19-0560; Rev 0; 5/06
MAX16802B Evaluation Kit
General Description
The MAX16802B evaluation kit (EV kit) demonstrates a
current-controlled, high-output-current LED driver
based on the MAX16802B. This EV kit is capable of
supplying stable output currents of up to 750mA, can
run at supply voltages between 10.8V and 30V, and can
operate at temperatures ranging from -40°C to +85°C.
The MAX16802B EV kit features two different types of
dimming controls using either a linear input voltage or a
PWM input signal to control the LED brightness. This EV
kit also has a UVLO feature to turn off the EV kit opera-
tion during low input supply voltage and an overvoltage
protection to protect the EV kit under an open-LED con-
dition. The MAX16802B EV kit is a fully assembled and
tested board.
Warning:
Under severe fault or failure conditions, this
EV kit may dissipate large amounts of power, which
could result in the mechanical ejection of a component
or of component debris at high velocity. Operate this
EV kit with care to avoid possible personal injury.
♦
Current-Controlled Output
♦
Up to 750mA LED Current at 12V Output
♦
Linear and PWM Dimming Control
♦
Over 80% Efficiency at Full Load
♦
Supply Undervoltage Lockout
♦
Output Overvoltage Protection
Features
♦
10.8V to 30V Wide Supply Voltage Range
Evaluates: MAX16802B
Ordering Information
PART
MAX16802BEVKIT
TEMP RANGE
-40°C to +85°C
IC PACKAGE
8 µMAX
®
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Component List
DESIGNATION
C1, C2, C5, C6
QTY
4
DESCRIPTION
4.7µF, 50V X7R ceramic capacitors
Murata GRM32ER71H475KA88L
0.1µF, 50V X7R SMD ceramic
capacitors
Murata GRM188R71H104KA93D or
TDK C1608X7R1H104K
470pF, 50V X7R ceramic capacitor
Murata GRM188R71H471KA01D or
TDK C1608X7R1H471K
1nF, 50V X7R ceramic capacitor
Murata GRM188R71H102KA01D or
TDK C1608X7R1H102K
22V, 1.5W zener diode
Vishay SMZG3797B
60V, 1A Schottky diode
Central Semiconductor CMSH1-60M
or Diodes Inc. B160
20V, small-signal Schottky diode
Vishay SD103CWS or
Diodes Inc. SD103CWS
0.1in, 2-pin hole headers
(through hole)
DESIGNATION
L1
Q1
R1
R2
R3
R4
R5, R7
R6
R8
R9
R10
U1
VIN, VLED,
PWM_IN,
LIN_IN
—
QTY
1
1
1
1
1
1
2
1
1
1
1
1
4
1
DESCRIPTION
4.7µH, 4.2A peak SMD inductor
Coilcraft DO3308P-472ML
60V, 3.2A n-channel MOSFET
Vishay Si3458DV
392kΩ ±1%, 1/8W resistor (0603)
11kΩ ±1%, 1/8W resistor (0603)
499kΩ ±1%, 1/8W resistor (0603)
73.2kΩ ±1%, 1/8W resistor (0603)
1kΩ ±1%, 1/8W resistors (0603)
330Ω ±1%, 1/4W resistor (1206)
220Ω ±1%, 1/8W resistor (0603)
0.10Ω ±1%, 1/2W resistor (1206)
Susumu RL1632R-R100-F
1Ω ±5%, 1/8W resistor (0603)
MAX16802B (8-pin µMAX)
0.1in, 2-pin male connectors
(through hole)
MAX16802B PC board
C3, C4, C7
3
C8
1
C9
D1
D2
1
1
1
D3
J1, J2
1
2
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAX16802B Evaluation Kit
Evaluates: MAX16802B
Quick Start
The MAX16802B EV kit is fully assembled and tested.
Follow these steps to verify operation.
Do not turn on
the power supply until all connections are completed.
1) Connect a DC power supply (0 to 30V or above, 1A)
to +VIN and GND.
2) Connect a voltmeter or oscilloscope and the LED
array (connected in series to drop about 12V at
750mA forward current) to +VLED and -VLED with
anode connected to +VLED and cathode to -VLED.
3) Close the jumpers J1 and J2 to disable dimming.
4) Turn on the power supply and increase the input
voltage to above 10.8V. The output voltage increas-
es to forward bias the LED array and delivers
approximately 750mA regulated average LED cur-
rent. Increase the supply further up to 30V and the
output average current will be regulated throughout
the range.
5) Open shunt J1 and apply a PWM signal to PWM_IN
with a frequency of 200Hz and 0 to 2V amplitude.
Vary the duty cycle from 0 to 100% and the LED
brightness varies from 100% to 0%. When the PWM
duty cycle is 0%, the LED brightness is 100%.
6) Close J1, and then open J2. Connect a variable volt-
age source to LIN_IN and vary the voltage between
0 and 1.6V. The LED brightness varies from 100% to
0%. When the voltage input at LIN_IN is 0V, the LED
brightness is 100%.
Caution: Avoid powering up the EV kit without con-
necting load.
This EV kit is based on a discontinuous current mode
(DCM) buck-boost converter operating at 262kHz to
deliver a finite amount of energy to the output every
cycle. The amount of this energy depends primarily on
the value of the inductor and the user-programmable
peak inductor current and does not depend on the sup-
ply voltage. Due to this configuration, the power output
of the EV kit, and thus the output current supplied to the
LED at a given LED operating voltage, becomes inde-
pendent of the supply voltage.
