DIODES ZXLD1356

A Product Line of
Diodes Incorporated
ZXLD1356
60V 550mA LED DRIVER with AEC-Q100
Description
Pin Assignments
The ZXLD1356 is a continuous mode inductive step-down
converter, designed for driving single or multiple series
connected LEDs efficiently from a voltage source higher than
the LED voltage. The device operates from an input supply
between 6V and 60V and provides an externally adjustable
output current of up to 550mA. Depending upon supply
voltage and external components, this can provide up to
30 watts of output power.
The ZXLD1356 has been qualified to AECQ100 Grade 1
enabling operation in ambient temperatures from -40 to
125°C
Output current can be adjusted above, or below the set
value, by applying an external control signal to the 'ADJ' pin.
Enhanced output current dimming can be achieved by
applying a PWM signal to the ‘ADJ’ pin.
GND
ADJ
ISENSE
TSOT23-5
Top View
(TOP VIEW)
6 VIN
LX 1
Features
• Typically better than 0.8% output current accuracy
• Simple and with low part count
• Single pin on/off and brightness control using DC voltage
or PWM
• PWM resolution up to 1000:1
• High efficiency (up to 97%)
• Wide input voltage range: 6V to 60V
• Inherent open-circuit LED protection
• Available in thermally enhanced packages
o
DFN3030-6
θJA
44° C/W
o
TSOT23-5
θJA
82° C/W
• Available in Green molding (no Br, Sb) with lead free
finish/RoHS compliant
• Qualified to AEC-Q100 Grade 1
o
TSOT23-5
ZXLD1356ET5TA
VIN
LX
GND 2
5 GND
ADJ 3
4 ISENSE
DFN3030-6
Typical Application Circuit
D1
Rs
VIN (24V)
0.36V
L1
C1
4.7µF
Applications
•
•
•
•
•
•
•
•
Low voltage halogen replacement LEDs
Automotive lighting
Low voltage industrial lighting
LED back-up lighting
Illuminated signs
Emergency lighting
SELV lighting
Refrigeration lights
ZXLD1356
Document number: DS33470 Rev. 3 - 2
100nF
VIN
I SENSE
ADJ
ZXLD1356
LX
GND
GND
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ZXLD1356
Block Diagram
D1
VIN
L1
RS
5
5V
C1
4.7μF
4
VIN
ISENSE
1
LX
R1
Voltage
regulator
+
0.2V
+
Low voltage
detector
MN
+
Adj
3
R4
50K
D1
1.25V
Gnd
R5
20K
600KHz
R2
+
R3
1.35V
2
Figure 1. Block diagram – Pin connections shown for TSOT23-5 package
Name
LX
GND
TSOT23-5
1
2
DFN3030-6
1
2, 5
ADJ
3
3
ISENSE
4
4
VIN
5
6
Pad
-
Pad
ZXLD1356
Document number: DS33470 Rev. 3 - 2
Description
Drain of NDMOS switch
Ground (0V)
Multi-function On/Off and brightness control pin:
•
Leave floating for normal operation.(VADJ= VREF =1.25V giving nominal average
output current
o IOUTnom = 0.2V/RS)
•
Drive to voltage below 0.2V to turn off output current
•
Drive with DC voltage (0.3V<VADJ<2.5V) to adjust output current from 24% to 200%
of IOUTnom
•
Connect a capacitor from this pin to ground to define soft-start time.
Soft-start time is approx.0.2ms/nF
Connect resistor RS from this to VIN to define nominal average output current
IOUTnom = 0.2/RS (Note: RSMIN=0.36V with ADJ pin open circuit)
Input voltage (6V to 60V). Decouple to ground with 4.7µF of higher X7R ceramic capacitor
close to device
Exposed pad (EP) - connected to device substrate.
To improve thermal impedance of package the EP must be connected to power ground
but should not be used as the 0V (GND) current path.
It can be left floating but must not be connected to any other voltage other than 0V.
