ZXLD1360Q

ZXLD1360Q
AUTOMOTIVE GRADE 30V 1A LED DRIVER
Description
Pin Assignments
The ZXLD1360Q is a continuous mode inductive step-down
converter with integrated switch and high side current sense.
(TOP VIEW)
It operates from an input supply from 7V to 30V driving single or
multiple series connected LEDs efficiently externally adjustable
output current up to 1mA.
LX 1
5 VIN
GND 2
The output current can be adjusted by applying a DC voltage or a
4 ISENSE
ADJ 3
PWM waveform to the ADJ pin; 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.
TSOT25
The ZXLD1360Q has been qualified to AEC-Q100 Grade 1 and is
Automotive Grade supporting PPAPs.
Features









Typical Application Circuit
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: 7V to 30V
40V transient capability
Up to 1MHz switching frequency
Typical 4% output current accuracy
Available in thermally enhanced Green molding packages
 TSOT25
JA = +82°C/W
 Totally Lead-free & Fully RoHS Compliant (Notes 1 & 2)
 Halogen and Antimony Free. “Green” Device (Note 3)
Automotive Grade


TSOT25
Qualified to AEC-Q100 Grade 1
Supports PPAP documents (Note 4)
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. Automotive, AEC-Q100 and standard products are electrically and thermally the
same, except where specified. For more information, please refer to http://www.diodes.com/quality/product_compliance_definitions/.
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
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ZXLD1360Q
Block Diagram
D1
VIN
L1
RS
5 VIN
5V
C1
4.7µF
`
4 ISENSE
1 LX
R1
Voltage
regulator
0.2V
Low voltage
detector
MN
ADJ
3
R4
200k
R5
20k
R2
D1
1.25V
R3
1.35V
GND
2
Figure 1 Block diagram – With Pin Connections
Pin Descriptions
Name
LX
GND
Pin No.
1
2
ADJ
3
ISENSE
4
VIN
5
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
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
•
Drive with PWM signal from open-collector or open-drain transistor, to adjust output current
•
Adjustment range 25% to 100% of IOUTnom for f>10kHz and 1% to 100% of IOUTnom for f < 500Hz
•
Connect a capacitor from this pin to ground to increase soft-start time
(Default soft-start time = 500µs. Additional soft-start time is approximately 500µs/nF)
Connect resistor RS from this to VIN to define nominal average output current IOUTnom=0.1/RS
(Note: RSMIN=0.1V with ADJ pin open circuit)
Input Voltage (7V to 30V)
Decouple to ground with 4.7µF of higher X7R ceramic capacitor close to device
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
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ZXLD1360Q
Absolute Maximum Ratings (Voltages to GND unless otherwise stated)
Symbol
Parameter
VIN
Input Voltage
VSENSE
ISENSE Voltage
VLX
LX Output Voltage
VADJ
Adjust Pin Input Voltage
ILX
Rating
-0.3 to +30
(40V for 0.5 sec)
+0.3 to -5
(measured with respect to VIN)
-0.3 to +30
(40V for 0.5 sec)
Unit
-0.3 to +6
V
1.25
A
1
W
V
V
V
PTOT
Switch Output Current
Power Dissipation
(Refer to Package thermal de-rating curve on page 20)
TST
Storage Temperature
-55 to 150
°C
TJ MAX
Junction Temperature
150
°C
ESD Susceptibility
HBM
Human Body Model
500
V
MM
Machine Model
<100
V
CDM
Charged Device Model
1000
V
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.
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
JA
Junction to Ambient
82
°C/W
ΨJB
Junction to Board
33
°C/W
Recommended Operating Conditions
Symbol
VIN
ILX
VADJ
VADJoff
tONmin_REC
fLX max
DLX
TA
Parameter
Input Voltage Range
Maximum Recommended Continuous/RMS Switch Current
External control voltage range on ADJ pin for DC brightness control
(Note 5)
DC voltage on ADJ pin to ensure devices is off
Recommended minimum switch “ON” time
Recommended maximum operating frequency (Note 6)
Duty cycle range
Ambient operating temperature range
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
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Min
7

