Constant Current Buck Regulator for Driving High Power LEDs

NCL30161
Constant-Current Buck
Regulator for Driving High
Power LEDs
The NCL30161 is a hysteretic step−down, constant−current driver
for high power LEDs. Ideal for industrial and general lighting
applications utilizing minimal external components. The NCL30161
operates with an input voltage range from 6.3 V to 40 V. The hysteretic
control gives good power supply rejection and fast response during
load transients and PWM dimming to LED arrays of varying number
and type. A dedicated PWM input (DIM/EN) enables a wide range of
pulsed dimming, and a high switching frequency allows the use of
smaller external components minimizing space and cost. Protection
features include resistor−programmed constant LED current, shorted
LED protection, under−voltage and thermal shutdown. The
NCL30161 is available in a DFN10 3 mm x 3 mm package.
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DFN10
CASE 485C
MARKING DIAGRAM
30161
ALYWG
G
Features
•
•
•
•
•
•
•
•
•
VIN Range 6.3 V to 40 V
Short LED Shutdown Protection: (NCL30161 Latching)
No Control Loop Compensation Required
Adjustable LED Current
Single Pin Brightness and Enable/Disable Control Using PWM
Supports All−Ceramic Output Capacitors and Capacitor−less Outputs
Thermal Shutdown Protection
Capable of 100% Duty Cycle Operation
This is a Pb−Free Device
TYPICAL Application
•
•
•
•
LED Driver
Constant Current Source
General Illumination
Industrial Lighting
30161 = Specific Device Code
A
= Assembly Location
L
= Wafer Lot
Y
= Year
W
= Work Week
G
= Pb−Free Package
(*Note: Microdot may be in either location)
PIN CONNECTIONS
CS 1
10 GATE
NC 2
9 VIN
8 DIM/EN
GND 3
NC 4
CIN
6 ROT
VCC 5
D1
VIN
7 NC
(Top View)
L1
LED
LED
VIN
ORDERING INFORMATION
Device
GATE
NCL30161MNTXG
DIM/Enable
CS
ROT
ROT
VCC
NCL30161
RSENSE
Package
Shipping†
DFN10
(Pb−Free)
3000 / Tape &
Reel
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifications
Brochure, BRD8011/D.
GND
CVCC
Figure 1. Typical Application Circuit
© Semiconductor Components Industries, LLC, 2013
May, 2013 − Rev. 0
1
Publication Order Number:
NCL30161/D
NCL30161
PIN FUNCTION DESCRIPTION
Pin
Pin Name
Description
Application Information
1
CS
Current Sense feedback pin
Set the current through the LED array by connecting a resistor from this pin to
ground.
2, 4, 7
NC
No Connect
3
GND
Ground Pin
5
VCC
Output of Internal 5 V linear
regulator
The VCC pin supplies the power to the internal circuitry. The VCC is the output of a linear regulator which is powered from VIN. A 2 mF ceramic capacitor
is recommended for bypassing and should be placed as close as possible to
the VCC and GND pins. Do not connect to an external load.
6
ROT
Initial Off−Time Setting
Resistor
Resistor ROT from this pin to VCC sets the initial off−time range for the hysteretic controller.
8
DIM/EN
PWM Dimming Control and
ENABLE
9
VIN
Input Voltage Pin
10
GATE
Driver Output
11
FLAG
Ground. Reference point for all voltages
Connect a logic−level PWM signal to this pin to enable/disable the power
MOSFET and LED array
Nominal operating input range is 6.3 V to 40 V. Input supply pin to the internal
circuitry and the positive input to the current sense comparators. Due to high
frequency noise, a 10 mF ceramic capacitor is recommended to be placed as
close as possible to VIN and power ground.
Connect to the gate of the external MOSFET.
Thermal flag. There is no electrical connection to the IC. Connect to ground
plane.
