19-0821; Rev 0; 5/07
MAX16809 Evaluation Kit
General Description
The MAX16809 evaluation kit (EV kit) is a 16-channel,
constant-current LED driver, capable of driving 40mA
each to 16 LED strings with a total forward voltage of
up to 32V. The MAX16809 EV kit is based on the
MAX16809 device, which has 16 constant-current-sink-
ing outputs with sink current settable using a single
resistor and a high-performance, current-mode pulse-
width-modulator (PWM) controller, for implementing a
DC-DC converter that generates the supply voltage to
drive the LED strings.
The MAX16809 EV kit operates at supply voltages
between 9V to 16V and temperatures ranging from
0°C to +70°C. It features a PWM dimming control,
adaptive control of the LED supply voltage, which
depends upon the operating voltage of the LED strings,
a built-in clock generator, and a low-current shutdown.
The MAX16809 EV kit is a fully assembled and tested
board.
♦
9V to 16V Supply Voltage Range
♦
40mA LED Current (Per Each LED String)
♦
Single-Resistor Current Adjust for 16 Channels
♦
Up to 32V LED String Voltage
♦
Boost Converter to Generate LED Supply Voltage
♦
Adaptive LED Supply Voltage Control Increases
Efficiency
♦
PWM Dimming Control
♦
Output-Voltage-Spike Protection for Inductive-
Output Lines
♦
Proven PCB Layout
Features
Evaluates: MAX16809
Ordering Information
PART
MAX16809EVKIT+
TEMP RANGE
0°C to +70°C*
IC PACKAGE
38 TQFN-EP
†
+Denotes
a lead-free and RoHS-compliant EV kit.
*This
limited temperature range applies to the EV kit PCB only.
The MAX16809 IC temperature range is -40°C to +125°C.
†
EP = Exposed paddle.
Component List
DESIGNATION
C1–C4, C6, C7,
C8, C10, C11,
C19–C23, C25,
C26
QTY
DESCRIPTION
1nF ±10%, 50V X7R capacitors
(0603)
Murata GRM188R71H103KA01D
KEMET C0603C103K5RACTU
0.1µF ± 10%, 50V X7R capacitors
(0603)
Murata GRM188R71H104KA93D
TDK C1608X7R1H104K
1µF ±20%, 16V X7R capacitor
(0805)
Murata GRM21BR71C105KA01L
TDK C2012X7R1C105K
22µF ±20% 35V electrolytic
capacitors
Panasonic EEEFK1V220R
1µF ±20%, 50V X7R capacitor
(1210)
KEMET C3225X7R1H105M
Murata GRM32ER71H105KA01L
DESIGNATION
C16, C17, C18
QTY
3
DESCRIPTION
22µF ±20%, 50V electrolytic
capacitors
Panasonic EEEFK1H220P
560pF ±10%, 50V C0G capacitor
(0603)
KEMET C0603C561K5RACTU
Murata GRM188R71H561KA01D
10pF ±10%, 50V C0G capacitor
(0603)
TDK C1608C0G1H00DB
Murata GRM1885C1H100JA01D
220pF ±10%, 50V C0G capacitor
(0603)
KEMET C0603C221K5RACTU
Murata GRM188R71H221KA01D
100pF ±10%, 50V C0G capacitor
(0603)
KEMET C0603C101K5RACTU
Murata GRM188R71H101KA01D
16
C5, C24, C30,
C31, C33
C27
1
5
C28
1
C9
1
C12, C13, C14
3
C29
1
C15
1
C32
1
________________________________________________________________
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.
