LTC3452 Linear Technology, LTC3452 Datasheet - Page 14

• Manufacturer Part Number: LTC3452
• Description: Synchronous Buck-Boost MAIN/CAMERA White LED Driver
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC3452
Unused Outputs
If fewer than 7 LED pins are to be used, unused LEDx pins
should be connected to V
current source outputs are not being used and shuts off
the corresponding output currents to save power. A small
trickle current (10µA: low power bank, 30µA: high power
bank) is still applied to unused outputs to detect if a white
LED is later switched in and also to distinguish unused
outputs from used outputs during start-up.
LED Failure Modes
If an individual LED fails as a short circuit, the current
source biasing it is shut off to save power. This is the same
operation as described previously (if the output were
14
U
OUT
U
. The LTC3452 senses which
W
U
initially designated unused at power-up by connecting its
LEDx pin to V
If an individual LED fails as an open circuit, the control loop
will initially attempt to regulate off of its current source
feedback signal, since it will appear to be the one requiring
the largest forward voltage drop to run at its programmed
current. This will drive V
LED will never accept its programmed current, V
be voltage-limited by means of a secondary control loop.
The LTC3452 limits V
other LEDs will still remain biased at the correct pro-
grammed current but the overall circuit efficiency will
decrease.
OUT
). Efficiency is not materially affected.
OUT
OUT
to 4.5V in this failure mode. The
higher. As the open circuited
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OUT
must
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