Maxim MAX16824 High-voltage, three-channel linear high-brightness led driver Datasheet

19-1107; Rev 0; 11/07
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
The MAX16824/MAX16825 three-channel LED drivers
operate over a 6.5V to 28V input voltage range. These
devices provide three open-drain constant-current-sinking outputs that are rated to 36V and deliver up to
150mA of current to each string of high-brightness LEDs
(HB LEDs). The current at each output is programmable
by means of an external current-sense resistor. The
MAX16824 features three PWM inputs that control the
duty cycle of the output current, allowing a wide LED
dimming range to be implemented. The PWM inputs
also function as on/off control for each corresponding
output. The MAX16825 offers a 2Mbps, 4-wire serial
interface, a 3-bit shift register, and a 3-bit transparent
latch. The serial interface allows a microcontroller to
configure the output channels using four inputs (DIN,
CLK, LE, OE) and a data output (DOUT). DOUT allows
multiple drivers to be cascaded and operated together.
The MAX16824/MAX16825’s on-board pass elements
minimize the need for external components, while at the
same time, providing ±5% LED current accuracy.
Additional features include a +5V (±5%) regulated output
with 4mA output current capability and thermal protection.
The MAX16824/MAX16825 are available in a thermally
enhanced 16-pin TSSOP-EP package and specified over
the -40°C to +85°C temperature range.
Features
♦ 6.5V to 28V Operating Range
♦ Outputs Connected to 36V Supply for Long LED
Strings
♦ Three 36V-Rated Output Channels with
Independently Adjustable LED Current
♦ 150mA Output Current Per Channel
♦ ±5% LED Current Accuracy
♦ PWM Dimming
Three Independent Dimming Control Inputs
(MAX16824)
4-Wire Serial Interface LED Current Chopping
(MAX16825)
♦ +5V (±5%) Regulated Output with 4mA Source
Capability
♦ Fast Transient Dimming Response
♦ 200mV Current-Sense Reference Reduces Power
Loss
♦ Thermal Shutdown
♦ -40°C to +85°C Operating Temperature Range
♦ Thermally Enhanced, 16-Pin TSSOP Exposed
Paddle Package
Ordering Information
Applications
PART
Industrial Lighting
Architectural and Decorative Lighting
Mood Lighting
Indoor and Outdoor LED Video Displays
Automotive Lighting
LCD Display Backlighting
PIN
PACKAGE
TEMP RANGE
PKG
CODE
MAX16824EUE+
-40°C to +85°C
16 TSSOP-EP*
U16E-3
MAX16825EUE+
-40°C to +85°C
16 TSSOP-EP*
U16E-3
+Denotes a lead-free package.
*EP = Exposed paddle.
Pin Configurations appear at end of data sheet.
Typical Operating Circuits
UP TO 36V
VIN
UP TO 36V
VIN
CIN
CIN
3
3
7
8
9
4
IN
1
OUT2
16
7
PWM2
OUT3
CS1
REG
GND
CS2
CS3
CLK
12
9
OE
4
15
RCS1
13
RCS2
RCS3
CREG
11
1
OUT2
16
12
OUT3
LE
2
OUT1
DIN
8
MICROCONTROLLER
PWM3
IN
MAX16825
6
PWM1 MAX16824
CREG
11
OUT1
CS1
CS2
2
15
REG
CS3
RCS1
13
RCS2
GND
RCS3
________________________________________________________________ Maxim Integrated Products
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.
