ZXLD1362

A Product Line of
Diodes Incorporated
ZXLD1362
60V 1A LED DRIVER WITH AEC-Q100
Description
Pin Assignments
The ZXLD1362 is a continuous mode inductive step-down converter
(Top View)
with integrated switch and high side current sense.
It operates from an input supply from 6V to 60V driving single or
LX
multiple series connected LEDs efficiently externally adjustable
output current up to 1A.
VIN
GND
The ZXLD1362 has been qualified to AEC-Q100 Grade 1 enabling
operation in ambient temperatures from -40°C to +125°C.
ISENSE
ADJ
The output current can be adjusted by applying a DC voltage or a
TSOT25
PWM waveform. 100.1 adjustment of output current is possible
using PWM control.
Applying 0.2V or lower to the ADJ pin turns the output off and
switches the device into a low current standby state.
Features
• Simple low parts count
• Single pin on/off and brightness control using DC voltage or
PWM
• High efficiency (up to 95%)
• Wide input voltage range: 6V to 60V
• Up to 1MHz switching frequency
• Qualified to AEC-Q100 Grade 1
• Automotive Grade version available (ZXLD1362Q)
• Typical 2% output current accuracy
• Thermally enhanced TSOT25: θJA 82°C/W
• Available in Green Molding
• Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
• Halogen and Antimony Free. “Green” Device (Note 3)
Notes:
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. 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.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
Typical Application Circuit
VIN
24V
C1
4.7µF
RS
L1
0.1Ω
68µH
VIN
ADJ
GND
ZXLD1362
Document number: DS33472 Rev. 6 - 2
C2
100nF
SET
LX
ZXLD1362
GND
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ZXLD1362
Pin Description
Name
LX
GND
Pin No.
1
2
Function
Drain of NDMOS switch
Ground (0V)
ADJ
3
Multi-function On/Off and brightness control pin:
Leave floating for normal operation.(VADJ = VREF = 1.25V giving nominal average output current
IOUTnom = 0.1/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 increase soft-start time.
Soft-start time increases approximately 200µs/nF.
ISENSE
4
Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom = 0.1/RS
(Note: RSMIN = 0.1Ω with ADJ pin open circuit)
VIN
5
Input voltage (6V to 60V). Decouple to ground with 4.7µF of higher X7R ceramic capacitor close to device.
Block Diagram
VIN
D1
L1
RS
5 VIN
5V
4 ISENSE
1 LX
R1
Voltage
regulator
C1
4.7µF
`
0.2V
Low voltage
detector
GND
MN
ADJ
3
R4
50k
R5
20k
R2
D1
1.25V
R3
1.35V
GND
GND
2
Figure 1 Block Diagram
ZXLD1362
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ZXLD1362
Absolute Maximum Ratings (Note 4) (@TA = +25°C, unless otherwise specified.)
Symbol
Rating
Unit
Input Voltage
-0.3 to +65
V
ISENSE Voltage (Note 5)
+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
1
W
VIN
VSENSE
Parameter
Switch Output Current
ILX
PTOT
Power Dissipation
(Refer to Package thermal de-rating curve on page 16)
TST
Storage Temperature
-55 to +150
°C
TJ MAX
Junction Temperature
150
°C
Note:
4 All voltages unless otherwise stated are measured with respect to GND.
5. VSENSE is measured with respect to VIN.
Caution:
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.
ESD Susceptibility
Rating
500
75
Human Body Model
Machine Model
Caution:
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
Rating
Unit
ΘJA
Junction to Ambient
82
°C/W
ΨJB
Junction to Board
33
°C/W
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Symbol
Parameter
VIN
Input Voltage Range (Note 6)
ILX
Maximum recommended continuous/RMS switch current
External control voltage range on ADJ pin for DC brightness control (Note 7)
Min
Max
6
60
V
1
A
2.5
V
DC voltage on ADJ pin to ensure devices is off
0.25
V
tONMIN
Minimum switch on-time
800
ns
fLXmax
Recommended maximum operating frequency (Note 8)
625
kHz
VADJ
VADJoff
Notes:
0.3
Units
DLX
Duty cycle range
0.01
0.99
TA
Ambient operating temperature range
-40
+125
°C
6. 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.
7. 100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE threshold and output current
proportionally.
8. ZXLD1362 will operate at higher frequencies but accuracy will be affected due to propagation delays.
ZXLD1362
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ZXLD1362
Electrical Characteristics (@ VIN = 24V, TA = +25°C, unless otherwise specified.)