Max
30
1
Units
V
A
0.3
2.5
V



0.01
-40
0.25
800
625
0.99
+125
V
ns
kHz

°C
September 2015
© Diodes Incorporated
ZXLD1360Q
Electrical Characteristics
Symbol
VSU
VSD
IINQoff
IINQon
VSENSE
VSENSEHYS
ISENSE
VREF
VREF/T
VADJ
VADJoff
VADJon
RADJ
DPWM(LF)
DPWM(HF)
tSS
fLX
tOFFMIN
tONMIN
tPD
Notes:
Parameter
Internal regulator start-up threshold
Internal regulator shutdown threshold
Quiescent supply current with output off
Quiescent supply current with output switching
(Note 7)
Mean current sense threshold voltage
(Defines LED current setting accuracy)
Sense threshold hysteresis
ISENSE pin input current
Internal reference voltage
Temperature coefficient of VREF
External control voltage range on ADJ pin for DC
brightness control (Note 5)
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
Condition
VIN rising
VIN falling
ADJ pin grounded
ADJ pin floating
f=250kHz
Measured on ISENSE pin with respect to
VIN VADJ = 1.25V

VSENSE = VIN-0.1
Measured on ADJ pin with pin floating

Min.



Typ.
5.65
5.55
20
Max.


40
Unit
V
V
µA

1.8
5.0
mA
95
100
105
mV




±15
1.25
1.25
50
10


%
µA
V
ppm/°C

0.3

2.5
V
VADJ falling
0.15
0.2
0.25
V
VADJ rising
0.2
0.25
0.3
V
135
13.5





0.5

250
25
1
1.0
5
0.01

1


100:1


0.16

1



5:1
5:1





500

µs

280

kHz



200
240
50



ns
ns
ns
0 < VADJ < VREF
VADJ > VREF +100mV
Continuous LX switch current

LX switch ‘On’ resistance
@ ILX=0.55A
LX switch leakage current

Duty cycle range of PWM signal applied to ADJ pin PWM frequency <500Hz
during low frequency PWM dimming mode
PWM amplitude = VREF
Measured on ADJ pin
Brightness control range
Duty cycle range of PWM signal applied to ADJ pin PWM frequency >10kHz
during high frequency PWM dimming mode
PWM amplitude = VREF
Measured on ADJ pin
Brightness control range
DC brightness control range
(Note 8)
Time taken for output current to reach
Soft start time
90% of final value after voltage on ADJ
pin has risen above 0.3V
ADJ pin floating
L = 33µH (0.093V)
Operating frequency
IOUT = 1A @ VLED = 3.6V
(See graphs for more details)
Driving 1 LED
Minimum switch off-time