1
MAX16824/MAX16825
General Description
MAX16824/MAX16825
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
ABSOLUTE MAXIMUM RATINGS
IN to GND ...............................................................-0.3V to +30V
OUT1, OUT2, OUT3 to GND ..................................-0.3V to +40V
CS1, CS2, CS3, REG to GND...................................-0.3V to +6V
PWM1, PWM2, PWM3 to GND .................................-0.3V to +6V
DIN, CLK, LE, OE, DOUT to GND ............................-0.3V to +6V
Maximum Current into Any Pin
(except OUT1, OUT2, OUT3) ........................................±20mA
Maximum Current into OUT1, OUT2, OUT3......................160mA
Continuous Power Dissipation (TA = +70°C)
16-Pin TSSOP-EP (derate 18.9mW/°C above +70°C)....1500mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = 12V, CREG = 1µF to GND, IREG = 0, RCS_ = 2Ω from CS_ to GND, TJ = TA = -40°C to +85°C, unless otherwise noted. Typical
values are at TJ = TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
Supply Voltage Range
CONDITIONS
VIN
GND Current
IGND
LED Current-Sense Accuracy
(Note 2)
ΔVDO
Dropout Voltage (Note 3)
Output Current Slew Rate
Output Current Leakage
ILEAK
MIN
TYP
6.5
IOUT1 = IOUT2 = IOUT3 =100mA
5
MAX
UNITS
28.0
V
10
mA
10mA < IOUT_ < 100mA,
0°C ≤ TJ ≤ 85°C
5
10mA < IOUT_ < 100mA,
-40°C ≤ TJ ≤ 85°C
7
%
IOUT_ = 100mA (current pulsed)
0.75
1.5
IOUT_ = 150mA (current pulsed)
1.2
2.25
Current rising, VOUT = 4V
100
PWM1 = PWM2 = PWM3 = 0V
V
mA/µs
1
µA
CURRENT SENSE
Regulated CS_ Voltage
VCS_
VCS1 = VCS2 = VCS3 , 0°C ≤ TJ ≤ +85°C
190
200
210
VCS1 = VCS2 = VCS3 , -40°C ≤ TJ ≤ +85°C
186
200
214
mV
OVERTEMPERATURE PROTECTION
Thermal Shutdown Temperature
165
°C
Thermal Shutdown Hysteresis
23
°C
+5V REGULATOR (REG)
Output Voltage
VREG
IREG = 0mA (Note 4)
IREG
4.75V < VREG
4
VREG = 0V (Note 5)
15
REG Output Current
REG Short-Circuit Current
IREGSC
4.75
5
5.25
V
40
90
mA
1
µA
mA
LOGIC INPUT (PWM1, PWM2, PWM3)
PWM_ Input Bias Current
IPWM
PWM_ Input-Voltage High
VIH
PWM_ Input-Voltage Low
VIL
VPWM1 = VPWM2 = VPWM3 = 5V
4
V
0.6
V
PWM_ Turn-On Delay
50% of VPWM_ to 50% of ΔVOUT_
475
ns
PWM_ Turn-Off Delay
50% of VPWM_ to 50% of ΔVOUT_
150
ns
2
_______________________________________________________________________________________
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
(VIN = 12V, CREG = 1µF to GND, IREG = 0, RCS_ = 2Ω from CS_ to GND, TJ = TA = -40°C to +85°C, unless otherwise noted. Typical
values are at TJ = TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
Turn-On Time
tR
Turn-Off Time
tF
MIN
TYP
MAX
UNITS
PWM_ rising time, tR, is measured from 20%
to 80% of IOUT
1
µs
PWM_ falling time, tF, is measured from
80% to 20% of IOUT
1
µs
1
µA
OUTPUTS (OUT1, OUT2, OUT3)
SPI INTERFACE (CLK, LE, OE, DIN, DOUT) (Figures 3 and 4)
