LTC3554 LINER [Linear Technology], LTC3554 Datasheet - Page 23

• Manufacturer Part Number: LTC3554
• Description: Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators
• Manufacturer: LINER [Linear Technology]

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 effi ciency 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 effi ciency is more
appreciable.
Low Supply Operation
An undervoltage lockout circuit on the V
UVLO) shuts down the step-down switching regulators
when V
mended that the step-down switching regulator input
supply (BVIN) be connected directly to the power path
output (V
Figure 4. 1.2V Output Effi ciency and Power Loss
vs Load Current
OUT
OUT
100
90
80
70
60
50
40
30
20
10
0.01
0
drops below about 2.6V. It is thus recom-
). The UVLO prevents the step-down switch-
BAT = 3.8V
EFFICIENCY
0.1
LOAD CURRENT (mA)
1
10
POWER LOSS
100
FSEL = L
FSEL = H
LTXXXX GXX
1000
OUT
1000
100
10
1
0.1
0
pin (V
OUT
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 V
regulators should not be operated outside the specifi ed
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 5. 3.3V Output Effi ciency and Power Loss
vs Load Current
100
90
80
70
60
50
40
30
20
10
0.01
0
BAT = 3.8V
0.1
EFFICIENCY
LOAD CURRENT (mA)
1
10
POWER LOSS
100
FSEL = L
FSEL = H
LTXXXX GXX
LTC3554
1000
100
10
1
0.1
1000
0
OUT
pin, the
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