Minimum switch on-time

Internal comparator propagation delay

Resistance between ADJ pin and VREF
ILXmean
RLX
ILX(leak)
DCADJ
(Test conditions: VIN = 12V, TA = +25°C, unless otherwise specified.)
kΩ
A
Ω
µA
5. 100% brightness corresponds to VADJ = VADJ(nom) = VREF (~1.25V). Driving the ADJ pin above VREF will increase the VSENSE threshold and output
current proportionally.
6. ZXLD1360Q will operate at higher frequencies, but due to propagation delays accuracy will be affected.
7. Static current of device is approximately 450 µA, see Supply Current Graph, Page 10.
8. Ratio of maximum brightness to minimum brightness before shutdown VREF = 1.25/0.3. VREF externally driven to 2.5V, ratio 10:1.
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
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ZXLD1360Q
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
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 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 V ADJ.
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 V ADJ ± 15%.
Switching thresholds
With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of 100mV (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 = 100mV/RS
Nominal ripple current is ±15mV/RS
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
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ZXLD1360Q
Device Description (cont.)
Actual operating waveforms: Normal operation
VIN=15V, RS=0.1V, L=33µH.
Output current (Ch1) and LX voltage (Ch2)
VIN=30V, RS=0.1V, L=33µH
Output current (Ch1) and LX voltage (Ch2)
Adjusting Output Current
The device contains a low pass filter between the ADJ pin and the threshold comparator and an internal current limiting resistor (200kV 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. The filter is third order, comprising three sections, each with a cut-off frequency of
nominally 4kHz.
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 20mA and switch leakage is below 5mA.
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
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© Diodes Incorporated
ZXLD1360Q
Typical Operating Characteristics
ZXLD1360 Output Current
L = 33µH
1060
ZXLD1360 Output Current
L = 33µH
10%
8%
Output Current Deviation (%)
1040
Output Current (mA)
1020
1000
980
960
940
920
900
6%
4%
2%
0%
-2%
-4%
-6%
-8%
0
1 LED
5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
5 LED s
30
6 LED s
-10%
35
7 LED s
8 LED s
0
1 LED
ZXLD1360 Switching Frequency
L = 33µH
5
2 LED s
3 LED s
4 LED s
5 LED s
30
6 LED s
35
7 LED s
8 LED s
ZXLD1360 Duty Cycle
L = 33µH
100
600
15
10
20
25
Supply Voltage V IN (V)
90
80
70
400
Duty Cycle (%)
Switching Frequency (kHz)
500
300
200
60
50
40
30
20
100
10
0
1 LED
0
5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
5 LED s
6 LED s
30
7 LED s
0
0
35
8 LED s
1 LED
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5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
5 LED s
30
6 LED s
7 LED s
35
8 LED s
September 2015
© Diodes Incorporated
ZXLD1360Q
Typical Operating Characteristics (cont.)
ZXLD1360 Output Current
L = 47µH
1060
ZXLD1360 Output Current
L = 47µH
10%
8%
Output Current Deviation (%)
1040
Output Current (mA)
1020
1000
980
960
940
920
900
6%
4%
2%
0%
-2%
-4%
-6%
-8%
0
1 LED
5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
5 LED s
30
6 LED s
-10%
35
7 LED s
8 LED s
0
1 LED
ZXLD1360 Switching Frequency
L = 47µH
5
2 LED s
3 LED s
4 LED s
5 LED s
30
6 LED s
35
7 LED s
8 LED s
ZXLD1360 Duty Cycle
L = 47µH
100
600
15
10
20
25
Supply Voltage V IN (V)
90
80
70
400
Duty Cycle (%)
Switching Frequency (kHz)
500
300
200
60
50
40
30
20
100
10
0
1 LED
0
5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
