Maxim MAX16814AGP/VY+ Integrated, 4-channel, high-brightness led driver with high-voltage dc-dc controller Datasheet

EVALUATION KIT AVAILABLE
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
General Description
Features
The MAX16814 high-efficiency, high-brightness LED (HB
LED) driver provides up to four integrated LED currentsink channels. An integrated current-mode switching
DC-DC controller drives a DC-DC converter that provides the necessary voltage to multiple strings of HB
LEDs. The MAX16814 accepts a wide 4.75V to 40V input
voltage range and withstands direct automotive loaddump events. The wide input range allows powering HB
LEDs for small to medium-sized LCD displays in automotive and general lighting applications.
S 4-Channel Linear LED Current Sinks with Internal
MOSFETs
Full-Scale LED Current Adjustable from 20mA
to 150mA
Drives One to Four LED Strings
An internal current-mode switching DC-DC controller
supports the boost, coupled-inductor boost-buck, or
SEPIC topologies and operates in an adjustable frequency range between 200kHz and 2MHz. It can also be
used for single-inductor boost-buck topology in conjunction with the MAX15054 and an additional MOSFET. The
current-mode control with programmable slope compensation provides fast response and simplifies loop
compensation. The MAX16814 also features an adaptive
output-voltage control scheme that minimizes the power
dissipation in the LED current-sink paths.
The MAX16814 consists of four identical linear current
source channels to drive four strings of HB LEDs. The
channel current is adjustable from 20mA to 150mA with
an accuracy of ±3% using an external resistor. The
external resistor sets all 4-channel currents to the same
value. The device allows connecting multiple channels
in parallel to achieve higher current per LED string. The
MAX16814 also features pulsed dimming control, on all
four channels through a logic input (DIM). In addition,the
MAX16814A_ _ and MAX16814U_ _ include a unique
feature that allows a very short minimum pulse width as
low as 1µs.
The MAX16814 includes an output overvoltage, openLED detection and protection, programmable shorted
LED detection and protection, and overtemperature protection. The device operates over the -40NC to +125NC
automotive temperature range. The MAX16814 is available in 6.5mm x 4.4mm, 20-pin TSSOP, 4mm x 4mm,
20-pin TQFN and QFND packages.
Applications
Automotive Displays LED Backlights
Automotive RCL, DRL, Front Position, and Fog
Lights
LCD TV and Desktop Display LED Backlights
Architectural, Industrial, and Ambient Lighting
S Boost, SEPIC, or Coupled-Inductor Boost-Buck
Current-Mode DC-DC Controller
200kHz to 2MHz Programmable Switching
Frequency
External Switching Frequency Synchronization
S Adaptive Output-Voltage Optimization to Minimize
Power Dissipation
S 4.75V to 40V Operating Input Voltage Range
S Less than 40µA Shutdown Current
S 5000:1 PWM Dimming at 200Hz (MAX16814A _ _
and MAX16814U_ _ Only)
S Open-Drain Fault Indicator Output
S Open-LED and LED Short Detection and
Protection
S Overtemperature Protection
S Thermally Enhanced, 20-Pin TQFN, QFND, and
TSSOP Packages
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX16814ATP+
-40°C to +125°C
20 TQFN-EP*
MAX16814ATP/V+
-40°C to +125°C
20 TQFN-EP*
MAX16814AGP/VY+ -40°C to +125°C
20 QFND-EP* (SW)
MAX16814AUP+
-40°C to +125°C
20 TSSOP-EP*
MAX16814AUP/V+
-40°C to +125°C
20 TSSOP-EP*
MAX16814BETP+
-40°C to +85°C
20 TQFN-EP*
MAX16814BEUP+
-40°C to +85°C
20 TSSOP-EP*
MAX16814BUTP+
0°C to +85°C
20 TQFN-EP*
MAX16814BUUP+
0°C to +85°C
20 TSSOP-EP*
MAX16814UTP+
0°C to +85°C
20 TQFN-EP*
MAX16814UUP+
0°C to +85°C
20 TSSOP-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
/V Denotes an automotive qualified part, (SW) = side wettable.
Typical Operating Circuit and Pin Configurations appear at
end of data sheet.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
19-4722; Rev 7; 1/13
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
ABSOLUTE MAXIMUM RATINGS
IN to SGND.............................................................-0.3V to +45V
EN to SGND................................................-0.3V to (VIN + 0.3V)
PGND to SGND.....................................................-0.3V to +0.3V
LEDGND to SGND................................................-0.3V to +0.3V
OUT_ to LEDGND..................................................-0.3V to +45V
VCC to SGND........... -0.3V to the lower of (VIN + 0.3V) and +6V
DRV, FLT, DIM, RSDT, OVP to SGND......................-0.3V to +6V
CS, RT, COMP, SETI to SGND.................. -0.3V to (VCC + 0.3V)
NDRV to PGND........................................-0.3V to (VDRV + 0.3V)
NDRV Peak Current (< 100ns).............................................. Q3A
NDRV Continuous Current............................................. Q100mA
OUT_ Continuous Current.............................................. Q175mA
VCC Short-Circuit Duration.........................................Continuous
Continuous Power Dissipation (TA = +70NC) (Note 1)
20-Pin TQFN (derate 25.6mW/NC above +70NC)........2051mW
20-Pin Side-Wettable QFND
(derate 26.5mW/NC above +70NC).............................2050mW
26-Pin TSSOP (derate 26.5mW/NC above +70NC)......2122mW
Operating Temperature Range
MAX16814A_ _............................................... -40NC to +125NC
MAX16814BE_ _.............................................. -40NC to +85NC
MAX16814U_ _and MAX16814BU_ _.................0NC to +85NC
Junction Temperature......................................................+150NC
Storage Temperature Range............................. -65NC to +150NC
Lead Temperature (soldering, 10s).................................+300NC
Soldering Temperature (reflow).......................................+260NC
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.
PACKAGE THERMAL CHARACTERISTICS (Note 1)
20 TQFN/QFND
Junction-to-Ambient Thermal Resistance (BJA)......... +39NC/W
Junction-to-Case Thermal Resistance (BJC)................ +6NC/W
20 TSSOP
Junction-to-Ambient Thermal Resistance (BJA)...... +37.7NC/W
Junction-to-Case Thermal Resistance (BJC)............. +2.0NC/W
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to http://www.maximintegrated.com/thermal-tutorial.