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ZXLD1356
Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated)
Symbol
Parameter
VIN
Input Voltage
VSENSE
ISENSE Voltage
V
+0.3 to -5
(measured with respect to VIN)
-0.3 to +60
LX Output Voltage
VADJ
ILX
Adjust Pin Input Voltage
Switch Output Current
TST
TJ MAX
Unit
(65V for 0.5 sec)
VLX
PTOT
Rating
-0.3 to +60
V
(65V for 0.5 sec)
-0.3 to +6
0.65
Power Dissipation
TSOT23-5
1
(Refer to Package thermal de-rating curve on page
25)
DFN3030-6
1.8
V
V
A
W
Storage Temperature
Junction Temperature
-55 to 150
150
°C
°C
These are stress ratings only. Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings, for extended
periods, may reduce device reliability.
ESD Susceptibility
Human Body Model
Machine Model
Rating
500
<100
Unit
V
V
Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and
transporting these devices.
The human body model is a 100pF capacitor discharge through a 1.5kΩ resistor pin. The machine model is a 200pF capacitor discharged directly into each pin
Thermal Resistance
Symbol
Parameter
θJA
Junction to Ambient
TSOT23-5
82
Rating
DFN3030-6
44
Unit
°C/W
ΨJB
Junction to Board
33
-
θJC
Junction to Case
-
14
°C/W
Min
6
Max
60
800
800
625
0.99
125
Units
V
ns
ns
kHz
°C/W
Recommended Operating Conditions
Symbol
VIN
tOFFMIN
tONMIN
fLX max
DLX
TOP
Notes:
Parameter
Input voltage (Note 1)
Minimum switch off-time
Minimum switch on-time
Recommended maximum operating frequency (Note 2)
Duty cycle range
Operating Temperature range
0.01
-40
°C
1. VIN > 16V to fully enhance output transistor. Otherwise out current must be derated - see graphs. Operation at low supply may cause excessive heating
due to increased on-resistance. Tested at 7V guaranteed for 6V by design.
2. ZXLD1356 will operate at higher frequencies but accuracy will be affected due to propagation delays.
ZXLD1356
Document number: DS33470 Rev. 3 - 2
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ZXLD1356
Electrical Characteristics
(Test conditions: VIN = 12V, Tamb = 25°C, unless otherwise specified.)
Symbol
VSU
VSD
IINQoff
Parameter
Internal regulator start-up threshold
Internal regulator shutdown threshold
Quiescent supply current with output off
IINQon
Quiescent supply current with output switching
(Note 3)
VSENSE
Mean current sense threshold voltage
(Defines LED current setting accuracy)
VSENSEHYS
ISENSE
Sense threshold hysteresis
ISENSE pin input current
VREF
Internal reference voltage
ΔVREF/ΔT
Temperature coefficient of VREF
External control voltage range on ADJ pin for DC
brightness control (Note 4)
DC voltage on ADJ pin to switch device from
active (on) state to quiescent (off) state
DC voltage on ADJ pin to switch device from
quiescent (off) state to active (on) state
VADJ
VADJoff
VADJon
Condition
4.4
Resistance between ADJ pin and VREF
ILXmean
RLX
ILX(leak)
Continuous LX switch current
LX switch ‘On’ resistance
LX switch leakage current
Duty cycle range of PWM signal applied to ADJ
pin during low frequency PWM dimming mode
Brightness control range
DCADJ
(*)
DC Brightness control range
tSS
Start up time
(See graphs for more details)
fLX
Operating frequency
(See graphs for more details)
fLXmax
Notes:
ADJ pin grounded
ADJ pin floating,
L=68mH, 3 LEDs
f=360kHz
Measured on ISENSE pin
with respect to VIN
VADJ=1.25V; VIN=18V
Typ.
4.85
4.75
65
Max.
5.2
108
1.6
195
200
±15
4
VSENSE=VIN-0.2
Measured on ADJ pin
with pin floating
RADJ
DPWM(LF)
Min.