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2
NCL30161
MAXIMUM RATINGS
Rating
Symbol
Min
Max
Unit
VIN
−0.3
40
V
Driver Output Voltage to GND
GATE
−
6.5
V
VCC to GND
VCC
−
6
V
DIM/EN to GND
DIM
−0.3
6
V
CS to GND
CS
−0.3
6
V
ROT
−0.3
VIN to GND
ROT to GND
6
TJ(MAX)
Operating Junction Temperature Range
TJ
Storage Temperature Range
Tstg
−55 to +125
°C
Thermal Characteristics
DFN10 3x3 Plastic Package
Maximum Power Dissipation @ TA = 25°C (Note 1)
PD
1.46
W
Thermal Resistance Junction−to−Ambient (Note 2)
RqJA
86
°C/W
TL
260
°C
MSL
1
−
Lead Temperature Soldering (10 sec):
Reflow (SMD styles only) Pb−Free (Note 3)
Moisture Sensitivity Level (Note 4)
150
V
Absolute Maximum junction temperature
−40
°C
125
°C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
1. The maximum package power dissipation limit must not be exceeded.
PD +
T J(max) * T A
R qJA
2. When mounted on a multi−layer board with 35 mm2 copper area, using 1 oz Cu.
3. 60−180 seconds minimum above 237°C.
4. Moisture Sensitivity Level (MSL): 1 per IPC/JEDEC standard: J−STD−020A.
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3
NCL30161
ELECTRICAL CHARACTERISTICS (Unless otherwise noted: VIN = 12 V, TA = 25°C, unless otherwise specified.)
Symbol
Characteristics
Min
Typ
Max
Unit
40
V
SYSTEM PARAMETERS
VIN
Input Supply Voltage Range
Normal Operation
8.0
Functional (Note 5)
6.3
IQ_IN
Quiescent Current into VIN
1.5
mA
VCC
Internal Regulator Output (Note 6)
5.0
V
VUV+
Under−Voltage Lock−out Threshold (VIN Rising)
5.5
6.0
6.5
V
VUV−
Under−Voltage Lock−out Threshold (VIN Falling)
5.2
5.6
6.3
V
220
226
mV
CURRENT LIMIT AND REGULATION
VCS_UL
CS Regulation Upper Limit
(CS Increasing, FET Turns−OFF)
25°C
213
−40 to 125°C
209
VCS_LL
CS Regulation Lower Limit
(CS Decreasing, FET Turns−ON)
25°C
174
−40 to 125°C
171
VHYS
CS Hysteresis
35
−
45
mV
VOCP
Over Current Protect Limit (Reference to CS Pin)
475
500
525
mV
FSW
Switching Frequency Range (Note 7)
2400
kHz
Cin_CS
231
180
186
mV
189
CS Pin Input Capacitance (Note 7)
4.0
5.0
6.0
pF
CS Blanking Timer (Note 7)
60
73
90
ns
VPWMH/L
PWM (DIM/EN) high level input voltage
1.4
VPWML
PWM (DIM/EN) low level input voltage
IDIM−PU
DIM/EN Pull−up Current
35
fpwm
PWM (DIM/EN) dimming frequency range
0.1
dmax
Maximum Duty Cycle (Note 7)
tBLANKING
DIM INPUT
V
50
0.4
V
65
mA
20
kHz
100
%
MOSFET DRIVER
RGATE_Source
RGATE_Sink
Sourcing Current
4.5
9.0
13.5
W
Sinking Current
0.2
0.4
0.6
W
THERMAL SHUTDOWN
TSD
Thermal Shutdown (Note 7)
160
165
180
°C
THyst
Thermal Hysteresis (Note 7)
30
40
60
°C
Minimum Off−time
110
137
165
ns
OFF TIMER
tOFF−MIN
5. The functional range of VIN is the voltage range over which the device will function. Output current and internal parameters may deviate from
normal values for VIN and VCC voltages between 6.3 V and 8 V, depending on load conditions
6. VCC should not be driven from a voltage higher than VIN or in the absence of a voltage at VIN.
7. Guaranteed by design.
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NCL30161
VIN
DIM / Enable
VCC
5 V Regulator
(6.3 V to 40 Vmax)
VCC
Enable Pull−Up
Resistor
VCC
Gate Driver
S
Q
R
Q
GATE
Peak Current
Comparator
220 mV
CS
Timer (toff)
ROT
Valley Current
Comparator
&
Thermal
Shutdown
180 mV
Short Circuit Protection
Comparator
500 mV
GND
Figure 2. Simplified Block Diagram
D1
VIN
CIN
L1
LED
LED
VIN
GATE
DIM/Enable
CS
ROT
ROT
VCC
NCL30161
RSENSE
GND
CVCC
Figure 3. Typical Application Circuit To Drive Multiple LEDs (Buck)
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5
NCL30161
Theory of Operation
triangular wave shape is halfway between the peak and
valley, so even with changes in duty cycle due to input
voltage variations or load changes, the average current will
remain constant.