Symbol
Parameter
Condition
Min
Typ
Max
Unit
VSU
Internal regulator start-up threshold
4.85
V
VSD
Internal regulator shutdown threshold
4.75
V
IINQoff
Quiescent supply current with output off
ADJ pin grounded
65
IINQon
Quiescent supply current with output switching
(Note 9)
ADJ pin floating, L = 68µH,
3 LEDs, f = 260kHz
1.8
Mean current sense threshold voltage
(Defines LED current setting accuracy)
Measured on ISENSE pin with
respect to VIN VADJ = 1.25V
VSENSE
VSENSEHYS
ISENSE
VREF
ΔVREF/ΔT
Sense threshold hysteresis
ISENSE pin input current
VSENSE = VIN -0.1
Internal reference voltage
Measured on ADJ pin with
pin floating
VADJon
DC voltage on ADJ pin to switch device from
quiescent (off) state to active (on) state
Resistance between ADJ pin and VREF
ILXmean
RLX
LX switch ‘On’ resistance
LX switch leakage current
DCADJ
10
1.25
tSS
Soft start time
fLX
Operating frequency
(See graphs for more details)
µA
V
ppm/°C
0.3
2.5
V
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
kΩ
1
A
0.5
@ ILX = 1A
Duty cycle range of PWM signal applied to ADJ pin PWM frequency <300Hz
during low frequency PWM dimming mode
PWM amplitude = VREF
Measured on ADJ pin
Brightness control range
DC Brightness control range
mV
%
Continuous LX switch current
ILX(leak)
DPWM(LF)
105
50
VADJoff
RADJ
100
4
Temperature coefficient of VREF
µA
mA
±10
External control voltage range on ADJ pin for DC
brightness control (Note 7)
DC voltage on ADJ pin to switch device from active
VADJ falling
(on) state to quiescent (off) state
VADJ
95
90
Note 10
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
ADJ pin floating
L = 68µH (0.1V)
IOUT = 1A @ VLED = 3.6V
Driving 3 LEDs
0.001
1.0
Ω
5
µA
1
1000:1
5:1
2
ms
300
kHz
tONmin
Minimum switch ‘ON’ time
LX switch ‘ON’
130
ns
tOFFmin
Minimum switch ‘OFF’ time
LX switch ‘OFF’
70
ns
Notes:
9. Static current of device is approximately 700µA, see Graph, Page 16.
10. Ratio of maximum brightness to minimum brightness before shutdown VREF = 1.25/0.3. VREF externally driven to 2.5V, ratio 10:1.
ZXLD1362
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ZXLD1362
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)
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
SENSE
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 (V
) 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 10% 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 ± 10%.
ZXLD1362
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ZXLD1362
Device Description (cont.)
Switching Thresholds
With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of 100mV (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 = 100mV/RS
Nominal ripple current is ±10mV/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.
Actual Operating Waveforms
VIN = 30V, RS = 0.1V, L = 100µH Normal Operation.
Output Current (Ch1) and LX Voltage (Ch2)
VIN = 15V, RS = 0.1V, L = 100µH Normal operation.
Output Current (Ch1) and LX Voltage (Ch2)
VIN = 60V, RS = 0.1V, L = 100µH Normal Operation.
Output Current (Ch1) and LX Voltage (Ch2)
ZXLD1362
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ZXLD1362
Typical Characteristics
ZXLD1362 Output Current
L = 68µH
1100
1090
1080
Output Current (mA)
1070
1060
1050
1040
1030
1020
1010
1000
0
10
20
30
40
50
60
70
Supply Voltage (V)
1 LED
3 LED
5 LED
7 LED
9 LED
11 LED
13 LED
15 LED
ZXLD1362 Output Current
L = 68µH
10%
8%
Output Current Deviation
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
20
30
40
50
60
70
Supply Voltage (V)
1 LED
3 LED
5 LED
7 LED
9 LED
11 LED
13 LED
15 LED
ZXLD1362 Efficiency
L = 68µH
100%
Efficiency (%)
90%
80%
70%
60%
50%
0
10
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
20
3 LED
30
40
Supply Voltage (V)
5 LED
7 LED
9 LED
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50
11 LED
60
13 LED
70
15 LED
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Diodes Incorporated
ZXLD1362
Typical Characteristics (cont.)
ZXLD1362 Switching Frequency
L = 68µH
500
Switching Frequency (kHz)
400
300
200
100
0
0
10
1 LED
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
50
11 LED
60
13 LED
70
15 LED
ZXLD1362 Duty Cycle
L = 68µH
100
90
80
Duty Cycle (%)
70
60
50
40
30
20
10
0
0
10
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
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50
11 LED
60
13 LED
70
15 LED
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ZXLD1362
Typical Characteristics (cont.)