Unit
V
V
µA
mA
205
mV
10
%
µA
1.25
V
50
ppm/°C
0.3
2.5
V
VADJ falling
0.15
0.2
0.27
V
VADJ rising
0.2
0.25
0.3
V
0< VADJ< VREF
VADJ>VREF +100mV
30
10.4
50
14.2
65
18
0.55
0.75
5
@ ILX=0.55A
PWM frequency
<300Hz PWM
amplitude =VREF
Measured on ADJ pin
Note 5
Time taken for output
current to reach 90% of
final value after voltage
on ADJ pin has risen
above 0.3V.
Requires external
capacitor 22nF.
ADJ pin floating
L=68mH (0.36V)
IOUT=0.55A @
VLED=3.6V
Driving 3 LEDs
Recommended maximum operating frequency
0.5
0.001
kΩ
A
Ω
µA
1
1000:1
5:1
2
ms
360
kHz
500
kHz
3. Static current of device is approximately 700 µA, see Graph, Page 17.
4. 100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE. threshold and output current
proportionally.
5. Ratio of maximum brightness to minimum brightness before shutdown VREF =1.25/0.25. VREF externally driven to 2.5V, ratio 10.1.
ZXLD1356
Document number: DS33470 Rev. 3 - 2
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ZXLD1356
Device Description
The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a self-oscillating continuous-mode buck
converter.
Device operation (refer to Figure 1 - Block diagram and Figure 2 Operating waveforms)
VIN
LX voltage
0V
Toff
Ton
VIN
230mV
170mV
200mV
SENSE voltage
VSENSEVSENSE+
IOUTnom +15%
IOUTnom
Coil current
IOUTnom -15%
0V
Comparator
input voltage
0.15VADJ
VADJ
0.15VADJ
Comparator
output
5V
0V
Figure 2. Theoretical Operating Waveforms
Operation can be best understood by assuming that the ADJ pin of the device is unconnected and the voltage on this pin (VADJ)
appears directly at the (+) input of the comparator.
When input voltage VIN is first applied, the initial current in L1 and RS is zero and there is no output from the current sense
circuit. Under this condition, the (-) input to the comparator is at ground and its output is high. This turns MN on and switches
the LX pin low, causing current to flow from VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by
VIN and L1 to produce a voltage ramp (VSENSE) across RS. The supply referred voltage VSENSE is forced across internal resistor
R1 by the current sense circuit and produces a proportional current in internal resistors R2 and R3. This produces a ground
referred rising voltage at the (-) input of the comparator. When this reaches the threshold voltage (VADJ), the comparator output
switches low and MN turns off. The comparator output also drives another NMOS switch, which bypasses internal resistor R3 to
provide a controlled amount of hysteresis. The hysteresis is set by R3 to be nominally 15% of VADJ.
When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to VIN. The current decays at a rate determined
by the LED(s) and diode forward voltages to produce a falling voltage at the input of the comparator. When this voltage returns
to VADJ, the comparator output switches high again. This cycle of events repeats, with the comparator input ramping between
limits of VADJ ± 15%.
ZXLD1356
Document number: DS33470 Rev. 3 - 2
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ZXLD1356
Device Description (Continued)
Switching thresholds
With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of 200mV (measured on the ISENSE
pin with respect to VIN). The average output current IOUTnom is then defined by this voltage and RS according to:
IOUTnom = 200mV/RS
Nominal ripple current is ±30mV/RS
Adjusting output current
The device contains a low pass filter between the ADJ pin and the threshold comparator and an internal current limiting resistor
(50kΩ nom) between ADJ and the internal reference voltage. This allows the ADJ pin to be overdriven with either DC or pulse
signals to change the VSENSE switching threshold and adjust the output current.
Details of the different modes of adjusting output current are given in the applications section.
Output shutdown
The output of the low pass filter drives the shutdown circuit. When the input voltage to this circuit falls below the threshold
(0.2V nom.), the internal regulator and the output switch are turned off. The voltage reference remains powered during
shutdown to provide the bias current for the shutdown circuit. Quiescent supply current during shutdown is nominally 60µA and
switch leakage is below 5µA.
