LM3552SDEV National Semiconductor, LM3552SDEV Datasheet - Page 8

• Manufacturer Part Number: LM3552SDEV
• Description: BOARD EVALUATION LM3552SD
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3552SDEV

• Current - Output / Channel: 700mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 4 V
• Features: Flash Timeout Protection
• Voltage - Input: 2.7 ~ 5.5V
• Utilized Ic / Part: LM3552
• Core Chip: LM3552
• Topology: Boost
• No. Of Outputs: 1
• Output Current: 1A
• Input Voltage: 2.7V To 5.5V
• Development Tool Type: Hardware - Eval/Demo Board
• Mcu Supported Families: LM3552
• Lead Free Status / RoHS Status: Not applicable / Not applicable

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Block Diagram
Circuit Description
OVERVIEW
The LM3551/2 are high power white LED flash drivers capa-
ble of delivering up to 1A of output current. The devices utilize
a highly efficient inductive DC/DC boost converter to achieve
the required output voltage. A current-mode PWM control
scheme regulates the output current over a wide input voltage
range. Both the LM3551 and the LM3552 have two low-side
load disconnect FET's allowing for a continuous low-power
Torch-mode and a high-power, short duration Flash-mode.
Several application specific safety features are integrated into
the LM3551/2 design. A flash timeout circuit is present on-
chip to prevent a failure in the flash LED caused by a timing
violation. Over-Voltage Protection protects the output capac-
itor, inductor and main power switch in the event of an open
circuit condition. Other safety features include inductor cur-
rent limit, thermal shutdown, and an undervoltage lockout.
CIRCUIT COMPONENTS
Inductive DC/DC Boost Converter
In order to achieve the output voltages required to power high
power white LEDs, the LM3551 and LM3552 utilize a highly
efficient inductive DC/DC converter. The boost converter uti-
lizes
(1.25MHz.), PWM architecture. This architecture creates a
predictable noise spectrum that allows for easy filtering and
low noise. A very low on-resistance power NFET(R
0.165Ω) and high value current limit (2.2A typ.) help efficiently
provide a high power output (700mA@5V) over the entire
lithium-ion voltage range. The feedback voltage for both the
LM3551 and LM3552 is tightly regulated to 1.265V.
a
current-mode
controlled,
constant
frequency
DSON
=
8
SD/EN Pin
The LM3551 and LM3552 provide two different options in re-
gards to turn-on control logic. The LM3551 utilizes a shut-
down pin (SD) that turns on the part when a voltage less than
0.3V is applied. An internal 1.2MΩ pull-up to V
to place the LM3551 into shutdown when no control signal is
provided. The LM3552 utilizes a enable pin (EN) that turns on
the part when a voltage greater than 1.2V is applied. An in-
ternal 1.2MΩ pull-down to GND is provided to place the
LM3552 into shutdown when no control signal is provided.
Low-side Load Disconnect FETs
The LM3551 and LM3552 have two low-side load disconnect
NFETs (FET-T and FET-F) that provide the physical mecha-
nism of Torch Mode and Flash Mode. In Torch Mode, FET-T
is enabled allowing current to flow through it. FET-T has an
on-resistance of 0.98Ω and is capable of handling currents up
to 200mA. In Flash Mode, both FET-T and FET-F are en-
abled. FET-F has an on-resistance of 0.36Ω and is capable
of handling currents up to 500mA. The total Flash current is
equal to the sum total of the current flowing through FET-T
and FET-F. See the CURRENT SET EQUATIONS in the Ap-
plication Informations section for more information regarding
setting LED current .
In shutdown mode, the LM3551/2 provide a true load discon-
nect helping to keep the total shutdown current to a minimum.
Over-Voltage Protection (OVP)
The over voltage protection (OVP) is engaged when a failure
mode occurs (FB pin grounded, Flash LED becomes open or
disconnected, etc.). In the event of a failure, OVP prevents
the output voltage from exceeding 12.4V (typ). When the OVP
level is reached, the switch FET shuts off preventing the out-
put voltage from climbing higher. Once the FET has shut off,
IN
20151203
is provided