Diodes ZXLD1350 User Manual

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ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

Description

The ZXLD1350 is a hysteretic mode inductive step-down
converter with integrated switch and high side current sense.

It operates from an input supply from 7V to 30V driving single
or multiple series connected LEDs efficiently external
adjustable output current up to 350mA.

The ZXLD1350 has been qualified to AECQ100 grade 2
allowing it to operate at ambient temperatures from -40 to
105°C.

The output current can be adjusted by applyi ng a DC voltage
or a PWM waveform. 100:1 adjustment of output current is
possible using PWM control. 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.

Features

• Simple low parts count

• Internal 30V NDMOS switch

• Internal PWM filter

• High efficiency (up to 95% (Note 1)

• Wide input voltage range: 7V to 30V

• 40V transient capability

• Up to 1MHz switching frequency

• Typical 4% output current accuracy

• Qualified to AEC-Q100 Grade 2

• Available in “Green” Molding Compound (No Br, Sb)

• Lead Free Finish/ RoHS Compliant (Note 2)

Notes: 1. Using standard external components as specified under electrical characteristics. Efficiency is dependent upon the number of LEDs driven and on

2. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at:

external component types and values.
http://www.diodes.com/products/lead_free.html

Pin Assignments

LX

GND

ADJ

TSOT23-5

To p View

Typical Application Circuit

R

0.33Ω

V

IN

S

SET

ZXLD1350

GND

V

IN

7~30V

C1

1µF

GND

ADJ

V

IN

I

SENSE

L1

47µH

LX

ZXLD1350

Document number: DS33468 Rev. 8 - 2

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V

Block Diagram

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ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

R

IN

V

IN

Voltage
regulator

C1

ADJ

200k

Vref

1.25V

GND

4KHz

5V

Shutdown
circuit

V

IN

R1

R2

R3

Current sense circuit

Figure 1. Block diagram – Pin Connection

S

D1

-

+

Comparator

-

+

I

SENSE

L1

LX

MN

Pin Description

Name Pin No. Description

LX 1 Drain of NDMOS switch

GND 2 Ground (0V)

Multi-function On/Off and brightness control pin:

• Leave floating for normal operation.(V
I

OUTnom

=0.1/RS)

• Drive to voltage below 0.2V to turn off output current

ADJ 3

• Drive with DC voltage (0.3V<V

ADJ

• Drive with PWM signal from open-collector or open-drain transistor, to adjust output current.
Adjustment range 25% to 100% of I

• Connect a capacitor from this pin to ground to increase soft-start time. (Default soft-start time=0.5ms.
Additional soft-start time is approx.0.5ms/nF)

I

SENSE

VIN

4

5

Connect resistor R
(Note: R

SMIN

Input voltage (7V to 30V). Decouple to ground with 1µF of higher X7R ceramic capacitor close to
device

ZXLD1350

Document number: DS33468 Rev. 8 - 2

from this to VIN to define nominal average output current I

S

=0.27V with ADJ pin open circuit)

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= V

ADJ

=1.25V giving nominal average output current

REF

<2.5V) to adjust output current from 25% to 200%

OUTnom

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for f>10kHz and 1% to 100% of I

OUTnom

OUTnom

(†)

of I

OUTnom

for f<500Hz

=0.1/RS

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ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated)

Symbol Parameter Rating Unit

VIN

V

SENSE

VLX

V

ILX

ADJ

Input Voltage

I

SENSE

Voltage

(measured with respect to VIN)
LX Output Voltage
Adjust Pin Input Voltage -0.3 to +6 V

Switch Output Current 500 mA
Power Dissipation

P

TOT

(Refer to Package thermal de-rating curve on
page 19)

TST

TJ

MAX

These are stress ratings only. Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings, for extended
periods, may reduce device reliability.

Storage Temperature -55 to 150 °C
Junction Temperature 150 °C

-0.3 to +30

(40V for 0.5 sec)

+0.3 to -5

-0.3 to +30

(40V for 0.5 sec)

V

V

V

450 mW

Thermal Resistance

Symbol Parameter Rating Unit

θ

JA

Junction to Ambient 200 °C/W

Recommended Operating Conditions

Symbol Parameter Min Typ. Max Units

VIN

t

OFFMIN

t

ONMIN

DLX

I

LX_CONT

f

LXmax

TPD

ZXLD1350

Document number: DS33468 Rev. 8 - 2

Input voltage 7
Minimum switch off-time
Minimum switch on-time
Duty cycle range 0.01

TA

Ambient operating temperature range -40
Average/RMS LX switch current 0.37 A
Recommended maximum operating frequency 1 MHz
Internal comparator propagation delay 50 ns

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30 V
800 ns
800 ns

0.99

+105 °C

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ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

Electrical Characteristics (Test conditions: V

= 12V, T

IN

= 25°C, unless otherwise specified.) (Note 3)

amb

Symbol Parameter Condition Min. Typ. Max. Unit

VSU
I

INQoff

I

INQon

V

SENSE

V

SENSEHYS

I

SENSE

V

REF

DV

REF

V

ADJ

V

ADJoff

V

ADJon

R

Resistance between ADJ pin and V

ADJ

I

LXmean

RLX
I

LX(leak)