ZXLD1356
Document number: DS33470 Rev. 3 - 2
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ZXLD1356
Actual operating waveforms [VIN=15V, RS=0.36V, L=68µH]
Normal operation. Output current (Ch3) and LX voltage (Ch2)
Actual operating waveforms [VIN=30V, RS=0.36V, L=68µH]
Normal operation. Output current (Ch3) and LX voltage (Ch2)
Actual operating waveforms [VIN=60V, RS=0.36V, L=68µH]
Normal operation. Output current (Ch3) and LX voltage (Ch2)
ZXLD1356
Document number: DS33470 Rev. 3 - 2
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ZXLD1356
Typical Operating Conditions
ZXLD1356 Output Current
L = 68µH
0.640
0.620
Output Current (A)
0.600
0.580
0.560
0.540
0.520
0.500
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD1356 Output Current Deviation (Normalized)
L = 68µH
10%
Output Current Deviation (%)
8%
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD1356 Efficiency
L = 68µH
100%
95%
90%
Efficiency (%)
85%
80%
75%
70%
65%
60%
55%
50%
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
5 LEDs
7 LEDs
9 LEDs
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11 LEDs
13 LEDs
15 LEDs
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ZXLD1356
Typical Operating Conditions (Cont.)
ZXLD1356 Switching Frequency
L = 68µH
700
Switching Frequency (kHz)
600
500
400
300
200
100
0
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD1356 Duty Cycle
L = 68µH
100
90
80
Duty Cycle (% )
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
5 LEDs
7 LEDs
9 LEDs
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11 LEDs
13 LEDs
15 LEDs
December 2010
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Diodes Incorporated
ZXLD1356
Typical Operating Conditions (Cont.)
ZXLD1356 Output Current
L = 100µH
0.640
0.620
Output Current (A)
0.600
0.580
0.560
0.540
0.520
0.500
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LED s
15 LED s
ZXLD1356 Output Current Deviation (N ormalized)
L = 100µH
10%
Output Current Deviation (%)
8%
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LED s
15 LED s
ZXLD1356 Efficiency
L = 100µH
100%
95%
90%
Efficiency (%)
85%
80%
75%
70%
65%
60%
55%
50%
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
5 LEDs
7 LEDs
9 LEDs
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11 LEDs
13 LEDs
15 LEDs
December 2010
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Diodes Incorporated
ZXLD1356
Typical Operating Conditions (Cont.)
ZXLD1356 Switching Frequency
L = 100µH
700
Switching Frequency (kHz)
600
500
400
300
200
100
0
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD1356 Duty Cycle
L = 100µH
100
90
80
Duty Cycle (%)
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
5 LEDs
7 LEDs
9 LEDs
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11 LEDs
13 LEDs
15 LEDs
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ZXLD1356
Typical Operating Conditions (Cont.)
ZXLD1356 Output Current
L = 150µH
0.640
0.620
Output Current (A)
0.600
0.580
0.560
0.540
0.520
0.500
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD 1356 Output Current Deviation (Normalized)
L = 150µH
10%
Output Current Deviation (%)
8%
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD1356 Efficiency
L = 150µH
100%
95%
90%
Efficiency (%)
85%
80%
75%
70%
65%
60%
55%
50%
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
5 LEDs
7 LEDs
9 LEDs
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11 LEDs
13 LEDs
15 LEDs
December 2010
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ZXLD1356
Typical Operating Conditions (Cont.)
ZXLD1356 Switching Frequency
L = 150µH
700
Switching Frequency (kHz)
600
500
400
300
200
100
0
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LED s
15 LED s
ZXLD1356 Duty Cycle
L = 150µH
100
90
80
Duty Cycle (%)
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
5 LEDs
7 LEDs
9 LEDs
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11 LEDs
13 LEDs
15 LEDs
December 2010
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ZXLD1356
Typical Operating Conditions (Cont.)
