LTC4088-1_12 LINER [Linear Technology], LTC4088-1_12 Datasheet - Page 17

• Manufacturer Part Number: LTC4088-1_12
• Description: High Efficiency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
V
The style and value of capacitors used with the
LTC4088-1/LTC4088-2 determine several important
parameters such as regulator control-loop stability and
input voltage ripple. Because the LTC4088-1/LTC4088-2
uses a step-down switching power supply from V
to V
quency components. It is strongly recommended that
a low equivalent series resistance (ESR) multilayer ce-
ramic 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 specification 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
is used in the compensation of the switching regula-
tor. At least 10µF with low ESR are required on V
Additional 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.
BUS
OUT
and V
, its input current waveform contains high fre-
OUT
Bypass Capacitors
OUT
Table 3. Recommended Inductors for the LTC4088-1/LTC4088-2
WE-TPC Type M1
INDUCTOR TYPE
voltage steps during transient
CDRH6D12
CDRH6D38
LPS4018
DB318C
D53LC
OUT
. The output capacitor
BUS
(µH)
3.3
3.3
3.3
3.3
3.3
3.3
. Tantalum and
L
MAX I
2.26
1.55
1.95
2.2
(A)
2.2
3.5
DC
OUT
BUS
BUS
MAX DCR
.
0.0625
0.034
0.070
0.065
0.020
0.08
(Ω)
There are several types of ceramic capacitors avail-
able each having considerably different characteristics.
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 specification 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 efficiency, 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
specifications. If there is insufficient current available to
charge the battery at the programmed rate, it will reduce
charge current until the system load on V
and the V
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
LTC4088-1/LTC4088-2
current limit is satisfied. Programming the
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AC test signal and, as a result,
BUS
to just above the voltage
OUT
is satisfied
17
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