ZXLD1366Q

ZXLD1366Q
AUTOMOTIVE COMPLIANT HIGH ACCURACY 1A, 60V LED DRIVER
ADVANCED INFORMATION
Description
Pin Assignments
The ZXLD1366Q 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 1A.
(TOP VIEW)
LX 1
5 VIN
GND 2
4 ISENSE
ADJ 3
The ZXLD1366Q uses a high-side output current sensing circuit
which uses an external resistor to set the nominal average output
current. The output current can be adjusted above or below the set
value by applying an external control signal to the 'ADJ' pin.
TSOT25
(TOP VIEW)
Enhanced output current dimming resolution can be achieved by
LX 1
6 VIN
applying a PWM signal to the ‘ADJ’ pin.
Soft-start can be forced using an external capacitor from the ADJ
pin to ground. Applying a voltage of 0.2V or lower to the ADJ pin
turns the output off and switches the device into a low current
standby state.
GND 2
5 GND
ADJ 3
4 ISENSE
U-DFN3030-6
V-DFN3030-6
The ZXLD1366Q is qualified to AEC-Q100 Grade 1 and is
Automotive Compliant supporting PPAPs.
Features
Typical Application Circuit

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%)

Switching Frequencies up to 1MHz

Wide Input Voltage Range: 6V to 60V

Inherent Open-Circuit LED Protection
Available in Thermally Enhanced Green Molding Packages
V-DFN3030-6 JA = +44°C/W
TSOT25 JA = +82°C/W
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Qualified to AEC-Q100 Standards for High Reliability
PPAP Capable (Note 4)




Applications

Automotive Lighting:
-
Internal Door Lights
Rear Fog Lamps
Position Lights
Notes: 1.
2.
3.
4.
No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free,
"Green" and Lead-free.
Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl)
and <1000ppm antimony compounds.
Automotive products are AEC-Q100 qualified and are PPAP capable. Refer to http://www.diodes.com/quality/product_compliance_definitions/.
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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ZXLD1366Q
Block Diagram
D1
VIN
L1
RS
5
5V
C1
4.7µF
4
VIN
ISENSE
1
LX
R1
Voltage
regulator
+
0.2V
+
Low voltage
dete ctor
MN
+
Adj
3
R4
50K
R5
20K
600KHz
R2
D1
1.25V
+
R3
1.35V
Gnd
2
Figure. 1 Pin Connection for TSOT25 Package
Pin Description
Name
TSOT25
V-DFN3030-6
LX
1
1
GND
2
2, 5
Function
Drain of NDMOS switch
Ground (0V)
Multi-function On/Off and brightness control pin:
ADJ
3
3
•
Leave floating for normal operation.(VADJ = VREF = 1.25V giving nominal average output
current 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 25% to 200% of
IOUTnom
•
Connect a capacitor from this pin to ground to set soft-start time.
Soft start time increases approximately 0.2ms/nF
Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom =
ISENSE
4
4
0.2V/RS.
(Note: RSMIN = 0.2V with ADJ pin open-circuit)
VIN
5
6
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.
Pad

Pad
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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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ZXLD1366Q
Absolute Maximum Ratings (Note 5) (@TA = +25°C, unless otherwise specified.)
Symbol
Parameter
Input Voltage
VIN
Rating
Unit
-0.3 to +65
V
ISENSE Voltage (Note 6)
+0.3 to -5
V
VLX
LX Output Voltage
-0.3 to +65
V
VADJ
Adjust Pin Input Voltage
-0.3 to +6
V
1.25
A
VSENSE
Switch Output Current
ILX
PTOT
Power Dissipation
(Refer to Package thermal de-rating curve on
page 25)
TOP
Operating Temperature
-40 to +125
°C
TST
Storage Temperature
-55 to +150
°C
+150
°C
500
1,000
V
V
TSOT25
V-DFN3030-6
Junction Temperature
TJ MAX
ESD Susceptibility
HBM
CDM
Notes:
Human Body Model
Charged Device Model
5.
6.
Caution:
1
W
1.8
All voltages unless otherwise stated are measured with respect to GND.
