Detailed Description
The MAX16804 is a high-current regulator capable of
providing up to 350mA of current to one or more strings
of HB LEDs. A wide operating input voltage range of
5.5V to 40V makes the MAX16804 ideal for automotive
applications. A +5V regulated output provides up to
2mA of current to power external circuitry. In addition,
the MAX16804 features thermal and output short-circuit
protection. The wide operating voltage range helps
protect the MAX16804 against large transients such as
those found in load-dump situations up to 45V.
The MAX16804 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 pass
device (see the
Functional Diagram
). The regulation
point is factory-set at (V
CS+
- V
CS-
) = 198 ±6mV. The
regulated current is user-defined by the value of R
SENSE
.
The MAX16804 is a current controller internally opti-
mized for driving the impedance range expected from
one to ten or more HB LEDs.
Dimming Input (DIM)
The MAX16804’s dimming input functions with either an
analog or PWM control signal. If the pulse detector
detects three edges of a PWM signal with a frequency
range between 80Hz to 2kHz, the MAX16804 synchro-
nizes to external PWM input signal and pulse-width-
modulates the LED current. If an analog control signal
is applied to DIM, the MAX16804 compares the DC
input to an internally generated 200Hz ramp to pulse-
width-modulate the LED current.
The output current duty cycle is adjustable from 0% to
100% (0.21V < V
DIM
< 3.1V).
Use the following formula to calculate the output cur-
rent duty cycle:
Duty cycle = (V
DIM
- 0.21V) / (2.895V) (1)
