LTC3455EUF#TRPBF Linear Technology, LTC3455EUF#TRPBF Datasheet - Page 24

• Manufacturer Part Number: LTC3455EUF#TRPBF
• Description: IC CONV DC/DC DUAL USBBATT 24QFN
• Manufacturer: Linear Technology

Specifications of LTC3455EUF#TRPBF

• Applications: Handheld/Mobile Devices
• Voltage - Supply: 3 V ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -

LTC3455/LTC3455-1
APPLICATIONS INFORMATION
Standalone USB Power Supply
with Temporary Backup Power
Although designed primarily for Li-Ion powered portable
applications, the LTC3455/LTC3455-1 are also good choices
for systems that are always powered by a USB supply
or wall adapter. The battery charger can then be used
to charge up a large capacitor or backup battery, which
briefl y provides power to the system after the external
power has been removed. This gives the microcontroller
enough time to follow proper shutdown procedures when
the main power source is abruptly removed. Figure 14
shows a standalone power supply for USB high power
applications (500mA maximum USB current) using the
LTC3455/LTC3455-1. The total system power should be
kept below 1.8W to ensure clean operation even under
worst-case USB conditions. With the resistor values
24
Figure 15. Recommended Board Layout and Component Placement for Power Sections of LTC3455/LTC3455-1
(Refer to Schematic on Back Page)
V
OUT1
VIAS TO LOCAL GROUND PLANE.
C1
GND
L1
C6
1
USB
V
BAT
C4
GND
shown, the low-battery indicator (AI and AO pins) trig-
gers when the V
the microcontroller of an impending dropout condition.
The 1MΩ resistor connected between the AI and AO pins
provides 150mV of hysteresis (the dropout indicator
stays low until the V
4700μF backup capacitor connected to the V
provides power to the system after the USB supply has
been removed, and also helps support transient loads
that slightly exceed the USB current limit. Connecting this
large capacitance to the V
It provides a large energy reservoir that is isolated from
both the USB pin (the USB specifi cation limits capacitance
on the USB supply pin to 10μF or less) and the V
(using a very large capacitance on this pin will delay the
system turn-on), and it prevents large inrush currents by
V
C5
MAX
D1
ADAPTER
5V WALL
L2
C7
MAX
MAX
GND
pin voltage drops to 4V, notifying
C2
pin rises back above 4.15V). A
BAT
V
OUT2
pin has several advantages.
BAT
pin briefl y
MAX
3455fc
pin