LTC4088 LINER [Linear Technology], LTC4088 Datasheet - Page 17

• Manufacturer Part Number: LTC4088
• Description: High Effi ciency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

V
The style and value of capacitors used with the LTC4088
determine several important parameters such as regula-
tor control-loop stability and input voltage ripple. Because
the LTC4088 uses a step-down switching power supply
from V
high frequency components. It is strongly recommended
that a low equivalent series resistance (ESR) multilayer
ceramic capacitor be used to bypass V
aluminum capacitors are not recommended because
of their high ESR. The value of the capacitor on V
directly controls the amount of input ripple for a given
load current. Increasing the size of this capacitor will
reduce the input ripple. The USB specifi cation allows a
maximum of 10µF to be connected directly across the
USB power bus. If additional capacitance is required
for noise performance, a soft-connect circuit may be
required to limit inrush current and avoid excessive
transient voltage drops on the bus (see Figure 5).
To prevent large V
load conditions, it is also recommended that a ceramic
capacitor be used to bypass V
used in the compensation of the switching regulator. At
least 10µF with low ESR are required on V
capacitance will improve load transient performance
and stability.
Multilayer ceramic chip capacitors typically have excep-
tional ESR performance. MLCCs combined with a tight
board layout and an unbroken ground plane will yield very
good performance and low EMI emissions.
There are several types of ceramic capacitors avail-
able each having considerably different characteristics.
APPLICATIO S I FOR ATIO
BUS
and V
BUS
to V
OUT
OUT
Bypass Capacitors
, its input current waveform contains
U
OUT
Table 3. Recommended Inductors for the LTC4088
WE-TPC Type M1
voltage steps during transient
INDUCTOR TYPE
U
CDRH6D12
CDRH6D38
LPS4018
DB318C
D53LC
OUT
. The output capacitor is
W
BUS
(µH)
3.3
3.3
3.3
3.3
3.3
3.3
OUT
. Tantalum and
L
. Additional
MAX I
U
2.26
1.55
1.95
2.2
2.2
3.5
(A)
DC
BUS
MAX DCR
0.0625
0.034
0.070
0.065
0.020
0.08
(Ω)
For example, X7R ceramic capacitors have the best voltage
and temperature stability. X5R ceramic capacitors have
apparently higher packing density but poorer performance
over their rated voltage and temperature ranges. Y5V
ceramic capacitors have the highest packing density,
but must be used with caution, because of their extreme
nonlinear characteristic of capacitance versus voltage. The
actual in-circuit capacitance of a ceramic capacitor should
be measured with a small AC signal and DC bias as is
expected in-circuit. Many vendors specify the capacitance
verse voltage with a 1V
over state the capacitance that the capacitor will present
in the application. Using similar operating conditions as
the application, the user must measure or request from
the vendor the actual capacitance to determine if the
selected capacitor meets the minimum capacitance that
the application requires.
Overprogramming the Battery Charger
The USB high power specifi cation allows for up to 2.5W
to be drawn from the USB port. The switching regulator
transforms the voltage at V
at BAT with high effi ciency, while limiting power to less
than the amount programmed at CLPROG. The charger
should be programmed (with the PROG pin) to deliver the
maximum safe charging current without regard to the USB
specifi cations. If there is insuffi cient current available to
charge the battery at the programmed rate, it will reduce
charge current until the system load on V
and the V
charger for more current than is available will not cause
the average input current limit to be violated. It will merely
allow the battery charger to make use of all available
3.9 × 3.9 × 1.7
3.8 × 3.8 × 1.8
4.8 × 4.8 × 1.8
6.7 × 6.7 × 1.5
SIZE IN mm
(L × W × H)
5 × 5 × 3
7 × 7 × 4
BUS
current limit is satisfi ed. Programming the
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MANUFACTURER
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Coilcraft
Sumida
RMS
Toko
AC test signal and, as a result,
BUS
to just above the voltage
LTC4088
OUT
is satisfi ed
17
4088f