LTC3454EDD#PBF Linear Technology, LTC3454EDD#PBF Datasheet - Page 8

• Manufacturer Part Number: LTC3454EDD#PBF
• Description: IC LED DRIVER PHOTO FLASH 10-DFN
• Manufacturer: Linear Technology
• Type: Photo Flash LEDr

Specifications of LTC3454EDD#PBF

• Topology: PWM, Step-Down (Buck), Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight, Flash/Torch
• Type - Secondary: White LED
• Frequency: 900MHz ~ 1.15MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 5.15V
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 1A
• Internal Switch(s): Yes
• Efficiency: 90%
• Led Driver Application: Flashlight, Digital Cameras, PDAs
• No. Of Outputs: 1
• Output Current: 1A
• Output Voltage: 5.35V
• Input Voltage: 2.7V To 5.5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
LTC3454
Boost Mode (V
In boost mode, switch A is always on and switch B is always
off. Referring to Figure 2, when the control voltage V
above voltage V3, switches C and D will alternate conduct-
ing similar to a typical synchronous boost regulator. The
maximum duty cycle of the converter is limited to 88%
typical and is reached when V
Forward Current Limit
If the current delivered from V
exceeds 3.4A (typical), switch A is shut off immediately.
Switches B and D are turned on for the remainder of the
cycle in order to safely discharge the forward inductor
current at the maximum rate possible.
Reverse Current Limit
If the current delivered from V
PMOS switch D exceeds 275mA (typical), switch D is
shut off immediately. Switches A and C are turned on for
the remainder of the cycle in order to safely discharge the
reverse inductor current at the maximum rate possible.
Undervoltage Lockout
To prevent operation of the power switches at high R
an undervoltage lockout is incorporated on the LTC3454.
When the input supply voltage drops below approximately
1.90V, the four power switches and all control circuitry are
turned off except for the undervoltage block, which draws
a few microamperes.
Overtemperature Protection
If the junction temperature of the LTC3454 exceeds 130°C
for any reason, all four switches are shut off immediately.
The overtemperature protection circuit has a typical hys-
teresis of 11°C.
Soft-Start
The LTC3454 includes an internally fi xed soft-start which
is active when powering up or coming out of shutdown.
The soft-start works by clamping the voltage on the V
node and gradually releasing it such that it requires 200μs
to linearly slew from 0.9V to 2.1V. This has the effect of
8
IN
< V
OUT
)
C
IN
is above V4.
OUT
through PMOS switch A
backwards through
DS(ON)
C
is
C
,
limiting the rate of duty cycle change as V
from the buck region through the buck-boost region into
the boost region. Once the soft-start times out, it can only
be reset by entering shutdown, or by an undervoltage or
overtemperature condition.
Autozero Error Amp
The error amplifi er is an autozeroing transconductance
amp with source and sink capability. The output of this
amplifi er drives a capacitor to GND at the V
capacitor sets the dominant pole for the regulation loop.
(See the Applications Information section for selecting
the capacitor value). The feedback signal to the error
amp is developed across a resistor through which LED
current fl ows.
Safety Error Amp
The safety error amplifi er is a transconductance amplifi er
with sink only capability. In normal operation, it has no
effect on the loop regulation. However, if the LED pin open-
circuits, the output voltage will keep rising, and the safety
error amp will eventually take over control of the regulation
loop to prevent V
this occurs is approximately 5.15V.
LED Current Programming and Enable Circuit
Two enable pins work in conjunction with dual external
resistors to program LED current to one of three nonzero
settings. The table below explains how the current can
be set.
With either enable pin pulled high, the buck-boost will
regulate the output voltage at the current programmed
by R
With both enable pins pulled to GND, the LTC3454 is in
shutdown and draws zero current. The enable pins are
high impedance inputs and should not be fl oated.
GND
GND
EN1
V
V
ISET1
IN
IN
and/or R
GND
GND
EN2
OUT
V
V
IN
IN
ISET2
runaway. The V
.
I
0 (SHUTDOWN)
3850 • 0.8V/R
3850 • 0.8V/R
3850 • (0.8V/R
LOAD
(A)
OUT
ISET1
ISET2
ISET1
threshold at which
+ 0.8V/R
C
C
transitions
ISET2
pin. This
)
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