
L
BOOST
VBAT
(PVDD
VBAT)
L =
I
PVDD
-
D
PVDD
BOOST
I
(PVDD
VBAT)
C = 1.5
V
PVDD
-
D
www.ti.com
SLOS638 – MAY 2010
Ripple current,
ΔIL, 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 2shows the relationship between inductance L, VBAT, PVDD, the switching frequency, fBOOST, and ΔIL. Insert the
maximum acceptable ripple current into
Equation 2 and solve for L.
(2)
ΔIL is inversely proportional to L. Minimize ΔIL 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 H, then use at least 10 F
capacitance on PVOUT to ensure boost converter stability.
The typical inductor value range for the TPA2015D1 is 2.2 mH to 3.3 H. Select an inductor with less than 0.5
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
DCR TYP
ISAT MAX
C RANGE
(mH)
(L×W×H mm)
(m
)
(A)
2.2
Chilisin
CLCN252012T-2R2M-N
2.5 x 2.0 x 1.2
105
1.2
Electronics Corp.
4.7 – 22 F / 16 V
2.2
Toko
1239AS-H-2R2N=P2
2.5 × 2.0 × 1.2
96
2.3
6.8 – 22 F / 10 V
2.2
Coilcraft
XFL4020-222MEC
4.0 x 4.0 x 2.15
22
3.5
3.3
Toko
1239AS-H-3R3N=P2
2.5 × 2.0 × 1.2
160
2.0
10 – 22 F / 10 V
3.3
Coilcraft
XFL4020-332MEC
4.0 x 4.0 x 2.15
35
2.8
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 F / 16 V
capacitor, or a 6.8 F / 10 V capacitor. Do not use above 22 F 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 (IPVDD, PVDD, ΔV, VBAT, and fBOOST 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.
(3)
Copyright 2010, Texas Instruments Incorporated
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