Datasheet

LED Driver with Integrated MOSFET
for MR16 and Other 12V AC Input Lamps
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 g
m
amplifier is the programmed input current level.
The output voltage of the g
m
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.
Functional Diagram
DRIVER
PWMC
CSLIMIT
0.65V
1.2V
IN
IN
EXT
DRAIN
SOURCE
GND
REFI
COMP
FB
5V
50µA
4pF
S
5kI
g
m
I
0
I
1
2V
P-P
OSCILLATOR
IN
BG
50ns
BLANKING
LDO +
BANDGAP
UVLO
POK
5V
1/6
200mV
BG
OVP
MAX16840
MAX16840
6
Maxim Integrated