ZXLD1362 Output Current
L = 100µH
1100 1090
1080
Output Current (mA)
1070
1060
1050
1040
1030
1020
1010
1000
0
10
20
30
40
50
60
70
Supply Voltage (V)
1 LED
3 LED
5 LED
7 LED
9 LED
11 LED
13 LED
15 LED
ZXLD1362 Output Current
L = 100µH
10%
8%
Output Current Deviation
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
20
30
40
50
60
11 LED
13 LED
70
Supply Voltage (V)
1 LED
3 LED
5 LED
7 LED
9 LED
15 LED
ZXLD1362 Efficiency
L = 100µH
100%
Efficiency (%)
90%
80%
70%
60%
50%
0
10
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
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50
11 LED
60
13 LED
70
15 LED
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ZXLD1362
Typical Characteristics (cont.)
ZXLD1362 Switching Frequency
L = 100µH
500
Switching Frequency (kHz)
400
300
200
100
0
0
10
1 LED
20
3 LED
30
40
Supply Voltage (V)
5 LED
7 LED
9 LED
50
11 LED
60
13 LED
70
15 LED
ZXLD1362 Switching Frequency
L = 100µH
100
90
80
Duty Cycle (%)
70
60
50
40
30
20
10
0
0
10
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
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50
11 LED
60
13 LED
70
15 LED
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ZXLD1362
Typical Characteristics (cont.)
ZXLD1362 Output Current
L = 150µH
1100 1090
Output Current (mA)
1080
1070
1060
1050
1040
1030
1020
1010
1000
0
10
20
30
40
50
60
70
Supply Voltage (V)
1 LED
3 LED
5 LED
7 LED
9 LED
11 LED
13 LED
15 LED
ZXLD1362 Output Current
L = 150µH
10%
8%
Output Current Deviation
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
20
30
40
50
60
70
Supply Voltage (V)
1 LED
3 LED
5 LED
7 LED
9 LED
11 LED
13 LED
15 LED
ZXLD1362 Efficiency
L = 150µH
100%
Efficiency (%)
90%
80%
70%
60%
50%
0
10
20
30
40
50
60
70
Supply Voltage (V)
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
3 LED
5 LED
7 LED
9 LED
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11 LED
13 LED
15 LED
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ZXLD1362
Typical Characteristics (cont.)
ZXLD1362 Switching Frequency
L = 150µH
500
Switching Frequency (kHz)
400
300
200
100
0
0
10
1 LED
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
50
60
11 LED
13 LED
50
60
70
15 LED
ZXLD1362 Duty Cycle
L = 150µH
100
90
80
Duty Cycle (%)
70
60
50
40
30
20
10
0
0
10
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
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11 LED
13 LED
70
15 LED
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ZXLD1362
Typical Characteristics (cont.)
ZXLD1362 Output Current
L = 220µH
1100
1090
1080
Output Current (mA)
1070
1060
1050
1040
1030
1020
1010
1000
0
10
1 LED
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
50
11 LED
60
13 LED
70
15 LED
ZXLD1362 Output Current
L = 220µH
10%
8%
Output Current Deviation
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
0
10
1 LED
20
3 LED
30
40
Supply Voltage (V)
5 LED
7 LED
9 LED
50
11 LED
60
13 LED
70
15 LED
ZXLD1362 Efficiency
L = 220µH
100%
Efficiency (%)
90%
80%
70%
60%
50%
0
10
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
20
3 LED
5 LED
30
40
Supply Voltage (V)
7 LED
9 LED
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50
11 LED
60
13 LED
70
15 LED
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ZXLD1362
Typical Characteristics (cont.)
ZXLD1362 Switching Frequency
L = 2200µH
500
Switching Frequency (kHz)
400
300
200
100
0
0
10
1 LED
20
3 LED
5 LED
30
40
Supply Voltage (V)
50
7 LED
9 LED
ZXLD1362 Duty Cycle
L = 2200µH
11 LED
30
40
Supply Voltage (V)
50
60
13 LED
70
15 LED
100
90
80
Duty Cycle (%)
70
60
50
40
30
20
10
0
0
10
1 LED
ZXLD1362
Document number: DS33472 Rev. 6 - 2
20
3 LED
5 LED
7 LED
9 LED
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11 LED
60
13 LED
70
15 LED
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ZXLD1362
Typical Characteristics (cont.)
LED Current vs Vadj
1200
1000
LED Current (mA)
800
600
400
200
0
0
1
2
3
ADJ Pin Voltage (V)
R=100mΩ
R=150mΩ
R=330mΩ
Supply current
800
Supply current (mA)
700
600
500
400
300
200
100
0
0
10
20
30
40
Supply voltage (V)
50
60
70
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)
Shutdow n 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)
ZXLD1362
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ZXLD1362
Typical Characteristics (cont.)