This switching power supply is comprised of an inverted
buck regulator controlled by a current mode, hysteretic
control circuit. The buck regulator operates exactly like a
conventional buck regulator except the power device
placement has been inverted to allow for a low side power
FET. Referring to Figure 1, when the FET is conducting,
current flows from the input, through the inductor, the LED
and the FET to ground.
When the FET shuts off, current continues to flow through
the inductor and LED, but is diverted through the diode
(D1). This operation keeps the current in the LED
continuous with a continuous current ramp.
The control circuit controls the current hysteretically.
Figure 2 illustrates the operation of this circuit. The CS
comparator thresholds are set to provide a 10% current
ripple. The peak current comparator threshold of 220 mV
sets Ipeak at 10% above the average current while the valley
current comparator threshold of 180 mV sets Ivalley at 10%
below the average current.
When the FET is conducting, the current in the inductor
ramps up. This current is sensed by the sense resistor that is
connected from CS to ground. When the voltage on the CS
pin reaches 220 mV, the peak current comparator turns off
the power FET. A conventional hysteretic controller would
monitor the load current and turn the switch back on when
the CS pin reaches 180 mV. But in this topology the current
information is not available to the control circuit when the
FET is off. To set the proper FET off time, the CS voltage is
sensed when the FET is turned back on and a correction
signal is sent to the off time circuit to adjust the off time as
necessary. When the FET is turned on, there can be a lot of
ringing on the CS pin that would make the voltage on the CS
pin be an unreliable measure of the current through the FET.
An 85 ns blanking timer is started when the GATE voltage
starts to go high, to allow this ringing to settle down. At the
end of this blanking timer, CS voltage is sensed to determine
the valley current.
Over Current Protection Feature
In the event there is a short−circuit across the LEDs, a
large amount of current could potentially flow through the
circuit during startup. To protect against this, the NCL30161
comes with a short circuit protection feature. If the voltage
on the CS pin is detected to be greater than the over current
protection limit, the NCL30161 will turn off the FET, and
prevent the FET from turning on again until power is
recycled to the NCL30161.
Undervoltage Lockout
When VIN rises above the UVLO threshold voltage,
switching operation of the FET will begin. However, until
the VIN voltage reaches 8 V, the VCC regulator may not
provide the expected gate drive voltage to the FET. This
could result in the RDS(on) of the FET being higher than
expected or there not being enough gate drive capability to
operate at the maximum rated switching frequency. For
optimal performance, it is recommended to operate the part
at a VIN voltage of 8 V or greater.
Setting The Output Current
The average output current is determined as being the
middle of the peak and valley of the output current, set by the
CS comparator thresholds. The nominal average output
current will be the current value equivalent to 200 mV at the
CS pin. The proper RSENSE value for a desired average
output current can be calculated by:
R SENSE +
200 mV
I LED
PWM Dimming
For a given RSENSE value, the average output current, and
therefore the brightness of the LED, can be set to a lower
value through the DIM/EN pin. When the DIM/EN pin is
brought low, the internal FET will turn off and switching
will remain off until the DIM/EN pin is brought back into its
high state.
By applying a pulsed signal to DIM/EN, the average
output current can be adjusted to the duty ratio of the pulsed
signal. It is recommended to keep the frequency of the
DIM/EN signal above 100 Hz to avoid any visible flickering
of the LED.
Figure 4. Typical Current Waveforms
The current wave shape is triangular, and the peak and
valley currents are controlled. The average value for a
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6
NCL30161
Inductor Selection
forward current of the diode. The average current through
the diode can be calculated as:
The inductor that is used directly affects the switching
frequency the driver operates at. The value of the inductor
sets the slope at which the output current rises and falls
during the switching operation. The slope of the current, in
turn, determines how long it takes the current to go from the
valley point of the current ripple to the peak when the FET
is on and the current and rising, and how long it takes the
current to go from the peak point of the current to the valley
when the FET is off and the current is falling. These times
can be approximated from the following equations:
I avg_diode + I OUT
t OFF
t ON ) t OFF
It is also important to select a diode that is capable of
withstanding the peak reverse voltage it will see in the
application. It is recommended to select a diode with a rated
reverse voltage greater than VIN. It is also recommended to
use a low−capacitance Schottky diode for better efficiency
performance.
