General Description
The MAX16812 evaluation kit (EV kit) demonstrates the
MAX16812 peak-current-mode PWM high-brightness LED
(HBLED) driver IC. The MAX16812 EV kit is configured in
a step-up/step-down topology with peak-current-mode
and average LED current control for the external LEDs.
The EV kit is capable of supplying stable LED output
currents up to 360mA and operates at supply voltages
between 7V and 28V. The maximum output voltage of
the LED string can be up to 15V.
The MAX16812 EV kit features two different types of
dimming controls, using either an analog linear input
voltage or a digital PWM input signal to control the
LEDs’ brightness. This EV kit also has an undervoltage
lockout (UVLO) feature that disables the EV kit and
overvoltage protection to protect the EV kit under
no-load conditions. The MAX16812 EV kit is a fully
assembled and tested surface-mount printed-circuit
board (PCB).
Features
♦7V to 28V Wide Supply Voltage Range
♦Peak-Current-Mode Control
♦Up to 360mA Output Current
♦Analog Linear Dimming Control
♦PWM Dimming Control
♦Programmable Switching Frequency
♦Shutdown Control
♦Output Overvoltage Protection
♦Fully Assembled and Tested
Evaluates: MAX16812
________________________________________________________________
Maxim Integrated Products
1
19-0965; Rev 0; 8/07
Component List
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Ordering Information
PART TYPE
MAX16812EVKIT+ EV Kit
D ESIG N A T IO N QTY DESCRIPTION
C1, C9, C10,
C11 4
4.7µF ±10%, 50V X7R ceramic
capacitors (1210)
Murata GRM32R71H475K
C2, C18 2
0.1µF ±10%, 50V X7R ceramic
capacitors (0603)
Murata GRM188R71H104K
C3, C8 2
3.3µF ±10%, 16V X7R ceramic
capacitors (0805)
Murata GRM21BR71C335KA73
C4, C6 2
0.22µF ±10%, 25V X7R ceramic
capacitors (0603)
Murata GRM188R71E224K
C5, C15,
C16, C17 4
1000pF ±10%, 50V X7R ceramic
capacitors (0603)
Murata GRM188R71H102K
C7 1
220pF ±10%, 50V X7R ceramic
capacitor (0603)
Murata GRM188R71H221K
C12 1
1µF ±10%, 16V X7R ceramic
capacitor (0603)
Murata GRM188R71C105K
D ESIG N A T IO N QTY DESCRIPTION
C13 1
0.47µF ±10%, 25V X7R ceramic
capacitor (0805)
Murata GRM219R71E474K
C14 1
0.047µF ±10%, 25V X7R ceramic
capacitor (0603)
Murata GRM188R71E473K
C19, C20 0 Not installed, capacitors
D1 1 3A, 60V Schottky diode (SMB)
Diodes Inc. B360B
D2 1 150mA, 100V diode (SOD-323)
Diodes Inc. 1N4148WS-7-4
JU1 1 3-pin header
JU2, JU3 2 2-pin headers
L1 1 68µH, 3A inductor
Coilcraft DO3340P-683ML
N1 1
60V, 4.3A n-channel MOSFET
(6-pin SuperSOT)
Fairchild Semiconductor FDC5612
R1 1 100kΩ ±1% resistor (0603)
R2, R9 2 100kΩ potentiometers (single turn)
R3 1 1kΩ ±1% resistor (0603)
R4, R15 2 10kΩ ±1% resistors (0603)
+
Denotes lead-free and RoHS-compliant.
MAX16812 Evaluation Kit
Evaluates: MAX16812
2 _______________________________________________________________________________________
Component List (continued)
D ESIG N A T IO N QTY DESCRIPTION
R5 1 2.49kΩ ±1% resistor (0603)
R6 1 113kΩ ±1% resistor (0603)
R7 1 100Ω ±5% resistor (0603)
R8 1 200kΩ ±1% resistor (0603)
R10, R11 2
0.6Ω ±1%, 500mW sense
resistors (1206)
IRC/TT Electronics
LRC-LRF-1206LF-01-R600-F
R12 1 10Ω ±1% resistor (0603)
R13 1
1.8Ω ±1%, 250mW sense
resistor (1206)
Panasonic ERJ-8RQF1R8V
SUPPLIER PHONE WEBSITE
Coilcraft, Inc. 847-639-6400 www.coilcraft.com
Diodes Inc. 805-446-4800 www.diodes.com
Fairchild Semiconductor 888-522-5372 www.fairchildsemi.com
IRC/TT Electronics 361-992-7900 www.irctt.com
Murata Mfg. Co., Ltd. 770-436-1300 www.murata.com
Panasonic Corp. 714-373-7366 www.panasonic.com
D ESIG N A T IO N QTY DESCRIPTION
R14 1
1.5Ω ±1%, 250mW sense
resistor (1206)
Panasonic ERJ-8RQF1R5V
R16 1 2.32kΩ ±1% resistor (0603)
TP1, TP2, TP3 3 PC mini red test points
U1 1
Maxim integrated high-voltage
LED driver with analog and PWM
dimming control
MAX16812ATI+ (28-pin TQFN,
5mm x 5mm x 0.8mm)
— 3 Shunts
— 1 PCB: MAX16812 Evaluation Kit+
Component Suppliers
Note: Indicate that you are using the MAX16812 when contacting these component suppliers.
