MAX16802BEVKIT Maxim Integrated Products, MAX16802BEVKIT Datasheet - Page 3

• Manufacturer Part Number: MAX16802BEVKIT
• Description: EVAL KIT FOR MAX16802
• Manufacturer: Maxim Integrated Products

Specifications of MAX16802BEVKIT

• Current - Output / Channel: 750mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 12V
• Features: Dimmable
• Voltage - Input: 10.8 ~ 30V
• Utilized Ic / Part: MAX16802B
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The maximum voltage at the positive pin of VLED with
respect to GND is limited to 45V by a feedback network
formed by R1 and R2, which is connected to the FB pin
of the MAX16802B. If the EV kit is turned on with no load
or if the LED connection opens, the voltage at the posi-
tive pin of VLED may rise to unsafe levels. This condition
is sensed by the internal error amplifier, which reduces
the peak inductor current to limit the voltage at the posi-
tive pin of VLED to 45V. Even if this protection is present,
it is recommended to connect the specified load before
powering up the EV kit.
The PWM dimming is for controlling the LED brightness
by adjusting the duty cycle of the PWM input signal
connected to the PWM_IN input. A HIGH at PWM_IN
input turns off the LED current and LOW turns on the
LED current. Connect a signal with peak amplitude
between 1.5V to 5.0V and with frequency between
100Hz to 1000Hz and vary the duty cycle to adjust the
LED brightness. Frequencies lower than 100Hz can
introduce flickering in the light output. LED brightness
reduces when duty cycle is increased and vice-versa.
When the PWM duty cycle is 0%, the LED brightness
will be 100%.
The linear dimming is for controlling the LED brightness
by varying the amplitude of the voltage connected to
the LIN_IN input. The voltage at the LIN_IN input modu-
lates the current-sense signal and makes the MOSFET
trip at a different current level. This process, in turn,
changes the output current and thus controls the LED
brightness. Since the LED is continuously on at all
brightness levels, flickering effect is not present with
linear dimming. Vary the LIN_IN voltage between 0 and
1.6V to adjust LED brightness from 100% to 0%. LED
brightness reduces when the voltage at LIN_IN is
increased and vice-versa. When the voltage at LIN_IN
is 0V the LED brightness is 100%.
To change the maximum output power of the EV kit
from 12V at 750mA to a different level, adjust the value
of the current-sense resistor, R9, using the following
equations. Note that the maximum output current of the
EV kit is limited to 750mA, the maximum output voltage
is limited to 15V, and the maximum output power is lim-
ited to 8.25W.
Initially calculate the approximate optimum ON duty
cycle required at the minimum input voltage:
Output Overvoltage Protection
_______________________________________________________________________________________
Adjusting the Output Power
Linear Dimming
PWM Dimming
MAX16802B Evaluation Kit
where V
V
LED current and V
Calculate the approximate required peak inductor current:
where k
for this circuit.
Calculate the approximate required inductor value and
choose the closest standard value smaller than the cal-
culated value:
where L is the inductance value of inductor L1, and f
is the switching frequency equal to 262kHz.
Power transferred to the output circuit by the flyback
process is:
Power consumed by the output circuit is:
Conservation of power requires that the above two
equations can be equated and solved for a more pre-
cise value of the required peak inductor current.
Set the value of the current-sense resistor, R9, based
on the I
where 0.292V is the current-sense trip threshold volt-
age. R7 and R8 form a voltage-divider, which scales
down the voltage across the current-sense resistor
before reaching the current-sense pin of the device.
Keep jumper J1 closed when PWM dimming is not
used. Keep jumper J2 closed when linear dimming is
not used.
LED
is the LED operating voltage, I
PEAK
f
INMIN
is a noncritical “fudge factor” set equal to 1.1
P
value using the following equation:
I
OUT
P
D
is the minimum input supply voltage,
=
ON
R
P
9
D
=
IN
⎛
⎜
⎝
L
I
=
=
P
V
2 (
is the forward voltage of D2.
=
=
LED
×
0 292
V
=
D
2
INMIN
1
.
k
V
ON
I
× ×
LED
PEAK
f
×
f
1
SW
L I
V
× ×
f
−
I
SW
LED
×
×
LED
2
D
+
(
+
V
×
P
R
ON
INMIN
×
V
V
×
2
I
8
I
P
+
D
LED
LED
+
R
L
×
Jumper Selection
+
7
V
V
)
f
R
SW
×
D
D
7
I
+
LED
×
)
LED
V
I
LED
D
⎞
⎟
⎠
is the desired
SW
3