MAX16840_15 Datasheet, PDF (6/12 Pages) Maxim Integrated Products – LED Driver with Integrated MOSFET

MAX16840
LED Driver with Integrated MOSFET
for MR16 and Other 12V AC Input Lamps
Functional Diagram
IN
200mV I₀
1/6
I1
5V
1.2V
S
50µA
REFI
5kI
gm
4pF
5V
LDO +
BANDGAP
BG
POK
UVLO
PWMC
COMP
2VP-P
0.65V
CSLIMIT
OSCILLATOR
50ns
FB
BLANKING
IN
BG
OVP
MAX16840
IN
DRIVER
EXT
DRAIN
SOURCE
GND
Detailed Description
The MAX16840 is an average current-mode control LED
driver IC for buck, boost, and buck-boost topologies in
low-voltage SSL applications. The IC has an integrated
0.2I (max), 48V switching MOSFET that allows the
device to be used in lighting applications for MR16 and
other SSL applications. The LED driver uses constant-
frequency average current-mode control to control the
duty cycle of the integrated switching MOSFET. The IC
has all the necessary features required for MR16 lighting
applications using LEDs. The IC uses an input-current
control scheme to achieve power factor correction. This
feature allows the IC to be compatible with electronic
transformers and dimmable with trailing-edge (for elec-
tronic transformers).
The switch current is sensed on FB. The voltage on FB
goes through an RC filter as shown in the Functional
Diagram. This voltage is then fed to the negative input
of a transconductance amplifier. The positive input of
the gm amplifier is the programmed input current level.
The output voltage of the gm amplifier is compared with
a ramp at the switching frequency to set the duty cycle.
The switching frequency is set at 300kHz. The average
current-mode controller inside the IC regulates the input
current. The IC also features an internal overvoltage
protection of 46V on IN to protect the internal switching
MOSFET from damage if the LED string is open or if the
voltage on the LED string is too high.
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