ELECTRICAL CHARACTERISTICS
(VIN = VEN = 12V, RRT = 12.25kI, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VRSDT = VDIM
= VCC, VOVP = VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40NC to +125NC for MAX16814A_ _, TA = -40NC to +85NC for
MAX16814BE_ _, and TA = TJ = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at
TA = +25NC.) (Note 2)
PARAMETER
Operating Voltage Range
Active Supply Current
SYMBOL
CONDITIONS
VIN
IIN
MIN
TYP
4.75
MAX
UNITS
40
V
MAX16814A_ _ and MAX16814U_ _
2.5
5
MAX16814B_ _ _ only
2.75
5.5
Standby Supply Current
VEN = 0V
IN Undervoltage Lockout
VIN rising
3.975
IN UVLO Hysteresis
15
40
4.3
4.625
170
mA
μA
V
mV
VCC REGULATOR
Regulator Output Voltage
VCC
Dropout Voltage
6.5V < VIN < 10V, 1mA < ILOAD < 50mA
10V < VIN < 40V, 1mA < ILOAD < 10mA
4.75
VIN - VCC, VIN = 4.75V, ILOAD = 50mA
VCC shorted to SGND
Short-Circuit Current Limit
VCC Undervoltage Lockout
Threshold
VCC rising
VCC UVLO Hysteresis
5.0
5.25
V
200
500
mV
100
mA
4
V
100
mV
RT OSCILLATOR
Switching Frequency Range
2 fSW
200
2000
kHz
Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VEN = 12V, RRT = 12.25kI, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VRSDT = VDIM
= VCC, VOVP = VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40NC to +125NC for MAX16814A_ _, TA = -40NC to +85NC for
MAX16814BE_ _, and TA = TJ = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at
TA = +25NC.) (Note 2)
PARAMETER
SYMBOL
Maximum Duty Cycle
Oscillator Frequency Accuracy
CONDITIONS
MIN
TYP
MAX
fSW = 200kHz to 600kHz, MAX16814A_ _
and MAX16814U_ _
85
89
93
fSW = 600kHz to 2000kHz, MAX16814A_ _
and MAX16814U_ _
82
86
90
fSW = 200kHz to 600kHz, MAX16814B_ _
90
94
98
fSW = 600kHz to 2000kHz, MAX16814B _ _ _
fSW = 200kHz to 2MHz, MAX16814A_ _
and MAX16814U_ _
fSW = 200kHz to 2MHz, MAX16814B_ _ _
86
90
94
Sync Rising Threshold
Minimum Sync Frequency
PWM COMPARATOR
PWM Comparator Leading-Edge
Blanking Time
PWM to NDRV Propagation Delay
-7.5
+7.5
-7
+7
UNITS
%
%
4
V
1.1fSW
Hz
Including leading-edge blanking time
60
ns
90
ns
SLOPE COMPENSATION
Current ramp added to the CS input,
MAX16814A_ _ only
Current ramp added to the CS input,
MAX16814U_ _ and MAX16814B_ _ _
Peak Slope Compensation
Current Ramp Magnitude
44
49
54
45
50
55
396
416
437
μA x fSW
CS LIMIT COMPARATOR
Current-Limit Threshold
CS Limit Comparator to NDRV
Propagation Delay
ERROR AMPLIFIER
(Note 3)
10mV overdrive, excluding leading-edge
blanking time
OUT_ Regulation Voltage
Transconductance
gM
340
mV
10
ns
1
V
600
880
75
μS
No-Load Gain
(Note 4)
dB
COMP Sink Current
VOUT_ = 5V, VCOMP = 2.5V
160
375
800
μA
COMP Source Current
VOUT_ = 0V, VCOMP = 2.5V
160
375
800
μA
MOSFET DRIVER
ISINK = 100mA (nMOS)
0.9
ISOURCE = 100mA (pMOS)
1.1
Peak Sink Current
VNDRV = 5V
2.0
Peak Source Current
VNDRV = 0V
2.0
A
Rise Time
CLOAD = 1nF
6
ns
Fall Time
CLOAD = 1nF
6
ns
NDRV On-Resistance
ω
A
LED CURRENT SOURCES
OUT_ Current-Sink Range
Channel-to-Channel Matching
Maxim Integrated
VOUT_ = VREF
IOUT_ = 100mA
IOUT_ = 100mA, all channels on
20
150
±2
±1.5
mA
%
3
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VEN = 12V, RRT = 12.25kI, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VRSDT = VDIM
= VCC, VOVP = VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40NC to +125NC for MAX16814A_ _, TA = -40NC to +85NC for
MAX16814BE_ _, and TA = TJ = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at
TA = +25NC.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
IOUT_ =
100mA
MIN
TYP
±3
TA = -40°C to +125°C,
MAX16814A_ _ only
±5
TA = +25°C, MAX16814U_ _ and
MAX16814B_ _ _
Output Current Accuracy
±2.75
IOUT_ =
TA = 0°C to +85°C, MAX16814U_
50mA to
_ and MAX16814BU _ _
150mA
TA = -40°C to +85°C for
MAX16814BE _ _
OUT_ Leakage Current
MAX
TA = +125°C, MAX16814A_ _
only
UNITS
%
±4
±4
VDIM = 0V, VOUT_ = 40V
1
μA
LOGIC INPUTS/OUTPUTS
EN Reference Voltage
EN Hysteresis
EN Input Current
DIM Input High Voltage
VEN rising, MAX16814A_ _ only
1.125
1.23
1.335
VEN rising, MAX16814U_ _ and
MAX16814B_ _ _
1.144
1.23
1.316
50
VEN = 40V
±600
mV
nA
V
0.8
V
2.1
DIM Input Low Voltage
DIM Hysteresis
250
DIM Input Current
V
mV
±2
μA
DIM to LED Turn-On Delay
DIM rising edge to 10% rise in IOUT_
100
ns
DIM to LED Turn-Off Delay
DIM falling edge to 10% fall in IOUT_
100
ns
IOUT_ Rise and Fall Times
200
ns
FLT Output Low Voltage
VIN = 4.75V and ISINK = 5mA
0.4
V
FLT Output Leakage Current
VFLT = 5.5V
1.0
μA
LED Short Detection Threshold
Gain = 3V
2.25
V
±600
nA
1.75
Short Detection Comparator Delay
2.0
6.5
RSDT Leakage Current
OVP Trip Threshold
Output rising
OVP Hysteresis
1.228
1.266
70
OVP Leakage Current
VOVP = 1.25V
Thermal-Shutdown Threshold
Temperature rising
Thermal-Shutdown Hysteresis
1.19
μs
V
mV
±200
nA
165
°C
15
°C
Note 2: All MAX16814A_ _ are 100% tested at TA = +125NC, while all MAX16814U_ _ and MAX16814B _ _ _ are 100% tested at
TA = +25°C. All limits overtemperature are guaranteed by design , not production tested.
Note 3: CS threshold includes slope compensation ramp magnitude.
Note 4: Gain = δVCOMP/δVCS, 0.05V < VCS < 0.15V.
4 Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Typical Operating Characteristics
(VIN = VEN = 12V, fSW = 300kHz, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VOVP = VCS =
VLEDGND = VDIM = VPGND = VSGND = 0V, load = 4 strings of 7 white LEDs, TA = +25NC, unless otherwise noted.)
SWITCHING WAVEFORM AT 5kHz
(50% DUTY CYCLE) DIMMING
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX16814 toc01
CNDRV = 13pF
3.4
0V
TA = +25NC
3.2
IIN (mA)
IOUT1
100mA/div
3.0
0A
FIGURE 2
TA = +125NC
3.6
VLX
10V/div
MAX16814 toc02
3.8
VOUT
10V/div
2.8
0V
2.4
TA = -40NC
2.6
5
40Fs/div
10
15
20
25
30
35
40
45
VIN (V)
SWITCHING FREQUENCY
vs. TEMPERATURE
3.6
3.4
3.2
306
304
302
300
298
1.232
1.228
296
1.224
294
292
1.220
290
3.0
-50
200 400 600 800 1000 1200 1400 1600 1800 2000
-25
0
25
50
75
100
-25
0
25
50
75
TEMPERATURE (NC)
TEMPERATURE (NC)
VSETI vs. PROGRAMMED CURRENT
EN THRESHOLD VOLTAGE
vs. TEMPERATURE
EN LEAKAGE CURRENT
vs. TEMPERATURE
1.231
1.230
VEN RISING
1.20
VEN FALLING
1.15
46
72
98
124
LED STRING CURRENT (mA)
Maxim Integrated
150
100
125
VEN = 2.5V
120
90
60
30
1.229
1.228
125
MAX16814 toc08
1.25
100
150
EN LEAKAGE CURRENT (nA)
1.232
1.30
EN THRESHOLD VOLTAGE (V)
MAX16814 toc06
1.233
20
-50
125
fSW (kHz)
1.234
VSETI (V)
1.236
VSETI (V)
3.8
308
MAX16814 toc07
IIN (mA)
4.0
1.240
MAX16814 toc04
CNDRV = 13pF
4.2
VSETI vs. TEMPERATURE
310
SWITCHING FREQUENCY (kHz)
MAX16814 toc03
4.4
MAX16814 toc05
SUPPLY CURRENT
vs. SWITCHING FREQUENCY
1.10
0
-50
-25
0
25
50
75
TEMPERATURE (NC)
100
125
-50
-25
0
25
50
75
TEMPERATURE (NC)
5
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Typical Operating Characteristics (continued)
(VIN = VEN = 12V, fSW = 300kHz, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VOVP = VCS =
VLEDGND = VDIM = VPGND = VSGND = 0V, load =4 strings of 7 white LEDs, TA = +25NC, unless otherwise noted.)
