Features
• AEC-Q100 qualified
• General
– ST SPI communication v4.1
– 5.5 to 24 V Operating battery voltage range
– Load dump protected
– QFN40L 6x6 (wettable flanks) with
exposed pad
– Timeout watchdog and limp home function
– Low standby current
• Boost Section
– Fixed frequency architecture,
programmable by SPI
– Peak current mode control
– Dual phase operation supported
– Input current limitation
– Soft start
– Overvoltage protection (OVP)
– Short feedback failure protection
– Constant voltage control
• Buck section
– Integrated switching mosfets
– Lossless current sensing without need of
external components
– Very accurate LED current setting
programming inductor's peak current and
peak-to-peak current ripple
– Adjustable peak current by SPI
– Adjustable current ripple by SPI
– Integrated PWM generation unit with 10-bit
resolution and phase shift
– Peak current control
– Constant VLED x TOFF architecture
• Protection and diagnostic
– Battery under voltage
– Temperature warning (2 thresholds)
– Overtemperature shutdown
– LED voltage digital feedback through SPI
– Buck outputs short circuit and open load
protection

Description
The L99LD21 is a flexible LED driver, which is
specifically designed for the control of two
independent high brightness LED strings for
automotive front lighting applications. It consists
of a high efficiency monolithic boost controller and
a dual buck converter.
The boost controller integrates a high current gate
driver for an external n-channel mosfet. It delivers
a constant output voltage, up to 60 V, which
supplies the inputs of the two integrated or
external buck converters.
The boost controller of two devices can be
stacked, in order to operate in dual phase for high
power applications, with an interleaving pattern
for an improved input current ripple.
The buck converters integrate n-channel mosfet
which is driven by a bootstrap circuit.

Applications
• Low Beam
• High beam
• Daytime running light
• Turn indicator
• Position light
• Side marker
• Fog light