ZXLD1350_07 ZETEX [Zetex Semiconductors], ZXLD1350_07 Datasheet

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ZXLD1350_07

Manufacturer Part Number
ZXLD1350_07
Description
350mA LED driver with internal switch
Manufacturer
ZETEX [Zetex Semiconductors]
Datasheet
ZXLD1350
350mA LED driver with internal switch
Description
The
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 supply between 7V and 30V and
provides an externally adjustable output
current of up to 350mA. Depending upon
supply voltage and external components, this
can provide up to 8 watts of output power.
The ZXLD1350 includes the output switch and
a high-side output current sensing circuit,
which uses an external resistor to set the
nominal average output current.
Output current can be adjusted above, or
below the set value, by applying an external
control signal to the 'ADJ' pin.
Features
(*) Using standard external components as specified under electrical characteristics. Efficiency is dependent upon the
Pin connections
Issue 6 - April 2007
© Zetex Semiconductors plc 2007
GND
ADJ
number of LEDs driven and on external component types and values.
LX
Simple low parts count
Internal 30V NDMOS switch
350mA output current
Single pin on/off and brightness control
using DC voltage or PWM
Internal PWM filter
Soft-start
High efficiency (up to 95%
Wide input voltage range: 7V to 30V
40V transient capability
Output shutdown
Up to 1MHz switching frequency
Inherent open-circuit LED protection
Typical 4% output current accuracy
ZXLD1350
1
2
3
TSOT23-5
Top view
is
5
4
V
I
a
SENSE
IN
continuous
(*)
)
mode
1
The ADJ pin will accept either a DC voltage or a
PWM waveform. Depending upon the control
frequency, this will provide either a continuous
or a gated output current. The PWM filter
components are contained within the chip.
The PWM filter provides a soft-start feature by
controlling the rise of input/output current. The
soft-start time can be increased 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.
The device is assembled in a TSOT23-5 pin
package.
Applications
Typical application circuit
V
IN
(12V - 30V)
Low voltage halogen replacement LEDs
Automotive lighting
Low voltage industrial lighting
LED back-up lighting
Illuminated signs
GND
C1
1 F
N/C
ADJ
V
IN
ZLLS1000
0.33
D1
Rs
ZXLD1350
I
SENSE
GND
L1
www.zetex.com
LX
47 H

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ZXLD1350_07 Summary of contents

Page 1

ZXLD1350 350mA LED driver with internal switch Description The ZXLD1350 is a continuous 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 ...

Page 2

Absolute maximum ratings (voltages to GND unless otherwise stated) Input voltage ( voltage (V ) SENSE SENSE LX output voltage ( Adjust pin input voltage (V ADJ Switch output current ( Power dissipation ...

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Electrical characteristics Symbol Parameter D Duty cycle range of PWM signal PWM(LF) applied to ADJ pin during low frequency PWM dimming mode Brightness control range D Duty cycle range of PWM signal PWM(HF) applied to ADJ pin during high frequency ...

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Block diagram V IN Voltage regulator C1 ADJ Vref GND Issue 6 - April 2007 © Zetex Semiconductors plc 2007 Shutdown circuit R2 4KHz 200k 1.25V R3 4 ZXLD1350 SENSE ...

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Device description The device, in conjunction with the coil (L1) and current sense resistor (R 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 ...

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voltage SENSE voltage Coil current 0V Comparator V input voltage ADJ 5V Comparator output 0V Issue 6 - April 2007 © Zetex Semiconductors plc 2007 Toff Ton 115mV 85mV 0.15V ADJ Figure 1 Operating ...

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Typical operating waveforms [V Normal operation. Output current (Ch3) and LX voltage (Ch1) Start-up waveforms. Output current (Ch3), LX voltage (Ch1) and VADJ (Ch2) Issue 6 - April 2007 © Zetex Semiconductors plc 2007 =12V, R =0.3 , L=100µH] IN ...

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Typical operating conditions For typical application circuit driving 1W Luxeon otherwise stated ...

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Typical operating conditions (continued ...

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Typical operating conditions (continued ...

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Typical operating conditions (continued ...

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Typical operating conditions (continued ...

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Application notes Setting nominal average output current with external resistor R The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (R ) connected between 0.1/R [for ...

Page 14

Output current adjustment by PWM control Directly driving ADJ input A Pulse Width Modulated (PWM) signal with duty cycle D shown below, to adjust the output current to a value above or below the nominal average value set by resistor ...

Page 15

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 will fall to a low standby level of 15µA nominal. Note that the ADJ pin is ...

Page 16

Inductor selection Recommended inductor values for the ZXLD1350 are in the range 220 H. Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays, which result in increased ...

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Example: For V =12V, L=47 H, rL=0. (47e-6 x 0.105)/(12 - 3.4 - 0.672) = 0.622 (47e-6 x 0.105)/(3.4 + 0.36 + 0.322)= 1.21 s OFF This gives an operating frequency ...

Page 18

Reducing output ripple Peak to peak ripple current in the LED can be reduced, if required, by shunting a capacitor C across the LED(s) as shown below LED SENSE ZXLD1350 A value ...

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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 ...

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Evaluation PCB The picture below shows the top copper layout of the 3 LED ZXLD1350EV2 evaluation board. This board and other evaluation boards for the ZXLD1350 are available upon request. ZXLD1350EV2 k EVALUATION BOARD D1 a JP1 JP2 +VIN SD1 ...

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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 V and a low level of zero, the output of the internal ...

Page 22

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 ...

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Package outline - TSOT23-5 DIM Min 0.01 A2 0.84 b 0. 0.30 L2 a° 4° Note: Controlling dimensions are in millimeters. Approximate dimensions are provided in inches Issue 6 - ...

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Definitions Product change Zetex Semiconductors reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. Customers are solely responsible for obtaining the latest relevant information before placing orders. Applications disclaimer The ...

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