driving power leds and standard leds with pfm ... power leds and standard leds with pfm controller...

ELMOS Semiconductor AG Application Note QM-No.: 03AN0201E.00

E910.26

1

Driving PowEr LEDS AnD STAnDArD LEDS wiTH PFM ConTroLLEr

general Description

Features

Applications

The PFM controller family 910.24/.25/.26 are flexible, easy to use switched mode power supplies. Low standby current, very wide input voltage range make them suitable for applications in automotive and industrial environment.

An advanced PFM control scheme gives these devices the benefits of PWM converters with high efficien-cy for heavy loads, while using very low operating current for light loads to maintain excellent behaviour with output load variation.

ÿ Supply voltage range VS 3.0V to 60Vÿ Up to 90% efficiencyÿ 40µA standby currentÿ 180µA circuit operating currentÿ Adjustable output voltage ≥ 1,22Vÿ Up to 300kHz switching frequencyÿ Improved current-limited PFM control schemeÿ High current driver for external MOSFETÿ Under-voltage lockout and thermal shutdownÿ -40°C to +125°C operating temperatureÿ SO8 package

ÿ LED driving applicationsÿ 14V, 28V or 42V automotive systemsÿ Minimum component DC-DC converters

Scope

This application note provides information, hints and complete schematics for driving low and high power LED Applications with 910.24/.26 SMPS familiy.

VINP = 4V ... 60V

E910.26

MDRV

ISEN

VSM

VFB

ON

VIN

AGND

PGND

R1

R4 C2M1

C5

R2

C3 C4

D1

L1

L2

LED Cluster

C1

R3

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1234

8765

PGNDAGNDISENVFB

MDRVVSMVSON

Package Pin out

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Pin Description

Pin-No. Name Typ 1) Description

1 PGND S Driver power ground pin. Connect pin to the current sense resistor, the (-) terminal of the input capacitor and the (-) terminal of the out-put capacitor. Due to high currents, and high frequency operation of the IC, a low impedance circuit ground plane is highly recommended

2 AGND S Analog ground pin. This pin provides a clean ground for the control-ler circuitry: The output voltage sensing resistors should be con-nected to this ground pin. This pin is connected to the IC substrate. Connect to the (-) terminal of the output capacitor

3 ISEN AI Current sense input pin. Voltage generated across an external sense resistor is fed into this pin. Filters extensive high-frequency noise

4 VFB AI Positive feedback pin. Connect to SMPS output via external resistor divider to set output voltage and is referenced to 1.22V. For best sta-bility, keep VFB lead as short as possible and VFB stray capacitance as small as possible

5 ON DI Switch ON input. Tie this pin to ground to force the IC into idle mode. A voltage of VSM or higher switches the controller in operat-ing mode

6 VS S Main supply input. Filters out high-frequency noise with a 100nF ce-ramic capacitor placed close to the pin to PGND

7 VSM A Internal 5V regulator output. The driver and all control circuits are powered from this voltage. Decouple this pin to PGND with a mini-mum of 4.7µF tantalum and 100nF ceramic capacitors

8 MDRV AO Drive output. Drives the gate of the external MOSFET between PGND and VSM. Connect the external MOSFET via a damping resis-tor to this pin

1) D = digital, A = Analog, S = Supply, I = Input, O = Output, HV = High Voltage (max. 40V)

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In this application note three schematics will be described driving Power LED‘s and furthermore one schematic for driving standard LED‘s.

