ZXLD1366DACTC - DIODES Incorporated

ZXLD1366

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HIGH ACCURACY 1A, 60V LED DRIVER WITH AEC-Q100

Description

The ZXLD1366 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 suppl y between 6V and 60V an d

provides an externally adjustable output current of up to 1A.

The ZXLD1366 has been qualified to AECQ100 Grade 1 enabling

operation in ambient temperatures from -40°C to +125°C

The ZXLD1366 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.

Enhanced output current dimming resolution can be achieved by

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.

Pin Assignments

(TOP VIEW)

TSOT25

I

SENSE

V

IN

2

1

34

5

ADJ

GND

LX

1

2

34

5

6

U-DFN3030-6

(TOP VI EW)

LX

GND

ADJ

V

IN

I

SENSE

GND

(TOP VIEW)

SO-8EP

46

5

1

7

28

3

LX

GND

ADJ

V

IN

GND

I

SENSE

Typical Application Circuit

V

IN

I

SENSE

LX

GND

ZXLD1366

ADJ

V

IN

(24V) Rs

0.2V

4.7µFC1

GND

100nF

D1

L1

Features

• Typically better than 0.8% output current accuracy

• Simple and with low part count

• Single pin on/off and brightness control using DC voltage or

PWM

• PWM resolution up to 1000:1

• High efficiency (up to 97%)

• Switching frequencies up to 1MHz

• Wide input voltage range: 6V to 60V

• Inherent open-circuit LED protection

• Available in thermally enhanced Green molding packages

 SO-8EP JA = +45°C/W

 U- 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 Grade 1

 SO-8EP ZXLD1366EN8TC

 TSOT25 ZXLD1366ET5TA

Applications

• Automotive lighting

• Low voltage industrial lighting

• LED back-up lighting

• Illuminated signs

• Emergency lighting

• SELV lighting

• Refrigeration lights

Notes: 1. EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant. All applicable RoHS exemptions applied.

2. See http://www.diodes.com for more information about Diodes In corpor ated’s definitions of Halogen- and Antimony-free, "Green" and Lead-free.

3. Halogen- and Antimony-free "Green” products are defined as tho se which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl)

and <1000ppm antimony compounds.

ZXLD1366

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Block Diagram



Low voltage

detector

Voltage

regulator

LX

MN

L1

D1

I

SENSE

Adj

Gnd

V

IN

V

IN

50K 20K

1.25V

1.35V

0.2V

600KHz

+

-

+

-

+

-

R4 R5

R2

R3

R1

2

3

54 1

D1

+

-

R

S

C1

4.7µF

5V

Figure. 1 Pin Connection for TSOT25 Package

Pin Description

Name TSOT25 U-DFN3030-6 SO-8EP Function

LX 1 1 1 Drain of NDMOS switch

GND 2 2, 5 2, 3, 6, 7 Ground (0V)

ADJ 3 3 4

Multi-function On/Off and brightness control pin:

• 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

ISENSE 4 4 5

Connect resistor RS from this pin to VIN to define nominal average output current

IOUTnom = 0.2V/RS.

(Note: RSMIN = 0.2V with ADJ pin open-circuit)

VIN 5 6 8

Input Voltage (6V to 60V). Decouple to ground with 4.7µF of higher X7R ceramic

capacitor close to device.

Pad - Pad Pad

Exposed Pad (EP) - connected to device substrate.

To improve thermal impedance of package the EP must be connected to power

ground but should not be used as the 0V (GND) current path.

It can be left floating but must not be connected to any other voltage other than

0V.

ZXLD1366

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Absolute Maximum Ratings (Note 4)

Symbol Parameter Rating Unit

VIN Input Voltage -0.3 to +65 V

VSENSE I

SENSE 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

ILX Switch Output Current 1.25 A

PTOT Power Dissipation

(Refer to Package thermal de-rating curve on

page 25)

TSOT25 1

W

U-DFN3030-6 1.8

SO-8EP 2.2

TOP Operating Temperature -40 to +125 °C

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 ex tended periods of time.

ESD Susceptibility Rating Unit

Human Body Model 500 V

Machine Model 75 V

Caution: 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 1.5k resistor pin. The machine model is a 200pF capacitor discharged directly

into each pin.

