TPA2015D1_10 Datasheet, PDF (19/27 Pages) Texas Instruments – 2 W Constant Output Power Class-D Audio Amplifier With Adaptive Boost Converter and Battery Tracking SpeakerGuard™ AGC

TPA2015D1
www.ti.com
SLOS638 – MAY 2010
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.
L = ^{VBAT ´ (PVDD - VBAT)}
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 mH, 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 PVOUT to ensure boost converter stability.
The typical inductor value range for the TPA2015D1 is 2.2 mH 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.
Table 3. Sample Inductors
L
SUPPLIER
COMPONENT CODE
SIZE
(mH)
(L×W×H mm)
2.2
Chilisin
CLCN252012T-2R2M-N
2.5 x 2.0 x 1.2
Electronics Corp.
2.2
Toko
1239AS-H-2R2N=P2
2.5 × 2.0 × 1.2
2.2
Coilcraft
XFL4020-222MEC
4.0 x 4.0 x 2.15
3.3
Toko
1239AS-H-3R3N=P2
2.5 × 2.0 × 1.2
3.3
Coilcraft
XFL4020-332MEC
4.0 x 4.0 x 2.15
DCR TYP
(mΩ)
105
96
22
160
35
I_SAT MAX
(A)
1.2
2.3
3.5
2.0
2.8
C RANGE
4.7 – 22 µF / 16 V
6.8 – 22 µF / 10 V
10 – 22 µF / 10 V
Boost Converter Capacitor Selection
The value of the boost capacitor is determined by the minimum value of working capacitance required for stability
and the maximum voltage ripple allowed on PVDD in the application. Working capacitance refers to the available
capacitance after derating the capacitor value for DC bias, temperature, and aging.
Do not use any component with a working capacitance less than 4.7 mF. This corresponds to a 4.7 µF / 16 V
capacitor, or a 6.8 µF / 10 V capacitor. Do not use above 22 µF capacitance as it will reduce the boost converter
response time to large output current transients.
Equation 3 shows the relationship between the boost capacitance, C, to load current, load voltage, ripple voltage,
input voltage, and switching frequency (I_PVDD, PVDD, ΔV, VBAT, and f_BOOST respectively).
Insert the maximum allowed ripple voltage into Equation 3 and solve for C. The 1.5 multiplier accounts for
capacitance loss due to applied dc voltage and temperature for X5R and X7R ceramic capacitors.
C = 1.5 ´ ^{IPVDD ´ (PVDD - VBAT)}
DV ´ ¦_BOOST ´ PVDD
(3)
Copyright © 2010, Texas Instruments Incorporated
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