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overview of discussed schematics

Circuit 1: ÿ 5 white power LED with IF = 350mA ÿ 9V to 20V input voltage range ÿ SEPIC transformer ÿ -40°C to +85°C

Circuit 2: ÿ 5 white power LED with IF = 350mA ÿ 6V to 20V input voltage range ÿ separate SEPIC chokes ÿ -40°C to +85°C

Circuit 3: ÿ 4 white power LED with IF = 700mA ÿ 6V to 20V input voltage range ÿ separate SEPIC chokes ÿ -40°C to +85°C

Circuit 3b: ÿ 4 white power LED with IF = 700mA ÿ as above ÿ dimming capability 10% to 100%

Circuit 4: ÿ 24 coloured standard LED with IF = 60mA ÿ 9V to 36V input voltage range ÿ Step Up topology ÿ -40°C to +85°C

Disclaimer

The components used in our simulations are especially designed to deliver meaningful results during develop-ment of switched mode power supplies. They are the basis for fast calculation of the circuits behaviour and give a good view to functionality and dependencies of component changes - in values or quality. Nevertheless the model based simulation does not show exactly the natural behaviour of a circuit board.Therefore the user of all ELMOS products is in charge for a save module and product development including among other things prototyping, measurements and qualification procedures. Additionally the customer is in charge for observing all security and protection standards and laws.

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Circuit 1

VBAT9V to 20V

D_reserve

ES2D

E910.26

MDRV

ISENVSM

VFBONVIN

AGND

PGND

R_snubber270 *

R_sense0.047

R_damping

4.7

C_snubber820p *

C_out_1220μF

ZL, 35V

C_out_2150μF

ZL, 35V

M_powerSUD40N06-25L

C_filter_1100n

C_filter_2100n

C_filter_4220n

C_filter_310n

C_input470μF

ZL, 25V

C_bat470µFZL, 25V

L0=47μHRDC=0.10L_EMC_1

R_LED_Current3.6

5x18R (parallel)

Operating Frequencyapprox. 120kHz

Fault

R_pullup10k

4µ7 100n

BC547B

Q_Fault

FB1D_rec

ES1D

22µH *L1

L222µH *

SMFBEMCSimple Bead

P1N970AD_safety

24V, 50mW

R_safety

1k

D1

D2

D3

D4

D5

LED Cluster

C_sepic330µFZL, 25V

1k

VOUT

100n

350mA

Both SEPIC chokes are build on one ferrite core, EF12.6, as described below. Therewith a compact, electrical ad-vantageous and cheap solution can be realised.

In the working range of 9V to 20V the output current through the LED string is controlled and regulated to 350mA. With a battery voltage below about 8V the LED current starts decreasing as shown in figure 1.1. The working frequency of the PFM converter will be about 120kHz at an input voltage of 12V. In case of a broken LED string, the zener diode will clamp the output voltage to an unperilous level. The fault signal is true (high) when the feedback voltage is too low.

The converter shown in figure one supplies the power for five white power LED‘s in series connection driven with a constant current of 350mA.

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Inductivity Technical specifications Name ProducerL_EMC_1 47µH Ms85 Neosid

FB1 742 792 411 WürthU_choke_1 2x22µH EF12.6

L1 L2

N11

N12

N21

N22

SEPiC - Choke

L1 = L2 = 22µH +/- 15%Core: EE13/7/4 (EF12.6)Material: N27 or N87 (EPCOS)Central Air Gap: 0.30mmCoil Former with 8 PinsN11=N12=N21=N22= 19 TurnsWire: 0.35mm Cul

Description

The SEPIC choke consists of four windings on the same standard core of ferrite material. Below you find the spec-ification suitable for building such a choke. Of course choke suppliers can build the transformer based on this specification.

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The converter uses a SEPIC topology. The current loaded into the choke is determined by the resistor R_sense. The snubber network is used to remove HF noise generated during switching the FET. Two safety parts, D_safety and R_safety are needed to protect the system against open load faults. Because the feedback path VFB controls the output current which in case of a broken wire is zero, the converter will try to increase Vout to infinity what will cause overvoltage at the C_out capacitors.The fault detection uses Q_fault as a simple voltage comparator. In case VFB is higher than Vth of Q_fault its output is low signalling „pass“. With an open load the current through R_LED_current will be zero and Q_fault will close, signalling high which is fault at the diagnostic line.

Components

All electrolytic capacitors used in the schematic are of the ZL-series of Rubicon. For inductances see table below.The snubber network strongly depends on components and layout. The given values are suitable for an example application and must be adapted to the final module. Also the R_damping depends on the used FET type and the layout. It might be necessary to modify or remove it.