DIN, CLK, LE, OE Input Bias
Current
DIN = CLK = LE = OE = 0 or 5V
DIN, CLK, LE, OE Input-Voltage
High
VIH
DIN, CLK, LE, OE Input-Voltage
Low
VIL
CLK Clock Period
tCP
50% of CLK rising to 50% of next CLK
rising, Figure 3
50
ns
CLK Pulse-Width High
tCH
50% of CLK rising to 50% of CLK falling,
Figure 3
24
ns
CLK Pulse-Width Low
tCL
50% of CLK falling to 50% of CLK rising,
Figure 3
24
ns
DIN Setup Time
tDS
50% of DIN rising to 50% of CLK rising,
Figure 3
5
ns
DIN Hold Time
tDH
50% of CLK rising to 50% of DIN falling,
Figure 3
10
ns
DOUT Propagation Delay
tDO
50% of CLK rising to 50% of DOUT rising/
falling, Figure 3
5
ns
2.2
V
0.5
DOUT Rise/Fall Time
tDR/tDF
CDOUT = 10pF, 10% to 90% of DOUT
rising/falling edge (Note 6)
DOUT Voltage High
VDOH
ISOURCE = 4mA
DOUT Voltage Low
VDOL
ISINK = 4mA
15
4.5
V
ns
V
0.5
V
LE Pulse-Width High
tLW
50% of LE rising to 50% of LE falling,
Figure 3
20
ns
LE Setup Time
tLS
50% of CLK rising to 50% of LE rising,
Figure 3
15
ns
LE Rising to OUT_ Rising Delay
tLRR
50% of LE rising to 50% of OUT_ rising,
Figure 4
150
ns
LE Rising to OUT_ Falling Delay
tLRF
50% of LE rising to 50% of OUT_ falling,
Figure 4
475
ns
_______________________________________________________________________________________
3
MAX16824/MAX16825
ELECTRICAL CHARACTERISTICS (continued)
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 12V, CREG = 1µF to GND, IREG = 0, RCS_ = 2Ω from CS_ to GND, TJ = TA = -40°C to +85°C, unless otherwise noted. Typical
values are at TJ = TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
MAX
UNITS
CLK Rising to OUT_ Rising Delay
tCRR
50% of CLK rising to 50% of OUT_ rising,
Figure 4
150
ns
CLK Rising to OUT_ Falling Delay
tCRF
50% of CLK rising to 50% of OUT_ falling,
Figure 4
475
ns
OE Rising to OUT_ Rising Delay
tOEH
50% of OE rising to 50% of OUT_ rising,
Figure 3
150
ns
OE Falling to OUT_ Falling Delay
tOEL
50% of OE falling to 50% of OUT_ falling,
Figure 3
475
ns
CONDITIONS
MIN
TYP
Note 1: All devices are 100% production tested at TJ = +25°C and TJ = +85°C. Limits to -40°C are guaranteed by design.
Note 2: This specification does not include sense resistor tolerance and ground error.
Note 3: Dropout is measured as follows: RSC_ = 1.21Ω from CS_ to GND. Force 100mA into OUT_ and measure the dropout voltage
from OUT_ to CS_. DVDO = (ΔOUT_ - VCS_).
Note 4: OUT’s current regulation varies with load across REG (see the Typical Operating Characteristics).
Note 5: Overtemperature protection does not function if the output of the 5V reference (REG) is shorted to ground.
Note 6: Guaranteed by design, not production tested.
Typical Operating Characteristics
(VIN = 12V, CREG = 1µF to GND, IREG = 0, RCS_ = 2Ω from CS_ to GND, TA = +25°C, unless otherwise noted. Typical values are at
TA = +25°C.)