Thermal Resistance

Symbol Parameter Rating Unit

TSOT25 SO-8EP U-DFN3030-6

JA Junction to Ambient 82 45 44

°C/W

JB Junction to Board 33 — —

JC Junction to Case — 7 14

Recommended Operating Conditions

Symbol Parameter Min Max Units

VIN Input voltage (Note 6) 6 60 V

ILX Maximum recommended continuous/RMS switch current 1 A

VADJ External control voltage range on ADJ pin for DC brightness control (Note 7) 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 8) 625 kHz

DLX Duty cycle range 0.01 0.99

DLX(LIMIT) Recommended duty cycle range of output switch at fLXMAX 0.3 0.7

TOP Operating Temperature range -40 +125 °C

Notes: 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) = V REF. Driving the ADJ pin above VREF will increase the VSENSE threshold and output current

proportionally.

8. ZXLD1366 will operate at higher frequencies but accuracy will be affected due to propagation delays.

ZXLD1366

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Electrical Characteristics (Test conditions: VIN = 24V, TA = +25°C, unless oth erwise specified.)

Symbol Parameter Condition 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 9) ADJ pin floating, L = 68µH,

3 LEDs, f = 260kHz 1.6 mA

VSENSE 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

VSENSEHYS Sense threshold hysteresis ±15 %

ISENSE I

SENSE pin input current VSENSE = VIN -0.2 4 10 µA

VREF Internal reference voltage Measured on ADJ pin with pin

floating 1.25 V

ΔVREF/ΔT Temperature coefficient of VREF 50 ppm/°C

VADJ External control voltage range on ADJ pin for DC

brightness control (Note 7) 0.3 2.5 V

VADJoff DC voltage on ADJ pin to switch device from active

(on) state to quiescent (off) state VADJ falling 0.15 0.20 0.27 V

VADJon DC voltage on ADJ pin to switch device from

quiescent (off) state to active (on) state VADJ rising 0.20 0.25 0.30 V

RADJ Resistance between ADJ pin and VREF 0 < VADJ < VREF

VADJ > VREF +100mV 30

10.4 50

14.2 65

18.0 k

ILXmean Continuous LX switch current 1 A

RLX LX switch ‘On’ resistance @ ILX = 1A 0.50 0.75 

ILX(leak) LX switch leakage current 5 µA

DPWM(LF) Duty cycle range of PWM signal applied to ADJ pin

during low frequency PWM dimming mode

PWM frequency < 300Hz PWM

amplitude = VREF

Measured on ADJ pin 0.001 1.000 V

Brightness control range 1000:1

DCADJ DC Brightness control range (Note 8) 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

Notes: 9. Static current of device is approximately 700 µA, see Graph, Page 16

10. 100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE threshold and output current

proportionally.

11. Ratio of maximum brightness to minimum brightness before shutdown VREF = 1.25/0.3. VREF externally driven to 2.5V, ratio 10:1.

ZXLD1366

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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).

0V

VIN 200mV230mV

0V

SENSE voltage

VSENSE+

VSENSE-

Toff Ton

170mV

0V

5V

VIN

0.15VADJ

I

OUTnom

I

OUTnom

+15%

I

OUTnom

-15%

VADJ

LX voltage

Coil current

Comparator

input voltage

Comparator

output

Figure 2. Theoretical Operating Waveforms

Operation can be best understood by assuming that the ADJ pin

of the device is unconnected and the voltage on this pin (VADJ)

appears directly at the (+) input of the comparator.

When input voltage VIN is first applied, the initial current in L1

and RS is zero and there is no output from the current sense

circuit. Under this condition, the (-) input to the comparator is at

ground and its output is high. This turns MN on and switches the

LX pin low, causing current to flow from VIN to ground, via RS, L1

and the LED(s). The current rises at a rate determined by VIN

and L1 to produce a voltage ramp (VSENSE) across RS. The

supply referred voltage VSENSE is forced across internal resistor

R1 by the current sense circuit and produces a proportional

current in internal resistors R2 and R3. This produces a ground

referred rising voltage at the (-) input of the comparator. When

this reaches the threshold voltage (VADJ), the comparator output

switches low and MN turns off. The comparator output also

drives another NMOS switch, which bypasses internal resistor

R3 to provide a controlled amount of hysteresis. The hysteresis

is set by R3 to be nominally 15% of VADJ.