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Simulation results

figure 1.1

Figure 1.1 shows the system behaviour in the moment of first battery contact and the following startup behav-iour. The LED voltage and the the fault signal indicating the current being roughly in specification is shown.

In figure 1.2 the LED current is plotted and within about 15ms it reaches the target level.

figure 1.2

figure 1.3

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Figure 1.3 shows the current through the chokes. In the first few ms the current reaches nearly 12A which may not cause the core to go into saturation.

After the startup is finished the following curves can be found:

figure 1.4

Here you see the LED current which has a small ripple and some noise resulting from parasitic components in the chokes, caps, and the FET. They can be eliminated by using appropriate filter elements at input and output side such as mentioned in the schematic.

figure 1.5

This figure shows the current through the SEPIC chokes. Continuous current mode is used leading to lower EMI and better efficiency of the system. The battery current is about 650mA DC at 12V into the filter elements.

The following figures will give important information about the power dissipation in the FET, the output diode and the reverse polarity diode, followed by graphs about the RMS current stress in the FET, the chokes and the capacitors.

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figure 1.6

figure 1.7

figure 1.8

There is a safe failure behaviour which can be adapted to the users needs by changing just one component: the value of the zener diode. This is a very easy way to detect a fault and protect the system against damage in case of an open load condition. The other fault mechanism, a shorted LED, cannot be detected so easy. It would be necessary to measure the output voltage in a kind of learning phase where the Vout vs. temperature as well as versus LED device variations if Vf must be taken into account and must be separated from an error condition. Tolerances in the sum of all LEDs Vf over temperature are very big compared to the voltage change caused by one failing LED. For that reason there is currently no planning for a detection system for that failure.

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The next graphs are to explain the system behaviour in case of an open load failure.

figure 1.9 The error occurs

figure 1.10 The fault signal is activated

figure 1.11 The output voltage increases up to zener voltage of D_safety

figure 1.13 The FET stopps switching

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figure 1.14

As mentioned above the LED current starts decreasing with an input voltage below about 9V which can be seen in the following plot. But current only decreases by about 10% which in many cases is not very critical due to the logarithmic light sensitivity of human eyes.

figure 1.15

An important fact is that current through the chokes and Csepic as well as from the battery increases signifi-cantly with decreasing input voltage. That is of course due to the converters natural behaviour as being a power converter delivering constant output-power and showing a negative input impedance to the supply system.

figure 1.16

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To give an impression of what happens during ignition phase of the vehicles engine as well as a principle view to the behaviour in the input voltage range, the next graphs will illustrate this scenario. The battery voltage, plotted green in figure 1.14 drops down to 6V. The converters input voltage follows with a delay due to the input caps.

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figure 1.17

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Finally an impression of the noise spectrum to be expected is given. The conducted disturbances fulfill the CIS-PR25 requirements. These are simulation results and therefore may vary from the final results which are depend-ing on the quality of all the components on the pcb as well as on the layout.

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Circuit 2

VBAT6V to 20V

D_reserve

ES2D

E910.26

MDRV

ISENVSM

VFBON

VIN

AGND

PGND

R_snubber270 *

R_sense0.039

R_damping

4.7

C_snubber820p *

C_out_1220μF

ZL, 35V

C_out_2150μF

ZL, 35V

M_powerSUD40N06-25L

C_filter_1100n

C_filter_2100n

C_filter_4220n

C_filter_310n

C_input470μF

ZL, 25V

C_bat470µFZL, 25V


R_LED_Current3.6

5x18R (parallel)

Operating Frequencyapprox. 120kHz

Fault

R_pullup10k

4µ7 100n

BC547B

Q_Fault

FB1D_rec

ES1D

47µHRDC=0.12

47µHRDC=0.12

L1

L2

SMFBEMCSimple Bead

P1N970AD_safety

24V, 50mW

R_safety

1k

D1

D2

D3

D4

D5

LED Cluster

C_sepic330µFZL, 25V

1k

VOUT

100n

350mA

The SEPIC chokes are realised as two standard parts for easy purchase and developing purpose.