MAX16812 Evaluation Kit
Evaluates: MAX16812
_______________________________________________________________________________________ 3
Quick Start
Recommended Equipment
Before beginning, the following equipment is needed:
• 5V to 28V, 2A power supply
• Two digital voltmeters
• A series-connected LED string rated at 350mA
(15V, max)
• One current probe to measure LED current
Procedures
The MAX16812 EV kit is fully assembled and tested.
Follow the steps below to verify operation. Caution: Do
not turn on the power supply until all connections
are completed. Avoid powering up the EV kit with-
out connecting a load to the LED+ and LED- pads.
1) Connect the power supply’s positive terminal to the
VIN PCB pad on the EV kit. Connect the power
supply’s ground terminal to PGND PCB pad.
2) Connect digital voltmeters across the IN and PGND
PCB pads and the LED+ and LED- PCB pads.
3) Install a shunt across jumper JU1 (MAX16812 EV kit
enabled).
4) Install a shunt across jumper JU2 and verify that a
shunt is not installed across jumper JU3 (analog
dimming control).
5) Connect the anode-end of the LED string to the
LED+ pad.
6) Connect the cathode-end of the LED string to the
LED- pad.
7) Adjust potentiometer R9 clockwise.
8) Clip the current probe across the LED wire to mea-
sure the LED current.
9) Turn on the power supply and increase the input
voltage to 7V.
10) Adjust potentiometer R2 counterclockwise until the
LED current amplitude is 350mA.
11) Measure the voltage between the LED+ to LED-
PCB pads.
Detailed Description
The MAX16812 evaluation kit (EV kit) demonstrates the
MAX16812 IC peak-current-mode PWM HBLED driver.
The MAX16812 EV kit is configured in a step-up/step-
down topology with peak-current-mode and average
LED current control for a string of user-supplied exter-
nal HBLEDs. The EV kit is capable of supplying stable
LED output currents up to 350mA and operates at sup-
ply voltages between 7V and 28V.
The MAX16812 EV kit sets the inductor peak current to 2A
using parallel resistors R10 and R11. The average LED
current is set to a maximum of 360mA using parallel resis-
tors R13 and R14, and by adjusting potentiometer R2.
The MAX16812 EV kit is set to a 300kHz switching fre-
quency using resistor R8. Refer to the
Internal Oscillator
Switching Frequency
section in the MAX16812 IC data
sheet for information on setting other switching frequen-
cies. A PCB pad is available to monitor the MAX16812 ref-
erence voltage output (REF). A PCB pad is also provided
for the external LED intensity voltage-control input DIM.
Input Supply UVLO
Jumper JU1 controls the MAX16812 EV kit enable mode.
Place a shunt across pins 1-2 to enable the MAX16812
EV kit when VIN voltage rises above the IC’s 5V UVLO
default threshold. Place a shunt across pins 2-3 to dis-
able the EV kit. See Table 1 for JU1 jumper selection.
Peak Inductor Current-Limit Setting
The parallel combination of current-sense resistors R10
and R11 sets the EV kit’s peak inductor current limit to
2A. Use the following equation to calculate the peak
current limit:
where IILIM is the inductor peak current and RTOTAL is
the total parallel resistance placed at the R10 and R11
PCB pads.
Refer to the
Internal Switching MOSFET Current Limit
section in MAX16812 IC data sheet for additional infor-
mation on setting the peak current-limit threshold.
Setting External LEDs Current
Resistors R13 and R14 set the MAX16812 EV kit aver-
age LED current up to a maximum 360mA. The poten-
tiometer R2 allows the external LED current to be
adjusted from 175mA (min) to 360mA (max). The LED
string current can be programmed using the following
equation:
where ILED is the LED current, VREFI is the voltage at
TP1, and 0.82Ωis the parallel resistance of R13 and R14.
ILED(A) = VREFI
4 x 0.82Ω
=600mV
RTOTAL
IILIM
SHUNT POSITION EN PIN EV KIT FUNCTION
1-2 Connected to IN Enabled
2-3 Connected to GND Disabled
Table 1. JU1 Jumper Selection (EN)
MAX16812 Evaluation Kit
Evaluates: MAX16812
PWM Dimming Control
(Jumpers JU2 and JU3)
PWM dimming is achieved by turning on and off the
MOSFET (N1) in series with the LED string. LED dim-
ming is achieved on the MAX16812 EV kit by applying
a digital PWM signal or an analog DC voltage at the
DIM PCB input pad, or by adjusting potentiometer R9.
The voltage at the MAX16812 DIM pin can be adjusted
using potentiometer R9 to control the external LEDs’
brightness. When adjusting the DC voltage using R9,
install a shunt across jumper JU2 and remove the shunt
at jumper JU3. The MAX16812 IC DIM pin voltage can
be monitored by placing a voltmeter across the DIM and
AGND PCB pads. LED dimming can also be accom-
plished by removing the shunt at jumper JU2 and con-
necting an external power source at the DIM PCB pad.
