MAX16819 Datasheet, PDF (8/10 Pages) Maxim Integrated Products – 2MHz High-Brightness LED Drivers with High-Side Current Sense and 5000:1 Dimming

2MHz High-Brightness LED Drivers with
High-Side Current Sense and 5000:1 Dimming
MOSFET Selection
The MAX16819/MAX16820’s gate driver is capable of
sourcing 0.5A and sinking 1A of current. MOSFET selec-
tion is based on the maximum input operating voltage
V_IN, output current I_LED, and operating switching fre-
quency. Choose a MOSFET that has a higher break-
down voltage than the maximum operation voltage, low
R_DS(ON), and low total charge for better efficiency.
MOSFET threshold voltage must be adequate if operat-
ed at the low end of the input-voltage operating range.
Freewheeling Diode Selection
The forward voltage of the freewheeling diode should
be as low as possible for better efficiency. A Schottky
diode is a good choice as long as the breakdown volt-
age is high enough to withstand the maximum operat-
ing voltage.
The forward current rating of the diode must be at least
equal to the maximum LED current.
LED Current Ripple
The LED current ripple is equal to the inductor current
ripple. In cases when a lower LED current ripple is
needed, a capacitor can be placed across the LED ter-
minals.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching
losses and stable operation. Use a multilayer board
whenever possible for better noise immunity. Minimize
ground noise by connecting high-current ground
returns, the input bypass-capacitor ground lead, and
the output-filter ground lead to a single point (star
ground configuration). In normal operation, there are
two power loops. One is formed when the MOSFET is
on and the high current flows through IN—R_SENSE—
LEDs—Inductor—MOSFET—GND. The other loop is
formed when the MOSFET is off when the high current
circulates through R_SENSE—LEDs—Inductor—free-
wheeling diode. To minimize noise interaction, each
loop area should be as small as possible.
Place R_SENSE as close as possible to the input filter
and IN. For better noise immunity, a Kelvin connection
is strongly recommended between CSN and R_SENSE.
Connect the exposed paddle to a large-area ground
plane for improved power dissipation.
PROCESS: BiCMOS
Chip Information
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