When MN is off, the current in L1 continues to flow via D1 and

the LED(s) back to VIN. The current decays at a rate determined

by the LED(s) and diode forward voltages to produce a falling

voltage at the input of the comparator. When this voltage returns

to VADJ, the comparator output switches high again. This cycle of

events repeats, with the comparator input ramping between limits

of VADJ ± 15%.

Switching Thresholds

With VADJ = VREF, the ratios of R1, R2 and R3 define an average

VSENSE switching threshold of 200mV (measured on the ISENSE

pin with respect to VIN). The average output current IOUTnom is

then defined by this voltage and RS according to:

IOUTnom = 200mV/RS

Nominal ripple current is ±30mV/RS

ZXLD1366

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Device Description (cont.)

Actual operating waveforms

VIN = 15V, RS = 0.2Ω, L = 68µH Normal operation.

Output Current (Ch 3) and LX voltage (Ch 2)

VIN = 30V, RS = 0.2Ω, L = 68µH Normal operation.

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

(50k 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 60A

and switch leakage is below 5A.

ZXLD1366

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Typical Operating Conditions

010 20 30 40 50 60

SUPPLY VOL TAGE (V)

Output Current, L = 68µH

1.100

1.080

1.060

1.040

1.020

1.000

0.980

OU

T

P

U

T

C

U

R

E

N

T

(

A

)

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLT AGE (V)

Output Current Devia tion, L = 68µH

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

1

0

8

6

4

2

0

-2

O

U

T

P

U

T

C

U

R

EN

T

DEVI

A

T

I

O

N (%)

-4

-6

-8

-10

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLT AGE (V)

Efficiency, L = 68µH

100

95

90

85

80

75

70

E

F

I

C

IEN

C

Y

(%)

65

60

55

50

ZXLD1366

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Typical Operating Conditions (cont.)

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPL Y VOLTAGE (V)

Sw it chin g Frequency, L = 68µ H

500

450

400

150

100

50

0

SWI

T

C

H

IN

G

F

R

E

Q

U

EN

C

Y

(k

H

z)

350

300

250

200

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLTAGE (V)

Duty Cycle, L = 68µH

100

90

80

30

20

10

0

D

U

T

Y

C

Y

C

LE ( %)

70

60

50

40

ZXLD1366

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Typical Operating Conditions (cont.)

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLT AGE (V)

Output Current, L = 100µH

1.100

1.080

1.060

1.040

1.020

1.000

0.980

O

UT

P

UT

C

U

R

ENT (

A

)

0.960

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLT AGE (V)

Output Current Deviation, L = 100µH

10

8

6

4

2

0

-2

O

UT

P

UT

C

U

R

ENT DEVI

A

TI

O

N (%)

-4

-6

-8

-10

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLTAGE (V)

Efficiency, L = 100µH

ZXLD1366

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Typical Operating Conditions (cont.)

1 LED

3 LEDs

5 LEDs

7 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPL Y VOLTAGE (V)

Sw it chin g Freq uency, L = 100µH

500

450

400

150

100

50

0

SWI

T

C

H

IN

G

F

R

E

Q

U

EN

C

Y

(k

H

z)

350

300

250

200

1 LED

3 LEDs

5 LEDs

7 LEDs

11 LEDs

13 LEDs

15 LEDs

0 102030405060

SUPPL Y VOLTAGE (V)

Duty Cycle, L = 100µH

100

90

80

30

20

10

0

D

U

T

Y

C

Y

C

LE ( %)

70

60

50

40

ZXLD1366

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Typical Operating Conditions (cont.)

0102030405060

SU PPLY VOLTAGE (V)

Outp ut C u rr ent, L = 150µ H

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

1.100

1.080

1.060

1.040

1.020

1.000

0.980

O

UT

P

UT

C

U

R

ENT (

A

)

0102030405060

SUPPLY VOL TAGE (V)

Output Current Deviation, L = 150µH

10

8

6

4

2

0

-2

O

U

T

P

U

T

C

U

R

EN

T

DEVI

A

T

I

O

N (%)

-4

-6

-8

-10

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLT AGE (V)

Efficiency, L = 150µH

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

ZXLD1366

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Typical Operating Conditions (cont.)

