MAX16819_15 Datasheet, PDF (7/9 Pages) Maxim Integrated Products – 2MHz High-Brightness LED Drivers with High-Side Current Sense and 5000:1 Dimming

MAX16819/MAX16820
2MHz High-Brightness LED Drivers with
High-Side Current Sense and 5000:1 Dimming
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:
R
SENSE
(Ω)
=¹
2
(
V_SNSHI + V_SNSLO
I_LEAD ( A )
)(V
)
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:
f_SW
=
(V_IN
−n×
V_LED ) × n × V_LED
V_IN × ∆V × L
× R _SENSE
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: www.maximintegrated.com/
MAX16819-20-Tool.
HYSTERETIC MODE
I_LED
AVG. LED
CURRENT
T_SW
=
1
f_SW
V_DIM
Figure 1. Current Regulator Operation
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∆I
t
t
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