VSENSE is measured with respect to VIN.
Stresses greater than the 'Absolute Maximum Ratings' specified above may cause permanent damage to the device. These are stress ratings only;
functional operation of the device at conditions between maximum recommended operating conditions and absolute maximum ratings is not implied.
Device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time.
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
Rating
Symbol
Parameter
JA
Junction to Ambient
82
44
ΨJB
Junction to Board
33
—
JC
Junction to Case
—
14
TSOT25
V-DFN3030-6
Unit
°C/W
Recommended Operating Conditions
Symbol
Min
Max
Units
VIN
Input voltage (Note 7)
6
60
V
ILX
Maximum recommended continuous/RMS switch current
—
1
A
External control voltage range on ADJ pin for DC brightness control (Note 8)
0.3
2.5
V
VADJOFF
DC voltage on ADJ pin to ensure devices is off
—
0.25
V
tOFFMIN
Minimum switch off-time
—
800
ns
tONMIN
Minimum switch on-time
—
800
ns
fLX MAX
Recommended maximum operating frequency (Note 9)
—
625
kHz
0.01
0.99
—
VADJ
DLX
Parameter
Duty cycle range
DLX(LIMIT) Recommended duty cycle range of output switch at f LXMAX
TOP
Notes:
Operating Temperature range
0.3
0.7
—
-40
+125
°C
7. 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.
8. 100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE threshold and output current
proportionally.
9. ZXLD1366Q will operate at higher frequencies but accuracy will be affected due to propagation delays.
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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ZXLD1366Q
Electrical Characteristics
Symbol
(Test conditions: (@ VIN = 24V, TA = +25°C, unless otherwise specified.))
Min
Typ
Max
Unit
VSU
Internal regulator start-up threshold
—
—
4.85
5.20
V
VSD
Internal regulator shutdown threshold
—
4.40
4.75
—
V
IINQoff
Quiescent supply current with output off
ADJ pin grounded
—
65
108
µA
IINQon
Quiescent supply current with output switching
(Note 11)
ADJ pin floating, L = 68µH,
3 LEDs, f = 260kHz
—
1.6
—
mA
Mean current sense threshold voltage
(Defines LED current setting accuracy)
Measured on ISENSE pin with
respect to VIN VADJ = 1.25V;
VIN = 18V
195
200
205
mV
Sense threshold hysteresis
—
—
±15
—
%
VSENSE = VIN -0.2
Measured on ADJ pin with pin
floating
—
—
4
10
µA
—
1.25
—
V
—
50
—
ppm/°C
0.3
—
2.5
V
0.15
0.20
0.27
V
0.20
0.25
0.30
V
30
10.4
50
14.2
65
18.0
kΩ
A
VSENSE
VSENSEHYS
ISENSE
VREF
VREF/T
VADJ
VADJoff
VADJon
Parameter
ISENSE pin input current
Internal reference voltage
Condition
Temperature coefficient of VREF
External control voltage range on ADJ pin for DC —
brightness control (Note 10)
DC voltage on ADJ pin to switch device from active
VADJ falling
(on) state to quiescent (off) state
DC voltage on ADJ pin to switch device from
VADJ rising
quiescent (off) state to active (on) state
Resistance between ADJ pin and VREF
0 < VADJ < VREF
VADJ > VREF +100mV
Continuous LX switch current
—
—
—
1
RLX
LX switch ‘On’ resistance
@ ILX = 1A
—
0.50
0.75
Ω
ILX(leak)
LX switch leakage current
—
—
—
5
µA
0.001
—
1.000
V
RADJ
ILXmean
DPWM(LF)
PWM frequency < 300Hz PWM
Duty cycle range of PWM signal applied to ADJ pin
amplitude = VREF
during low frequency PWM dimming mode
Measured on ADJ pin
Brightness control range
—
—
1000:1
—
—
DC Brightness control range
(Note 12)
—
5:1
—
—
tSS
Soft-start time
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. See graphs for
more details
—
2
—
ms
fLX
Operating frequency
(See graphs for more details)
ADJ pin floating
L = 68µH (0.2V)
IOUT = 1A @ VLED = 3.6V
Driving 3 LEDs
—
260
—
kHz
tONmin
Minimum switch ‘ON’ time
LX switch ‘ON’
—
130
—
—
tOFFmin
Minimum switch ‘OFF’ time
LX switch ‘OFF’
—
70
—
—
DCADJ
Notes:
10. 100% brightness corresponds to V ADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE threshold and output current
proportionally.