The DC voltage at the DIM PCB pad sets the MAX16812
duty cycle of the driver controlling the gate of the dim-
ming MOSFET (N1), which controls the external LED
brightness.
Use the following equation to calculate the voltage at
the DIM PCB pad, necessary for the N1 dimming FET
output duty cycle (D):
DIM ≈D x 1.24V
where DIM is the DC voltage at the MAX16812 EV kit
DIM PCB pad in volts and D is the output duty cycle of
the LED current.
To control LED dimming using a PWM signal at the DIM
PCB pad, remove the shunt from jumper JU2 and place
a shunt across jumper JU3. Connect a digital PWM sig-
nal with a 5V TTL or 3.3V CMOS logic level and switch-
ing frequencies up to 2kHz. See Table 2 for jumpers
JU2 and JU3 settings for PWM dimming operation.
For additional information on operating the MAX16812
EV kit in linear dimming or PWM dimming operation,
refer to the
PWM Dimming
section in the MAX16812 IC
data sheet.
During PWM dimming, there may be audible noise due
to the piezo effect of the output capacitors connected at
LED+. To alleviate the audible noise, remove ceramic
capacitors C9, C10, and C11, and add electrolytic
capacitors at the C19 and C20 pads. For proper PWM
dimming operation, when using electrolytic capacitors, it
may be required to change some of the compensation
components.
Output Overvoltage Protection
The maximum voltage on the LED+ pin is limited to
54.4V with respect to GND, by a feedback network
formed by resistors R5 and R6. When the voltage at
LED+ exceeds the programmed 54.4V threshold, PWM
switching is terminated and no further energy is trans-
ferred to the load connected between LED+ and LED-.
If the MAX16812 EV kit is turned on with no load, the
voltage at LED+ may rise to unsafe levels. Even
though the EV kit has overvoltage protection, it is rec-
ommended to connect the specified load before pow-
ering up the EV kit. Refer to the
Setting the Overvoltage
Threshold
section in the MAX16811/MAX16812 IC data
sheet for setting the overvoltage threshold.
4 _______________________________________________________________________________________
SHUNT POSITION
JU2 JU3 EV KIT DIMMING OPERATION
Not
installed
Not
installed
Analog DC voltage applied
at DIM PCB pad
Not
installed Installed PWM signal applied
at DIM PCB pad
Installed Not
installed
Analog DC voltage at DIM pin
adjusted using potentiometer R9
Installed Installed Not applicable
Table 2. PWM Dimming Operation
(Jumpers JU2 and JU3)
MAX16812 Evaluation Kit
Evaluates: MAX16812
_______________________________________________________________________________________ 5
R15
10kΩ
1%
MAX16812
U1
8IN
9L_REG
25 TGRM
11 DD
123
4DGT
28
OV
27
RT
26
DIM
24
SLP
15
LV
16
12
D2
D1
H_REG
7
EN
6
AGND
4
REF
3
REFI
2
COMP
1
FB
C14
0.047μF
C5
1000pF
C4
0.22μF
C16
1000pF
C12
1μF
17
HV
18
DRV
C13
0.47μF
C3
3.3μF
C6
0.22μF
C8
3.3μF
C2
0.1μF
C15
1000pF
L_REG
JU3
JU2
R16
2.32kΩ
1%
N1
VIN
TP2
TP1
LED+
L_REG
3
1
2
13 CS+
14 CS-
19
GT
1256
TP3
R13
1.8Ω
1%
R14
1.5Ω
1%
VIN
VREF
VREF AGND
VIN
LED+
LED+
DIM
AGND
VIN
PGND
LED-
L1
68μH
R12
10Ω
1%
20
LX
21
LX
C9
4.7μF
C11
4.7μF
C19
OPEN
C10
4.7μF
50V 50V50V
R7
100Ω
AGND PGND
1
3
2JU1
C1
4.7μF
50V
R2
100kΩ
R1
100kΩ
1%
3
1
2R9
100kΩ
R3
1kΩ
1%
5
CS_OUT
R4
10kΩ
1% R6
113kΩ
1%
R5
2.49kΩ
1%
C17
1000pF
R8
200kΩ
1%
C7
220pF
23
SRC
22
SRC
10
SGND
C18
0.1μF
R10
0.6Ω
1%
R11
0.6Ω
1%
C20
OPEN
Figure 1. MAX16812 EV Kit Schematic
MAX16812 Evaluation Kit
Evaluates: MAX16812
MAX16812 Evaluation Kit
6 _______________________________________________________________________________________
Figure 2. MAX16812 EV Kit Component Placement Guide—
Component Side
Figure 3. MAX16812 EV Kit PCB Layout—Component Side
Evaluates: MAX16812
MAX16812 Evaluation Kit
_______________________________________________________________________________________ 7
Figure 4. MAX16812 EV Kit PCB Layout—GND Layer 2 Figure 5. MAX16812 EV Kit PCB Layout—VCC Layer 3
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.
8
_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Evaluates: MAX16812
MAX16812 Evaluation Kit
Figure 6. MAX16812 EV Kit PCB Layout—Solder Side
