MAX16835 Maxim Integrated Products, MAX16835 Datasheet - Page 6

• Manufacturer Part Number: MAX16835
• Description: Adjustable Linear High-Brightness LED Driver
• Manufacturer: Maxim Integrated Products

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High-Voltage, 350mA, Adjustable Linear
High-Brightness LED Driver
power series pass device (see the Functional Diagram ).
The regulation point is factory set at (V
200mV ±3.5%. The regulated current is user defined by
the value of R
The MAX16835 is a current controller internally opti-
mized for driving the impedance range expected from
one or more HB LEDs.
The MAX16835 includes a fixed +5V output regulator
that delivers up to 4mA of load current for low-power
applications throughout the +6.5V to +40V input volt-
age 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.
The MAX16835 enters a thermal-shutdown mode in the
event of overheating. This typically occurs in overload or
output short-circuit conditions. When the junction tem-
perature exceeds T
mal-protection circuitry turns off the series pass device.
The MAX16835 recovers from thermal-shutdown mode
once the junction temperature drops by 24°C (typ). The
part therefore protects itself by thermally cycling in the
event of a short-circuit or overload condition. Shorting V5
to ground disables the thermal shutdown.
The MAX16835 uses a sense resistor across CS+ and
CS- to set the LED current. The differential sense amplifier
Figure 1. Pulse Application with V
6
V
V
EN
IN
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
C1
1
2
3
4
SENSE
OUT
IN
IN
N.C.
Applications Information
OUT
N.C.
Programming the LED Current
16
5
.
J
MAX16835
N.C.
= +159°C (typ), the internal ther-
15
EN
6
N.C.
N.C.
14
7
IN
Thermal Protection
N.C.
N.C.
13
at a Constant Voltage
8
GND
CS+
CS-
V5
+5V Regulator
12
11
10
9
CS+
C2
D1
- V
R
CS-
SENSE
I
LED
) =
connected across R
nity and low-frequency noise rejection. The LED current
is given by the equation below:
For proper operation, the minimum input voltage must
always be:
where V
connected LEDs. The minimum operating voltage of the
device is +6.5V. The device operates below +6.5V;
However, the output current may not meet the full regu-
lation specification.
The MAX16835 provides pulsed or chopped current
dimming. Generally, HB LEDs are binned to match at
their full-rated current; however, LEDs from the same
bin exhibit poor matching at currents other than full-
rated current. To achieve uniformity, HB LED manufac-
turers recommend PWM pulsing of the LED current at
their full-rated value. There are two methods for pro-
ducing a PWM output. One method is by pulsing the
enable input (EN) while having a constant voltage at IN.
The other method is to connect EN to IN and pulse both
EN and IN. Both methods generate a regulated-ampli-
tude PWM current (variable duty cycle) that can pro-
vide control over the LED brightness (see Figures 1
and 2).
Figure 2. Pulse Application with EN Connected to V
C1
V
V
IN
IN(MIN)
FT(MAX)
≥ V
1
2
3
4
OUT
IN
IN
N.C.
SENSE(MAX)
I
is the total forward voltage of all series-
LED
OUT
N.C.
Input Voltage Considerations
16
5
SENSE
= V
MAX16835
N.C.
15
EN
6
SENSE
provides ground-loop immu-
N.C.
N.C.
14
+ V
7
Low-Frequency PWM
/R
FT(MAX
N.C.
N.C.
13
8
SENSE
GND
CS+
CS-
V5
12
11
10
at the Output
9
+ ΔV
DO(MAX)
IN
C2
D1
R
SENSE
I
LED