11. Static current of device is approximately 700µA, see graph, Page 16.
12. Ratio of maximum brightness to minimum brightness before shutdown VREF = 1.25/0.3. VREF externally driven to 2.5V, ratio 10:1.
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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ZXLD1366Q
Device Description
The device, in conjunction with the coil (L1) and current sense resistor (R S), 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
SENSE voltage
200mV
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 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 R S 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 V IN 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 V IN. 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 V ADJ, the comparator
output switches high again. This cycle of events repeats, with the comparator input ramping between limits of VADJ ± 15%.
Switching Thresholds
With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of 200mV (measured on the I SENSE 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
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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ZXLD1366Q
Device Description (continued)
Actual operating waveforms
VIN = 15V, RS = 0.2Ω, L = 68µH Normal operation.
VIN = 30V, RS = 0.2Ω, L = 68µH Normal operation.
Output Current (Ch. 3) and LX voltage (Ch. 2)
Output Current (Ch. 3) and LX voltage (Ch. 2)
VIN = 60V, RS = 0.2Ω, L = 68µH Normal operation.
Output Current (Ch. 3) and LX voltage (Ch. 2)
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.
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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ZXLD1366Q
Typical Operating Conditions
1.100
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
OUTPUT CURRENT (A)
1.080
1.060
1.040
1.020
1.000
0.980
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Output Current, L = 68µH
10
OUTPUT CURRENT DEVIATION (%)
8
6
4
2
0
-2
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
-4
-6
-8
-10
0
10
20
30
40
50
60
50
60
SUPPLY VOLTAGE (V)
Output Current Deviation, L = 68µH
100
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0
10
20
30
40
SUPPLY VOLTAGE (V)
Efficiency, L = 68µH
ZXLD1366Q
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ZXLD1366Q
Typical Operating Conditions (continued)
500
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
SWITCHING FREQUENCY (kHz)
450
400
350
300
250
200
150
100
50
0
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Switching Frequency, L = 68µH
100
90
80
DUTY CYCLE (%)
70
60
50
40
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
30
20
10
0
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Duty Cycle, L = 68µH
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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ZXLD1366Q
Typical Operating Conditions (cont.)
1.100
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
OUTPUT CURRENT (A)
1.080
1.060
1.040
1.020
1.000
0.980
0.960
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Output Current, L = 100µH
10
OUTPUT CURRENT DEVIATION (%)
8
6
4
2
0
-2
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
-4
-6
-8
-10
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Output Current Deviation, L = 100µH
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Efficiency, L = 100µH
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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ZXLD1366Q
Typical Operating Conditions (cont.)
500
1 LED
3 LEDs
5 LEDs
7 LEDs
SWITCHING FREQUENCY (kHz)
450
400
11 LEDs
13 LEDs
15 LEDs
350
300
250
200
150
100
50
0
0
10
20
30
40
50
60
50
60
SUPPLY VOLTAGE (V)
Switching Frequency, L = 100µH
100
90
80
DUTY CYCLE (%)
70
60
50
40
30
1 LED
3 LEDs
5 LEDs
7 LEDs
20
10
0
0
11 LEDs
13 LEDs
15 LEDs
10
20
30
40
SUPPLY VOLTAGE (V)
Duty Cycle, L = 100µH
ZXLD1366Q
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ZXLD1366Q
Typical Operating Conditions (cont.)
1.100
OUTPUT CURRENT (A)
1.080
1.060
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
1.040
1.020
1.000
0.980
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Output Current, L = 150µH
10
OUTPUT CURRENT DEVIATION (%)
8
6
4
2
0
-2
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
-4
-6
-8
-10
0
10
20
30
40
50
60
50
60
SUPPLY VOLTAGE (V)
Output Current Deviation, L = 150µH
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
0
10
20
30
40
SUPPLY VOLTAGE (V)
Efficiency, L = 150µH
ZXLD1366Q
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ZXLD1366Q
Typical Operating Conditions (cont.)
