Diodes ZXLD381 User Manual

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ZXLD381

SINGLE OR MULTI CELL LED DRIVER SOLUTION

Summary

The ZXLD381 is a single cell LED driver designed for a pplications where step-up voltage conversion from a very low input voltage is required. These applications mainly operate from 1.5V or 1.2V c ells. The IC generates constant current pulses that are ideal for driving single or multiple LEDs over a wide range of operating voltages.

The ZXLD381 uses a PFM control technique to drive an internal switching transistor which a low saturation resistance. This ensures high efficiency, even for input voltages as low as 1V.

The IC can start up under full load and operates down to an input voltage of only 0.9V. The ZXLD381 is offered in the space saving SOT23 packag e or in die form, offering an excellent cost vs performance s olution

for single cell LED driving applications.

Features

• 85% Efficiency

• User adjustable output current

• Single cell operation (0.9V minimum)

• Low saturation voltage switching transistor

• SOT23-3 package

• Available also in Die form

• Simple Application circuit

Application

Pin Assignments

SOT23-3

(Top View)

• LED flashlights and torches

• LED backlights

• White LED driver

Typical Application Circuit

OUT

GND

ZXLD381

Document number: DS32188 Rev. 3 - 2

LED

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Block Diagram

1.5V

VCC

ZXLD381

Pulse Control

Cof fCon

Rsense

GND

Fig 1. ZXLD381 Block Diagram

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ZXLD381

VOUT

LED

Pin Description

Pin No. Name Description

1 GND Ground 2

OUT

ZXLD381

Document number: DS32188 Rev. 3 - 2

Switch output external inductor/LED Supply voltage, generally Alkaline, NiMH or NiCd single cell

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Absolute Maximum Ratings

Parameter Rating Unit

Supply Voltage (VCC) Output Voltage (V

Supply Current 20 mA Output Switch Current 800 mA Power Dissipation SOT23-3 450 mW Power Dissipation Die 1 W Operating Temperature Range 0 to 85 °C Storage Temperature Range -55 to 150 °C

OUT

)

-0.6 to 10 V

-0.6 to 20 V

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ZXLD381

Electrical Characteristics Measured at T

Parameter Conditions

Supply Voltage Operating Range L = 10μH 0.9 2.2 V Minimum Supply Start-up Voltage L = 10μH 0.8 0.9 V Switch Current At turn-off 250 320 400 mA

Switch Saturation Voltage Switch Leakage Current Mean LED Current Efficiency

Operating Frequency Discharge Pulse Width 0.7 1.5 2.5 µs

OUT

V V V

OUT LED LED

LED

= 200mA

= 25°C, L = 4.7µH and VCC = 1.5V unless otherwise specified.

AMB

Min Typ. Max

100 300 mV

= 20V = 3.5V = 3.5V

= 3.5V

40 70 120 µA 40 55 70 mA

85 %

350 kHz

Limits

Units

ZXLD381

Document number: DS32188 Rev. 3 - 2

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ZXLD381

Device Description

The ZXLD381 is a simple PFM, DC-DC controller com bined with a high performance internal switching transistor, enabling the production of a high efficiency boost converter for use in single cell applications. A block diagr am is sho wn for the ZXLD381 in Fig 1.

When power is applied, an oscillator within the pulse control block forces the internal switching transistor to s witch on to start an energy charge cycle. The low saturation voltag e switch pulls the V

across the external inductor L1. This causes a current to build up, storing energ y in the inductor. During this phase, switch current and supply voltage are monitored and use d by the pulse control circuit to determ ine the optimum drive cond itions and on-time. At the end of the energy charge cycle, the internal switch is turne d off rapidly, in terrupting the current fl ow through L1

which causes the voltage on V voltage, the inductor current is transferred from the internal switch to the LED, starting the energ y discharge cycle. With the voltage across the inductor reversed, the current flowing through it (and the LED) no w falls. When the inductor current reach e s

zero, the voltage on the V next energy charge cycle. Except for low level losses, all the energy stored in the inductor during a charge cycle will be channeled to the load LED during the following discharge cycle.