1 LED

3 LEDs

5 LEDs

7 LEDs

11 LEDs

13 LEDs

15 LEDs

500

450

400

150

100

50

0

SWI

T

C

H

IN

G

F

R

E

Q

U

EN

C

Y

(k

H

z)

350

300

250

200

0102030405060

SUPPLY VOLTAGE (V)

Sw itching Frequency, L = 150 µH

100

90

80

30

20

10

0

D

U

T

Y

C

Y

C

LE (%)

70

60

50

40

0102030405060

SUPPL Y VOLTAGE (V)

Duty Cycle, L = 150µH

1 LED

3 LEDs

5 LEDs

7 LEDs

11 LEDs

13 LEDs

15 LEDs

ZXLD1366

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Typical Operating Conditions (cont.)

0102030405060

SUPPLY VOL TAGE (V)

Output Current, L = 220µH

1.100

1.080

1.060

1.040

1.020

1.000

0.980

OU

T

P

U

T

C

U

R

E

N

T

(

A

)

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOL TAGE (V)

Output Current Deviation, L = 220µH

10

8

6

4

2

0

-2

OU

T

P

U

T

C

U

R

E

N

T

D

E

VI

A

T

ION (

%

)

-4

-6

-8

-10

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

0102030405060

SUPPLY VOLTAGE (V)

Effic iency, L = 220µH

1 LED

3 LEDs

5 LEDs

7 LEDs

9 LEDs

11 LEDs

13 LEDs

15 LEDs

EFFICIENCY (%)

ZXLD1366

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Typical Operating Conditions (cont.)

0102030405060

SUPPLY VOLTAGE (V)

Sw it chin g Frequency, L = 220 µH

500

450

400

150

100

50

0

SWI

T

C

H

IN

G

F

R

E

Q

U

EN

C

Y

(k

H

z)

350

300

250

200

1 LED

3 LEDs

5 LEDs

7 LEDs

11 LE Ds

13 LEDs

15 LEDs

0 102030405060

SUPPL Y VOLTAGE (V)

Duty Cycle, L = 220µH

100

90

80

30

20

10

0

D

U

T

Y

C

Y

C

LE ( %)

70

60

50

40

1 LED

3 LEDs

5 LEDs

7 LEDs

11 LE Ds

13 LEDs

15 LEDs

ZXLD1366

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Typical Operating Conditions (cont.)

ADJ PIN VOL TAGE (V)

LED Current vs. ADJ

0321

1200

1000

800

600

400

200

0

LED

C

U

R

E

N

T

(mA)

R = 200m

Ω

R = 300m

Ω

R = 680m

Ω

SUPPLY VOLTAGE (V)

0705010 20 30 40 60

800

500

400

300

200

100

0

S

U

P

L

Y

C

U

R

E

N

T

(mA)

600

700

SUPPLY VOLTAGE (V)

0705010 20 30 40 60

1.2430

1.2415

1.2410

1.2405

1.2400

1.2395

1.2380

ADJ

P

I

N

V

O

L

T

A

G

E (V)

1.2420

1.2425

1.2385

1.2390

SUPPL Y VOLTAGE (V)

0705010 20 30 40 60

90

60

50

40

30

0

S

H

U

T

D

O

WN

C

U

R

EN

T

(mA)

70

80

10

20

ZXLD1366

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Typical Operating Conditions (cont.)

05 303510 15 20 25

SUPPLY VOLT AGE (V)

LX On-Resi stance vs. Supply Volt age

-40°C

20°C

150°C

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

O

N-

R

E

S

I

S

T

A

N

C

E ( )

Ω

7V

9V

12V

20V

30V

-50 0 20050 100 150

TEMP ERATURE (°C)

V vs. Temperature

ADJ

1.262

1.260

1.258

1.256

1.254

1.250

1.248

1.246

1.244

V (V)

ADJ

1.252

7V

9V

12V

30V

20V

-50 0 20050 100 150

DI E TE MP E RATU R E (° C )

LX On-Resisitance vs. Die Temperature

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

O

N

-

R

E

S

I

S

T

A

N

C

E

()

Ω

ZXLD1366

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Application Information

Setting Nominal Average Outpu t Cu rrent with External Resistor RS

The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (R S) 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 setting resistor (RS) in the typical

application circuit shown on page 1:

RS (Ω) Nominal Average Output

Current (mA)

0.20 1000

0.27 740

0.56 357

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 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 50k ±25% for voltages below VREF and 14.2k ±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:

GND

ZXLD1366

ADJ

GND

+

DC

PW

M

GND

0V

V

ADJ

GND

ZXLD1366

ADJ

ZXLD1366

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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:

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 ADJ

input of the ZXLD1366 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 tha n approximately 100s will turn off the output and suppl y current to a low standby

level of 65A 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).