500
1 LED
3 LEDs
5 LEDs
7 LEDs
SWITCHING FREQUENCY (kHz)
450
400
11 LEDs
13 LEDs
15 LEDs
350
300
250
200
150
100
50
0
0
10
20
30
40
50
60
50
60
SUPPLY VOLTAGE (V)
Switching Frequency, L = 150µH
100
90
80
DUTY CYCLE (%)
70
60
50
40
30
1 LED
3 LEDs
5 LEDs
7 LEDs
20
10
11 LEDs
13 LEDs
15 LEDs
0
0
10
20
30
40
SUPPLY VOLTAGE (V)
Duty Cycle, L = 150µH
ZXLD1366Q
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ZXLD1366Q
Typical Operating Conditions (cont.)
1.100
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
OUTPUT CURRENT (A)
1.080
1.060
1.040
1.020
1.000
0.980
0
10
20
30
40
50
60
SUPPLY VOLTAGE (V)
Output Current, L = 220µH
10
OUTPUT CURRENT DEVIATION (%)
8
6
4
2
0
-2
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
-4
-6
-8
-10
0
10
20
30
40
50
60
50
60
SUPPLY VOLTAGE (V)
Output Current Deviation, L = 220µH
EFFICIENCY (%)
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
0
10
20
30
40
SUPPLY VOLTAGE (V)
Efficiency, L = 220µH
ZXLD1366Q
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ZXLD1366Q
Typical Operating Conditions (cont.)
500
1 LED
3 LEDs
5 LEDs
7 LEDs
SWITCHING FREQUENCY (kHz)
450
400
11 LEDs
13 LEDs
15 LEDs
350
300
250
200
150
100
50
0
0
10
20
30
40
50
60
50
60
SUPPLY VOLTAGE (V)
Switching Frequency, L = 220µH
100
90
80
DUTY CYCLE (%)
70
60
50
40
1 LED
3 LEDs
5 LEDs
7 LEDs
30
20
11 LEDs
13 LEDs
15 LEDs
10
0
0
10
20
30
40
SUPPLY VOLTAGE (V)
Duty Cycle, L = 220µH
ZXLD1366Q
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ZXLD1366Q
Typical Operating Conditions (cont.)
1200
800
R = 300m
700
1000
SUPPLY CURRENT (mA)
LED CURRENT (mA)
R = 200m
800
R = 680m
600
400
600
500
400
300
200
200
100
0
0
1
2
ADJ PIN VOLTAGE (V)
LED Current vs. ADJ
0
0
3
20
30
40
50
60
70
SUPPLY VOLTAGE (V)
1.2430
90
1.2425
80
SHUTDOWN CURRENT (mA)
1.2420
ADJ PIN VOLTAGE (V)
10
1.2415
1.2410
1.2405
1.2400
1.2395
1.2390
70
60
50
40
30
20
10
1.2385
1.2380
0
10
20
30
40
50
60
70
SUPPLY VOLTAGE (V)
ZXLD1366Q
Document number: DS37078 Rev. 1 - 2
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0
10
20
30
40
50
60
70
SUPPLY VOLTAGE (V)
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ZXLD1366Q
Typical Operating Conditions (cont.)
1.6
-40°C
20°C
150°C
1.4
ON-RESISTANCE ()
1.2
1.0
0.8
0.6
0.4
0.2
0
0
5
10
15
20
25
SUPPLY VOLTAGE (V)
LX On-Resistance vs. Supply Voltage
30
35
1.262
1.260
1.258
7V
9V
12V
20V
30V
VADJ (V)
1.256
1.254
1.252
1.250
1.248
1.246
1.244
-50
0
50
100
TEMPERATURE (°C)
VADJ vs. Temperature
150
200
1.6
ON-RESISTANCE ()
1.4
1.2
7V
9V
12V
20V
30V
1.0
0.8
0.6
0.4
0.2
0
-50
ZXLD1366Q
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0
50
100
150
DIE TEMPERATURE (°C)
LX On-Resisitance vs. Die Temperature
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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 ≥ 0.2Ω
The table below gives values of nominal average output current for several preferred values of current sense resistor (RS) in the typical
application circuit shown on page 1:
RS (Ω)
Nominal Average Output
Current (mA)
0.20
0.27
0.56
1,000
740
357
The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (= 1.25V). Note that RS = 0.2Ω 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.
