MAX8939 Datasheet, PDF (40/43 Pages) Maxim Integrated Products – System Power Management for Mobile Handset Hardware Input Enable

System Power Management
for Mobile Handset
Applications Information
Inductor Selection
The OUT1 step-up converter is designed to use a 2.2FH
to 10FH inductor (see Table 22). To prevent core satura-
tion, ensure that the inductor saturation current rating
exceeds the peak inductor current for the application.
Calculate the worst-case peak inductor current with the
following formula:
I_PEAK
=
V_OUT × I_OUT(MAX)
0.9 × V_IN(MIN)
+
V_IN(MIN) × 0.5Fs
2×L
The OUT2 LED driver is optimized for using a 10FH
inductor, although larger or smaller inductors may be
used. Using a smaller inductance results in discontinu-
ous current mode operation over a larger range of output
power, whereas use of a larger inductance results in
continuous conduction for most of the operating range.
To prevent core saturation, ensure that the inductor’s
saturation current rating exceeds the peak inductor cur-
rent for the application. For larger inductor values and
continuous conduction operation, calculate the worst-
case peak inductor current with the following formula:
I_PEAK
=
V_OUT × I_OUT(MAX)
0.9 × V_IN(MIN)
+
V_IN(MIN) × 0.5Fs
2×L
For small values of L in discontinuous conduction opera-
tion, IPEAK is 860mA (typ). Table 23 provides a list of
recommended inductors.
Capacitor Selection
Ceramic capacitors are recommended due to their low
ESR. Ensure that the capacitor maintains its capaci-
tance over temperature and DC bias. Generally ceramic
capacitors with X5R or X7R temperature characteristics
perform well. Note that some small size ceramic capaci-
tors fail to maintain their capacitance when a DC bias is
applied and should be avoided. Place the capacitors as
close as possible to the IC.
The recommended input and output capacitor values are
shown in Figure 1, however, larger value capacitors can
be used to further reduce ripple at the expense of size
and higher cost.
Compensation
The OUT1 step-up converter is compensated for sta-
bility through an external compensation network from
COMP1 to ground. A 2200pF ceramic capacitor is rec-
ommended.
The OUT2 LED driver is compensated for stability
through an external compensation network from COMP2
to ground. A 0.22FF ceramic capacitor is recommended
for most applications. Higher CCOMP2 values increase
soft-start duration, as well as the time delay between
enabling the step-up converter to initiating soft-start. See
the Soft-Start OUT2 section for more information.
Table 22. Recommended Inductors for L1
MANUFACTURER
Cooper (Coiltronics)
FDK
TDK
TOKO
PART
SD3114
MIPF2520
MIPW3226
VLS3012ET
VLS3010T
DE2812C
DE2812C
INDUCTANCE
(µH)
2.2
2.2
2.2
2.2
10
2.7
10
DCR
(mI)
110
80
100
80
390
75
325
ISAT
(A)
1.74
1.3
1.1
1.35
0.65
1.8
0.78
DIMENSIONS
(LTYP x WTYP x HMAX) (mm)
3.0 x 3.0 x 1.45
2.5 x 2.0 x 1.0
3.2 x 2.6 x 1.0
3 x 3 x 1.2
3 x 3 x 1.0
3.0 x 3.2 x 1.2
3.0 x 3.2 x 1.2
Table 23. Recommended Inductors for L2
MANUFACTURER
PART
INDUCTANCE
(µH)
DCR
(mI)
1098AS-100M
10
290
TOKO
1069AS-220M
22
570
FDK
MIP3226D100M
10
160
ISAT
(A)
0.75
0.47
0.9
DIMENSIONS
(LTYP x WTYP x HMAX) (mm)
2.8 x 3.0 x 1.2
3 x 3 x 1.8
3.2 x 2.6 x 1.0
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