0.202
0.7
VCS_ (V)
0.6
0.5
0.197
0.4
0.192
0.3
0.2
0.1
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
170
ILOAD = 150mA
150
130
110
ILOAD = 100mA
90
70
50
0.187
30
0.182
-10
10
ILOAD = 100mA
0
4
0.207
190
OUTPUT CURRENT (mA)
0.8
MAX16824 toc02
MAX16824toc01
0.9
OUTPUT CURRENT vs. INPUT VOLTAGE
CS_ VOLTAGE vs. OUTPUT CURRENT
MAX16824 toc03
DROPOUT VOLTAGE vs. TEMPERATURE
1.0
DROPOUT VOLTAGE (V)
MAX16824/MAX16825
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
0
15 30 45 60 75 90 105 120 135 150
OUTPUT CURRENT (mA)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
VIN (V)
_______________________________________________________________________________________
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
SUPPLY CURRENT
vs. TEMPERATURE
120
IOUT = 95mA
100
80
60
40
5.04
2.85
ILOAD = 0
5.02
5.00
4.98
2.65
4.96
ILOAD = 4mA
ILOAD = 1mA
4.94
4.92
VPWM = VPWM = VPWM = 0
2.25
4.90
-40 -25 -10 5 20 35 50 65 80 95 110 125
-40 -25 -10 5 20 35 50 65 80 95 110 125
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT VOLTAGE vs. INPUT VOLTAGE
LED CURRENT FALL TIME
CS_ VOLTAGE vs. REG OUTPUT CURRENT
MAX16824 toc09
5.000
MAX16824 toc07
0.200
0.199
0.198
0.197
0.196
0.195
0.194
0.193
0.192
0.191
0.190
0.189
0.188
0.187
0.186
0.185
0.184
0.183
0.182
4.995
IREG = 0
4.990
ILOAD = 100mA
VREG (V)
VCS_ (V)
VIN = 6.5V
2.45
0
5.06
3.05
IOUT = 10mA
20
5.08
MAX16824 toc08
OUTPUT CURRENT (mA)
140
VIN = 28V
3.25
SUPPLY CURRENT (mA)
IOUT = 150mA
160
5.10
VREG (V)
180
OUTPUT VOLTAGE vs. TEMPERATURE
3.45
MAX16824 toc06
MAX16824toc04
200
MAX16824 toc05
OUTPUT CURRENT vs. TEMPERATURE
ILED = 150mA
VIN = 12V
PULSED AT 200Hz
(50% DUTY CYCLE)
VPWM_
2V/div
4.985
4.980
IREG = 1mA
0V
IREG = 4mA
IOUT_
100mA/div
4.975
ILOAD = 150mA
4.970
4.965
0A
4.960
0
1
2
3
4
5
6
7
8
9
0
10
4
8
IREG (mA)
12
16
20
24
28
2μs/div
VIN (V)
330Hz DIMMED OPERATION
LED CURRENT RISE TIME
MAX16824 toc11
MAX16824 toc10
VPWM_
2V/div
ILOAD = 150mA
VIN = 12V
PWM_ PULSED
AT 330Hz
(1% DUTY CYCLE)
0V
0V
ILED = 150mA
VIN = 12V
PULSED AT 200Hz
(50% DUTY CYCLE)
2μs/div
VPWM_
2V/div
IOUT_
100mA/div
IOUT_
100mA/div
0A
0A
20μs/div
_______________________________________________________________________________________
5
MAX16824/MAX16825
Typical Operating Characteristics (continued)
(VIN = 12V, CREG = 1µF to GND, IREG = 0, RCS_ = 2Ω from CS_ to GND, TA = +25°C, unless otherwise noted. Typical values are at
TA = +25°C.)
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
MAX16824/MAX16825
Pin Description
PIN
6
NAME
FUNCTION
MAX16824
MAX16825
1
1
OUT1
Channel 1 LED Driver Output. OUT1 is an open-drain, constant-current-sinking output
rated to 36V.
2
2
CS1
Channel 1 Sense Amplifier Negative Input. Connect a current-sense resistor between
CS1 and GND to program the output current level for channel 1.
3
3
IN
Positive Input Supply. Bypass with a 0.1µF (min) capacitor to GND.
4
4
REG
+5V-Regulated Output. Connect a 1µF capacitor from REG to GND.
5, 6, 10, 14
5, 14
N.C.
No Connection. Must be left unconnected.
7
—
PWM1
Dimming Input 1. PWM1 is a dimming input for channel 1. A logic-low turns off OUT1 and
a logic-high turns on OUT1.