This EV kit is designed to drive LED loads capable of
taking up to 750mA of maximum current at a 12V operat-
ing voltage. If an LED load with lower operating voltage
is used, then the maximum output current will increase
by the same ratio to maintain the output power constant.
To drive an LED array with a different operating voltage,
the value of the current-sense resistor needs to be
adjusted. Calculation of the current-sense resistor for a
different output operating voltage is explained in later
sections.
Input Supply UVLO
Input supply UVLO is implemented by using a resistor
network that combines R3 and R4, which senses the
input supply voltage and uses the EN pin to turn on the
circuit when the input supply voltage goes above
10.8V. The wake-up threshold of EN is 1.23V when the
voltage at EN is rising, and it has a hysteresis of 50mV.
Once the device is turned on, due to the hysteresis, the
device turns off only if the input supply voltage goes
below 10.4V.
The UVLO threshold can be adjusted by varying R1 or
R2 using the equation below:
⎛
V
⎞
R3
= ⎜
UVLO
−
1
⎟ ×
R4
⎝
1.23
⎠
where V
UVLO
is the desired UVLO threshold. To main-
tain threshold accuracy, keep the value of R4 less than
100kΩ.
Detailed Description
The MAX16802B evaluation kit is a current-controlled,
high-output-current LED driver capable of supplying
constant currents up to 750mA, irrespective of supply
voltage variations.
Component Suppliers
SUPPLIER
Central Semiconductor
Coilcraft
Diodes Inc.
Murata
Susumu Co Ltd.
TDK
Vishay
PHONE
631-435-1110
847-639-6400
805-446-4800
770-436-1300
208-328-0307
847-390-4373
402-563-6866
FAX
631-435-3388
847-639-1469
805-446-4850
770-436-3030
208-328-0308
847-390-4428
402-563-6296
WEBSITE
www.centralsemi.com
www.coilcraft.com
www.diodes.com
www.murata.com
www.susumu-usa.com
www.component.tdk.com
www.vishay.com
Note:
Indicate you are using the MAX16802B when contacting these manufacturers.
2
_______________________________________________________________________________________
MAX16802B Evaluation Kit
Output Overvoltage Protection
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.
Evaluates: MAX16802B
D
ON
=
V
LED
+
V
D
V
INMIN
+
V
LED
+
V
D
where V
INMIN
is the minimum input supply voltage,
V
LED
is the LED operating voltage, I
LED
is the desired
LED current and V
D
is the forward voltage of D2.
Calculate the approximate required peak inductor current:
k
×
2
×
I
LED
I
P
=
f
1
−
D
ON
where k
f
is a noncritical “fudge factor” set equal to 1.1
for this circuit.
Calculate the approximate required inductor value and
choose the closest standard value smaller than the cal-
culated value:
L
=
D
ON
×
V
INMIN
f
SW
×
I
P
PWM Dimming
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%.
where L is the inductance value of inductor L1, and f
SW
is the switching frequency equal to 262kHz.
Power transferred to the output circuit by the flyback
process is:
P
IN
=
1
×
L
×
I
P2
×
f
SW
2
Linear Dimming
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%.
Power consumed by the output circuit is:
P
OUT
=
V
LED
×
I
LED
+
V
D
×
I
LED
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.
⎛
2
×
(V
LED
+
V
D
)
×
I
LED
⎞
I
P
= ⎜
⎟
⎝
⎠
f
SW
×
L
Set the value of the current-sense resistor, R9, based
on the I
PEAK
value using the following equation:
R9
=
0.292
×
(R8
+
R7)
I
PEAK
×
R7
Adjusting the Output Power
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:
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.
Jumper Selection
Keep jumper J1 closed when PWM dimming is not
used. Keep jumper J2 closed when linear dimming is
not used.
3
_______________________________________________________________________________________
MAX16802B Evaluation Kit
Evaluates: MAX16802B
+VIN
-VLED
GND
R1
392kΩ
1%
R5
1kΩ
1%
D3
SD103CWS
J1
R3
499kΩ
1%
C1
4.7µF
50V
C2
4.7µF
50V
D1
22V
R6
330Ω
1%
C3
0.1µF
50V
L1
4.7µH
C4
0.1µF
50V
C5
4.7µF
50V
C6
4.7µF
50V
+VLED
PWM_IN
1
UVLO/EN
U1
IN
8
D2
CMSH1-60M
MAX16802B
2
R4
73.2kΩ
1%
C9
1nF
50V
R2
11kΩ
1%
DIM/FB
V
CC
NDRV
GND
7
6
5
R10
1Ω
12 56
3
C7
0.1µF
50V
Q1
Si3458DV
4
PWM_GND
3 COMP
4
LIN_IN
C8
470pF
50V
CS
LIN_GND
J2
R7
1kΩ
1%
R8
220Ω
1%
R9
0.10Ω
1%
Figure 1. MAX16802B EV Kit Schematic
4
_______________________________________________________________________________________
MAX16802B Evaluation Kit
Evaluates: MAX16802B
Figure 2. MAX16802B EV Kit Component Placement Guide—
Component Side
Figure 3. MAX16802B EV Kit PC Board Layout—Component
Side
Figure 4. MAX16802B EV Kit PC Board Layout—Solder Side
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________
5
© 2006 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
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