5.02
TA = +25NC
5.00
4.98
TA = -40NC
5.00
5.02
4.96
TA = -40NC
4.94
4.98
1.80
10
15
20
25
30
35
0
40
1.40
1.20
1.00
0.80
0.60
0.20
4.90
5
1.60
0.40
4.92
4.96
MAX16814 toc11
TA = +125NC
5.04
2.00
SWITCHING FREQUENCY (MHz)
5.06
TA = +125NC
TA = +25NC
MAX16814 toc10
5.08
VCC (V)
VCC (V)
5.10
MAX16814 toc09
5.06
5.04
SWITCHING FREQUENCY vs. 1/RT
VCC LOAD REGULATION
VCC LINE REGULATION
5.08
20
VIN (V)
STARTUP WAVEFORM WITH
DIM ON PULSE WIDTH < tSW
MAX16814 toc12
40
IVCC (mA)
60
80
0.02
0.06
0.10
0.14
VIN
20V/div
0V
MAX16814 toc13
VDIM
5V/div
0V
IOUT_
100mA/div
0A
IOUT1
100mA/div
0A
FIGURE 2
40ms/div
40ms/div
STARTUP WAVEFORM WITH DIM
CONTINUOUSLY ON
MOSFET DRIVER ON-RESISTANCE
vs. TEMPERATURE
FIGURE 2
40ms/div
1.3
ON-RESISTANCE (I)
0V
MAX16814 toc15
1.5
VIN
20V/div
0V
0V
0.30
VLED
10V/div
0V
IOUT1
100mA/div
0A
VLED
10V/div
0.26
VIN
20V/div
0V
VDIM
5V/div
0V
VDIM
5V/div
0V
0.22
STARTUP WAVEFORM WITH DIM
ON PULSE WIDTH = 10tSW
VLED
20V/div
MAX16814 toc14
0.18
1/RT (mS)
pMOS
1.1
0.9
nMOS
0.7
0.5
-50
-25
0
25
50
75
100
125
TEMPERATURE (NC)
6 Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Typical Operating Characteristics (continued)
(VIN = VEN = 12V, fSW = 300kHz, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VOVP = VCS =
VLEDGND = VDIM = VPGND = VSGND = 0V, load = 4 strings of 7 white LEDs, TA = +25NC, unless otherwise noted.)
LED CURRENT RISING AND FALLING
WAVEFORM
LED CURRENT SWITCHING WITH DIM
AT 5kHz AND 50% DUTY CYCLE
MAX16814 toc17
MAX16814 toc16
FIGURE 2
IOUT1
100mA/div
0A
VDIM
5V/div
0V
IOUT2
100mA/div
0A
IOUT3
100mA/div
0A
ILED
50mA/div
0A
IOUT4
100mA/div
0A
100Fs/div
4Fs/div
OUT_ CURRENT vs. 1/RSETI
COMP LEAKAGE CURRENT
vs. TEMPERATURE
VDIM = 0V
COMP LEAKAGE CURRENT (nA)
140
120
100
80
60
40
0.040
0.055
0.070
0.085
0.6
VCOMP = 4.5V
0.4
VCOMP = 0.5V
0.2
0
0.100
-25
-50
0
1/RSETI (mS)
OUT_ LEAKAGE CURRENT
vs. TEMPERATURE
75
10
1
100
125
RSDT LEAKAGE CURRENT
vs. TEMPERATURE
MAX16814 toc21
2.0
VOVP = 1.25V
1.8
OVP LEAKAGE CURRENT (nA)
VDIM = 0V
VOUT = 40V
50
OVP LEAKAGE CURRENT
vs. TEMPERATURE
MAX16814 toc20
OUT_ LEAKAGE CURRENT (nA)
100
25
TEMPERATURE (NC)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
250
MAX16814 toc22
0.025
0.8
RSDT LEAKAGE CURRENT (nA)
20
0.010
MAX16814 toc19
1.0
MAX16814 toc18
160
IOUT_ (mA)
FIGURE 2
200
VRSDT = 0.5V
150
100
VRSDT = 2.5V
0.2
0.1
-50
-25
0
25
50
75
TEMPERATURE (NC)
Maxim Integrated
100
125
50
0
-50
-25
0
25
50
75
TEMPERATURE (NC)
100
125
-50
-25
0
25
50
75
100
125
TEMPERATURE (NC)
7
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Pin Description
PIN
NAME
FUNCTION
TQFN/
QFND
TSSOP
1
4
IN
Bias Supply Input. Connect a 4.75V to 40V supply to IN. Bypass IN to SGND with a ceramic
capacitor.
2
5
EN
Enable Input. Connect EN to logic-low to shut down the device. Connect EN to logic-high or IN
for normal operation. The EN logic threshold is internally set to 1.23V.
3
6
COMP
8 Switching Converter Compensation Input. Connect the compensation network from COMP to
SGND for current-mode control (see the Feedback Compensation section).
4
7
RT
Oscillator Timing Resistor Connection. Connect a timing resistor (RT) from RT to SGND to program
the switching frequency according to the formula RT = 7.350 x 109/fsw (for the MAX16814A_ _
and the MAX16814U_ _) or to the formula RT = 7.72 x 109/fsw (for the MAX16814B_ _ _). Apply an
AC-coupled external clock at RT to synchronize the switching frequency with an external clock.
5
8
FLT
Open-Drain Fault Output. FLT asserts low when an open LED, short LED, or thermal shutdown
is detected. Connect a 10kω pullup resistor from FLT to VCC.
6
9
OVP
Overvoltage Threshold Adjust Input. Connect a resistor-divider from the switching converter
output to OVP and SGND. The OVP comparator reference is internally set to 1.23V.
7
10
SETI
LED Current Adjust Input. Connect a resistor (RSETI) from SETI to SGND to set the current
through each LED string (ILED) according to the formula ILED = 1500/RSETI.
8
11
RSDT
LED Short Detection Threshold Adjust Input. Connect a resistive divider from VCC to RSDT and
SGND to program the LED short detection threshold. Connect RSDT directly to VCC to disable
LED short detection. The LED short detection comparator is internally referenced to 2V.
9
12
SGND
Signal Ground. SGND is the current return path connection for the low-noise analog signals.
Connect SGND, LEDGND, and PGND at a single point.
10
13
DIM
Digital PWM Dimming Input. Apply a PWM signal to DIM for LED dimming control. Connect
DIM to VCC if dimming control is not used.
11
14
OUT1
LED String Cathode Connection 1. OUT1 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT1. OUT1 sinks up to 150mA. If
unused, connect OUT1 to LEDGND.
Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Pin Description (continued)
PIN
NAME
FUNCTION
15
OUT2
LED String Cathode Connection 2. OUT2 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT2. OUT2 sinks up to 150mA. If
unused, connect OUT2 to LEDGND.
13
16
LEDGND
14
17
OUT3
LED String Cathode Connection 3. OUT3 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT3. OUT3 sinks up to 150mA. If
unused, connect OUT3 to LEDGND.
15
18
OUT4
LED String Cathode Connection 4. OUT4 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT4. OUT4 sinks up to 150mA. If
unused, connect OUT4 to LEDGND.
Current-Sense Input. CS is the current-sense input for the switching regulator. A sense resistor
connected from the source of the external power MOSFET to PGND sets the switching current
limit. A resistor connected between the source of the power MOSFET and CS sets the slope
compensation ramp rate (see the Slope Compensation section).
TQFN/
QFND
TSSOP
12
LED Ground. LEDGND is the return path connection for the linear current sinks. Connect
SGND, LEDGND, and PGND at a single point.
16
19
CS
17
20
PGND
Power Ground. PGND is the switching current return path connection. Connect SGND,
LEDGND, and PGND at a single point.
18
1
NDRV
Switching n-MOSFET Gate-Driver Output. Connect NDRV to the gate of the external switching
power MOSFET.
19
2
DRV
MOSFET Gate-Driver Supply Input. Connect a resistor between VCC and DRV to power the
MOSFET driver with the internal 5V regulator. Bypass DRV to PGND with a minimum of 0.1μF
ceramic capacitor.
20
3
VCC
5V Regulator Output. Bypass VCC to SGND with a minimum of 1μF ceramic capacitor as close
as possible to the device.
—
—
EP
Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective power
dissipation. Do not use as the main IC ground connection. EP must be connected to SGND.
Maxim Integrated
9
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
FLT
RSDT
VREF
POKD
MAX16814
SHORT LED
DETECTOR
FAULT FLAG
LOGIC
UNUSED
STRING
DETECTOR
OPEN-LED
DETECTOR
SHDN
DRV
TSHDN
PWM
LOGIC
NDRV
PGND
CLK
SLOPE
COMPENSATION
RAMP/RT OSC
RT
MIN STRING
VOLTAGE
ILIM
OUT_
0.425V
1.8V
di
( dt = 50FA x fsw)
CS BLANKING
CS
COMP
OVP
COMP
THERMAL
SHUTDOWN
R
LOGIC
gM
TSHDN
REF
FB
VBG
SHDN
BANDGAP
IN
UVLO
LEDGND
LOGIC
(REF/FB
SELECTOR)
VBG = 1.235V
DIM
5V LDO
REGULATOR
VCC
SS_DONE
SS_REF
UVLO
VREF
TSHDN
POK
SOFT-START
100ms
SHDN
POKD
VBG
P
EN
SHDN
1.23V
TSHDN
SGND
SGND
OVP
SETI
Figure 1. Simplified Functional Diagram
10 Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
VIN
L2
C2
C1
C5
C6
7 HBLEDS
PER STRING
D1
L1
C7
R1
M1
C8
R2
D2
IN
R7
NDRV
RCOMP
RCS
CS
OVP
EN
OUT1
VCC
C3
OUT2
OUT3
R5
MAX16814
VDRV
OUT4
RSETI
C4
SETI
DIM
R6
VCC
FLT
COMP
R3
RSDT
R4
RCOMP
RT
RT
CCOMP
SGND
PGND
LEDGND
Figure 2. Circuit Used for Typical Operating Characteristics
Maxim Integrated
11
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Detailed Description
The MAX16814 high-efficiency HB LED driver integrates all the necessary features to implement a highperformance backlight driver to power LEDs in small
to medium-sized displays for automotive as well as
general applications. The device provides load-dump
voltage protection up to 40V in automotive applications.
The MAX16814 incorporates two major blocks: a DC-DC
controller with peak current-mode control to implement
a boost, coupled-inductor boost-buck, or a SEPIC-type
switched-mode power supply and a 4-channel LED driver with 20mA to 150mA constant current-sink capability
per channel. Figure 1 is the simplified functional diagram
and Figure 2 shows the circuit used for typical operating
characteristics.
The MAX16814 features a constant-frequency peak
current-mode control with programmable slope compensation to control the duty cycle of the PWM controller. The high-current FET driver can provide up to 2A of
current to the external n-channel MOSFET. The DC-DC
converter implemented using the controller generates
the required supply voltage for the LED strings from
a wide input supply range. Connect LED strings from
the DC-DC converter output to the 4-channel constant
current-sink drivers that control the current through the
LED strings. A single resistor connected from the SETI
input to ground adjusts the forward current through all
four LED strings.
The MAX16814 features adaptive voltage control that
adjusts the converter output voltage depending on the
forward voltage of the LED strings. This feature minimizes the voltage drop across the constant current-sink
drivers and reduces power dissipation in the device.
A logic input (EN) shuts down the device when pulled
low. The device includes an internal 5V LDO capable of
powering additional external circuitry.
All the versions of the MAX16814 include PWM dimming.
The MAX16814A_ and the MAX16814U_ versions, in particular, provide very wide (5000:1) PWM dimming range
where a dimming pulse as narrow as 1µs is possible at
a 200Hz dimming frequency. This is made possible by
a unique feature that detects short PWM dimming input
pulses and adjusts the converter feedback accordingly.
Advanced features include detection and string-disconnect for open-LED strings, partial or fully shorted
strings and unused strings. Overvoltage protection
clamps the converter output voltage to the programmed
OVP threshold in the event of an open-LED condition.
12 Shorted LED string detection and overvoltage protection thresholds are programmable using RSDT and OVP
inputs, respectively. An open-drain FLT signal asserts to
indicate open-LED, shorted LED, and overtemperature
conditions. Disable individual current-sink channels by
connecting the corresponding OUT_ to LEDGND. In this
case, FLT does not assert indicating an open-LED condition for the disabled channel. The device also features
an overtemperature protection that shuts down the controller if the die temperature exceeds +165NC.
Current-Mode DC-DC Controller
The peak current-mode controller allows boost, coupledinductor buck-boost, or SEPIC-type converters to generate the required bias voltage for the LED strings. The
switching frequency can be programmed over the 200kHz
to 2MHz range using a resistor connected from RT to
SGND. Programmable slope compensation is available
to compensate for subharmonic oscillations that occur at
above 50% duty cycles in continuous conduction mode.
The external MOSFET is turned on at the beginning of
every switching cycle. The inductor current ramps up
linearly until it is turned off at the peak current level set by
the feedback loop. The peak inductor current is sensed
from the voltage across the current-sense resistor RCS
connected from the source of the external MOSFET to
PGND. The MAX16814 features leading-edge blanking to
suppress the external MOSFET switching noise. A PWM
comparator compares the current-sense voltage plus the
slope compensation signal with the output of the transconductance error amplifier. The controller turns off the external MOSFET when the voltage at CS exceeds the error
amplifier’s output voltage. This process repeats every
switching cycle to achieve peak current-mode control.
Error Amplifier
The internal error amplifier compares an internal feedback (FB) with an internal reference (REF) and regulates
its output to adjust the inductor current. An internal
minimum string detector measures the minimum currentsink voltage with respect to SGND out of the 4 constantcurrent-sink channels. During normal operation, this
minimum OUT_ voltage is regulated to 1V through
feedback. The error amplifier takes 1V as the REF and
the minimum OUT_ voltage as the FB input. The amplified error at the COMP output controls the inductor peak
current to regulate the minimum OUT_ voltage at 1V. The
resulting DC-DC converter output voltage is the highest
LED string voltage plus 1V.
Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
The converter stops switching when the LED strings are
turned off during PWM dimming. The error amplifier is
disconnected from the COMP output to retain the compensation capacitor charge. This allows the converter
to settle to steady-state level almost immediately when
the LED strings are turned on again. This unique feature
provides fast dimming response, without having to use
large output capacitors.
For the MAX16814A_ _ and the MAX16814U_ _, if the
PWM dimming on-pulse is less than or equal to five
switching cycles, the feedback controls the voltage on
OVP so that the converter output voltage is regulated at
95% of the OVP threshold. This mode ensures that narrow
PWM dimming pulses are not affected by the response
time of the converter. During this mode, the error amplifier
remains connected to the COMP output continuously and
the DC-DC converter continues switching.
Undervoltage Lockout (UVLO)
The MAX16814 features two undervoltage lockouts that
monitor the input voltage at IN and the output of the internal LDO regulator at VCC. The device turns on after both
VIN and VCC exceed their respective UVLO thresholds.
The UVLO threshold at IN is 4.3V when VIN is rising and
4.15V when VIN is falling. The UVLO threshold at VCC
is 4V when VCC is rising and 3.9V when VCC is falling.
Enable
EN is a logic input that completely shuts down the
device when connected to logic-low, reducing the current consumption of the device to less than 40FA. The
logic threshold at EN is 1.23V (typ). The voltage at EN
must exceed 1.23V before any operation can commence. There is a 50mV hysteresis on EN. The EN input
also allows programming the supply input UVLO threshold using an external voltage-divider to sense the input
voltage as shown below.
Use the following equation to calculate the value of R1
and R2 in Figure 3:
soft-start, the DC-DC converter output ramps towards
95% of the OVP voltage and uses feedback from the OVP
input. Soft-start terminates when the minimum current-sink
voltage reaches 1V or when the converter output reaches
95% OVP. The typical soft-start period is 100ms. The 1V
minimum OUT_ voltage is detected only when the LED
strings are enabled by PWM dimming. Connect OVP to
the boost converter output through a resistive divider
network (see the Typical Operating Circuit).
When there is an open-LED condition, the converter output
hits the OVP threshold. After the OVP is triggered, openLED strings are disconnected and, at the beginning of the
dimming PWM pulse, control is transferred to the adaptive
voltage control. The converter output discharges to a level
where the new minimum OUT_ voltage is 1V.
Oscillator Frequency/External Synchronization
The internal oscillator frequency is programmable
between 200kHz and 2MHz using a resistor (RT) connected from the RT input to SGND. Use the equation
below to calculate the value of RT for the desired switching frequency, fSW.
RT =
7.35 × 10 9 Hz
fSW
(for the MAX16814A_ _ and the MAX16814U_ _).
RT =
7.72 × 10 9
fSW
(for the MAX16814B_ _ _).
Synchronize the oscillator with an external clock by
AC-coupling the external clock to the RT input. The
capacitor used for the AC-coupling should satisfy the
following relation:
 9.862

C SYNC ≤ 
-0.144×10 -3 (µF)
 RT

V

=
R1  UVLO - 1 × R2
1.23V


where VUVLO is the desired undervoltage lockout level
and 1.23V is the EN input reference. Connect EN to IN
if not used.
Soft-Start
The MAX16814 provides soft-start with internally set timing. At
power-up, the MAX16814 enters soft-start once unused LED
strings are detected and disconnected (see the Open-LED
Management and Overvoltage Protection section). During
Maxim Integrated
VIN
MAX16814
R1
EN
R2
1.23V
Figure 3. Setting the MAX16814 Undervoltage Lockout
Threshold
13
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
where RT is in Ω.
The pulse width for the synchronization pulse should
satisfy the following relations:
t PW
VS < 0.5
t CLK


t PW
VS  + VS > 3.4
 0.8 −
t CLK


t
t PW < CLK (t CI − 1.05 ×t CLK )
t CI
where tPW is the synchronization source pulse width,
tCLK is the synchronization clock time period, tCI is the
programmed clock period, and VS is the synchronization
pulse voltage level.
5V LDO Regulator (VCC)
The internal LDO regulator converts the input voltage
at IN to a 5V output voltage at VCC. The LDO regulator
supplies up to 50mA current to provide power to internal
control circuitry and the gate driver. Connect a resistor
between VCC and DRV to power the gate-drive circuitry;
the recommended value is 4.7I. Bypass DRV with a
capacitor to PGND. The external resistor and bypass
capacitor provide noise filtering. Bypass VCC to SGND
with a minimum of 1FF ceramic capacitor as close to the
device as possible.
PWM MOSFET Driver
The NDRV output is a push-pull output with the on-resistance of the pMOS typically 1.1I and the on-resistance
of the nMOS typically 0.9I. NDRV swings from PGND to
DRV to drive an external n-channel MOSFET. The driver
typically sources 2.0A and sinks 2.0A allowing for fast
turn-on and turn-off of high gate-charge MOSFETs.
R SETI = 1500 IOUT_
where IOUT_ is the desired output current for each of the
four channels.
If more than 150mA is required in an LED string, use two
or more of the current source outputs (OUT_) connected
together to drive the string as shown in Figure 4.
LED Dimming Control
The MAX16814 features LED brightness control using an
external PWM signal applied at DIM. A logic-high signal
on the DIM input enables all four LED current sources
and a logic-low signal disables them.
For the MAX16814A_ _ and the MAX16814U_ _, the duty
cycle of the PWM signal applied to DIM also controls the
DC-DC converter’s output voltage. If the turn-on duration
of the PWM signal is less than 5 oscillator clock cycles
(DIM pulse width decreasing) then the boost converter
regulates its output based on feedback from the OVP
input. During this mode, the converter output voltage
is regulated to 95% of the OVP threshold voltage. If
the turn-on duration of the PWM signal is greater than
or equal to 6 oscillator clock cycles (DIM pulse width
increasing), then the converter regulates its output so
that the minimum voltage at OUT_ is 1V.
Fault Protections
Fault protections in the MAX16814 include cycle-bycycle current limiting using the PWM controller, DC-DC
converter output overvoltage protection, open-LED
detection, short LED detection and protection, and
overtemperature shutdown. An open-drain LED fault
BOOST CONVERTER
OUTPUT
The power dissipation in the MAX16814 is mainly a function of the average current sourced to drive the external
MOSFET (IDRV) if there are no additional loads on VCC.
IDRV depends on the total gate charge (QG) and operating frequency of the converter. Connect DRV to VCC with
a 4.7I resistor to power the gate driver with the internal
5V regulator.
LED Current Control
The MAX16814 features four identical constant-current
sources used to drive multiple HB LED strings. The current through each one of the four channels is adjustable
between 20mA and 150mA using an external resistor
(RSETI) connected between SETI and SGND. Select
RSETI using the following formula:
40mA TO 300mA
PER STRING
OUT1
MAX16814
OUT2
OUT3
OUT4
Figure 4. Configuration for Higher LED String Current
14 Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
flag output (FLT) goes low when an open-LED string is
detected, a shorted LED string is detected, and during
thermal shutdown. FLT is cleared when the fault condition is removed during thermal shutdown and shorted
LEDs. FLT is latched low for an open-LED condition
and can be reset by cycling power or toggling the EN
pin. The thermal shutdown threshold is +165NC and has
15NC hysteresis.