5 LED s
6 LED s
30
7 LED s
0
0
35
8 LED s
1 LED
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5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
5 LED s
30
6 LED s
7 LED s
35
8 LED s
September 2015
© Diodes Incorporated
ZXLD1360Q
Typical Operating Characteristics (cont.)
ZXLD1360 Output Current
L = 100µH
1060
ZXLD1360 Output Current
L = 100µH
10%
8%
Output Current Deviation (%)
1040
Output Current (mA)
1020
1000
980
960
940
920
900
6%
4%
2%
0%
-2%
-4%
-6%
-8%
0
1 LED
5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
5 LED s
30
6 LED s
-10%
35
7 LED s
8 LED s
0
1 LED
ZXLD1360 Switching Frequency
L =100µH
5
2 LED s
3 LED s
4 LED s
5 LED s
30
6 LED s
35
7 LED s
8 LED s
ZXLD1360 Duty Cycle
L = 100µH
100
600
15
10
20
25
Supply Voltage V IN (V)
90
80
70
400
Duty Cycle (%)
Switching Frequency (kHz)
500
300
200
60
50
40
30
20
100
10
0
1 LED
0
5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
5 LED s
6 LED s
30
7 LED s
0
0
35
8 LED s
1 LED
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5
2 LED s
15
10
20
25
Supply Voltage V IN (V)
3 LED s
4 LED s
5 LED s
30
6 LED s
7 LED s
35
8 LED s
September 2015
© Diodes Incorporated
ZXLD1360Q
Typical Operating Characteristics (cont.)
1.4
1.2372
1.2
1.2371
V REF (V)
1.2370
1.2369
V REF (V)
V REF (V)
1
0.8
0.6
1.2368
1.2367
0.4
1.2366
0.2
0
0
1.2365
1
2
3
4
5
6
Supply Voltage V IN (V)
VREF vs. Supply Voltage
7
1.2364
0
8
15
10
20
25
Supply Voltage V IN (V)
VREF vs. Supply Voltage
5
30
35
18
600
16
500
14
12
IIN (µA)
IIN (µA)
400
300
10
8
6
200
4
100
0
2
0
0
15
10
20
25
30
Supply Voltage V IN (V)
Supply Current vs. Supply Voltage
5
35
0
15
10
20
25
30
Supply Voltage VIN (V)
Shutdown Current vs. Supply Voltage
5
35
1200
LED Current (mA)
1200
800
600
400
200
0
0
1
2
ADJ Pin Voltage (V)
R = 100m
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
R = 150m
10 of 22
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3
R = 330m
September 2015
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ZXLD1360Q
Typical Operating Characteristics (cont.)
LX Switch “On” Resistance vs. Temperature
ZXLD1360 Response Time vs. Temperature
Ty pical minimum LX ‘on’ and ‘off’ time
350
0.80
300
0.70
Response Time (ns)
250
0.60
200
0.50
150
0.40
100
0.30
50
0
-55
-35
-15
5
25 45 65 85
Ambient Temperature (C)
Min LX on
0.20
-50
105 125
50
100
150
Ambient Temperature ( C)
200
Voltage Across RSENSE (0.333 ) vs. Temperature
V ADJ vs. Temperature
L = 470µH, RS = 0.33
1.24
0
Min LX of f
100.4
100.2
100
1.235
99.8
V SENSE (V)
V ADJ (V)
1.23
1.225
99.6
99.4
99.2
1.22
99
98.8
1.215
98.6
1.21
-55
-35
12V, Single LED
12V, Three LED
24V, Single LED
98.4
-55
105 125
24V, Three LED
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
0.4
-0.4
-0.5
-55
-35
-15
5
25 45 65 85
Ambient Temperature ( C)
12V, Single LED
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
-35
-15
5
25 45 65 85
Ambient Temperature ( C)
12V, Single LED
Output Current Change vs. Temperature
V IN = 12V, L = 470µH, RS = 0.33
Deviation from Nominal Set Value (%)
Deviation from Nominal Set Value (%)
0.5
-15
5
25 45 65 85
Ambient Temperature ( C)
12V, Three LED
24V, Three LED
0
-0.2
-0.4
-0.6
-0.8
-35
-15
5
25 45 65 85
Ambient Temperature ( C)
24V, Single LED
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24V, Single LED
Output Current Change vs. Temperature
V IN = 24V, L = 470µH, RS = 0.33
0.2
-1
-55
105 125
12V, Three LED
105 125
105 125
24V, Three LED
September 2015
© Diodes Incorporated
ZXLD1360Q
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 (R S) in the typical
application circuit shown on page 1:
RS (Ω)
Nominal Average
Output Current (mA)
0.1
1000
0.13
760
0.15
667
