LTC3577-3 Datasheet, PDF (37/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
OPERATION
To keep the average steady-state inductor current below
300mA the maximum output current is reduced as pro-
grammed output voltage increases. The output current
available is given by:
I_BOOST(MAX)
=
300mA
•
V_OUT(MIN)
V_BOOST
Note that the maximum boost output current must be
set by the minimum V_OUT operating voltage. If the boost
converter is allowed to operate down to the V_OUT UVLO
then 2.5V must be assumed as the minimum operating
V_OUT voltage.
Inductor Selection
The LED boost converter is designed to work with a 10μH
inductor. The inductor must be able to handle a peak
current of 1A and should have a low ESR value for good
efficiency. Table 7 shows several inductors that work
well with the LED boost converter. These inductors offer
a good compromise in current rating, DCR and physical
size. Consult each manufacturer for detailed information
on their entire selection of inductors.
Diode Selection
When boosting to increasingly higher voltages, parasitic
capacitance at the switch pin becomes an increasing
large component of the switching loses. For this reason
it is important to minimize the capacitance on the switch
node. The diode selected should be sized to handle the
peak inductor current and the average output current.
At high boost voltages a diode with the lowest possible
junction capacitance will often result in a more efficient
solution than one with a lower forward drop.
I²C OPERATION
I²C Interface
The LTC3577-3/LTC3577-4 may communicate with a
bus master using the standard I²C 2-wire interface. The
Timing Diagram shows the relationship of the signals on
the bus. The two bus lines, SDA and SCL, must be high
when the bus is not in use. External pull-up resistors or
current sources, such as the LTC1694 SMBus accelerator,
are required on these lines. The LTC3577-3/LTC3577-4 are
both a slave receiver and slave transmitter. The I²C control
signals, SDA and SCL are scaled internally to the DV_CC
supply. DV_CC should be connected to the same power
supply as the bus pull-up resistors.
Table 7. Recommended Inductors for Boost Switching Reguators
INDUCTOR TYPE
LPS4018-103
L (μH)
10
MAX I_DC (A) MAX DCR (Ω)
1.1
0.200
DB62LCB
10
1.22
0.118
CDRH4D16NP-100M
10
1.05
0.155
SD18-100-R
10
1.28
0.158*
*Typical
SIZE in mm (L × W × H)
4.0 × 4.0 × 1.8
6.2 × 6.2 × 2
4.8 × 4.8 × 1.8
5.2 × 5.2 × 1.8
MANUFACTURER
Coil Craft
www.coilcraft.com
Toko
www.toko.com
Sumida
www.sumida.com
Cooper
www.cooperet.com
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