19-5671; Rev 1; 2/11
LED Driver with Integrated MOSFET
for MR16 and Other 12V AC Input Lamps
General Description
The MAX16840 is an LED driver IC for lighting applica-
tions. It includes all the necessary features to design
low-component-count LED drivers for 12V AC and 24V
AC input (e.g., MR16) light bulbs. A proprietary input-
current control scheme allows LED lamps based on this
device to be compatible with electronic transformers,
and dimmable with standard trailing-edge dimmers
(where electronic transformers are present).
The IC can be used in buck, boost, and buck-boost
topologies and features. It has an integrated 0.2I (max),
48V switching MOSFET.
The IC uses constant-frequency average current-mode
control. It senses the input current through the voltage
at the FB pin, and regulates its average. An input pin
(REFI) allows the setting of the input-current level. When
the voltage at this pin is set below a certain threshold, the
input current is proportional to this voltage, while when
that voltage is beyond the threshold, the input current is
set at a fixed, predefined level. This nonlinear behavior
of REFI allows its use to achieve thermal foldback, by
connecting it to an NTC resistor.
Features
S
Control of the Average Input Current to Achieve
MAX16840
Operation with Electronic Transformers and
Dimmability
S
Buck, Boost, SEPIC, and Buck-Boost Topologies
S
Integrated 0.2I (max) 48V Switching MOSFET
S
Analog Dimming and Thermal Foldback
S
Output Overvoltage Protection
S
Internal Overtemperature Protection
S
-40°C to +125°C Operating Temperature Range
S
3mm x 3mm, 10-Pin TDFN Package
ed
PART
MAX16840ATB+
R3
L1
12V AC
BD1
C1
Ordering Information
PIN-PACKAGE
10 TDFN-EP*
TEMP RANGE
-40NC to +125NC
Ab
r
The IC also features an internal overvoltage protection on
the IN pin 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.
The IC has a separate EXT pin that can be used to guar-
antee that there is a kick-start of current at turn-on for
low-input voltages for proper operation with electronic
transformers. EXT drives an external npn transistor.
Once the UVLO threshold of 5.5V is crossed on IN, EXT
is pulled to ground and the external npn transistor is
turned off.
The IC is available in a 3mm x 3mm, 10-pin TDFN power
package, and is rated over the -40NC to +125NC operat-
ing temperature range.
id
g
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
Typical Operating Circuit
LED-
L2
D1
C2
LED+
DRAIN
REFI
EXT
MAX16840
IN
COMP
C4
R2
GND
SOURCE
FB
R1
Applications
MR16 and Other 12V AC or DC Input LED
Lighting Applications
_______________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
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