The above values assume that the ADJ pin is floating and at a nominal voltage of V REF (=1.25V). Note that RS = 0.1V 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 (100mV/RS) [for 0.3< VADJ <2.5V]
Note that 100% brightness setting corresponds to V ADJ = 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 20kΩ ±25% for voltages above VREF +100mV.
ZXLD1360Q
Document number: DS37115 Rev. 1 - 2
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September 2015
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ZXLD1360Q
Application Information (cont.)
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:
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 200k 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 Drain / Source capacitance, this arrangement can inject a negative spike into ADJ
input of the 1360 and cause erratic operation but the addition of a Schottky clamp diode (cathode to ADJ) to ground and inclusion of a series
resistor (10k) 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 (cont.)
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 V REF will increase output current above the 100% nominal
average value. (See graphs for details).
Soft-start
The device has inbuilt soft-start action due to the delay through the PWM filter. An external capacitor from the ADJ pin to ground will provide
additional 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. With no external capacitor, the time taken for the output to reach 90% of its final
value is approximately 500μs. Adding capacitance increases this delay by approximately 0.5ms/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
10
Soft Start time (ms)
8
6
4
2
0
0
5
10
15
20
25
Capacitance (nF)
Actual operating waveforms: Soft-start operation
VIN=15V, RS=0.1V, L=33μH, 100nF on ADJ
Output current (CH2) and LX voltage (Ch1)
VIN=15V, RS=0.1V, L=33µH, 0nF on ADJ
Output current (Ch2) and LX voltage (Ch1)
The trace above left shows the typical soft startup time (tSS) of 500µs with no additional capacitance added to the ADJ pin. The trace above
left has had its soft-start time extended on the trace by adding a 100nF ceramic capacitor which gives a soft-start time (tSS) of 40 ms
approximately.
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Application Information (cont.)
Inherent open-circuit LED protection
If the connection to the LED(s) is open-circuited, the coil is isolated from the LX pin of the chip, so the device will not be damaged, unlike in
many boost converters, where the back EMF may damage the internal switch by forcing the drain above its breakdown voltage.
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. A minimum value of 4.7μF is acceptable if the input source is close to the device, but 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 are recommended. Capacitors with Y5V
dielectric are not suitable for decoupling in this application and should NOT be used.
A suitable Murata capacitor would be GRM42-2X7R475K-50.
The following web sites are useful when finding alternatives:
www.murata.com
www.t-yuden.com
www.kemet.com
www.avxcorp.com
Inductor Selection
Recommended inductor values for the ZXLD1360Q are in the range 33µH to 100µH.
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). 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 ZXLD1360Q are listed in the table below:
Part No.
MSS1038-333
MSS1038-683
NPIS64D330MTRF
L
(µH)
33
68
33
DCR
(V)
0.093
0.213
0.124
ISAT
(A)
2.3
1.5
1.1
Manufacturer
Coilcraft www.coilcraft.com
NIC www.niccomp.com
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.
The following equations can be used as a guide, with reference to Figure 2 - Operating Waveforms.
LX Switch ‘On’ time
t ON
LX Switch ‘Off’ time
LI