In the working range of 6V to 20V the output current through the LED string is controlled and regulated to 350mA. With a battery voltage below about 6V the LED current starts decreasing as shown in figure 2.1. The working frequency of the PFM converter will be about 80kHz at an input voltage of 12V.

Description

The converter is similar to the one used in circuit 1. The component values have changed to match the require-ments of lower input voltage.

This converter shown in figure two also supplies the power for five white power LED‘s in series connection driven with a constant current of 350mA but in contrast to the first one it is designed to work with lower input voltage: 6V to 20V.

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E910.26



L1 47µH Ms95a NeosidL2 47µH Ms95a NeosidFB1 742 792 411 Würth

In the following figures will illustrate the output current and choke currents during ignition phase.

figure 2.1

As mentioned above the LED current starts decreasing with an input voltage below about6V which can be seen in the following plot. But current only decreases a few percent which in many cases may not be very critical.

figure 2.2

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Components

All electrolytic capacitors used in the schematic are of the ZL-series of Rubicon. For inductances see table below.

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14


figure 2.3

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15

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figure 2.4


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16



L1 22µH Ms95a Neosid

L2 22µH Ms95a NeosidL_EMC_2 10µH Ms85 Neosid

Description

The SEPIC chokes are realised as two standard parts for easy purchase and developing purpose.

In the working range of 6V to 20V the output current through the LED string is controlled and regulated to 350mA. With a battery voltage below about 6V the LED current starts decreasing as shown in figure 2.1. The working frequency of the PFM converter will be about 110kHz at an input voltage of 12V.

Circuit 3

VBAT6V to 20V

D_reserve

ES3D

E910.26

MDRV

ISENVSM

VFBONVIN

AGND

PGND

R_snubber270 *

R_sense0.022

R_damping

4.7

C_snubber820p *

C_out_1470μF

ZL, 25V

C_out_2220μF

ZL, 25V

M_powerSUD40N06-25L

C_filter_1100n

C_filter_2100n

C_filter_4220n

C_filter_310n

C_input470μF

ZL, 25V

C_bat470µFZL, 25V


R_LED_Current1.743

(10x18R+1x56R)

Fault

R_pullup10k

4µ7 100n

BC547B

Q_Fault

L_EMC_2D_rec

ES2D

L0=22µHRDC=0.10

L0=22µHRDC=0.12

L1

L2

L0=10µHRDC=0.15

P1N968AD_safety

20V, 50mW

R_safety

1k

D1

D2

D3

D4

LED ClusterC_sepic470µFZL, 25V

1k

VOUT

100n

700mA

R_spike_filter*

C_spike_filter*

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This converter shown in figure three supplies the power for four white power LED‘s in series connection driven with a constant current of 700mA. Also this one is designed to work with lower input voltage: 6V to 20V.

The converter is similar to the one used in circuit 1. The component values have changed to match the require-ments of lower input voltage.

Components


17

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The following graphs will illustrate the component requirements regarding current stress during ignition phase.

The RMS currents will be L1= 1.6A, L2= 1.1A, Cinput= 800mA, Csepic= 1.3A, Coutput= 1.4A

figure 3.2

figure 3.3

As mentioned above the LED current starts decreasing with an input voltage below about 6V which can be seen in the following plot. But current only decreases a few percent which in many cases may not be very critical.