8
—
PWM2
Dimming Input 2. PWM2 is a dimming input for channel 2. A logic-low turns off OUT2 and
a logic-high turns on OUT2.
9
—
PWM3
Dimming Input 3. PWM3 is a dimming input for channel 3. A logic-low turns off OUT3 and
a logic-high turns on OUT3.
11
11
GND
Ground
12
12
OUT3
Channel 3 LED Driver Output. OUT3 is an open-drain, constant-current-sinking output
rated to 36V.
13
13
CS3
Channel 3 Sense Amplifier Negative Input. Connect a current-sense resistor between
CS3 and GND to program the output current level for channel 3.
15
15
CS2
Channel 2 Sense Amplifier Negative Input. Connect a current-sense resistor between
CS2 and GND to program the output current level for channel 2.
16
16
OUT2
Channel 2 LED Driver Output. OUT2 is an open-drain, constant-current-sinking output
rated to 36V.
—
7
DIN
Serial-Data Input. Data is loaded into the internal 3-bit shift register on the rising edge of
CLK.
—
8
LE
Latch-Enable Input. Data loaded transparently from the internal shift register to the
output latch while LE is high. Data is latched into the output latch on the LE’s falling edge
and retained while LE is low.
—
9
OE
Output Enable Input. Drive OE high to place all outputs into a high-impedance mode
without altering the contents of the output latches. Drive OE low to force all outputs to
follow the state of the output latches.
—
10
DOUT
—
6
CLK
—
—
EP
Serial-Data Output. Data is clocked out of the internal 3-bit shift register to DOUT on the
rising edge of CLK. DOUT is a replica of the shift register’s last bit.
Clock Input
Exposed Paddle. Connect EP to a large-area ground plane for effective power
dissipation. Do not use as the IC ground connection.
_______________________________________________________________________________________
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
MAX16824/MAX16825
OUT1
200mV
IN
BANDGAP AND
5V REGULATOR
REG
CS1
OUT2
THERMAL
SHUTDOWN
CS2
OUT3
PWM1
PWM2
PWM
CONTROL AND
LOGIC
CS3
PWM3
MAX16824
GND
Figure 1. Internal Block Diagram (MAX16824)
Detailed Description
The MAX16824/MAX16825 are three-channel LED drivers that operate from a 6.5V to 28V input voltage
range. These devices provide three independent opendrain, constant-current-sinking outputs rated to 36V
and deliver up to 150mA of current to each HB LED
string. The current in each channel is programmable
using an external current-sense resistor in series with
each internal power MOSFET’s source. The MAX16824
features three separate PWM inputs that allow a wide
range of independent dimming level at each of the
three outputs. The PWM inputs also function as on/off
control inputs for each corresponding output (Figure 1).
The MAX16825 includes a 2Mbps, 4-wire serial interface to control the state of each output (Figure 2).
The 4-wire serial interface comprises a 3-bit shift register and a 3-bit transparent latch. The shift register is
updated using a clock input CLK and a data input DIN.
DOUT is the last bit of the shift register. This feature
allows multiple drivers to be cascaded and operated
together. The latch is transparent from the shift register
outputs to the LED output when LE is high while it latches the shift register state on the falling edge of LE. The
output-enable input OE allows simultaneous enabling
or disabling of all three outputs.
_______________________________________________________________________________________
7
MAX16824/MAX16825
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
OUT1
IN
200mV
BANDGAP AND
5V REGULATOR
REG
CS1
OUT2
THERMAL
SHUTDOWN
CS2
OUT3
DIN
CS3
CLK
DOUT
LE
OE
SHIFT
REGISTER
SHIFT
REGISTER
SHIFT
REGISTER
LATCH
LATCH
LATCH
LOGIC
MAX16825
GND
Figure 2. Internal Block Diagram (MAX16825)
8
_______________________________________________________________________________________
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
+5V Regulator (REG)
The MAX16824/MAX16825 include a fixed +5V output
regulator that delivers up to 4mA of load current for
auxiliary low power applications throughout the 6.5V to
28V input voltage range. Connect a 1µF compensation
capacitor from REG to ground.