t ON
Selecting The Off−Time Setting Resistor
+
VIN * V LED * I OUT
t OFF +
ǒ
L
DI
FET R
L
The off−time setting resistor (ROT) programs the
NCL30161 with the initial time duration that the MOSFET
is turned off when the switching operation begins. During
subsequent switching cycles, the voltage at the CS pin is
sensed every time the MOSFET is turned on, and the
off−time will be adjusted depending on how much of a
discrepancy exists between the sensed value and the CS
lower limit threshold value. Selecting an appropriate ROT
value allows the system to quickly achieve the intended
current regulation. The ROT value can be calculated using
the following equation:
Ǔ
(on) ) DCR L ) R SENSE
DS
DI
V LED ) V diode ) I OUT
DCR L
Where DCRL is the dc resistance of the inductor, VLED is the
forward voltages of the LEDs, FETRDS(ON) is the
on−resistance of the power MOSFET, and Vdiode is the
forward voltage of the catch diode.
The switching frequency can then be approximated from
the following:
f SW +
R OT + t OFF
1
t ON ) t OFF
10 11 W
Where tOFF is the expected off time during normal switching
operation, calculated in the Inductor Selection section
above.
Every time the DIM/EN pin is brought from a low state to
a high state, the initial off−time program is reset. The first
off−time of the MOSFET after the DIM/EN is brought high
will be set by the ROT value. The off−time will then be
adjusted in subsequent switching cycles.
Higher values of inductance lead to slower rates of rise
and fall of the output current. This allows for smaller
discrepancies between the expected and actual output
current ripple due to propagation delays between sensing at
the CS pin and the turning on and off of the power MOSFET.
However, the inductor value should be chosen such that the
peak output current value does not exceed the rated
saturation current of the inductor.
Input Capacitor
A decoupling capacitor from VIN to ground should be
used to provide the current needed when the power
MOSFET turns on. A 10 mF ceramic capacitor is
recommended.
Catch Diode Selection
The catch diode needs to be selected such that the average
current through the diode does not exceed the rated average
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7
NCL30161
PACKAGE DIMENSIONS
DFN10, 3x3, 0.5P
CASE 485C
ISSUE C
D
PIN 1
REFERENCE
2X
2X
L1
ÇÇÇ
ÇÇÇ
ÇÇÇ
0.15 C
EDGE OF PACKAGE
A
B
E
DETAIL A
Bottom View
(Optional)
EXPOSED Cu
TOP VIEW
MOLD CMPD
0.15 C
(A3)
DETAIL B
0.10 C
A1
A
10X
A1
D2
10X
1
DIM
A
A1
A3
b
D
D2
E
E2
e
K
L
L1
C
DETAIL A
e
L
A3
DETAIL B
Side View
(Optional)
SEATING
PLANE
0.08 C
SIDE VIEW
ÉÉÉ
ÉÉÉ
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b APPLIES TO PLATED
TERMINAL AND IS MEASURED BETWEEN
0.25 AND 0.30 MM FROM TERMINAL.
4. COPLANARITY APPLIES TO THE EXPOSED
PAD AS WELL AS THE TERMINALS.
5. TERMINAL b MAY HAVE MOLD COMPOUND
MATERIAL ALONG SIDE EDGE. MOLD
FLASHING MAY NOT EXCEED 30 MICRONS
ONTO BOTTOM SURFACE OF TERMINAL b.
6. DETAILS A AND B SHOW OPTIONAL VIEWS
FOR END OF TERMINAL LEAD AT EDGE OF
PACKAGE.
7. FOR DEVICE OPN CONTAINING W OPTION,
DETAIL B ALTERNATE CONSTRUCTION IS
NOT APPLICABLE.
SOLDERING FOOTPRINT*
5
MILLIMETERS
MIN
MAX
0.80
1.00
0.00
0.05
0.20 REF
0.18
0.30
3.00 BSC
2.40
2.60
3.00 BSC
1.70
1.90
0.50 BSC
0.19 TYP
0.35
0.45
0.00
0.03
2.6016
10X
E2
K
10
10X
0.10 C A B
0.05 C
6
1.8508
2.1746
b
3.3048
BOTTOM VIEW
NOTE 3
10X
0.5651
10X
0.5000 PITCH
0.3008
DIMENSIONS: MILLIMETERS
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
ON Semiconductor and
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reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any
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limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications
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NCL30161/D