figure 3.4

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figure 3.5

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Circuit 3b

R139k

R_spike_filter

C_spike_filter

*

*

D31N4148

+-

57

6

IC2b

+-

48

21

3

IC2a

VSM

GND

C11µ

C21µ

C31µ

GND GND

PWM Input100k

R5

100k

R2

D2

R3 10k

10k

R4 10k

R6 39k

1N41

48

D1

1N4148

VBAT D_reserve

ES3D

E910.26

MDRV

ISENVSM

VFBON

VIN

AGND

PGND

R_snubber270 *

R_sense0.022

R_damping

4.7

C_snubber820p *

C_out_1470μF

ZL, 25V

C_out_2220μF

ZL, 25V

M_powerSUD40N06-25L

C_filter_1100n

C_filter_2100n

C_filter_4220n

C_filter_310n

C_input470μF

ZL, 25V

C_bat470µFZL, 25V

10μHRDC=0.10L_EMC_1

4µ7 100n

L_EMC_2D_rec

ES2D

22µHRDC=0.10

22µHRDC=0.10

L1

L2

L0=10µHRDC=0.15

P1N968AD_safety

20V, 50mW

R_safety

1k

D1

D2

D3

D4

LED ClusterC_sepic470µFZL, 25V

VOUT

100n

700mA

R_LED_Current1.743

(10x18R+1x56R)

The PWM signal is used in two ways. First it is used as the ON signal to start the converter. In the main path the signal is converted into an analog voltage which is added to the current signal of the shunt resistor. The cir-cuit can be used for dimming in the range of about 10% to 100%. Below 10% the converter starts discontinuous mode which can be seen as blinking of the LEDs.With the same principle a temperature control unit can be build up using an NTC.

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This converter is exactly the same as circuit 3 with a dimming capability is beeing added.

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20


Circuit 4

The Step Up converter serves up to about 59V at the cluster output. It uses a standard choke many suppliers offer.

In the working range of 9V to 36V the output current through the LED string is controlled and regulated to 60mA. With a battery voltage below about 9V the LED current starts decreasing as shown in figure 2.1. The working frequency of the PFM converter will be about 29kHz at an input voltage of 9V and 60kHz at 27V. To make use of smaller chokes the 910.24 is used which offers an extended maximum ON time for the gate driver. That ensures that with lower battery voltage the choke can be loaded with the required amount of energy.

VBAT9V to 36V

D_reserve

ES1D

E910.24

MDRV

ISENON

VFBVSM

VIN

AGND

PGND

R_snubber330 *

R_sense150m

R_damping

4.7

C_snubber1n *

C_out_182μF

ZL, 63V

C_out_282μF

ZL, 63V

M_powerBUK9875-100A

C_filter_1100n

C_filter_2100n

C_filter_4220n

50mW68V

C_filter_310n

C_input100μF

ZL, 50V

C_bat100µFZL, 50V

4.7µF 100n

WE-PD4SL0=10μH

RDC=0.20L_EMC_1

WE-PD4LL_StepUpL0=100μHRDC=0.33

LED1

LED2

LED3

LED4

LED5

LED6

LED7

LED8

LED17

LED18

LED19

LED20

LED21

LED22

LED23

LED24

LED9

LED10

LED11

LED12

LED13

LED14

LED15

LED16

R_LED_Current20.76

33E//56E

FB1

FerriteBead

D_rec

ES1D

VOUT (42V to 59V)

R_safety60mA

1k

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This converter shown in figure four supplies the power for 24 coloured standard LED‘s in series connection driven with a constant current of 60mA.

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E910.26


Name Technical specifications Comment Producer

C_filter_1 100nF, 50V, 10%, X7R 1206, SMD EpcosC_bat 100µF, 50V. 74mOhm, 0,72Arms ZL-Series, 105°C RubyconC_filter_2 100nF, 50V, 10%, X7R 1206, SMD Epcos