Thermal Protection
The MAX16824/MAX16825 enter a thermal shutdown
mode in the event of overheating. When the junction
temperature exceeds TJ = +165°C, the internal thermal
protection circuit turns off the series pass elements.
The MAX16824/MAX16825 recover from thermal shutdown mode when the junction temperature drops by
23°C. The thermal protection does not operate if the
regulator (REG) is in a short-circuit condition.
4-Wire Serial Interface (MAX16825)
The MAX16825 features a 4-wire serial interface (DIN,
CLK, LE, OE) and a data output (DOUT) that allows the
use of a microcontroller to write brightness data to the
MAX16825. The serial-interface data word length is 3
bits (D0, D1, D2). The functions of the interface inputs
are as follows: DIN is the serial-data input, which must
be stable when it is sampled by the MAX16825 on the
rising edge of CLK. Data shifts in with the MSB first.
This means that data bit D2 is clocked in first, followed
by 2 more data bits (D1 and finishing with the LSB D0).
CLK is the serial-clock input, which shifts data at DIN
into the MAX16825’s 3-bit shift register on the rising
edge. LE is the latch-enable input that allows the transfer of data from the MAX16825’s 3-bit shift register to its
3-bit latch when LE is high (transparent latch) and
latches the data on the falling edge of LE (Figure 4).
Output enable (OE) provides simultaneous control of
the output drivers. Driving OE high places outputs
OUT1, OUT2, and OUT3 into a high-impedance mode
without altering the contents of the output latches.
Driving OE low allows outputs OUT1, OUT2, and OUT3
to follow the state of the output latches.
OE is independent of the operation of the serial interface. Data can be shifted into the serial-interface shift
register and latched regardless of the state of OE.
DOUT is the serial-data output that shifts data out from
the MAX16825’s 3-bit shift register on the rising edge of
CLK. Data at DIN propagates through the shift register
and appears at DOUT three clock cycles later.
Applications Information
Programming the LED Current
The MAX16824/MAX16825 use sense resistors to set the
output current in each channel. To set the LED current
for a particular channel, connect a sense resistor across
the corresponding current-sense input (CS_) and GND.
For better performance, connect the low side of the current-sense resistors to the IC’s ground terminal and the
high side to the CS_ terminal with short traces. The value
of the sense resistor for a given desired current is calculated with the following equation:
RCS _ (Ω) =
VCS _ (V)
IOUT _ (A)
where V CS_ is 200mV and I OUT_ is I LED (see the
Electrical Characteristics table).
Input Voltage Considerations
For proper operation, the minimum input voltage must
always be:
VIN(MIN) ≥ VCS _ + VFT(MAX) + ΔVDO
where VCS_ is the voltage drop across the sense resistor RCS_, VFT(MAX) is the total forward voltage of all
series connected LEDs and ΔV DO is the maximum
dropout voltage of the regulator. The minimum operating voltage of the device is 6.5V. If the device is operated below 6.5V, the output current may not meet the full
regulation specification (see the Typical Operating
Characteristics).
Pulse-Width Dimming (MAX16824)
The MAX16824 includes pulsed-width current dimming
inputs (PWM_) to control the LED brightness. An application of up to 5kHz signal or less is recommended at
PWM_ input for proper operation. PWM_ also functions
as an active-high enable input for each output channel.
A logic-low at PWM_ turns off OUT_ and a logic-high
turns on OUT_.
_______________________________________________________________________________________
9
MAX16824/MAX16825
On-board pass elements minimize the need for external
components while providing ±5% LED current accuracy. Additional features include a +5V (±5%) regulated
output with 4mA output current capability and thermal
protection.
The MAX16824/MAX16825 use a feedback loop to linearly control the current at each output. The voltage
across each sense resistor is regulated to 200mV by
the internal feedback loop. The output current is set by
selecting the value of RCS.