The current fed into the load LED has a sawtooth waveform, the average (DC) value of which is kept constant by the pulse control circuit for varying supply voltage and temperature. It is possible to change the output current given by the ZXLD38 1 by changing the value of inductor L1. The larger the inductance of L1, the lower the output current. A table/graph showing the relationship between inductance and output current is given later in this datasheet. Since the output current of the ZXLD3 81 is a sawtooth waveform, its peak value is substantially larger than the DC/average value. The table also provid es this data.

The internal switching transistor has a minimum collector-emitter breakd own voltage of 20V and this sets the maximum load voltage allowable. The minimum value is set by a f eature of the pulse control circuit that requires the load voltage to be at least

0.8V greater than V impaired.) Higher than nominal load voltages will lower the average (DC) output current generated for a given inductor value.

OUT

. (The device will function with load voltages smaller than this but output current regulation will be

to rise dramatically. When the voltage on V

OUT

pin falls back towards VCC. This action is sensed by the pulse control circuit, which initiates the

pin close to ground which forces the supply voltage

OUT

reaches the load LED's forward (on)

OUT

ZXLD381

Document number: DS32188 Rev. 3 - 2

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Typical Characteristics

100

90 80 70

2.2µH

3.3µH

100

90 80

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22µH

47µH

15µH

10µH

ZXLD381

OUT

I (mA)

350

300

250

200

I (mA)

150

60 50

30 20 10

0.8

11.2

I vs. V for L = 2.2µH to 47µH

OUT(AVERA GE) CC

2.2µH

3.3µH

6.8µH

4.7µH

1.4 1.6

V (V)

4.7µH

10µH

47µH

1.8

6.8µH

15µH

22µH

60 50

6.8µH

Efficiency (%)

4.7µH

30 20

3.3µH

2.2µH

0.8 1 1.2 1.4 1.6 1.8 2

V (V)

Efficiency vs. V for L = 2.2µH to 47µH

10µH

100

15µH

22µH

47µH

0.8 1 1.2 1.4 1.6 1.8 2

I vs. V for L = 2.2µH to 47µH

IN CC

V (V)

Channel-1 (Upper): I @ 100mA/cm

Channel-2 (Low er): V @ 1V/cm

LED

OUT

Timebase: 500ns/cm

Operating Waveforms for L = 4.7µH, V = 1.5V

Notes: V

= 3.5V for all graphs

LED

ZXLD381

Document number: DS32188 Rev. 3 - 2

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Typical Characteristics (Cont.)



450 400 350

300

250

200

OSC

f (kHz)

150

100

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ZXLD381

0.8 1 1.2 1.4 1.6 1.8 2

f vs. V for L = 47µH

OSC CC

V (V)

Notes: V

= 3.5V for all graphs

LED

ZXLD381

Document number: DS32188 Rev. 3 - 2

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Application Examples

Standard Operating Mode

Notes: V

Low Ripple LED Current Mode

Notes: V

= 3.5V

LED

= 3.5V, D1 = ZHCS1000, C1 = 1F (low ESR)

LED

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ZXLD381

Document number: DS32188 Rev. 3 - 2

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ZXLD381

Ordering Information

Part Number Package Part Mark

ZXLD381FHTA SOT23 381 8 3000

Tape Width

(mm)

Quantity

(per reel)

Package Outline Dimensions

b 3leads

Dim.

A - 1.12 - 0.044 e1 1.90 NOM 0.075 NOM

A1 0.01 0.10 0.0004 0.004 E 2.10 2.64 0.083 0.104

b 0.30 0.50 0.012 0.020 E1 1.20 1.40 0.047 0.055 c 0.085 0.20 0.003 0.008 L 0.25 0.60 0.0098 0.0236 D 2.80 3.04 0.110 0.120 L1 0.45 0.62 0.018 0.024 e 0.95 NOM 0.037 NOM - - - - -

ZXLD381

Document number: DS32188 Rev. 3 - 2

Millimeters Inches

Min. Max. Min. Max. Min. Max. Min. Max.

Millimeters Inches

Dim.

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ZXLD381

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).

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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 products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems.

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IMPORTANT NOTICE

LIFE SUPPORT

ZXLD381

Document number: DS32188 Rev. 3 - 2

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