PWM GND

ZXLD1366

ADJ

GND

ZXLD1366

ADJ

MCU 3.3k

ZXLD1366

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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 ti me 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.

60 80 100 12002040

CAPACI TANCE (nF)

Soft-S tart T ime vs. Capacitance form A DJ to Ground

16

14

12

10

4

2

0

-2

8

6

S

O

F

T

-S

T

A

R

T

IME (ms)

Actual Operating Waveforms [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 VIN voltage:

VIN = 6 to 40V CIN = 2.2F

VIN = 40 to 50V CIN = 4.7F

VIN = 50 to 60V CIN = 10F

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 2.2F may need to be increased to 4.7F; 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 = 10F, 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 NACEW100M1006.3x8T R13F (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 ZXLD1366 are in the range 68H to 220H.

Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to s witching 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 ZXLD1366 may be selected from the MSS range ma nufactured by Coilcraft, or the NPIS range manufa ctured

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.

The graph Figure 3 below can be used to select a recommended inductor based on maintaining the ZXLD1366 case temperature below

+60°C. For detailed performance characteristics for the inductor values 68, 100, 150 and 220H see graphs on pages 10-17.

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Application Information (cont.)

Minimum Recommended Inductor

2% Accuracy, <60°C Case Temperature

0 102030405060

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Number of LEDs

Supply Voltage (V)

Legend

68uH

100uH

150uH

220uH

Figure. 3 ZXLD1366 Minimum Recommende d Inductor (TSOT25)

Minimum Recommended Inductor

2% Accuracy, <60°C Case Temperature

0.00 10.00 20.00 30.00 40.00 50.00 60.00

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Number of LEDs

Supply Voltage (V)

Legend

68µH

100µH

150µH

220µH

Figure. 4 ZXLD1366 Minimum Recommende d Inductor (U- DF N3030-6 )

ZXLD1366

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Application Information (cont.)

Figure. 5 ZXLD1366 Minimum Recommended Indu ctor (SO-8E P)

Diode Selection

For maximum efficiency and perfo rmance, the rectifier (D1) shoul d be a fast lo w 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 B3100 (Diodes Inc).

0 102030405060

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Legend

47µH

68µH

100µH

150µH

47µH

68µH

100µH

150µH

T < 70°C, I = 1A

CLED

Number of LE Ds

Supply Voltage (V)

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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:

Figure. 6 Reduced Output Ripple

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 Suppl y Voltage

Below the under-voltage lockout threshold (VSD) the drive to the output transistor is turned off to prevent device operation with excessive on-

resistance of the output transistor. The output tran sistor is not full enhanced until the supply voltage exceeds approximately 17V. At s upply

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.

V

IN

V

IN

I

SENSE

LX

ZXLD1366

Rs

L1

Cled

LED

D1

ZXLD1366

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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 exceedi ng the

package power dissipation limits. The graph below gives details for power derating. This assumes the device to be mounted on a 25mm2

PCB with 1oz copper standing in still air.

-40 -25 -10 5 20 35 50 65 80 -5 110 125

AMBIENT TEMPERA TURE (°C)

Maximum Power Dissipation

POWER DISSIPAT ION (W)

2.

5

2.0

1.5

1.0

0.5

0

SO-8EP

U-DFN3030-6

TSOT25

Note that the device power dissipation will most often be a m aximum at minimum suppl y 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 DFN3030-6 and the SO-8EP packages thermal vias should be incorporated into the PCB.

See figures 7 and 8 for examples used in the ZXLD1366 evaluation boards.

Figure. 7 Suggested Layout for U-DFN3030-6 Package

ZXLD1366

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Figure. 8 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 0.5 hole

size.

Finally the same scheme in Figure 7 (without the exposed paddle) can be usde for the TSOT25 package guaranteeing an effective thermal

path.

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 ZXLD1366 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 Schottk y diode does not flow in a track between RS and VIN as this may give an

apparent higher measure of current than is actual because of track resistance.

ADJ Pin

The ADJ pin is a high impedance input for voltages up to 1.35V so, when left floating, PCB tracks to this pin should be as short as possible

to reduce noise pickup. A 100nF capacitor from the ADJ pin to ground will reduce frequency modulation of the output under these

conditions. An additional series 3.3k 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.

ZXLD1366

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Application Information (cont.)