MAX16824/MAX16825
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
50%
tLW
50%
LE
tCH
tCL
50%
50%
50%
50%
tLS
tCP
CLK
tDH
tDS
DIN
50%
DO
D1
50%
D2
tDO
50%
DOUT
DO
tOEW
50%
50%
OE
tOEH
tOEL
80%
OUT_
20%
tF
tR
Figure 3. 4-Wire Serial-Interface Timing Diagram
Pulse-Width Dimming (MAX16825)
The MAX16825 provides three methods of pulsed-width
current dimming.
One method of pulse dimming the output channels is to
drive OE low while latching a different set of three bits
10
data. Holding OE low allows the output channels to follow the state of the output latches. The duty cycle
depends on LE’s frequency. All output channels are
affected at the same time.
______________________________________________________________________________________
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
MAX16824/MAX16825
50%
LE
tLRF
OUT_
50%
50%
LE
tLRR
50%
OUT_
50%
CLK
tCRF
OUT_
50%
50%
CLK
tCRR
50%
OUT_
Figure 4. LE and CLK to OUT_ Timing
______________________________________________________________________________________
11
MAX16824/MAX16825
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
Another method of pulse dimming the outputs is to hold
LE high and drive OE with a PWM signal. Because the
input bits are always latched, the serial input constantly
refreshes the register. The control bits must be carefully
selected to dim the outputs properly.
A third method is to hold both LE and OE in the
enabled state. This allows the data bits to directly control the output channels, and hence, pulse dim the output current. Make sure that the clock frequency does
not exceed the maximum rate at which the device can
change the state of the output channels.
Power Dissipation
The power dissipation (P D ) of the MAX16824/
MAX16825 is determined from the following equation:
PD = (VIN × IIN ) + (VINL − VLED1 − VCS1) × (ILED1 × DUTY1)
+ (VINL − VLED2 − VCS2 ) × (ILED2 × DUTY2)
The worst-case power dissipation occurs when the
drop across each internal MOSFET is at its maximum
with all three channels delivering the maximum allowable output current. The maximum drop across the
internal MOSFETs is determined by:
VINL - VLED_ - VCS_ when VLED_ is at its minimum.
Higher ambient temperature increases the thermal stress
even further due to the reduction in voltage drop across
the LEDs. The MAX16824/MAX16825 thermal specifications are given according to the JEDEC-51 guidelines.
Good mechanical/thermal design practices must be
applied to help maintain the device junction temperature
below the absolute maximum ratings at all times.
Chip Information
PROCESS: BiCMOS-DMOS
+ (VINL − VLED3 − VCS3 ) × (ILED3 × DUTY3)
where:
VIN = supply voltage
VINL = supply Voltage to the LED strings
IIN = supply current
VLED_ = total forward voltage for one LED string
ILED_ = LED current
VCS = 200mV drop across RCS_
DUTY = PWM_ duty cycle
12
______________________________________________________________________________________
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
TOP VIEW
TOP VIEW
OUT1 1
+
CS1 2
16 OUT2
OUT1 1
15 CS2
CS1 2
+
16 OUT2
15 CS2
14 N.C.
14 N.C.
IN 3
REG 4
13 CS3
REG 4
13 CS3
N.C. 5
12 OUT3
N.C. 5
12 OUT3
IN 3
MAX16825
MAX16824
N.C. 6
11 GND
CLK 6
11 GND
PWM1 7
10 N.C.
DIN 7
10 DOUT
PWM2 8
9 PWM3
TSSOP-EP
9 OE
LE 8
TSSOP-EP
______________________________________________________________________________________
13
MAX16824/MAX16825
Pin Configurations
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
AA AA
TSSOP 4.4mm BODY.EPS
MAX16824/MAX16825
High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products
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is a registered trademark of Maxim Integrated Products, Inc.