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 the 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 1A maximum.
The input impedance of the ADJ pin is 50kΩ ±25% for voltages below V REF and 14.2kΩ ±25% for voltages above VREF +100mV.
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:
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Application Information (continued)
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:
This scheme uses the 50k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the external transistor.
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:
If the NMOS transistor within the microcontroller has high Gate / Drain capacitance, this arrangement can inject a negative spike into the ADJ
input of the ZXLD1366Q 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.
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 V REF will increase output current above the 100% nominal
average value. (See page 18 graphs for details).
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Application Information (cont.)
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.
16
14
SOFT-START TIME (ms)
12
10
8
6
4
2
0
-2
0
20
40
60
80
100
120
CAPACITANCE (nF)
Soft-Start Time vs. Capacitance form ADJ to Ground
Actual Operating Waveform [VIN = 60V, RS = 0.2Ω, 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 (cont.)
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 V IN 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 used with the CIN = 10μF, an electrolytic capacitor can be used provided that a suitable 1µF 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
Inductor Selection
Recommended inductor values for the ZXLD1366Q are in the range 68μH to 220μH.
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 10-17). 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 ZXLD1366Q 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.
Figure 3, (below), can be used to select a recommended inductor based on maintaining the ZXLD1366Q case temperature below +60°C. For
detailed performance characteristics for the inductor values 68, 100, 150 and 220μH see graphs on pages 10-17.
ZXLD1366Q
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Application Information (cont.)
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 ZXLD1366QET5 Minimum Recommended Inductor (TSOT25)
M in im u m R e c o m m e n d e d In d u c to r
2% Accuracy, <60°C C ase T em perature
16
15
14
Legend
68µH
100µH
13
150µH
12
220µH
N um ber of LED s
11
10
9
8
7
6
5
4
3
2
1
0.00
10.00
20.00
30.00
40.00
50.00
60.00
S u p p ly V o lta g e (V )
Figure 5 ZXLD1366 Minimum Recommended Inductor (U-DFN3030-6)
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Application Information (cont.)
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 PDS3100Q (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:
Figure 6 Reduced Output Ripple
A value of 1µF will reduce the supply ripple current by a factor of three (approximately). Proportionally, lower ripple can be achieved with
higher capacitor values. Note that the capacitor will not affect operating frequency or efficiency, but 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 undervoltage lockout threshold (VSD), the drive to the output transistor is turned off to prevent device operation with excessive onresistance of the output transistor. The output transistor is not fully 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.
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Application Information (cont.)
Thermal Considerations
When operating the device at high ambient temperatures, or when driving maximum load current, care must be taken to avoid exceeding the
2
package power dissipation limits. The graph below gives details for power derating. This assumes the device to be mounted on a 25mm
PCB with 1oz copper standing in still air.
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.
In order to maximize the thermal capabilities of the SO-8EP package, thermal vias should be incorporated into the PCB. See figure 7 for
examples used in the ZXLD1366 evaluation boards.
Figure 7 Suggested Layout for SO-8EP Package
Vias ensure an effective path to the ground plane for the heat flow therefore reducing the thermal impedance between junction and ambient
temperature. Diodes came to the conclusion that the compromise is reached by using more than 10 vias with 1mm of diameter and a 0.5 hole
size.
The use of vias for the TSOT25 package should also be implemented to guarantee an effective thermal path.
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Application Information (cont.)
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 ZXLD1366Q is 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.
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. It is 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 actually present, 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 next page). This resistor will provide
filtering for low-frequency noise and provide protection against high-voltage transients.