C_filter_3 10nF, 50V, 10%, X7R 1206, SMD Epcos

C_input 100µF, 50V, 74mOhm, 0,72Arms ZL-Series, 105°C Rubycon

C_snubber 1nF, 1000V, 10%, NP0 1206, SMD Kemet

C_VSM_2 4.7µF,25V (Low ESR) Tantal, SMD Epcos

C_VSM_1 100nF, 50V, 10%, X7R 1206, SMD Epcos

C_output_1 82µF, 63V, 150mOhm, 0.68Arms ZL-Series, 105°C Rubycon

C_output_2 82µF, 63V, 150mOhm, 0.68Arms ZL-Series, 105°C Rubycon

C_filter_4 220nF, 25V, 10%, X7R 1206, SMD Epcos

L_EMC_1 10µH, 35MHz, 1.2A, 160mOhm WE-PD4S Würth

L_EMC_2 100µH, 8MHz, 1.2A, 330mOhm WE-PD4L Würth

L_FB1 742792411 Würth

R_snubber 330Ohm

R_damping 4.7Ohm

R_LED_Current 33 Ohm // 56 Ohm

R_sense 150mOhm

R_safety 1k

D_reverse ES1D

D_rec_1 ES1D

M_power BUK9875-100A Logic Level Philips Semi

U_E91024 E91024A ELMOS

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Components


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22


figure 4.1 behariour at VBAT = 9V

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Simulation results

In the following figures the output current and some interesting values can be seen with respect to input volt-age variations.

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record of revisions

Chapter Rev. Change and Reason for Change Date Released1 Initial Revision 12.02.2007 TZIE/RL

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Contents

Scope ....................................................................................................................................................... . 1general Description ............................................................................................................................... . 1Features .................................................................................................................................................. . 1Applications ............................................................................................................................................ . 1Package Pin out ..................................................................................................................................... 2Pin Description ....................................................................................................................................... 2overview of discussed schematics ...................................................................................................... .3Disclaimer ............................................................................................................................................... .3Circuit 1...................................................................................................................................................... 4Description ............................................................................................................................................. .5Components ........................................................................................................................................... .5Simulation results .................................................................................................................................. 6Circuit 2.....................................................................................................................................................12Description ............................................................................................................................................ 12Components ........................................................................................................................................... 13Circuit 3.....................................................................................................................................................16Description ............................................................................................................................................. 16Components ........................................................................................................................................... 16Circuit 3b ................................................................................................................................................. 19Circuit 4................................................................................................................................................... 20Components ........................................................................................................................................... 21Simulation results .................................................................................................................................. 22record of revisions ................................................................................................................................ 25

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E910.26


wArning – Life Support Applications Policy

ELMOS Semiconductor AG is continually working to improve the quality and reliability of its products. Never-theless, semiconductor devices in general can malfunction or fail due to their inherent electrical sensitivity and vulnerability to physical stress. It is the responsibility of the buyer, when utilizing ELMOS Semiconductor AG products, to observe standards of safety, and to avoid situations in which malfunction or failure of an ELMOS Semiconductor AG Product could cause loss of human life, body injury or damage to property. In development your designs, please ensure that ELMOS Semiconductor AG products are used within specified operating ranges as set forth in the most recent product specifications.

general Disclaimer

Information furnished by ELMOS Semiconductor AG is believed to be accurate and reliable. However, no respon-sibility is assumed by ELMOS Semiconductor AG for its use, nor for any infringements of patents or other rights of third parties, which may result from its use. No license is granted by implication or otherwise under anypatent or patent rights of ELMOS Semiconductor AG.

ELMOS Semiconductor AG reserves the right to make changes to this document or the products containedtherein without prior notice, to improve performance, reliability, or manufacturability .

Application Disclaimer

Circuit diagrams may contain components not manufactured by ELMOS Semiconductor AG, which are included as means of illustrating typical applications. Consequently, complete information sufficient for construction purposes is not necessarily given. The information in the application examples has been carefully checked and is believed to be entirely reliable. However, no responsibility is assumed for inaccuracies. Furthermore, such infor-mation does not convey to the purchaser of the semiconductor devices described any license under the patent rights of ELMOS Semiconductor AG or others.

Copyright © 2006 ELMOS Semiconductor AGReproduction, in part or whole, without the prior written consent of ELMOS Semiconductor AG, is prohibited.

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Heinrich-Hertz-Str. 1 | 44227 Dortmund | Germany

Phone + 49 (0) 231 - 75 49 - 0 | Fax + 49 (0) 231 - 75 49 - 149

[email protected] | www.elmos.de

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driving power leds and standard leds with pfm ... power leds and standard leds with pfm controller...

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