Open-LED Management and Overvoltage Protection
On power-up, the MAX16814 detects and disconnects
any unused current-sink channels before entering softstart. Disable the unused current-sink channels by
connecting the corresponding OUT_ to LEDGND. This
avoids asserting the FLT output for the unused channels. After soft-start, the MAX16814 detects open LED
and disconnects any strings with an open LED from the
internal minimum OUT_ voltage detector. This keeps the
DC-DC converter output voltage within safe limits and
maintains high efficiency. During normal operation, the
DC-DC converter output regulation loop uses the minimum OUT_ voltage as the feedback input. If any LED
string is open, the voltage at the opened OUT_ goes
to VLEDGND. The DC-DC converter output voltage then
increases to the overvoltage protection threshold set by
the voltage-divider network connected between the converter output, OVP input, SGND. The overvoltage protection threshold at the DC-DC converter output (VOVP) is
determined using the following formula:
 R1  (see the Typical Operating Circuit)
VOVP= 1.23 × 1 +

 R2 
where 1.23V (typ) is the OVP threshold. Select R1 and
R2 such that the voltage at OUT_ does not exceed the
absolute maximum rating. As soon as the DC-DC converter output reaches the overvoltage protection threshold, the PWM controller is switched off setting NDRV
low. Any current-sink output with VOUT_ < 300mV (typ) is
disconnected from the minimum voltage detector.
Connect the OUT_ of all channels without LED connections to LEDGND before power-up to avoid OVP triggering at startup. When an open-LED overvoltage condition
occurs, FLT is latched low.
Maxim Integrated
Short LED Detection
The MAX16814 checks for shorted LEDs at each rising
edge of DIM. An LED short is detected at OUT_ if the
following condition is met:
VOUT_ > VMINSTR + 3 x VRSDT
where VOUT_ is the voltage at OUT_, VMINSTR is the
minimum current-sink voltage, and VRSDT is the programmable LED short detection threshold set at the
RSDT input. Adjust VRSDT using a voltage-divider resistive network connected at the VCC output, RSDT input,
and SGND.
Once a short is detected on any of the strings, the LED
strings with the short are disconnected and the FLT output flag asserts until the device detects that the shorts
are removed on any of the following rising edges of DIM.
Connect RSDT directly to VCC to always disable LED
short detection.
Applications Information
DC-DC Converter
Three different converter topologies are possible with
the DC-DC controller in the MAX16814, which has the
ground-referenced outputs necessary to use the constant current-sink drivers. If the LED string forward voltage is always more than the input supply voltage range,
use the boost converter topology. If the LED string forward voltage falls within the supply voltage range, use
the boost-buck converter topology. Boost-buck topology
is implemented using either a conventional SEPIC configuration or a coupled-inductor boost-buck configuration. The latter is basically a flyback converter with 1:1
turns ratio. 1:1 coupled inductors are available with tight
coupling suitable for this application. Figure 6 shows
the coupled-inductor boost-buck configuration. It is also
possible to implement a single inductor boost-buck converter using the MAX15054 high-side FET driver.
The boost converter topology provides the highest
efficiency among the above mentioned topologies. The
coupled-inductor boost-buck topology has the advantage of not using a coupling capacitor over the SEPIC
configuration. Also, the feedback loop compensation for
SEPIC becomes complex if the coupling capacitor is not
large enough. A coupled-inductor boost-buck is not suitable for cases where the coupled-inductor windings are
not tightly coupled. Considerable leakage inductance
requires additional snubber components and degrades
the efficiency.
15
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Power-Circuit Design
First select a converter topology based on the above
factors. Determine the required input supply voltage
range, the maximum voltage needed to drive the LED
strings including the minimum 1V across the constant
LED current sink (VLED), and the total output current
needed to drive the LED strings (ILED) as follows:
=
ILED I STRING × N STRING
Use the following equations to calculate the maximum
average inductor current (ILAVG) and peak inductor current (ILP) in amperes:
IL AVG =
Allowing the peak-to-peak inductor ripple DIL to be
+30% of the average inductor current:
where ISTRING is the LED current per string in amperes
and NSTRING is the number of strings used.
Calculate the maximum duty cycle (DMAX) using the following equations:
For boost configuration:
D MAX =
∆=
IL IL AVG × 0.3 × 2
and:
IL P IL AVG +
=
(VLED + VD1 − VIN_MIN )
(VLED + VD1 − VDS − 0.3V)
For SEPIC and coupled-inductor boost-buck-configurations:
(VLED + VD1)
D MAX =
(VIN_MIN − VDS − 0.3V + VLED + VD1)
where VD1 is the forward drop of the rectifier diode in
volts (approximately 0.6V), VIN_MIN is the minimum input
supply voltage in volts, and VDS is the drain-to-source
voltage of the external MOSFET in volts when it is on,
and 0.3V is the peak current-sense voltage. Initially, use
an approximate value of 0.2V for VDS to calculate DMAX.
Calculate a more accurate value of DMAX after the power
MOSFET is selected based on the maximum inductor
current. Select the switching frequency (fSW) depending
on the space, noise, and efficiency constraints.
Inductor Selection
Boost and Coupled-Inductor
Boost-Buck Configurations
In all the three converter configurations, the average
inductor current varies with the line voltage and the
maximum average current occurs at the lowest line
voltage. For the boost converter, the average inductor
current is equal to the input current. Select the maximum
peak-to-peak ripple on the inductor current (DIL). The
recommended peak-to-peak ripple is 60% of the average inductor current.
16 ILED
1 − D MAX
∆IL
2
Calculate the minimum inductance value, LMIN, in henries with the inductor current ripple set to the maximum
value:
L MIN =
(VINMIN − VDS − 0.3V) × D MAX
fSW × ∆IL
where 0.3V is the peak current-sense voltage. Choose
an inductor that has a minimum inductance greater
than the calculated LMIN and current rating greater than
ILP. The recommended saturation current limit of the
selected inductor is 10% higher than the inductor peak
current for boost configuration. For the coupled-inductor
boost-buck, the saturation limit of the inductor with only
one winding conducting should be 10% higher than ILP.
SEPIC Configuration
Power circuit design for the SEPIC configuration is very
similar to a conventional boost-buck design with the
output voltage referenced to the input supply voltage.
For SEPIC, the output is referenced to ground and the
inductor is split into two parts (see Figure 5 for the SEPIC
configuration). One of the inductors (L2) takes LED current as the average current and the other (L1) takes
input current as the average current.
Use the following equations to calculate the average
inductor currents (IL1AVG, IL2AVG) and peak inductor
currents (IL1P, IL2P) in amperes:
I
× D MAX × 1.1
IL1AVG = LED
1 − D MAX
Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
The factor 1.1 provides a 10% margin to account for the
converter losses:
IL2 AVG = ILED
For simplifying further calculations, consider L1 and
L2 as a single inductor with L1 and L2 connected in
parallel. The combined inductance value and current is
calculated as follows:
Assuming the peak-to-peak inductor ripple DIL is Q30%
of the average inductor current:
∆=
IL1 IL1AVG × 0.3 × 2
and:
L MIN =
L1MIN × L2 MIN
L1MIN + L2 MIN
and:
IL
=
AVG IL1AVG + IL2 AVG
IL1P IL1AVG +
=
∆IL1
2
∆IL2
= IL2 AVG × 0.3 × 2
and:
IL2 P IL2 AVG +
=
∆IL2
2
Calculate the minimum inductance values L1MIN and
L2MIN in henries with the inductor current ripples set to
the maximum value as follows:
L1MIN =
(VINMIN − VDS − 0.3V) × D MAX
fSW × ∆IL1
L2 MIN =
(VINMIN − VDS − 0.3V) × D MAX
fSW × ∆IL2
where 0.3V is the peak current-sense voltage. Choose
inductors that have a minimum inductance greater than
the calculated L1MIN and L2MIN and current rating
greater than IL1P and IL2P, respectively. The recommended saturation current limit of the selected inductor
is 10% higher than the inductor peak current:
Maxim Integrated
where ILAVG represents the total average current through
both the inductors together for SEPIC configuration. Use
these values in the calculations for SEPIC configuration
in the following sections.
