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LTC3554 Datasheet(PDF) 23 Page - Linear Technology

Part # LTC3554
Description  Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators
PDF  36 Pages
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Manufacturer  LINER [Linear Technology]
Direct Link  http://www.linear.com
Logo LINER - Linear Technology

LTC3554 Datasheet(HTML) 23 Page - Linear Technology

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LTC3554
23
3554f
OPERATION
When FSEL is low, the frequency of the switching regulators
is reduced to 1.125Mhz. The slower switching frequency
reduces switching losses and raises efficiency as shown
in Figures 4 and 5. Switch node slew rate is also increased
to minimize transition losses. As the programmed output
voltage decreases, the difference in efficiency is more
appreciable.
Low Supply Operation
An undervoltage lockout circuit on the VOUT pin (VOUT
UVLO) shuts down the step-down switching regulators
when VOUT drops below about 2.6V. It is thus recom-
mended that the step-down switching regulator input
supply (BVIN) be connected directly to the power path
output (VOUT). The UVLO prevents the step-down switch-
ing regulators from operating at low supply voltages
where loss of regulation or other undesirable operation
may occur. If driving the step-down switching regulator
input supply from a voltage other than the VOUT pin, the
regulators should not be operated outside the specified
operating range as operation is not guaranteed beyond
this range.
Inductor Selection
Many different sizes and shapes of inductors are avail-
able from numerous manufacturers. Choosing the right
inductor from such a large selection of devices can be
overwhelming, but following a few basic guidelines will
make the selection process much simpler.
Figure 4. 1.2V Output Efficiency and Power Loss
vs Load Current
Figure 5. 3.3V Output Efficiency and Power Loss
vs Load Current
LOAD CURRENT (mA)
0.01
0.1
0
70
100
1
10
100
1000
LTXXXX GXX
60
50
40
30
20
10
80
0
1000
10
1
0.1
100
90
BAT = 3.8V
FSEL = L
FSEL = H
EFFICIENCY
POWER LOSS
LOAD CURRENT (mA)
0.01
0.1
0
70
100
1
10
100
1000
LTXXXX GXX
60
50
40
30
20
10
80
0
1000
10
1
0.1
100
90
BAT = 3.8V
FSEL = L
FSEL = H
EFFICIENCY
POWER LOSS



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