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 PCB
ZXLD1366 evaluation boards are available upon request. Terminals allow users to interface the boards to their preferred LED products.
ZXLD1366Q
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Application Information (cont.)
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 V ADJ, 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 8 - 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.
VADJ
Ton
PWM Voltage
Toff
0V
IOUTnom
0.2/Rs
Output Current
IOUTavg
0
Figure 8 Low Frequency PWM Operating Waveforms
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Applications Information (cont.)
Fault Condition Operation
The ZXLD1366Q has by default, open LED protection. If the LEDs should become open circuit, the ZXLD1366Q will stop oscillating; the
SET pin will rise to VIN and the SW pin will then fall to GND. No excessive voltages will be seen by the ZXLD1366Q.
If the LEDs should become shorted together, the ZXLD1366Q will continue to switch, however, the duty cycle at which it will operate will
change dramatically and the switching frequency will most likely decrease. The on-time of the internal power MOSFET switch will be
significantly reduced because almost all of the input voltage is now developed across the inductor. The off-time will be significantly
increased because the reverse voltage across the inductor is now just the Schottky diode voltage (See Figure 9) causing a much slower
decay in inductor current. During this condition, the inductor current will remain within its controlled levels and so no excessive heat will be
generated within the ZXLD1366Q.
Figure 9 Switching Characteristics (normal open to short LED chain)
ZXLD1366Q
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Ordering Information
Part Number
Packaging
(Note 13)
Pack
Code
ZXLD1366QDACTC
ZXLD1366QET5TA
V-DFN3030-6
TSOT25
DAC
ET5
Notes:
Reel Size Reel Width
(inches)
(mm)
13
7
8
8
Quantity
Per Reel
Part Number
Suffix
Qualification
(Note 14)
3,000
3,000
TC
TA
Automotive Grade
Automotive Grade
13. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at
http://www.diodes.com/datasheets/ap02001.pdf.
14. ZXLD1366Q has been qualified to AEC-Q100 grade 1 and is classified as “Automotive Grade” supporting PPAP documentation. See ZXLD1366
datasheet for commercial qualified versions.
Marking Information
TSOT25:
Identification Code: 1366
V-DFN3030-6
Package Outline Dimensions
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for the latest version.
1) TSOT25
D
e1
01(4x)
E1/2
E/2
E1
c
E
Gauge Plane
0
L
e
Seating Plane
L2
01(4x)
b
A2
A
A1
Seating Plane
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TSOT25
Dim
Min
Max
Typ
A
-
1.00
A1
0.01 0.10
A2
0.84 0.90
b
0.30 0.45
c
0.12 0.20
D
2.90
E
2.80
E1
1.60
e
0.95 BSC
e1
1.90 BSC
L
0.30 0.50
L2
0.25 BSC
θ
0°
8°
4°
θ1
4°
12°
All Dimensions in mm
December 2015
© Diodes Incorporated
ZXLD1366Q
Package Outline Dimensions (continued)
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for the latest version.
2) V-DFN3030-6
A1
A3
Seating Plane
A
D
e
L
D2
E
E2
V-DFN3030-6
Dim Min Max Typ
A 0.80 0.90 0.85
A1
0
0.05
A3
0.203
b 0.30 0.40 0.35
D 2.95 3.05 3.00
D2 1.95 2.05 2.00
E 2.95 3.05 3.00
E2 1.15 1.25 1.20
e
0.95
e1
1.90
L 0.45 0.55 0.50
All Dimensions in mm
Pin #1 ID
Chamfer 0.300X45°
b
e1
Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.
1) TSOT25
C
Y1
Dimensions
C
X
Y
Y1
Y
Value (in
mm)
0.950
0.700
1.000
3.199
X
2) V-DFN3030-6
Y
Dimensions
C
X
X1
Y
Y1
Y2
X1
Y2
Y1
Value (in mm)
0.950
0.450
2.100
0.630
1.300
3.160
C - 0.329
C
ZXLD1366Q
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X
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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.
This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is
the final and determinative format released by Diodes Incorporated.
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 systemsrelated 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 © 2015, Diodes Incorporated
www.diodes.com
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