Lx on-resistance vs supply voltage
1.6
On-resistance (Ohms)
1.4
1.2
1
-40C
20C
150C
0.8
0.6
0.4
0.2
0
0
5
10
15
20
25
30
35
Supply Voltage (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
ZXLD1362
Document number: DS33472 Rev. 6 - 2
0
50
100
Die Temperature (C)
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150
200
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ZXLD1362
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 = 0.1/RS [for RS > 0.1Ω]
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)
0.1
0.13
0.15
1000
760
667
The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (= 1.25V). Note that RS = 0.1Ω 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.
ZXLD1362
ADJ
+
GND
DC
GND
The nominal average output current in this case is given by:
IOUTdc = (VADJ /1.25) x (100mV/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 1A maximum.
The input impedance of the ADJ pin is 50kΩ ±25% for voltages below VREF 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:
PWM
VADJ
ADJ
0V
ZXLD1362
GND
GND
ZXLD1362
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Application Information (cont.)
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
ZXLD1362
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.
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
ZXLD1362
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 1362 and cause erratic operation but the addition of a Schottky clamp diode (cathode to ADJ) 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 20µA 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 18 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 200µs/nF. The graph below shows the variation of soft-start time for different values of capacitor.
16
VIN = 24V, RS = 0.1Ω, L = 68µH, 22nF on ADJ
Soft-start operation. Output current (Ch2) and LX voltage (Ch1)
SOFT START TIME (ms)
14
12
10
8
6
4
2
0
-2
0
20
40
60
80
100
CAPACITANCE (nF)
Soft Start Time vs. Capacitance from
ADJ Pin to Ground
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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 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 approaches the output voltage the input current will increase putting 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.
If higher voltages are used and the CIN is 10μF. This can be an electrolytic capacitor provided a suitable 1µF ceramic capacitor is also used and
positioned as close the VIN of the IC as possible.
A suitable capacitor would be NACEW100M1006.3x8TR13F.
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 ZXLD1362 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 ZXLD1362 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.
ZXLD1362
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Application Information (cont.)
The graph Figure 3 below can be used to select a recommended inductor based on maintaining the ZXLD1362 case temperature below 60°C.
For detailed performance characteristics for the inductor values 68, 100, 150 and 220μH see graphs on pages 10-17.
ZXLD1362 Minimum Recommended Inductor
Aluminium board, 2%Accuracy, <60°C CaseTemperature
16
15
14
13
12
Number of LEDs
11
10
9
8
7
6
5
4
3
2
1
0
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 3 ZXLD1362 Minimum Recommended Inductor
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 PDS3100.
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Application Information (cont.)
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:
Rs
V
IN
LED
Cled
L1
D1
VIN
ISE NSE
LX
ZXLD1362
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 onresistance 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.
If the supply voltage is always less than 30V continuous an alternative device is available, the ZXLD1360 or the AL8805.
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.
ZXLD1362
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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.
1100
1000
900
POWER (mW)
800
700
600
500
400
300
200
100
0
-50 -30 -10 10 30 50 70 90 110 130 150
AMBIENT TEMPERATURE (°C)
Maximum Power Dissipation
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 ZXLD1362 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.
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.
ZXLD1362
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Application Information (cont.)
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
ZXLD1362
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 PCB
ZXLD1362 evaluation boards are available on request and provide quick testing of the ZXLD1362 device.
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).
Figure 4 Low Frequency PWM Operating Waveforms
The average value of output current in this mode is given by:
IOUTavg = 0.1DPWM/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.
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Ordering Information
Device
(Note 12)
ZXLD1362ET5TA
ZXLD1362QET5TA
Note:
1362
Package
Code
ET5
1362
ET5
Part Mark
TSOT25
Reel size
(mm)
180
Reel width
(mm)
8
Quantity
per reel
3000
TSOT25
180
8
3000
Packaging
Part Number
Qualification
Suffix
(Note 11)
TA
AEC-Q100 grade 1
TA
Automotive Grade
11. ZXLD1362QET5 is classified as “Automotive Grade” and supports PPAP documentation. See ZXLD1362Q datasheet for more information.
Marking Information
Package Outline Dimensions
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.
D
e1
E
E1
L2
c
4x θ1
e
L
θ
5x b
A
A2
A1
ZXLD1362
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TSOT25
Dim Min Max Typ
A
1.00
−
−
A1
0.01 0.10
−
A2
0.84 0.90
−
D
2.90
−
−
E
2.80
−
−
E1
1.60
−
−
b
0.30 0.45
−
c
0.12 0.20
−
e
0.95
−
−
e1
1.90
−
−
L
0.30 0.50
L2
0.25
−
−
θ
0°
8°
4°
θ1
4°
12°
−
All Dimensions in mm
March 2014
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ZXLD1362
Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for latest version.
C
C
Dimensions Value (in mm)
C
0.950
X
0.700
Y
1.000
Y1
3.199
Y1
Y (5x)
X (5x)
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