LTC3586_15 Datasheet, PDF (25/36 Pages) Linear Technology – High Efficiency USB Power Manager with Boost, Buck-Boost and Dual Bucks

LTC3586/LTC3586-1
applications information
PowerPath CONTROLLER APPLICATIONS SECTION
CLPROG Resistor and Capacitor
As described in the High Efficiency Switching PowerPath
Controller section, the resistor on the CLPROG pin deter-
mines the average input current limit when the switching
regulator is set to either the 1x mode (USB 100mA), the
5x mode (USB 500mA) or the 10x mode. The input cur-
rent will be comprised of two components, the current
that is used to drive V_OUT and the quiescent current of the
switching regulator. To ensure that the USB specification is
strictly met, both components of input current should be
considered. The Electrical Characteristics table gives the
worst-case values for quiescent currents in either setting
as well as current limit programming accuracy. To get as
close to the 500mA or 100mA specifications as possible,
a 1% resistor should be used. Recall that I_VBUS = I_VBUSQ
+ V_CLPROG/R_CLPPROG • (h_CLPROG +1).
An averaging capacitor is required in parallel with the
CLPROG resistor so that the switching regulator can
determine the average input current. This network also
provides the dominant pole for the feedback loop when
current limit is reached. To ensure stability, the capacitor
on CLPROG should be 0.1µF.
Choosing the PowerPath Inductor
Because the input voltage range and output voltage range
of the power path switching regulator are both fairly nar-
row, the LTC3586/LTC3586-1 are designed for a specific
inductance value of 3.3µH. Some inductors which may be
suitable for this application are listed in Table 4.
Table 4. Recommended Inductors for PowerPath Controller
MAX MAX
INDUCTOR L I_DC DCR
TYPE
(µH) (A) (Ω)
SIZE IN mm
(L × W × H) MANUFACTURER
LPS4018 3.3 2.2 0.08 3.9 × 3.9 × 1.7 Coilcraft
www.coilcraft.com
D53LC
DB318C
3.3 2.26 0.034 5 × 5 × 3 Toko
3.3 1.55 0.070 3.8 × 3.8 × 1.8 www.toko.com
WE-TPC
Type M1
3.3 1.95 0.065 4.8 × 4.8 × 1.8 Wurth Elektronik
www.we-online.com
CDRH6D12 3.3 2.2 0.0625 6.7 × 6.7 × 1.5 Sumida
CDRH6D38 3.3 3.5 0.020 7 × 7 × 4 www.sumida.com
V_BUS and V_OUT Bypass Capacitors
The style and value of capacitors used with the LTC3586/
LTC3586-1 determine several important parameters
such as regulator control-loop stability and input volt-
age ripple. Because the LTC3586/LTC3586-1 use a buck
switching power supply from V_BUS to V_OUT, its input
current waveform contains high frequency components.
It is strongly recommended that a low equivalent series
resistance (ESR) multilayer ceramic capacitor be used to
bypass V_BUS. Tantalum and aluminum capacitors are not
recommended because of their high ESR. The value of the
capacitor on V_BUS directly controls the amount of input
ripple for a given load current. Increasing the size of this
capacitor will reduce the input ripple.
To prevent large V_OUT voltage steps during transient load
conditions, it is also recommended that a ceramic capaci-
tor be used to bypass V_OUT. The output capacitor is used
in the compensation of the switching regulator. At least
4µF of actual capacitance with low ESR are required on
V_OUT. 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.
There are several types of ceramic capacitors available
each having considerably different characteristics. For
example, X7R ceramic capacitors have the best voltage and
temperature stability. X5R ceramic capacitors have appar-
ently 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 non-linear
characteristic of capacitance verse voltage. The actual
in-circuit capacitance of a ceramic capacitor should be
measured with a small AC signal as is expected in-circuit.
Many vendors specify the capacitance verse voltage with
a 1V RMS AC test signal and as a result overstate the ca-
pacitance 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.
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