Rainbow Electronics MAX16840 User Manual

19-5671; Rev 0; 12/10

LED Driver with Integrated MOSFET

for MR16 and Other 12V AC Input Lamps

General Description

The MAX16840 is an LED driver IC for lighting applica­tions. It includes all the necessary features to design low­component-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) or leading-edge
dimmers (where magnetic transformers are present).

The IC can be used in buck, boost, and buck-boost
topologies. It has an integrated 0.2I (max), 48V switching
MOSFET that allows for output power levels up to 10W.

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.

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 guar­antee 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 0NC to +125NC operating
temperature range.

Features

S Control of the Average Input Current to Achieve

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 External npn Driver to Guarantee Minimum Load

to Electronic Transformer at Startup

S Output Overvoltage Protection

S Internal Overtemperature Protection

S 0°C to +125°C Operating Temperature Range

S 3mm x 3mm, 10-Pin TDFN Package

Ordering Information

PART TEMP RANGE PIN-PACKAGE

MAX16840ATB+ 0NC to +125NC 10 TDFN-EP*

+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.

Typical Operating Circuit

LED-

C2

LED+

R1

12V AC

L1 BD1

L2 D1

R3

C1

C4

R2

DRAIN

REFI

EXT

MAX16840

COMP SOURCE

GND

IN

FB

MAX16840

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.