Internal regulator start-up threshold
Quiescent supply current with output off ADJ pin grounded 15 20 µA

Quiescent supply current with output switching

Mean current sense threshold voltage
(Defines LED current setting accuracy)

Sense threshold hysteresis ±15 %

I

pin input current V

SENSE

Internal reference voltage

/DT Temperature coefficient of V

External control voltage range on ADJ pin for
DC brightness control (Note 4)

DC voltage on ADJ pin to switch device from
active (on) state to quiescent (off) state

DC voltage on ADJ pin to switch device from
quiescent (off) state to active (on) state

Continuous LX switch current 0.37 A
LX switch ‘On’ resistance 1.5 2 
LX switch leakage current 1 µA
Duty cycle range of PWM signal applied to ADJ

D

PWM(LF)

pin during low frequency PWM dimming mode
Brightness control range 100:1
Duty cycle range of PWM signal applied to ADJ

D

PWM(HF)

pin during high frequency PWM dimming mode
Brightness control range 5:1

fLX

Operating frequency

(See graphs for more details)

REF

REF

VIN rising

ADJ pin floating
f = 250kHz
Measured on I
with respect to V
V

= 1.25V

ADJ

= V

SENSE

IN

SENSE

IN

-0.1

pin

Measured on ADJ pin with
pin floating

50

4.8 V

250 500 µA

95 100 105 mV

1.25 10 µA

1.21 1.25 1.29 V
ppm/°

C

0.3 2.5 V

V

V

ADJ

ADJ

falling

rising

0.15 0.2 0.25 V

0.2 0.25 0.3 V

135 250 k

PWM frequency <500Hz
PWM amplitude = V

REF

0.01 1

Measured on ADJ pin
PWM frequency <10kHz

PWM amplitude = V

REF

0.16 1

Measured on ADJ pin

ADJ pin floating
L = 100H (0.82V)

= 350ma @ V

I

OUT

Driving 1 LED

LED

= 3.4V

250 kHz

Time taken for output

tSS

Start up time
(See graphs for more details)

current to reach 90% of final
value after voltage on ADJ

500 µs

pin has risen above 0.3V.

Notes: 3. Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified over a -40°C to +105°C
temperature range, are guaranteed by design, characterization and process control.

4. 100% brightness corresponds to V
proportionally.

ZXLD1350

Document number: DS33468 Rev. 8 - 2

ADJ

= V

ADJ(nom)

= V

. Driving the ADJ pin above V

REF

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will increase the V

REF

threshold and output current

SENSE

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ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

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 block diagram and Figure 1 - Operating waveforms)
Operation can be best understood by assuming that the ADJ pin of the device is unconnected a nd the voltage on this pin

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

(V

ADJ

When input voltage V
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 V
by V

and L1 to produce a voltage ramp (V

IN

resistor R1 by the current sense circuit and produces a proportional current in internal resistors R2 and R3. T his produces a
ground referred rising voltage at the (-) input of the comparator. When this reaches the threshold voltage (V

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

When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to V
determined by the LED and diode forward voltages to produce a falling voltage at the input of the comparator. When this

voltage returns to V
ramping between limits of V

Switching thresholds

With V
I

SENSE

I

OUTnom

Nominal ripple current is ±15mV/R

=V

ADJ

REF

pin with respect to VIN). The average output current I

=100mV/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 (200k 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 V
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
15mA and switch leakage is below 1mA.

ZXLD1350

Document number: DS33468 Rev. 8 - 2

is first applied, the initial current in L1 and RS is zero and there is no output from the current sense

IN

to ground, via RS, L1 and the LED(s). The current rises at a rate determined

IN

) across RS. The supply referred voltage V

SENSE

IN

, the comparator output switches high again. This cycle of events repeats, with the comparator inpu t

ADJ

± 15%.

ADJ

, the ratios of R1, R2 and R3, define an average V

is then defined by this voltage and Rs according to:

OUTnom

S

switching threshold and adjust the output current. The filter is third order,

SENSE

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switching threshold of 100mV (measured on the

SENSE

is forced across internal

SENSE

. The current decays at a rate

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ADJ

.

ADJ

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Device Description (Continued)

Figure 1. Theoretical Operating Waveforms

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30V 350mA LED DRIVER with AEC-Q100

ZXLD1350

Document number: DS33468 Rev. 8 - 2

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ZXLD1350

30V 350mA LED DRIVER with AEC-Q100

Device Description (Continued)

Typical Operating Waveforms [VIN = 12V, RS = 0.3V, L = 100 μH]

Normal operation. Output current (Ch3) and LX voltage (Ch1)

Start-up waveforms. Output current (Ch3), LX voltage (Ch1) and V

ZXLD1350

Document number: DS33468 Rev. 8 - 2

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ADJ

(Ch2)

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