MAX16819 Maxim Integrated Products, MAX16819 Datasheet - Page 7

• Manufacturer Part Number: MAX16819
• Description: (MAX16819 / MAX16820) step-down constant-current high-brightness LED drivers
• Manufacturer: Maxim Integrated Products

The MAX16819/MAX16820 include a 4.5V undervoltage
lockout (UVLO) with 500mV hysteresis. When V
below 4.5V, DRV goes low, turning off the external n-chan-
nel MOSFET. DRV goes high once V
V
10mA. Bypass V
The MAX16819/MAX16820 allow dimming with a PWM
signal at the DIM input. A logic level below 0.6V at DIM
forces the MAX16819/MAX16820’s DRV output low,
turning off the LED current. To turn the LED current on,
the logic level at DIM must be at least 2.8V.
The MAX16819/MAX16820 feature a programmable LED
current using a resistor connected between IN and CSN.
Use the following equation to calculate the sense resistor:
Figure 1. Current Regulator Operation
CC
Selecting R
V
I
LED
DIM
is the output of a 5V regulator capable of sourcing
High-Side Current Sense and 5000:1 Dimming
R
CURRENT
SENSE
AVG. LED
Applications Information
HYSTERETIC MODE
CC
Undervoltage Lockout (UVLO)
( )
Ω
SENSE
_______________________________________________________________________________________
to GND with a 1µF capacitor.
2MHz High-Brightness LED Drivers with
=
1
2
(
V
to Set the LED Current
SNSHI
I
LED
+
V
IN
SNSLO
( )
A
is 5V or higher.
5V Regulator
T
SW
=
)( )
f
DIM Input
SW
1
V
IN
falls
For the values of V
Characteristics .
The MAX16819/MAX16820 regulate the LED output
current using an input comparator with hysteresis
(Figure 1). As the current through the inductor ramps
up and the voltage across the sense resistor reaches
the upper threshold, the voltage at DRV goes low, turn-
ing off the external MOSFET. The MOSFET turns on
again when the inductor current ramps down through
the freewheeling diode until the voltage across the
sense resistor equals the lower threshold. Use the fol-
lowing equation to determine the operating frequency:
where n = number of LEDs, V
drop of one LED, and ∆V = (V
For proper component selection, please use the design
tool available at: http://www.maxim-ic.com/MAX16819-
20-Tool.
f
SW
=
(
V
IN
− ×
SNSHI
Current Regulator Operation
n V
LED
and V
V
IN
)
× ×
∆I
×
n V
SNSHI
∆
SNSLO,
V L
LED
×
LED
- V
= forward voltage
×
see the Electrical
SNSLO
t
t
R
SENSE
).
7