LM3553 Datasheet, PDF (17/26 Pages) National Semiconductor (TI) – 1.2A Dual Flash LED Driver System with I2C Compatible

LM3553
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SNVS414B – FEBRUARY 2008 – REVISED MAY 2013
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 power 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 conduction to keep the junction
temperature within the specified operating ratings.
LM26LV (GAIN2)
(Trip 70qC to 110qC)
OVERTEMP
PP/PC
SDA
SCL
Tx
LM3553
FEN
Imager
Figure 22. External Temperature Sensor Diagram
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 registering an over-temperature condition. Placing the
temperature 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 ambient environment.
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