Rainbow Electronics MAX16803 - Manual (Page 6)

MAX16803
High-Voltage, 350mA, High-Brightness LED
Driver with PWM Dimming and 5V Regulator
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Functional Diagram
MAX16803
ENABLE
EN REFERENCE
GENERATOR
REGULATOR
IN V5
DIFFERENTIAL
SENSE
AMPLIFIER
THERMAL
SHUTDOWN
DIM
I_ REG
IN
OUT
CS+
CS-
Detailed Description
The MAX16803 is a high-current regulator capable of
providing up to a total of 350mA of current to one or
more strings of HB LEDs. A wide operating input volt-
age range of +6.5V to +40V makes the MAX16803
ideal for automotive applications. A +5V regulated out-
put provides up to 4mA of current to power external cir-
cuitry. In addition, the MAX16803 features thermal and
output short-circuit protection. The wide operating volt-
age range helps protect the MAX16803 against large
transients such as those found in load-dump situations
up to 40V.
The MAX16803 uses a feedback loop to control the out-
put current. The differential voltage across the sense
resistor is compared to a fixed reference voltage, and
the error is amplified to serve as the drive to the internal
power series pass device (see the Functional
Diagram). The regulation point is factory-set at (V
CS+ -
V CS- ) = 203mV ±3.5%. The regulated current is user
defined by the value of R SENSE .
The MAX16803 is a current controller internally opti-
mized for driving the impedance range expected from
one or more HB LEDs.
+5V Regulator
The MAX16803 includes a fixed +5V output regulator
that delivers up to 4mA of load current throughout the
+6.5V to +40V input voltage range. Connect a 0.1µF
compensation capacitor from V5 to ground. Shorting
V5 to ground disables the thermal shutdown. When EN
is low, V5 is off. V5 stays on during PWM dimming.
Thermal Protection
The MAX16803 enters a thermal-shutdown mode in the
event of overheating. This typically occurs in overload or
output short-circuit conditions. If the junction tempera-
ture exceeds T
J = +155°C (typ), the internal thermal-pro-
tection circuitry turns off the series pass device. The
MAX16803 recovers from thermal-shutdown mode once
the junction temperature drops by 23°C (typ). The part
therefore protects itself by thermally cycling in the event
of a short-circuit or overload condition.
Applications Information
Programming the LED Current
The MAX16803 uses a sense resistor across CS+ and
CS- to set the LED current. The differential sense ampli-
fier connected across R
SENSE provides ground-loop
immunity and low-frequency noise rejection. The LED
current is given by
I LED = V SENSE / R SENSE