Select coupling capacitor CS so that the peak-to-peak
ripple on it is less than 2% of the minimum input supply voltage. This ensures that the second-order effects
created by the series resonant circuit comprising L1,
CS, and L2 does not affect the normal operation of the
converter. Use the following equation to calculate the
minimum value of CS:
CS ≥
ILED × D MAX
VIN_MIN × 0.02 × fSW
where CS is the minimum value of the coupling capacitor
in farads, ILED is the LED current in amperes, and the
factor 0.02 accounts for 2% ripple.
Slope Compensation
The MAX16814 generates a current ramp for slope compensation. This ramp current is in sync with the switching frequency and starts from zero at the beginning of
every clock cycle and rises linearly to reach 50FA at the
end of the clock cycle. The slope-compensating resistor,
RSCOMP, is connected between the CS input and the
source of the external MOSFET. This adds a programmable ramp voltage to the CS input voltage to provide
slope compensation.
17
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Use the following equation to calculate the value of slope
compensation resistance, RSCOMP.
For boost configuration:
R SCOMP =
(VLED − 2VIN_MIN ) × R CS × 3
L MIN × 50FA × fSW × 4
For SEPIC and coupled-inductor boost-buck:
R SCOMP =
( VLED − VIN_MIN ) × R CS × 3
L MIN × 50FA × fSW × 4
where VLED and VIN_MIN are in volts, RSCOMP and RCS
are in ohms, LMIN is in henries and fSW is in hertz.
The value of the switch current-sense resistor, RCS, can
be calculated as follows:
For boost:
0.396 × 0.9 = ILP ×RCS +
(DMAX × (VLED − 2VIN_MIN)×RCS × 3)
4 ×L MN × fSW
For SEPIC and boost-buck:
0.396 × 0.9 = ILP ×RCS +
(DMAX × (VLED − VIN_MIN ) ×RCS × 3)
4 ×L MN × fSW
PWM dimming, the amount of ceramic capacitors on the
output are usually minimized. In this case, an additional
electrolytic or tantalum capacitor provides most of the
bulk capacitance.
External MOSFET Selection
The external MOSFET should have a voltage rating sufficient to withstand the maximum output voltage together
with the rectifier diode drop and any possible overshoot
due to ringing caused by parasitic inductances and
capacitances. The recommended MOSFET VDS voltage
rating is 30% higher than the sum of the maximum output
voltage and the rectifier diode drop.
The recommended continuous drain current rating of the
MOSFET (ID), when the case temperature is at +70NC, is
greater than that calculated below:


ID RMS=  IL AVG 2 × D MAX  × 1.3


The MOSFET dissipates power due to both switching
losses and conduction losses. Use the following equation to calculate the conduction losses in the MOSFET:
PCOND = IL AVG 2 × D MAX × RDS (ON)
where RDS(ON) is the on-state drain-to-source resistance
of the MOSFET.
Use the following equation to calculate the switching
where 0.396 is the minimum value of the peak curlosses in the MOSFET:
rent-sense threshold. The current-sense threshold also
includes the slope compensation component. The minimum current-sense threshold of 0.396 is multiplied by
IL AVG × VLED 2 × C GD × fSW  1
1 
=
×
+
PSW

0.9 to take tolerances into account.
2
I
I
 GON GOFF 
Output Capacitor Selection
where IGON and IGOFF are the gate currents of the
For all the three converter topologies, the output capaciMOSFET in amperes, with VGS at the threshold voltage
tor supplies the load current when the main switch is
in volts, when it is turned on and turned off, respectively.
on. The function of the output capacitor is to reduce the
CGD is the gate-to-drain MOSFET capacitance in farads.
converter output ripple to acceptable levels. The entire
output-voltage ripple appears across constant currentRectifier Diode Selection
sink outputs because the LED string voltages are stable
Using a Schottky rectifier diode produces less forward
due to the constant current. For the MAX16814, limit
drop and puts the least burden on the MOSFET during
the peak-to-peak output voltage ripple to 200mV to get
reverse recovery. A diode with considerable reversestable output current.
recovery time increases the MOSFET switching loss.
Select a Schottky diode with a voltage rating 20% higher
The ESR, ESL, and the bulk capacitance of the output
than the maximum boost-converter output voltage and
capacitor contribute to the output ripple. In most of the
current rating greater than that calculated in the followapplications, using low-ESR ceramic capacitors can
ing equation:
dramatically reduce the output ESR and ESL effects.
To reduce the ESL and ESR effects, connect multiple
ceramic capacitors in parallel to achieve the required
bulk capacitance. To minimize audible noise during
18 ID =
1.2 × IL AVG
1 − D MAX
Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Feedback Compensation
During normal operation, the feedback control loop regulates the minimum OUT_ voltage to 1V when LED string
currents are enabled during PWM dimming. When LED
currents are off during PWM dimming, the control loop
turns off the converter and stores the steady-state condition in the form of capacitor voltages, mainly the output
filter capacitor voltage and compensation capacitor
voltage. For the MAX16814A_ _ and the MAX16814U_
_, when the PWM dimming pulses are less than five
switching clock cycles, the feedback loop regulates the
converter output voltage to 95% of the OVP threshold.
The worst-case condition for the feedback loop is when
the LED driver is in normal mode regulating the minimum
OUT_ voltage to 1V. The switching converter small-signal
transfer function has a right-half plane (RHP) zero for
boost configuration if the inductor current is in continuous
conduction mode. The RHP zero adds a 20dB/decade
gain together with a 90N-phase lag, which is difficult to
compensate.
The worst-case RHP zero frequency (fZRHP) is calculated as follows:
For boost configuration:
fZRHP =
VLED (1 − D MAX ) 2
2π × L × ILED
For SEPIC and coupled-inductor boost-buck configurations:
fZRHP =
VLED (1 − D MAX ) 2
2π × L × ILED × D MAX
where fZRHP is in hertz, VLED is in volts, L is the inductance value of L1 in henries, and ILED is in amperes. A
simple way to avoid this zero is to roll off the loop gain
to 0dB at a frequency less than one fifth of the RHP zero
frequency with a -20dB/decade slope.
The switching converter small-signal transfer function
also has an output pole. The effective output impedance
together with the output filter capacitance determines the
output pole frequency fP1 that is calculated as follows:
For boost configuration:
fP1 =
Maxim Integrated
ILED
2 × π × VLED × C OUT
For SEPIC and coupled-inductor boost-buck configurations:
fP1 =
ILED × D MAX
2 × π × VLED × C OUT
where fP1 is in hertz, VLED is in volts, ILED is in amperes,
and COUT is in farads.
Compensation components, RCOMP and CCOMP, perform two functions. CCOMP introduces a low-frequency
pole that presents a -20dB/decade slope to the loop
gain. RCOMP flattens the gain of the error amplifier for
frequencies above the zero formed by RCOMP and
CCOMP. For compensation, this zero is placed at the
output pole frequency fP1 so that it provides a -20dB/
decade slope for frequencies above fP1 to the combined
modulator and compensator response.