ZXLD1356 Output Current
L = 220µH
0.640
0.620
Output Current (A)
0.600
0.580
0.560
0.540
0.520
0.500
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD1356 Output Current Deviation (N ormalized)
L = 220µH
10%
Output Current Deviation (%)
8%
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
20
30
40
50
60
Supply Voltage (V)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
ZXLD1356 Efficiency
L = 220µH
100%
95%
90%
Efficiency (%)
85%
80%
75%
70%
65%
60%
55%
50%
0
10
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
20
5 LEDs
30
Supply Voltage (V)
7 LEDs
9 LEDs
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40
11 LEDs
50
13 LEDs
60
15 LEDs
December 2010
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Diodes Incorporated
ZXLD1356
Typical Operating Conditions (Cont.)
ZXLD1356 Switching Frequency
L = 220µH
700
Switching Frequency (kHz)
600
500
400
300
200
100
0
0
10
1 LED
3 LEDs
20
5 LEDs
30
Supply Voltage (V)
7 LEDs
40
9 LEDs
11 LEDs
50
13 LEDs
60
15 LEDs
ZXLD1356 Duty Cycle
L = 220µH
100
90
80
Duty Cycle (%)
70
60
50
40
30
20
10
0
0
10
1 LED
ZXLD1356
Document number: DS33470 Rev. 3 - 2
3 LEDs
20
5 LEDs
30
Supply Voltage (V)
7 LEDs
9 LEDs
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40
11 LEDs
50
13 LED s
60
15 LEDs
December 2010
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Diodes Incorporated
ZXLD1356
Typical Operating Conditions (Cont.)
LED Current vs Vadj
600
500
LED Current (mA)
400
300
200
100
0
0
1
2
3
ADJ Pin Voltage (V)
R=0.36Ω
R=0.56Ω
R=1.33Ω
Supply current
800
Supply current (mA)
700
600
500
400
Output transistor
fully enhanced
300
Output transistor
not fully enhanced
200
100
0
0
10
20
30
40
50
60
70
Supply voltage (V)
Vref
ADJ pin voltage (V)
1.243
1.2425
1.242
1.2415
1.241
1.2405
1.24
1.2395
1.239
1.2385
1.238
0
10
20
30
40
50
60
70
Supply voltage (V)
Shutdown current
Shutdown current (mA)
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
Supply voltage (V)
ZXLD1356
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ZXLD1356
Typical Operating Conditions (Cont.)
Lx on-resistance vs supply voltage
2.5
O n -resistan ce (O h m s)
2
1.5
-40 oC
25 oC
125 oC
1
0.5
0
0
10
20
30
40
50
60
70
S u p p ly V o ltag e (V )
Vadj vs Temperature
1.262
1.26
1.258
Vadj (V)
1.256
7V
9V
12V
20V
30V
1.254
1.252
1.25
1.248
1.246
1.244
-50
0
50
100
Temperature (C)
150
200
Lx on-resistance vs die temperature
1.6
On-resistance (Ohms)
1.4
1.2
1
7V
9V
12V
20V
30V
0.8
0.6
0.4
0.2
0
-50
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0
50
100
Die Temperature (C)
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200
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Application Information
Setting nominal average output current with external resistor RS
The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS)
connected between VIN and ISENSE and is given by:
IOUTnom = 0.2/RS [for RS > 0.36Ω]
The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the
typical application circuit shown on page 1:
RS (Ω)
Nominal average output
current (mA)
0.36
555
0.56
357
1.33
150
The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V). Note that RS = 0.36V is the
minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value.
It is possible to use different values of RS if the ADJ pin is driven from an external voltage. (See next section).
Output current adjustment by external DC control voltage
The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current to a value above or below the
nominal average value defined by RS.
+
ADJ
ZXLD1356
GND
DC
GND
The nominal average output current in this case is given by:
IOUTdc = (VADJ /1.25) x (0.2/RS) [for 0.3< VADJ <2.5V]
Note that 100% brightness setting corresponds to VADJ = VREF. When driving the ADJ pin above 1.25V, RS must be increased in
proportion to prevent IOUTdc exceeding 550mA maximum.
The input impedance of the ADJ pin is 50kΩ ±25% for voltages below VREF and 14.2kΩ ±25% for voltages above VREF +100mV.
