Diodes ZXLD1352 User Manual

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ZXLD1352

30V 350mA LED DRIVER WITH 1000:1 PWM DIMMING AND AEC-Q100

Description

The ZXLD1352 is a continuous 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 and multiple series connected LEDs effciently
externally adjustable output current up to 350mA.

The ZXLD1352 has been qualified to AEC-Q100 Grade
2 allowing it to operate at ambient temperatures from -40 to
105°C.

DC voltage or a PWM waveform. 1000:1 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

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

or PWM

• 1000:1 PWM dimming range

• 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

• Qualified to AEC-Q100 Grade 2

• Available in Green molding (no Br, Sb) with lead free

finish/RoHS compliant

Applications

• Low voltage halogen replacement LEDs

• Automotive lighting

• Low voltage industrial lighting

• LED back-up lighting

• Illuminated signs

* Using standard external components as specified under electrical characteristics. Efficiency is dependent upon the number of LEDs driven and on external
component types and values.

Pin Assignments

LX

GND

ADJ

TSOT23-5

Top View

Typical Application Circuit

V

IN

(12V- 30V)

C1

GND

1µF

PW M

V

ADJ

IN

ZLLS1000

Rs

0.33

D1

I

SENSE

ZXLD1352

GND

V

IN

I

SENSE

47mHL1

LX

ZXLD1352

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V

Block Diagram

IN

C1

ADJ

GND

Vref

V

IN

Voltage
regulator

50k

1.25V

V

IN

R1

Current sense circuit

5V

Shutdown
circuit

600KHz

R2

R3

Figure 1. Block Diagram

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R

S

D1

I

SENSE

-

+

Comparator

-

+

ZXLD1352

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
=0.1/RS)

I

OUTnom

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

ADJ 3

• Drive with DC voltage (0.3V<V

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

ADJ

• Drive with PWM signal from open-collector or open-drain transistor, to adjust output current.

o Adjustment range 0.1% to 100% of I

• Connect a capacitor from this pin to ground to define soft-start time. Soft-start time is

approx.0.5ms/nF)

I

4

SENSE

VIN 5

Connect resistor R
(Note: R

=0.27V with ADJ pin open circuit)

SMIN

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

ZXLD1352

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from this to VIN to define nominal average output current I

S

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= V

ADJ

OUTnom

=1.25V giving nominal average output current

REF

for 100Hz < f < 1kHz

OUTnom

=0.1/RS

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OUTnom

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ZXLD1352

Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated)

Symbol Parameter Rating Unit

VIN

V

SENSE

VLX

V

ADJ

ILX

P

TOT

TST

TJ

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.

Input Voltage

I

SENSE

Voltage

LX Output Voltage
Adjust Pin Input Voltage -0.3 to +6 V

Switch Output Current 500 mA
Power Dissipation

(Refer to Package thermal de-rating curve on page 17)

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

MAX

-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)

450 mW

V

V

V

Thermal Resistance

Symbol Parameter Rating Unit

θ

Junction to Ambient 200 °C/W

JA

Recommended Operating Conditions

Symbol Parameter Min Max Units

VIN

t

OFFMIN

t

ONMIN

f

LXmax

DLX

TA

ZXLD1352

Document number: DS33469 Rev. 3 - 2

Input voltage 7 30 V
Minimum switch off-time 200 ns
Minimum switch on-time 200 ns

Recommended maximum operating frequency 1 MHz

Duty cycle range 0.01 0.99
Ambient Temperature range -40 105

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ZXLD1352

Electrical Characteristics (Test conditions: V

Symbol

Parameter Conditions Min. Typ. Max.

VSU Internal regulator start-up threshold V

I

INQoff

I

INQon

V

SENSE

V

SENSEHYS

I

SENSE

V

Internal reference voltage Measured on ADJ pin with pin floating 1.21 1.25 1.29 V

REF

ΔV

REF

V

ADJ

Quiescent supply current
with output off

Quiescent supply current
with output switching

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

Sense threshold hysteresis ±15 %

I

/ΔT

pin input current V

SENSE

Temperature coefficient of V
External control voltage range on ADJ

pin for dc brightness control

50 ppm/°C

REF

1

= 12V, T

IN

rising 4.8 V

IN

= 25°C, unless otherwise specified.)