MAX16809 Evaluation Kit
Evaluates: MAX16809
Component List (continued)
DESIGNATION
QTY
DESCRIPTION
10nF ±10%, 50V X7R capacitor
(0603)
KEMET C0603C103K5RACTU
Murata GRM188R71H103KA01D
Not installed, capacitor
33V zener diode (SOD323)
Diodes Inc. MMSZ5257BS-7
1A, 40V Schottky diode (SMA)
Diodes Inc. CMSH1-40M
Central Semiconductor CMSH1-40M
15V dual zener diodes (SOT323)
Diodes AZ23C15-7-F
20mA switching diode (SOD323)
Diodes Inc. 1N4148WS-7
40V small-signal Schottky diode
(SOD523)
Diodes Inc. SDM03U40
DESIGNATION
Q2
R1
R2
R3
R4, R6, R10
R5
R7
R8
R9
R10
R11
R12
R13
R14
R15
U1
6
1
1
1
Wire loops
U2
0.1in 20-pin header
27µH, 3.2A inductor
Coilcraft MSS1260-273ML
Switching transistor (SOT523)
Diodes Inc. MMBT2222AT-7-F
U3
1
1
QTY
1
1
1
1
3
1
1
1
1
1
1
1
0
1
1
1
DESCRIPTION
60V, 5.5A N-channel MOSFET
Vishay Si4450DY
430Ω ±1% resistor (0603)
330kΩ ±1% resistor (0603)
8.45kΩ ±1% resistor (0603)
22kΩ ±1% resistors (0603)
180kΩ ±1% resistor (0603)
10.5kΩ ±1% resistor (0603)
10Ω ±1% resistor (0603)
1.2kΩ ±1% resistor (0603)
22kΩ ±1% resistor (0603)
50kΩ ±1% resistor (0603)
75mΩ ±1% resistor (0603)
Not installed, resistor
2.2kΩ ±1% resistor (0603)
10kΩ ±1% resistor (0603)
MAX16809ATU+ (38-pin TQFN,
5mm x 7mm)
Digital pnp transistor
ROHM DTA114WKA
Digital npn transistor
ROHM DTC114WKA
Dual inverter with hysteresis
Texas Instruments
SN74LVC2G14DCKR
PCB: MAX16809 Evaluation Kit+
C34
1
C35
D1
0
1
D2
1
D3–D10
D11
8
1
D12
1
GND, GND,
PWM,
SHDN,
VBIAS, VIN
J1
L1
Q1
U4
—
1
1
Component Suppliers
SUPPLIER
Central Semiconductor Corp.
Coilcraft, Inc.
Diodes Inc.
KEMET Corp.
Murata Mfg. Co., Ltd.
ROHM Co., Ltd.
TDK Corp.
Texas Instruments Inc.
Vishay
PHONE
631-435-1110
847-639-6400
805-446-4800
978-658-1663
770-436-1300
858-625-3630
847-390-4373
—
402-563-6866
FAX
631-435-3388
847-639-1469
805-446-4850
978-658-1790
770-436-3030
858-625-3670
847-390-4428
—
402-563-6296
WEBSITE
www.centralsemi.com
www.coilcraft.com
www.diodes.com
www.kemet.com
www.murata.com
www.rohm.com
www.component.tdk.com
www.ti.com
www.vishay.com
Note:
Indicate that you are using the MAX16809 when contacting these component suppliers.
2
_______________________________________________________________________________________
MAX16809 Evaluation Kit
Quick Start
•
One 16V, 5A adjustable power supply
•
One 5V power supply
•
16 LED strings with a total forward voltage
≤
32V
•
One multimeter
•
One PWM signal generator (optional)
controller that can control a DC-DC converter to generate
the supply voltage for driving the LED strings. The
MAX16809 EV kit uses the PWM controller to drive a
boost converter, which takes a 9V to 16V input and gen-
erates a 33V LED supply voltage. To drive a constant cur-
rent into an LED string, connect the LED string between
the 33V output and any of the 16 constant-current-sink
outputs. The resistor (R1) from the SET pin to ground pro-
grams the sink current of each output. The sink current of
any output can be up to 55mA and the amplitude is the
same value for all the outputs. The difference between the
total forward voltage and the LED supply voltage drops
between the constant-current-sink output and ground,
and is dissipated as power in the device.
The LED supply voltage generated by the boost con-
verter in the MAX16809 EV kit is adaptive. The LED
string with the highest total forward voltage dominates
the control loop, and the boost-converter voltage is
adjusted so that the driver associated with that string
receives just enough voltage required for current drive.
All the other strings, with lower total forward voltages,
will have excess supply voltage, which is then dropped
in the associated driver. This feedback mechanism
ensures that the linear-current-control circuit dissipates
the minimum possible power. An on-board inverter
(U4A) is configured to generate the clock input for the
MAX16809. The constant-current output-driver circuits
and U4 need a 3.3V to 5V input, which should be sup-
plied externally. If 5V is not available, it can be generat-
ed using an emitter-follower buffer from the REF output
of MAX16809.
Evaluates: MAX16809
Recommended Equipment
Procedure
The MAX16809 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.
1) Connect LED strings with operating voltage of
approximately 32V between VLED (pins 1-4 of J1)
and OUT0–OUT15 (pins 5-20 of J1). All 16 channels
should have an LED string load connected of the
same type.
2) Connect the DC power supply (16V, 5A) to VIN and
GND.
3) Connect a DC power supply (0 to 5V) to VBIAS and
GND.
4) Turn on the power supplies and apply 10V to VIN
and 3V to 5V to VBIAS. Connect
SHDN
and PWM to
3V to 5V. All of the LEDs should turn on. Measure
the current through any LED string, which should be
40mA ±7%.
5) Increase the supply voltage to 16V and the LED
currents will be stable. Measure the current through
any LED string, which should be 40mA ±7%.