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Application Information (Continued)
Output Current Adjustment by PWM Control
Directly driving ADJ input
A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as shown below, to adjust the output
current to a value above or below the nominal average value set by resistor RS:
PWM
VADJ
ADJ
ZXLD1356
0V
GND
GND
Driving the ADJ input via open collector transistor
The recommended method of driving the ADJ pin and controlling the amplitude of the PWM waveform is to use a small NPN
switching transistor as shown below:
ADJ
PWM
ZXLD1356
GND
GND
This scheme uses the 50k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the external
transistor eg MMBT3904.
Driving the ADJ input from a microcontroller
Another possibility is to drive the device from the open drain output of a microcontroller. The diagram below shows one method
of doing this:
MCU
3.3k
ADJ
ZXLD1356
GND
If the NMOS transistor within the microcontroller has high Gate / Drain capacitance, this arrangement can inject a negative spike
into ADJ input of the ZXLD1356 and cause erratic operation but the addition of a Schottky clamp diode (eg Diodes Inc.
SD103CWS) to ground and inclusion of a series resistor (3.3k) will prevent this. See the section on PWM dimming for more
details of the various modes of control using high frequency and low frequency PWM signals.
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Application Information (Continued)
Shutdown Mode
Taking the ADJ pin to a voltage below 0.2V for more than approximately 100µs will turn off the output and supply current to a low
standby level of 65µA nominal.
Note that the ADJ pin is not a logic input. Taking the ADJ pin to a voltage above VREF will increase output current above the
100% nominal average value. (See page 17 graphs for details).
Soft-start
An external capacitor from the ADJ pin to ground will provide a soft-start delay, by increasing the time taken for the voltage on
this pin to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator.
Adding capacitance increases this delay by approximately 0.2ms/nF. The graph below shows the variation of soft-start time for
different values of capacitor.
Soft Start Time vs Capacitance from ADJ pin to Ground
16
14
Soft Start Time (ms)
12
10
8
6
4
2
0
-2
0
20
40
60
Capacitance (nf)
80
100
120
Actual operating waveforms [VIN=60V, RS=0.36V, L=68µH, 22nF on ADJ]
Soft-start operation. LX voltage (Ch2) and Output current (Ch3) using a 22nF external capacitor on the ADJ pin.
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Application Information (Continued)
VIN Capacitor Selection
A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source
impedance and lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the
current ripple on the input supply.
To avoid transients into the IC, the size of the input capacitor will depend on the VIN voltage:
VIN = 6 to 40V
CIN = 2.2µF
VIN = 40 to 50V
CIN = 4.7µF
VIN = 50 to 60V
CIN = 10µF
When the input voltage is close to the output voltage the input current increases which puts more demand on the input capacitor.
The minimum value of 2.2µF may need to be increased to 4.7µF; higher values will improve performance at lower input voltages,
especially when the source impedance is high. The input capacitor should be placed as close as possible to the IC.
For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric is recommended. Capacitors
with Y5V dielectric are not suitable for decoupling in this application and should NOT be used.
When higher voltages are with CIN = 10µF, an electrolytic capacitor can be used provided that a suitable 1mF ceramic capacitor
is also used and positioned as close to the VIN pin as possible.
A suitable capacitor would be NACEW100M1006.3x8TR13F (NIC Components).
The following web sites are useful when finding alternatives:
www.murata.com
www.niccomp.com
www.kemet.com
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Application Information (Continued)
Inductor Selection
Recommended inductor values for the ZXLD1356 are in the range 68 µH to 220 µH.
Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays,
which result in increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current
over the supply voltage range. (see graphs pages 10-16). The inductor should be mounted as close to the device as possible
with low resistance connections to the LX and VIN pins.
The chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the
required mean output current.
Suitable coils for use with the ZXLD1356 may be selected from the MSS range manufactured by Coilcraft, or the NPIS range
manufactured by NIC components. The following websites may be useful in finding suitable components
www.coilcraft.com
www.niccomp.com
www.wuerth-elektronik.de
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the specified limits over
the supply voltage and load current range.