GND

ZXLD1366

ADJ

3.3k

100nF

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 conta mination. 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 on request. Terminals allow users to interface the boards to their preferred LED products.

Dimming Output Current Using PWM

Low Frequency PWM Mode

When the ADJ pin is driven with a low frequenc y PWM signal (eg 100Hz), with a high level voltage VADJ and a lo w level of zero, the ou tput 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 9 - 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 (app rox. 1000:1) and

higher efficiency at the expense of greater output ripple.

V

ADJ

PWM Voltage Ton

IOUTavg

0V

0

Toff

0.2/RsIOUTnom

Output Current

Figure. 9 Low Frequency PWM Operating Waveforms

ZXLD1366

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Ordering Information

ZXLD1366 DAC : U-DFN3030-6

EN8 : SO-8EP

ET5 : TSOT25

TC : 13” Tape & Reel

TA : 7” Tape & Reel

Part Number Package Packing

ZXLD1366 XXX X

X

Device Part

Mark Packaging Reel Size

(inches) Reel Width

(mm) Quantity

Per Reel Part Number

Suffix AEC-Q100

ZXLD1366DACTC 1366 U-DFN3030-6 13 12 3000 TC

ZXLD1366EN8TC ZXLD

1366

YYWW SO-8EP 13 12 2500 TC Grade 1

ZXLD1366ET5TA 1366 TSOT25 7 8 3000 TA Grade 1

Where YY stands for last 2 digits of year - 10, 11 and WW stands for week number.

Package Outline Dimensions

1) TSOT25

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

c

A1

L

E1 E

A2

D

e1

e5x b

θ

4x 1

θ

L2

A

ZXLD1366

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Package Outline Dimensions (cont.)

2) U-DFN3030-6

3) SO-8EP

U-DFN3030-6

Dim Min Max Typ

A 0.57 0.63 0.60

A1 0 0.05 0.02

A3 ⎯ ⎯ 0.15

b 0.29 0.39 0.34

D 2.9 3.1 3.0

D2 2.65 2.85 2.75

E 2.9 3.1 3.0

e ⎯ ⎯ 1.205

E2 1.76 1.96 1.86

L 0.30 0.60 0.45

All Dimensions in mm

SO-8EP (SOP-8L-EP)

Dim Min Max Typ

A 1.40 1.50 1.45

A1 0.00 0.13 -

b 0.30 0.50 0.40

C 0.15 0.25 0.20

D 4.85 4.95 4.90

E 3.80 3.90 3.85

E0 3.85 3.95 3.90

E1 5.90 6.10 6.00

e - - 1.27

F 2.75 3.35 3.05

H 2.11 2.71 2.41

L 0.62 0.82 0.72

N - - 0.35

Q 0.60 0.70 0.65

All Dimensions in mm

Gauge Plane

Seating Plane

E1

E

N

e

b

A

45

°

E0

H

F

Exposed Pad

Bottom View

L

QC

7

°

4° ± 3°

9° (Al l si de s )

A1

D

14

85

D

A1

AA3

E2

e

b

L

E

D2

ZXLD1366

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Suggested Pad Layout

1) TSOT25

2) U-DFN3030-6

3) SO-8EP

Dimensions Value (in mm)

C 0.950

X 0.700

Y 1.000

Y1 3.199

Dimensions Value (in mm)

Z 2.75

G 0.57

X1 1.86

X2 0.45

Y 0.34

C 1.205

Dimensions Value (in mm)

X 0.60

Y 1.55

X1 3.30

Y1 2.66

C1 5.4

C2 1.27

Y1

C C

X (5x)

Y (5x)

X1

G

X2

Z

C

Y

X

C1

C2

Y

Exposed Pad

X1

Y1

ZXLD1366

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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, corre ctions 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 herei n; neither does D iodes Incorporated conve y 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 unaut horized application, Customers shall indemnify

and hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of,

directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.

Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and

markings noted herein may also be covered by one or more United States, international or foreign trademarks.

LIFE SUPPORT

Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the

express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:

A. Life support devices or systems are devices or systems which:

1. are intended to implant into the body, or

2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the

labeling can be reasonably expected to result in significant injury to the user.

B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause

the failure of the life support device or to affect its safety or effectiveness.

Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems,

and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their

products and any use of Diodes Incorporated prod ucts in such safety-critical, life support devices or systems, notwithstanding any devices- or

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Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life

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