6) Apply a PWM signal with amplitude of 3V to 5V and
a frequency between 100Hz and 2kHz to the PWM
input. The LED brightness should increase as the
PWM duty cycle increases and viceversa.
7) Connect
SHDN
to GND and all LEDs should turn off.
Boost Converter
The boost converter that generates the 33V LED supply
voltage operates at a switching frequency of 350kHz in
continuous-conduction mode (CCM). The current-mode
PWM controller in the MAX16809 drives the external
MOSFET (Q2) to control the boost converter. The
MOSFET is turned on at the beginning of every switching
cycle and turned off when the current through the induc-
tor (L1) reaches the peak value set by the error-amplifier-
output voltage. Inductor current is sensed from the volt-
age across the ground-referenced current-sense resis-
tor (parallel combination of R12 and R13). This current-
sense information is passed on to the current-sense
comparators in the MAX16809 through the CS pin.
During the on period of the MOSFET, the inductor
stores energy from the input supply. When the switch is
turned off, the inductor generates sufficient voltage in
reverse direction to discharge the stored energy to
VLED. This generated voltage forms a source, in series
with the input supply voltage, and drives VLED through
the rectifier diode (D2).
3
Detailed Description
The MAX16809 EV kit is a 16-channel, constant-current
LED driver capable of driving 40mA each to 16 LED
strings, with a total forward voltage of up to 32V. The
MAX16809 EV kit can drive a total of 160 white LEDs in
16 strings, with operating current up to 40mA. The
MAX16809 EV kit can operate at input supply voltages
between 9V and 16V.
The MAX16809 EV kit evaluates the MAX16809 IC, which
has two major sections. The first section consists of 16
constant-current LED drivers capable of sinking up to
55mA when on and blocking up to 36V when off. The sec-
ond section is a high-performance current-mode PWM
_______________________________________________________________________________________
MAX16809 Evaluation Kit
As the boost converter is operated in CCM, only part of
the stored energy in the inductor is discharged to VLED.
The advantages of CCM include reduced input and out-
put filtering, reduced EMI due to lower peak currents,
and higher converter efficiency. However, these advan-
tages come at the cost of a right-half-plane zero in the
converter-transfer function. Compensating this zero
requires reducing the system bandwidth, which affects
the converter-dynamic response. As the 16-channel,
constant-current-sink outputs control the current through
the LEDs, slower control of VLED does not affect the
LED operation. Compensation of the feedback circuit is
explained in the
Feedback Compensation
section.
An internal comparator turns off the gate pulse to the
external MOSFET if the voltage at the CS pin exceeds
0.3V. The current through the inductor that produces
0.3V at the CS pin is the maximum inductor current
possible (the actual current can be a little higher than
this limit due to the 60ns propagation delay from the CS
pin to the MOSFET drive output). This condition can
happen when the feedback loop is broken, when the
output capacitor charges during power-up, or when
there is an overload at the output. This feature protects
the MOSFET by limiting the maximum current passing
through it during such conditions.
The RC filter, consisting of R9 and C10, removes the
voltage spike across the current-sense resistors pro-
duced by the turn-on gate current of the MOSFET and
the reverse-recovery current of D2. Without filtering,
these current spikes can cause sense comparators to
falsely trigger and turn off the gate pulse prematurely.
The filter time constant should not be higher than
required (the MAX16809 EV kit uses a 120ns time con-
stant), as a higher time constant adds additional delay
to the current-sense voltage, effectively increasing the
current limit.
During normal operating conditions, the feedback loop
controls the peak current. The error amplifier compares
a scaled-down version of the LED supply voltage
(VLED) with a highly accurate 2.5V reference. The error
amplifier and compensation network then amplify the
error signal, and the current comparator compares this
signal to the sensed-current voltage to create a PWM
drive output.
Evaluates: MAX16809
Calculate maximum duty cycle D
MAX
using the following
equation:
D
MAX
=
VLED
+
V
D
−
VIN
MIN
VLED
+
V
D
−
V
FET
where V
D
is the forward drop of the rectifier diode D2
(~0.6V), VIN
MIN
is the minimum input supply voltage (in
this case, 9V), and V
FET
is the average drain-to-source
voltage of the MOSFET Q2 when it is on.
Select the switching frequency F
SW
based on the
space, noise, dynamic response, and efficiency con-
straints. Select the maximum peak-to-peak ripple on
the inductor current IL
PP
. For the MAX16809 EV kit,
F
SW
is 350kHz and IL
PP
is ±30% of the average induc-
tor current. Use the following equations to calculate the
maximum average-inductor current IL
AVG
and peak
inductor current IL
PEAK
:
IL
AVG
=
I
OUT
1
−
D
MAX
Since IL
PP
is ±30% of the average-inductor current
IL
AVG
:
IL
PP
=
IL
AVG
×
0.3
×
2
IL
PEAK
=
IL
AVG
+
IL
PP
2
Calculate the minimum inductance value L
MIN
with the
inductor current ripple set to the maximum value:
L
MIN
=
(VIN
MIN
−
V
FET
)
×
D
MAX
F
SW
×
IL
PP
Choose an inductor that has a minimum inductance
greater than this calculated value.