The value of RCOMP needed to fix the total loop gain at
fP1 so that the total loop gain crosses 0dB with -20dB/
decade slope at 1/5 the RHP zero frequency is calculated as follows:
For boost configuration:
R COMP =
fZRHP × R CS × ILED
5 × fP1 × GM COMP × VLED × (1 − D MAX )
For SEPIC and coupled-inductor boost-buck configurations:
R COMP =
fZRHP × R CS × ILED × D MAX
5 × fP1 × GM COMP × VLED × (1 − D MAX )
where RCOMP is the compensation resistor in ohms,
fZRHP and fP2 are in hertz, RCS is the switch currentsense resistor in ohms, and GMCOMP is the transconductance of the error amplifier (600FS).
The value of CCOMP is calculated as follows:
C COMP =
1
2π × R COMP × fZ1
where fZ1 is the compensation zero placed at 1/5 of
the crossover frequency that is, in turn, set at 1/5 of the
fZRHP.
If the output capacitors do not have low ESR, the ESR
zero frequency may fall within the 0dB crossover frequency. An additional pole may be required to cancel
out this pole placed at the same frequency. This is usually implemented by connecting a capacitor in parallel
19
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
with CCOMP and RCOMP. Figure 5 shows the SEPIC
configuration and Figure 6 shows the coupled-inductor
boost-buck configuration.
the current through SETI to get analog dimming functionality by connecting the external control voltage to
SETI through the resistor RSETI2. The resulting change
in the LED current with the control voltage is linear and
inversely proportional. The LED current control range
remains between 20mA to 150mA.
Analog Dimming Using External
Control Voltage
Connect a resistor RSETI2 to the SETI input as shown in
Figure 7 for controlling the LED string current using an
external control voltage. The MAX16814 applies a fixed
1.23V bandgap reference voltage at SETI and measures
the current through SETI. This measured current multiplied by a factor of 1220 is the current through each
one of the four constant current-sink channels. Adjust
Use the following equation to calculate the LED current
set by the control voltage applied:
1500 (1.23 − VC )
× 1220
I OUT = +
R SETI
R SETI2
VIN
4.75V TO 40V
CS
L1
C1
N
NDRV
UP TO 40V
L2
CS
R2
OVP
EN
OUT1
VCC
OUT2
C3
MAX16814
R5
C2
R1
RCS
RSCOMP
IN
D1
OUT3
OUT4
DRV
RSETI
C4
SETI
DIM
VCC
FLT
R3
COMP
RSDT
RCOMP
RT
SGND
CCOMP
PGND
LEDGND
R4
RT
Figure 5. SEPIC Configuration
20 Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
PCB Layout Considerations
LED driver circuits based on the MAX16814 device use
a high-frequency switching converter to generate the
voltage for LED strings. Take proper care while laying
out the circuit to ensure proper operation. The switchingconverter part of the circuit has nodes with very fast voltage changes that could lead to undesirable effects on
the sensitive parts of the circuit. Follow the guidelines
below to reduce noise as much as possible:
1) Connect the bypass capacitor on VCC and DRV as
close to the device as possible and connect the
capacitor ground to the analog ground plane using
vias close to the capacitor terminal. Connect SGND
of the device to the analog ground plane using a via
close to SGND. Lay the analog ground plane on the
inner layer, preferably next to the top layer. Use the
analog ground plane to cover the entire area under
critical signal components for the power converter.
2) Have a power ground plane for the switching-converter power circuit under the power components
(input filter capacitor, output filter capacitor, inductor,
MOSFET, rectifier diode, and current-sense resistor).
Connect PGND to the power ground plane as close
to PGND as possible. Connect all other ground connections to the power ground plane using vias close
to the terminals.
Maxim Integrated
3) There are two loops in the power circuit that carry
high-frequency switching currents. One loop is when
the MOSFET is on (from the input filter capacitor
positive terminal, through the inductor, the internal
MOSFET, and the current-sense resistor, to the input
capacitor negative terminal). The other loop is when
the MOSFET is off (from the input capacitor positive
terminal, through the inductor, the rectifier diode,
output filter capacitor, to the input capacitor negative terminal). Analyze these two loops and make the
loop areas as small as possible. Wherever possible,
have a return path on the power ground plane for the
switching currents on the top layer copper traces, or
through power components. This reduces the loop
area considerably and provides a low-inductance
path for the switching currents. Reducing the loop
area also reduces radiation during switching.
4) Connect the power ground plane for the constantcurrent LED driver part of the circuit to LEDGND as
close to the device as possible. Connect SGND to
PGND at the same point.
21
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
VIN
4.75V TO 40V
T1
(1:1)
D1
C1
UP TO 40V
IN
NDRV
R2
RCS
RSCOMP
CS
OVP
EN
OUT1
VCC
OUT2
C3
MAX16814
R5
C2
R1
N
OUT3
OUT4
DRV
RSETI
C4
SETI
DIM
VCC
FLT
R3
COMP
RSDT
RCOMP
RT
SGND
PGND
CCOMP
LEDGND
R4
RT
Figure 6. Coupled-Inductor Boost-Buck Configuration
MAX16814
1.23V
SETI
RSETI2
RSETI
VC
Figure 7. Analog Dimming with External Control Voltage
22 Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
EN 5
17 OUT3
RT 7
14 OUT1
FLT 8
13 DIM
OVP 9
EP*
SETI 10
OUT1
CS 16
10
DIM
PGND 17
9
SGND
8
RSDT
7
SETI
6
OVP
MAX16814
DRV 19
EP*
VCC 20
12 SGND
1
11 RSDT
IN
15 OUT2
11
NDRV 18
16 LEDGND
COMP 6
12
2
3
4
5
FLT
MAX16814
IN 4
13
RT
18 OUT4
14
COMP
19 CS
VCC 3
15
EN
DRV 2
OUT2
20 PGND
LEDGND
+
NDRV 1
OUT3
TOP VIEW
TOP VIEW
OUT4
Pin Configurations
TQFN/QFND
TSSOP
*EXPOSED PAD.
Typical Operating Circuit
VIN
4.75V TO 40V
D1
L
C1
UP TO 40V
IN
NDRV
R2
RCS
RSCOMP
CS
C2
R1
N
OVP
EN
OUT1
VCC
OUT2
C3
MAX16814
R5
OUT3
OUT4
DRV
RSETI
C4
SETI
DIM
VCC
FLT
R3
COMP
RSDT
RCOMP
RT
SGND
CCOMP
Maxim Integrated
PGND
LEDGND
R4
RT
23
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Chip Information
PROCESS: BiCMOS DMOS
24 Package Information
For the latest package outline information and land patterns, go
to www.maximintegrated.com/packages. Note that a “+”, “#”,
or “-” in the package code indicates RoHS status only. Package
drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND PATTERN
NO.
20 TSSOP-EP
U20E+1
21-0108
90-0114
20 TQFN-EP
T2044+3
21-0139
90-0037
20 QFND-EP
(Side Wettable)
G2044Y+1
21-0576
90-0360
Maxim Integrated
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Revision History
REVISION
NUMBER
REVISION
DATE
0
7/09
Initial release
1
9/09
Correction to slope compensation description and block diagram
2
11/09
Correction to synchronization description frequency and minor
edits
3
2/10
Correction to CSYNC formula
4
6/10
Added MAX16814BE _ _ parts; corrected specification
5
3/11
Correction to output current accuracy specification and Absolute
Maximum Ratings
6
10/11
Correction to the last formula and description
1/13
Added side-wettable package option and updated EN leakage in
Electrical Characteristics
7
DESCRIPTION
PAGES CHANGED
—
10, 18
1–4, 8, 12–20, 22, 25
13
1–4, 8, 13, 25
1, 2, 4
19
1, 2, 4, 8, 9, 23, 24
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
©
2013 Maxim Integrated Products, Inc.
25
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.