boost Terms
The following is a list of terms and definitions used in the boost equations found later in this document.
C
L
f_BOOST
I_PVDD
I_L
PVDD
VBAT
ΔI_L
ΔV
Minimum boost capacitance required for a given ripple voltage on PVDD.
Boost inductor
Switching frequency of the boost converter.
Current pulled by the Class-D amplifier from the boost converter.
Average current through the boost inductor.
Supply voltage for the Class-D amplifier. (Voltage generated by the boost converter output)
Supply voltage to the IC.
Ripple current through the inductor.
Ripple voltage on PVDD.
Inductor Equations
Inductor current rating is determined by the requirements of the load. The inductance is determined by two
factors: the minimum value required for stability and the maximum ripple current permitted in the application. Use
Equation 1 to determine the required current rating. Equation 1 shows the approximate relationship between the
average inductor current, I_L, to the load current, load voltage, and input voltage (I_PVDD, PVDD, and VBAT,
respectively). Insert I_PVDD, PVDD, and VBAT into Equation 1 and solve for I_L. The inductor must maintain at least
90% of its initial inductance value at this current.
I_L
= I_PVDD
´
æ PVDD ö
çè _{VBAT ´ 0.8} ÷ø
(1)
Ripple current, ΔI_L, is peak-to-peak variation in inductor current. Smaller ripple current reduces core losses in the
inductor and reduces the potential for EMI. Use Equation 2 to determine the value of the inductor, L. Equation 2
shows the relationship between inductance L, VBAT, PVDD, the switching frequency, f_BOOST, and ΔI_L. Insert the
maximum acceptable ripple current into Equation 2 and solve for L.
VBAT ´ (PVDD - VBAT)
L=
DI_L ´ ¦_BOOST ´ PVDD
(2)
ΔI_L is inversely proportional to L. Minimize ΔI_L as much as is necessary for a specific application. Increase the
inductance to reduce the ripple current. Do not use greater than 4.7 μH, as this prevents the boost converter
from responding to fast output current changes properly. If using above 3.3 µH, then use at least 10 µF
capacitance on PVDD to ensure boost converter stability.
The typical inductor value range for the TPA2080D1 is 2.2 μH to 3.3 µH. Select an inductor with less than 0.5 Ω
dc resistance, DCR. Higher DCR reduces total efficiency due to an increase in voltage drop across the inductor.
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