Calculate the current-sense resistor (R12 in parallel
with R13) using the equation below:
R
CS
=
0.3
×
0.75
IL
PEAK
Power-Circuit Design
Initially, decide the input supply voltage range, output
voltage VLED (the sum of the maximum LED total for-
ward voltage and 1V bias voltage for the constant-cur-
rent-sink output), and the output current I
OUT
(the sum
of all the LED string currents).
where 0.3V is the maximum current-sense signal volt-
age. The factor 0.75 is for compensating the reduction
of maximum current-sense voltage due to the addition
of slope compensation. Check this factor and adjust
after the slope compensation is calculated. See the
Slope Compensation
section for more information.
4
_______________________________________________________________________________________
MAX16809 Evaluation Kit
The saturation current limit of the selected inductor
(IL
SAT
) should be greater than the value given by the
equation below. Selecting an inductor with 10% higher
IL
SAT
rating is a good choice:
IL
SAT
=
1.1
×
IL
PEAK
Calculate the output capacitor C
OUT
(parallel combina-
tion of C16, C17, C18, and C24) using the following
equation:
C
OUT
=
D
MAX
×
I
OUT
VLED
PP
×
F
SW
The continuous drain-current rating of the selected
MOSFET when the case temperature is at +70°C should
be greater than that calculated by the following equation.
The MOSFET must be mounted on a board, as per
manufacturer specifications, to dissipate the heat:
⎛
⎞
IL
AVG2
⎟ ×
1.3
ID
RMS
= ⎜
⎜
D
MAX
⎟
⎝
⎠
The MOSFET dissipates power due to both switching
losses, as well as conduction losses. Use the following
equation to calculate the conduction losses in the
MOSFET:
IL
AVG2
P
COND
=
×
RDS
ON
D
MAX
where RDS
ON
is the on-state drain-source resistance of
the MOSFET with an assumed junction temperature of
100°C.
Use the following equation to calculate the switching
losses in the MOSFET:
P
SW
=
1
⎞
IL
AVG
×
VLED
2
×
C
GD
×
F
SW
⎛
1
×⎜
+
⎟
2
⎝
I
GON
I
GOFF
⎠
Evaluates: MAX16809
where VLED
PP
is the peak-to-peak ripple in the LED
supply voltage. The value of the calculated output
capacitance will be much lower than what is actually
necessary for feedback loop compensation. See the
Feedback Compensation
section to calculate the out-
put capacitance based on the compensation require-
ments.
Calculate the input capacitor C
IN
(parallel combination
of C12, C13, C14, and C5) using the following equation:
IL
PP
C
IN
=
8
×
F
SW
×
VIN
PP
where VIN
PP
is the peak-to-peak input ripple voltage.
This equation assumes that input capacitors supply
most of the input ripple current.
Selection of Power Semiconductors
The switching MOSFET (Q2) should have a voltage rat-
ing sufficient to withstand the maximum output voltage,
together with the diode drop of D2, and any possible
overshoot due to ringing caused by parasitic induc-
tances and capacitances. Use a MOSFET with voltage
rating higher than that calculated by the following
equation:
V
DS
=
(
VLED
+
V
D
)
×1
.3
The factor of 1.3 provides a 30% safety margin.
where I
GON
and I
GOFF
are the gate currents of the
MOSFET (with V
GS
equal to the threshold voltage)
when it is turned on and turned off, respectively, and
C
GD
is the gate-to-drain MOSFET capacitance. Choose
a MOSFET that has a higher power rating than that cal-
culated by the following equation when the MOSFET
case temperature is at +70°C:
P
TOT
=
P
COND
+
P
SW
The MAX16809 EV kit uses a Schottky diode as the
boost-converter rectifier (D2). A Schottky rectifier diode
produces less forward drop and puts the least burden
on the MOSFET during reverse recovery. If a diode with
considerable reverse-recovery time is used, it should be
considered in the MOSFET switching-loss calculation.
The Schottky diode selected should have a voltage rat-
ing 20% above the maximum boost-converter output
voltage. The current rating of the diode should be
greater than I
D
in the following equation:
⎛
IL
AVG2
I
D
= ⎜
⎜
1
−
D
MAX
⎝
⎞
⎟ ×
1.2
⎟
⎠
5
_______________________________________________________________________________________
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