VIN  VLED  Iavg  R S  rL  RLX 
Note: tONmin > 240ns
t OFF 
LI
VLED  VD  Iavg  R S  rL 
Note: tOFFmin > 200ns
Where:
L is the coil inductance (H)
rL is the coil resistance (Ω)
RS is the current sense resistance (Ω)
Iavg is the required LED current (A)
I is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg}
VIN is the supply voltage (V)
VLED is the total LED forward voltage (V)
RLX is the switch resistance (Ω) {=0.5 nominal}
VD is the diode forward voltage at the required load current (V)
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Application Information (cont.)
Example:
For VIN =12V, L=33µH, rL=0.093, RS=0.1Ω , RLX=0.15, VLED=3.6V, Iavg =1A and VD =0.49V
tON = (33e-6 x 0.3)/(12 - 3.6 - 0.693) = 1.28µs
tOFF = (33e-6 x 0.3)/(3.6 + 0.49 + 0.193) = 2.31µs
This gives an operating frequency of 280kHz and a duty cycle of 0.35.
These and other equations are available as a spreadsheet calculator from the Diodes website at www.diodes.com.
Note that in practice, the duty cycle and operating frequency will deviate from the calculated values due to dynamic switching delays, switch
rise/fall times and losses in the external components.
Optimum performance will be achieved by setting the duty cycle close to 0.5 at the nominal supply voltage. This helps to equalize the
undershoot and overshoot and improves temperature stability of the output current.
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. A suitable device is the PDS3100Q.
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.
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:
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Application Information (cont.)
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
The internal regulator disables the drive to the switch until the supply has risen above the start-up threshold (VSU). Above this threshold, the
device will start to operate. However, with the supply voltage below the specified minimum value, the switch duty cycle will be high and the
device power dissipation will be at a maximum. Care should be taken to avoid operating the device under such conditions in the application,
in order to minimize the risk of exceeding the maximum allowed die temperature. (See next section on thermal considerations). The drive to
the switch is turned off when the supply voltage falls below the under-voltage threshold (VSD). This prevents the switch working with
excessive 'on' resistance under conditions where the duty cycle is high.
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.
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 x
25mm PCB with 1oz copper standing in still air.
Maximum Power Dissipation
1100
1000
900
800
Power (mW)
700
600
500
400
300
200
100
0
-50
-30
-10
10
30
50
70
90
110
130
150
Ambient Temperature (Deg C)
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 ZXLD1360Q 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.
ZXLD1360Q
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ZXLD1360Q
Application Information (cont.)
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 R S 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 10kΩ 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.
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
A number of ZXLD1360 evaluation boards are available on request for qualified opportunities.
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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 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 3 - Low frequency PWM operating waveforms).
VADJ
Ton
PWM Voltage
Toff
0V
VADJ
Filter Output
300mV
200mV
0V
IOUTnom
0.1/Rs
Output Current
IOUTavg
0
Figure 3 Low Frequency PWM Operating Waveforms
The average value of output current in this mode is given by:
IOUTavg = 0.1DPWM/RS [for DPWM >0.01]
This mode is preferable if optimum LED 'whiteness' is required. It will also provide the widest possible dimming range (approx. 100:1) and
higher efficiency at the expense of greater output ripple.
Note that the low pass filter introduces a small error in the output duty cycle due to the difference between the start-up and shut-down times.
This time difference is a result of the 200mV shutdown threshold and the rise and fall times at the output of the filter. To minimize this error,
the PWM frequency should be as low as possible consistent with avoiding flicker in the LED(s).
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Application Information (cont.)
High Frequency PWM mode
At PWM frequencies above 10kHz and for duty cycles above 0.16, the output of the internal low pass filter will contain a DC component that
is always above the shutdown threshold. This will maintain continuous device operation and the nominal average output current will be
proportional to the average voltage at the output of the filter, which is directly proportional to the duty cycle (See Figure 4 – High frequency
PWM operating waveforms). For best results, the PWM frequency should be maintained above the minimum specified value of 10kHz, in
order to minimize ripple at the output of the filter. The shutdown comparator has approximately 50mV of hysteresis, to minimize erratic
switching due to this ripple. An upper PWM frequency limit of approximately one tenth of the operating frequency is recommended, to avoid
excessive output modulation and to avoid injecting excessive noise into the internal reference.
VADJ
Ton
PWM voltage
Toff
0V
VADJ
Filter output
200mV
0V
0.1/RS
Output current
IOUTnom
0
Figure 4 High Frequency PWM Operating Waveforms
The nominal average value of output current in this mode is given by:
IOUTnom »0.1DPWM/RS [for DPWM >0.16]
This mode will give minimum output ripple and reduced radiated emission, but with a reduced dimming range (approximately 5:1). The
restricted dimming range is a result of the device being turned off when the DC component on the filter output falls below 200mV.
Open and Shorted LED Protection
The ZXLD1360Q has by default open LED protection. If the LEDs should become open circuit the ZXLD1360Q 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 ZXLD1360Q.
If the LEDs should become shorted together, the ZXLD1360Q 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,
causing a much slower decay in inductor current.
During this condition the inductor current will remain within its controlled levels and no excessive heat will be generated within the
ZXLD1360Q.
ZXLD1360Q
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Ordering Information
Device
Packaging
(Note 9)
Part Mark
Package
Code
ZXLD1360QET5TA
TSOT25
1360
ET5
Packing: 7” Tape and Reel
Quantity per reel Reel width Part Number Suffix
3,000
8mm
TA
Qualification
(Note 10)
Automotive Grade
Notes: 9.
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.
10. ZXLD1360Q has been qualified to AEC-Q100 grade 1 and is classified as “Automotive Grade” supporting PPAP documentation.
See ZXLD1360 datasheet for commercial qualified versions.
Marking Information
TSOT25
XXXX : Identification code: 1360
Package Outline Dimensions
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for the latest version.
D
e1
01(4x)
E1/2
E/2
E1
c
E
Gauge Plane
0
L
e
Seating Plane
L2
01(4x)
b
A2
A1
A
Seating Plane
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
Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.
C
TSOT25
Dimensions Value (in mm)
C
0.950
X
0.700
Y
1.000
Y1
3.199
Y1
Y
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
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Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and
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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.
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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.
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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
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any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
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representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or
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Copyright © 2014, Diodes Incorporated
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