amb

ADJ pin grounded 20 30 µA

ADJ pin floating
f = 250kHz

Measured on I
to V

SENSE

=1.25V

IN VADJ

= VIN -0.1 1.25 10 µA

pin with respect

SENSE

250 500 µA

95 100 105 mV

0.3 2.5 V

DC voltage on ADJ pin to switch device

V

ADJoff

from active (on) state to quiescent (off)

V

falling 0.15 0.2 0.25 V

ADJ

state
DC voltage on ADJ pin to switch device

V

ADJon

from quiescent (off) state to active (on)

V

rising 0.2 0.25 0.3 V

ADJ

state

Unit

R

Resistance between ADJ pin and V

ADJ

I

Continuous LX switch current 0.37 A

LXmean

35 65 kΩ

REF

RLX LX Switch ‘On’ resistance 1.5 2 Ω
I

LX switch leakage current 1 µA

LX(leak

D

PWM(LF)

Duty cycle range of PWM signal
applied to ADJ pin during PWM
dimming mode

PWM frequency 100Hz – 1kHz
PWM amplitude = V

REF

Measured on ADJ pin

0.001 1

Brightness control range 1000:1

ADJ pin floating

fLX

Operating frequency
(See graphs for more detail)

L=100µH (0.82V)

=350mA @ V

I

OUT

LED

=3.4V

250 kHz

Driving 1 LED

tPD Internal comparator propagation delay 50 ns

Notes: 1. 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.

2. 100% brightness corresponds to V
proportionally.

ADJ

= V

ADJ(nom)

= V

. Driving the ADJ pin above V

REF

will increase the V

REF

threshold and output current

SENSE

ZXLD1352

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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 block diagram and Figure 1 - Operating waveforms)

Operation can be best understood by assuming that the ADJ pin of the device is unconnected and the voltage on this pin (V
appears directly at the (+) input of the comparator.

ADJ

)

When input voltage V

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

IN

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
and L1 to produce a voltage ramp (V

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

IN

) across RS. The supply referred voltage V

SENSE

is forced across internal resistor R1

SENSE

by the current sense circuit and produces a proportional c urrent in inter nal resist ors R2 and R3. T his produces a gro und referred
rising voltage at the (-) input of the comparator. When this reaches the threshold voltag e (V

), the comparator output switches

ADJ

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

.

ADJ

. The current decays at a rate determined

IN

by the LED and diode forward voltages to produc e a falling voltage at the input of the comparator. When th is voltage returns to
V

, the comparator output switches high again. This cycle of events repeats, with the comparator input ramping b etween limits

ADJ

of V

± 15%.

ADJ

Switching thresholds

With V
pin with respect to V

I

OUTnom

Nominal ripple current is ±15mV/R

=V

ADJ

REF

=100mV/R

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

). The average output current I

IN

S

S

is then defined by this voltage and Rs according to:

OUTnom

switching threshold of 100mV (measured on the I

SENSE

SENSE

Adjusting output current

The device contains a low pass filter for noise suppression bet ween the ADJ pin and the threshold comparator and an internal
current limiting resistor (50k nom) between ADJ and the internal reference voltage. This allo ws the ADJ pin to be overdriven with
either DC or PWM signals to adjust the output current. The filter is first order, comprising one s ection with a cut-off frequency of
nominally 600kHz.

Details of the different modes of adjusting output current are given in the applications section.

Output shutdown

The ADJ pin drives the shutdown circuit. When the input voltage to this c ircuit 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 1mA.

ZXLD1352

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Device Description

ZXLD1352

Document number: DS33469 Rev. 3 - 2

LX voltage

SENSE voltage

Coil current

Comparator
input voltage

Comparator
output

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ZXLD1352

V

IN

0V

V

IN

0V

0.15V

ADJ

V

ADJ

5V

0V

Figure 2. Operating Waveforms

Toff Ton

85mV

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100mV115m V

V

SENSE-

V

SENSE+

0.15V

I
I
I

ADJ

+15%

OUTnom
OUTnom

-15%

OUTnom

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ZXLD1352

Typical Operating Waveforms [V

Normal Operation. Output Current (Ch3) and LX Voltage (Ch1)

ZXLD1352

Document number: DS33469 Rev. 3 - 2

2

3

Ch3 100mA
Ch 2 20.0V

Start-up Waveforms. Output Current (Ch3), LX Voltage (Ch2)

= 12V, R

IN

= 0.3Ω, L = 100µH]

S

M 400μs5.0S/s

\ 12.0 V

ACh2

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200 ns/pt

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