zxld1352 Zetex Semiconductors plc., zxld1352 Datasheet

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zxld1352

Manufacturer Part Number
zxld1352
Description
350ma Led Driver With Internal Switch And Enhanced Pwm Dimming Range
Manufacturer
Zetex Semiconductors plc.
Datasheet

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ZXLD1352
350mA LED driver with internal switch and enhanced PWM dimming
range
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 ZXLD1352 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 1 - August 2008
© Diodes Incorporated 2008
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
1000:1 PWM dimming range
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
ZXLD1352
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. DC voltages between 0.3V and
2.5V allow adjustment of output current from
25% to 200% of nominal. 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.
The device is assembled in a TSOT23-5 pin
package.
Applications
Typical application circuit
Low voltage halogen replacement LEDs
Automotive lighting
Low voltage industrial lighting
LED back-up lighting
Illuminated signs
V
(12V - 30V)
IN
Diodes Incorporated
GND
C1
A Product Line of
1 F
PWM
ADJ
V
IN
0.33
Rs
ZLLS1000
ZXLD1352
D1
I
SENSE
GND
L1
www.diodes.com
LX
47 H
www.zetex.com

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zxld1352 Summary of contents

Page 1

... Depending upon supply voltage and external components, this can provide watts of output power. The ZXLD1352 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. ...

Page 2

... ADJ pin grounded ADJ pin floating f=250kHz Measured on I SENSE respect =1.25V ADJ V =V -0.1 SENSE IN Measured on ADJ pin with pin floating REF (†) V falling ADJ V rising ADJ 2 ZXLD1352 Min. Typ. Max 4 250 500 95 100 105 pin with ±15 1.25 10 1.21 1.25 1.29 50 0.3 2.5 0.15 0.2 ...

Page 3

... S <2.5V) to adjust output current from 25% to 200% ADJ for 100Hz < f < 1KHZ OUTnom from this pin define nominal average output current with ADJ pin open-circuit) Reel width (mm ZXLD1352 Min. Typ. Max. 0.01 1 1000:1 =3.4V 250 200 200 1 0.3 0.7 50 will increase the V REF =1 ...

Page 4

... Block diagram V IN Voltage regulator C1 ADJ Vref GND Issue 1 - August 2008 © Diodes Incorporated 2008 Current sense circuit 5V Shutdown circuit R2 600KHz 50k 1.25V R3 4 ZXLD1352 SENSE - + Comparator - + www.zetex.com www.diodes.com MN ...

Page 5

... L1 and the LED(s). The current rises at a rate determined across R . The supply referred voltage V SENSE S pin with respect The average output current ZXLD1352 ), forms a self-oscillating S is zero and there the comparator output switches ADJ . The current IN , the comparator output switches ADJ ...

Page 6

... LX voltage SENSE voltage Coil current 0V Comparator V input voltage ADJ 5V Comparator output 0V Issue 1 - August 2008 © Diodes Incorporated 2008 Toff Ton 115mV 85mV 0.15V ADJ Figure 1 Operating waveforms 6 ZXLD1352 100mV V SENSE- V SENSE+ I +15% OUTnom I OUTnom I -15% OUTnom 0.15V ADJ www.zetex.com www.diodes.com ...

Page 7

... Typical operating waveforms [V Normal operation. Output current (Ch3) and LX voltage (Ch1 Ch3 100mA Ch 2 20.0V Start-up waveforms. Output current (Ch3), LX voltage (Ch2) Issue 1 - August 2008 © Diodes Incorporated 2008 =12V, R =0.3 , L=100µ 400μs 5.0 S/s 200 ns/pt A Ch2 \ 12 ZXLD1352 www.zetex.com www.diodes.com ...

Page 8

... ZXLD1352 =12V and T =25°C unless IN amb ...

Page 9

... ZXLD1352 ...

Page 10

... ZXLD1352 ...

Page 11

... ZXLD1352 Vref vs Vin at low supply voltage Vin ( ...

Page 12

... ZXLD1352 ...

Page 13

... Diodes Incorporated 2008 and I IN SENSE if the ADJ pin is driven from an external voltage. (See shown, to adjust the output current ADJ <2.5V] ADJ = V ADJ REF exceeding 370mA maximum. OUTdc ±25%. 13 ZXLD1352 S and is given by: (=1.25V). REF . S . When driving the ADJ pin above www.zetex.com www.diodes.com ...

Page 14

... ADJ If the NMOS transistor within the microcontroller has high Gate / Drain capacitance, this arrangement can inject a negative spike into ADJ input of the ZXLD1352 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 ...

Page 15

... NOT be used. A table of recommended manufacturers is provided below: Manufacturer Website Murata www.murata.com Taiyo Yuden www.t-yuden.com Kemet www.kemet.com AVX www.avxcorp.com Issue 1 - August 2008 © Diodes Incorporated 2008 ZXLD1352 will increase REF www.zetex.com www.diodes.com ...

Page 16

... Inductor selection Recommended inductor values for the ZXLD1352 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 ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range ...

Page 17

... This gives an operating frequency of 546kHz and a duty cycle of 0.34. These and other equations are available as a spreadsheet calculator from the Zetex website www.zetex.com/ZXLD1352 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 ...

Page 18

... Issue 1 - August 2008 © Diodes Incorporated 2008 Cled ZXLD1352 led 2 PCB www.zetex.com www.diodes.com ...

Page 19

... The LEDs are usually mounted remotely from the device, so for this reason, the temperature coefficients of the internal circuits for the ZXLD1352 have been optimized to minimize the change in output current when no compensation is employed. If output current compensation is required 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) ...

Page 20

... PWM dimming is preferable to DC dimming if optimum LED 'whiteness' is required. It will also provide the widest possible dimming range (approx. 1000:1) and higher efficiency at the expense of greater output ripple. Issue 1 - August 2008 © Diodes Incorporated 2008 proportional to the PWM duty cycle. (See Figure 2 OUTavg Ton Toff >0 01] PWM 20 ZXLD1352 0.1/Rs IOUTavg www.zetex.com www.diodes.com ...

Page 21

... Note: Controlling dimensions are in millimeters. Approximate dimensions are provided in inches Issue 1 - August 2008 © Diodes Incorporated 2008 Millimeters Max. - 1.00 0.10 0.90 0.45 0.20 2.90 BSC 2.80 BSC 1.60 BSC 0.95 BSC 1.90 BSC 0.50 0.25 BSC 12° 21 ZXLD1352 Inches Min. Max. - 0.0393 0.0003 0.0039 0.0330 0.0354 0.0118 0.0177 0.0047 0.0078 0.114 BSC 0.110 BSC 0.062 BSC 0.0374 BSC 0.0748 BSC 0.0118 ...

Page 22

... Diodes Zetex (Asia) Ltd Diodes Incorporated 3701-04 Metroplaza Tower 1 15660 N. Dallas Parkway Hing Fong Road, Kwai Fong Suite 850, Dallas, Hong Kong X57248, USA Telephone: (852) 26100 611 Telephone (1) 972 385 2810 Fax: (852) 24250 494 asia.sales@zetex.com www.diodes.com 22 ZXLD1352 www.zetex.com www.diodes.com ...

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