Figures 3 and 4 (following) can be used to select a recommended inductor based on maintaining the ZXLD1356 case
temperature below 60°C for the different package types. For detailed performance characteristics for the inductor values 68, 100,
150 and 220µH see graphs on pages 10-16.
Minimum Recommended Inductor
2% Accuracy, <60°C Case Temperature
15
Legend
14
68uH
13
100uH
12
150uH
Number of LEDs
11
220uH
10
9
8
7
6
5
4
3
2
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 3. ZXLD1356 Minimum Recommended Inductor
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Application Information (Continued)
Diode selection
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low reverse
leakage at the maximum operating voltage and temperature.
They also provide better efficiency than silicon diodes, due to a combination of lower forward voltage and reduced recovery time.
It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than
the maximum output load current. It is very important to consider the reverse leakage of the diode when operating above 85°C.
Excess leakage will increase the power dissipation in the device and if close to the load may create a thermal runaway condition.
The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the LX
output. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the LX pin including supply
ripple, does not exceed the specified maximum value.
*A suitable Schottky diode would be B1100B (Diodes Inc).
Reducing Output Ripple
Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor, Cled, across the LED(s) as shown
below:
D1
Rs
VIN
LED
Cled
L1
V IN
ISENSE
LX
ZXLD1356
A value of 1µF will reduce the supply ripple current by a factor three (approx.). Proportionally lower ripple can be achieved with
higher capacitor values. Note that the capacitor will not affect operating frequency or efficiency, but it will increase start-up delay,
by reducing the rate of rise of LED voltage.
By adding this capacitor the current waveform through the LED(s) changes from a triangular ramp to a more sinusoidal version
without altering the mean current value.
Operation at low supply voltage
Below the under-voltage lockout threshold (VSD) the drive to the output transistor is turned off to prevent device operation with
excessive on-resistance of the output transistor. The output transistor is not full enhanced until the supply voltage exceeds
approximately 17V. At supply voltages between VSD and 17V care must be taken to avoid excessive power dissipation due to the
on-resistance.
Note that when driving loads of two or more LEDs, the forward drop will normally be sufficient to prevent the device from
switching below approximately 6V. This will minimize the risk of damage to the device.
ZXLD1356
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Application Information (Continued)
Thermal considerations
When operating the device at high ambient temperatures, or when driving maximum load current, care must be taken to avoid
exceeding the package power dissipation limits. The graph below gives details for power derating. This assumes the device to be
mounted on a (25mm)2 PCB with 1oz copper standing in still air.
Maximum Power Dissipation
2
1.8
DFN3030-6
Power Dissipation (W)
1.6
1.4
1.2
1
0.8
TSOT23-5
0.6
0.4
0.2
0
-40
-25
-10
5
20
35
50
65
Ambient Temperature (°C)
80
95
110
125
140
Note that the device power dissipation will most often be a maximum at minimum supply voltage. It will also increase if the
efficiency of the circuit is low. This may result from the use of unsuitable coils, or excessive parasitic output capacitance on the
switch output.
Thermal compensation of output current
High luminance LEDs often need to be supplied with a temperature compensated current in order to maintain stable and reliable
operation at all drive levels. The LEDs are usually mounted remotely from the device so, for this reason, the temperature
coefficients of the internal circuits for the ZXLD1356 have been optimized to minimize the change in output current when no
compensation is employed. If output current compensation is required, it is possible to use an external temperature sensing
network - normally using Negative Temperature Coefficient (NTC) thermistors and/or diodes, mounted very close to the LED(s).
The output of the sensing network can be used to drive the ADJ pin in order to reduce output current with increasing
temperature.
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Application information (Continued)
Layout Considerations
LX pin
The LX pin of the device is a fast switching node, so PCB tracks should be kept as short as possible. To minimize ground
'bounce', the ground pin of the device should be soldered directly to the ground plane.
