TPA2013D1_15 Datasheet, PDF (14/31 Pages) Texas Instruments – 2.7-W CONSTANT OUTPUT POWER CLASS-D AUDIO AMPLIFIER WITH INTEGRATED BOOST CONVERTER

TPA2013D1
SLOS520 – AUGUST 2007
www.ti.com
SETTING THE BOOST VOLTAGE
Use Equation 1 to determine the value of R1 for a given V_CC. The maximum recommended value for V_CC is
5.5 V. The typical value of the V_CCFB pin is 500 mV. The current through the resistor divider should be about 100
times greater than the current into the V_CCFB pin, typically 0.01 μA. Based on those two values, the
recommended value of R2 is 500 kΩ. V_CC must be greater than 3 V and less than or equal to 5.5 V.
V_CC
=
æ 0.5
çè
´
(R1
R1
+
R2) ö
÷ø
(1)
INDUCTOR SELECTION
SURFACE MOUNT INDUCTORS
Working inductance decreases as inductor current increases. If the drop in working inductance is severe enough,
it may cause the boost converter to become unstable, or cause the TPA2013D1 to reach its current limit at a
lower output power than expected. Inductor vendors specify currents at which inductor values decrease by a
specific percentage. This can vary by 10% to 35%. Inductance is also affected by dc current and temperature.
TPA2013D1 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 2 to determine the required current rating. Equation 2 shows the approximate relationship between
the average inductor current, I_L, to the load current, load voltage, and input voltage (I_CC, V_CC, and V_DD,
respectively). Insert I_CC, V_CC, and V_DD into Equation 2 to solve for I_L. The inductor must maintain at least 90% of
its initial inductance value at this current.
I_L
= I_CC
´
æ
ç
è
V_CC
V_DD ´
0.8
ö
÷
ø
(2)
The minimum working inductance is 2.2 μH. A lower value may cause instability.
Ripple current, ΔI_L, is peak-to-peak variation in inductor current. Smaller ripple current reduces core losses in the
inductor as well as the potential for EMI. Use Equation 3 to determine the value of the inductor, L. Equation 3
shows the relationship between inductance L, V_DD, V_CC, the switching frequency, f_boost, and ΔI_L. Insert the
maximum acceptable ripple current into Equation 3 to solve for L.
L = ^{VDD ´ (VCC - VDD )}
DI_L ´ fboost ´ V_CC
(3)
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. Note that making the inductance too large will prevent the boost
converter from responding to fast load changes properly. Typical inductor values for the TPA2013D1 are 4.7 μH
to 6.8 μH.
Select an inductor with a small dc resistance, DCR. DCR reduces the output power due to the voltage drop
across the inductor.
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