Datasheet

Undervoltage Lockout (UVLO)
The MAX16819/MAX16820 include a 4.5V undervoltage
lockout (UVLO) with 500mV hysteresis. When V
IN
falls
below 4.5V, DRV goes low, turning off the external n-chan-
nel MOSFET. DRV goes high once V
IN
is 5V or higher.
5V Regulator
V
CC
is the output of a 5V regulator capable of sourcing
10mA. Bypass V
CC
to GND with a 1µF capacitor.
DIM Input
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, turn-
ing off the LED current. To turn the LED current on, the
logic level at DIM must be at least 2.8V.
Applications Information
Selecting R
SENSE
to Set the LED Current
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:
SNSHI SNSLO
SENSE
LEAD
(V V )(V)
1
R ()
2 I (A)
+
Ω=
For the values of V
SNSHI
and V
SNSLO
, see the Electrical
Characteristics.
Current Regulator Operation
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, turning 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 following equation to deter-
mine the operating frequency:
IN LED LED SENSE
SW
IN
(V nV )nV R
f
V VL
−× ×× ×
=
×∆ ×
where n = number of LEDs, V
LED
= forward voltage drop
of one LED, and ∆V = (V
SNSHI
- V
SNSLO
).
For proper component selection, please use the design
tool available at: http://www.maxim-ic.com/MAX16819-
20-Tool.
Figure 1. Current Regulator Operation
HYSTERETIC MODE
AVG. LED
CURRENT
1
f
SW
T
SW
=
I
LED
t
t
V
DIM
∆I
MAX16819/MAX16820 2MHz High-Brightness LED Drivers with
High-Side Current Sense and 5000:1 Dimming
www.maximintegrated.com
Maxim Integrated │ 7