MAX16804
High-Voltage, 350mA LED Driver with
Analog and PWM Dimming Control
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The dimming feature can be used for LED brightness
adjustment (see the
Simplified Diagrams
) and theater
dimming. If an external PWM signal is used, the theater-
dimming effect can be achieved by varying the PWM
duty cycle. Figure 1 shows a simple circuit that imple-
ments theater dimming with a DC input signal.
+5V Regulator
The MAX16804 includes a fixed +5V output regulator
that delivers up to 2mA of load current throughout the
6.5V to 40V input voltage range. Connect a 0.1µF com-
pensation 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 MAX16804 enters a thermal-shutdown mode in the
event of overheating. This typically occurs in overload or
short-circuit conditions on the output. If the junction tem-
perature exceeds T
J
= +155°C (typ), the internal ther-
mal-protection circuitry turns off the series pass device.
The MAX16804 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 MAX16804 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 (2)
Input-Voltage Considerations
For proper operation, the minimum input voltage must
always be:
V
IN(MIN)
≥ V
RSENSE(MAX)
+ V
FT(MAX)
+ ΔV
DO(MAX) (3)
where V
FT(MAX)
is the maximum forward voltage of all
series connected LEDs and ΔV
DO(MAX)
is the maximum
drop output voltage. The minimum operating voltage of
the device is +5.5V.
Two Brightness Levels for
TAIL/STOP Lights
Figure 2 shows two-level brightness adjustment using
the MAX16804 with minimum external components. Set
the dimming level with a resistive divider connected to
DIM. See Equation 1 for details.
