LM3553SDEV National Semiconductor, LM3553SDEV Datasheet - Page 13

• Manufacturer Part Number: LM3553SDEV
• Description: BOARD EVALUATION FOR LM3553S
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3553SDEV

• Current - Output / Channel: 1.2A
• Outputs And Type: 1, Non-Isolated
• Features: Camera Flash and Torch Modes, I²C Interface, Programmable Output Current
• Voltage - Input: 2.7 ~ 5.5V
• Utilized Ic / Part: LM3553
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -

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THERMAL PROTECTION
Internal thermal protection circuitry disables the LM3553
when the junction temperature exceeds 150°C (typ.). This
feature protects the device from being damaged by high die
temperatures that might otherwise result from excessive pow-
er dissipation. The device will recover and operate normally
when the junction temperature falls below 140°C (typ.). It is
important that the board layout provide good thermal conduc-
tion to keep the junction temperature within the specified
operating ratings.
Connect the inductor and the anode of D1(schottky) as
close together as possible and place this connection as
close as possible to the SW pin. This reduces the
inductance and resistance of the switching node which
minimizes ringing and excess voltage drops.
Connect the return terminals of the input capacitor and
the output capacitor as close as possible to the exposed
DAP and through low impedance traces.
Bypass V
Connect the positive terminal of this capacitor as close
as possible to V
Connect C
(schottky). This reduces the inductance and resistance
of the output bypass node which minimizes ringing and
voltage drops. This will improve efficiency and decrease
the noiseinjected into the current sources.
Route the trace for R
minimize noise injection.
Do not connect any external capacitor to the R
External Temperature Sensor Diagram
IN
OUT
with at least a 4.7µF ceramic capacitor.
as close as possible to the cathode of D1
IN
.
SET
away from the SW node to
20171434
SET
pin.
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Using an external temperature sensor, such as the LM26LV,
can help aid in the thermal protection of the flash LEDs as well
as other components in a design. Connecting the
OVERTEMP pin of the LM26LV to the TX pin on the LM3553
prevents the high current flash from turning on when the set
temperature threshold on the LM26LV is reached. When the
temperature trip point is reached, the OVERTEMP pin on the
LM26LV will transition from a '0' to a '1' which in turn enables
the LM3553's TX mode. When a flash is instantiated by either
the imager or microprocessor, the LM3553 will only allow the
flash LED current to reach the current level set in the Torch
Current register as long as the temperature sensor is regis-
tering an over-temperature condition. Placing the tempera-
ture sensor close to the flash LEDs can help prevent the LEDs
from reaching a temperature above the maximum specified
limit due to high-current flashing in a high temperature ambi-
ent environment.
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