Coil and decoupling capacitors and current sense resistor
It is particularly important to mount the coil and the input decoupling capacitor as close to the device pins as possible to minimize
parasitic resistance and inductance, which will degrade efficiency. It is also important to minimize any track resistance in series
with current sense resistor RS. Its best to connect VIN directly to one end of RS and Isense directly to the opposite end of RS with
no other currents flowing in these tracks. It is important that the cathode current of the Schottky diode does not flow in a track
between RS and VIN as this may give an apparent higher measure of current than is actual because of track resistance.
ADJ pin
The ADJ pin is a high impedance input for voltages up to 1.35V so, when left floating, PCB tracks to this pin should be as short
as possible to reduce noise pickup. A 100nF capacitor from the ADJ pin to ground will reduce frequency modulation of the output
under these conditions. An additional series 3.3kΩ resistor can also be used when driving the ADJ pin from an external circuit
(see below). This resistor will provide filtering for low frequency noise and provide protection against high voltage transients.
3.3k
ADJ
100nF
ZXLD1356
GND
GND
High voltage tracks
Avoid running any high voltage tracks close to the ADJ pin, to reduce the risk of leakage currents due to board contamination.
The ADJ pin is soft-clamped for voltages above 1.35V to desensitize it to leakage that might raise the ADJ pin voltage and cause
excessive output current. However, a ground ring placed around the ADJ pin is recommended to minimize changes in output
current under these conditions.
Evaluation Boards
ZXLD1356 evaluation boards are available on request, which have connection terminals that allow customers to connect their
own LED products to the board.
ZXLD1356
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Application Information (Continued)
Dimming Output Current Using PWM
Low frequency PWM mode
When the ADJ pin is driven with a low frequency PWM signal (eg 100Hz), with a high level voltage VADJ and a low level of zero,
the output of the internal low pass filter will swing between 0V and VADJ, causing the input to the shutdown circuit to fall below
its turn-off threshold (200mV nom) when the ADJ pin is low. This will cause the output current to be switched on and off at the
PWM frequency, resulting in an average output current IOUTavg proportional to the PWM duty cycle. (See Figure 4 - Low
frequency PWM operating waveforms).
Low frequency PWM operating waveforms
The average value of output current in this mode is given by:
IOUTavg = 0.2DPWM
RS
for DPWM > 0.001
This mode is preferable if optimum LED 'whiteness' is required. It will also provide the widest possible dimming range (approx.
1000:1) and higher efficiency at the expense of greater output ripple.
ZXLD1356
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Ordering Information
Device
Part Package
mark
Code
ZXLD1356DACTC 1356
ZXLD1356ET5TA 1356
DAC
ET5
Packaging
(Note 4)
DFN3030-6
TSOT23-5
Reel size
(inches)
Reel width
(mm)
13
7
12
8
Part
Quantity per reel Number
Suffix
3000
TC
3000
TA
AEC-Q100
Grade 1
Package Outline Dimensions
TSOT23-5
ZXLD1356
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Package Outline Dimensions (Continued)
DFN3030-6
e1
D
E
E2
L
D2
b
PIN 1 DOT
BY MARKING
BOTTOM VIEW
A3
A1
A
TOP VIEW
PIN #1 IDENTIFICATION
CHAMFER 0.300X45°
e
SIDE VIEW
DIM
Millimeters
Inches
DIM
Min.
Max.
Min.
Max.
A
0.700
0.800
0.0275
0.0315
D2
A1
0.000
0.050
0.000
0.00197
e
A3
0.203 REF
0.008
Millimeters
Inches
Min.
Max.
Min.
Max.
1.950
2.050
0.0768
0.0807
0.950 BSC
0.0374 BSC
E
2.950
3.050
0.116
0.120
b
0.300
0.400
0.0118
0.0157
E2
1.150
1.250
0.0452
0.0492
D
2.950
3.050
0.116
0.120
e1
L
ZXLD1356
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1.900REF
0.450
0.550
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0.0748
0.0177
0.0216
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ZXLD1356
IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume
all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated
website, harmless against all damages.
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales
channel.
Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and
hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or
indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.
Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings
noted herein may also be covered by one or more United States, international or foreign trademarks.
LIFE SUPPORT
Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and
any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its
representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or
systems.
Copyright © 2010, Diodes Incorporated
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