PT6901 参数

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High Brightness LED Driver Reference PT6901

DESCRIPTION

PT6901 is a PWM high brightness LED driver control IC. The output current can be programmed between a few milliamps and up to more than 1.0A. It allows efficient operation of driver current up to more than 1A output, and the input range is from 8V to 18V. PT6901 controls the external MOS at fixed switch frequency up to 300KHz. PT6901 drive a single or multiple series LEDs at a constant-current control method; thus, providing constant current light output and enhanced reliability.

The functions of linear and PWM dimming are included. Output current to LED string can be programmed to any value between 0 to its maximum value at the linear dimming control input of PT6901. PT6901 provides a low-frequency PWM dimming input that can accept an external control signal with a duty cycle of 0~100% and a frequency between 100Hz and a few KHz.

FEATURES

• >85% Efficiency

• 8V to 18V input range • Constant –Current Driver

• Applications from a few mA to more than 1A LED driver • LED string from one to hundreds diodes

• PWM low-frequency dimming and linear Dimming

APPLICATIONS

• DC/DC or AC/DC LED Driver • Backlighting LED driver • Constant –Current Driver • Charger

PT6901 REF2.0 - 1 - Nov, 2006

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High Brightness LED Driver Reference PT6901

BLOCK DIAGRAM 8V-18VVINLEDVDDRegulatorPT6901LD-+COMPLEDUVLORQSDriver240mVPWMD100KΩ-+GDCOMPCSOSCRFGND

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High Brightness LED Driver Reference PT6901

PIN CONFIGURATION

8 PINS, SOP

PWMDVDDPT6901LDRFVINGDGNDCS

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High Brightness LED Driver Reference PT6901

PIN DESCRIPTION

Pin Name

Description

Pin No. 1

2 3 4 5

6 7 8

CS Senses LED string current GND Ground GD Drives the gate of external MOSFET VIN Input voltage 8V-18V DC PWMD Low frequency PWM dimming pin, also enable pin VDD Internal regulated voltage LD Linear dimming RF Oscillator frequency control

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High Brightness LED Driver Reference PT6901

FUNCTION DESCRIPTION

LED DRIVER OPERATION

PT6901 can control all basic types of converters. When the GD via the external power MOSFET, the LED driver stores the input energy in an inductor or delivers the energy directly to LEDs (depending on the application circuit). The sampling resistor that connects to CS pin controls the maximum value of LED current. When the voltage at CS pin exceeds the internally set, 240mV threshold, the power MOSFET turns off. It can be programmed externally by applying voltage to the LD pin that will be limited the LED maximum current. When soft start is required, a capacitor can be connected to the LD pin to allow the voltage to ramp at a desired rate.

SETTING LIGHT OUTPUT

The peak CS voltage is a good representation of the average current in the LED. There is a certain error when the peak-to-peak current is exceeded to the average current. In order to get the accurate average current, the resistor of CS pin has to figure as the following:

If the peak-to-peak ripple current in the inductor is 100mA, to get a 300mA LED current, the sense resistor should be:

RCS=240mV/(300mA+100mA/2)=0.68Ω

DIMMING

PT6901 can be controlled in two methods: Linear or PWM. The linear dimming can be implemented by applying a control voltage from 0 to 240mV to the LD pin. When the LD voltage underrides the internal set 240mV threshold, the internal clamp voltage, 240mV, is terminated. And when it overrides the internally set 240mV threshold, the LD control voltage is dead.

The PWM dimming scheme can be implemented by external low frequency PWM signal to the PWMD pin. By using the duty cycle of the PWM control method that can change the working and the closing time, and the light output can be adjusted between zero and the internal set. In addition, the PWM dimming method is limited because the output current cannot be exceeded the internal set.

PROGRAMMABLE OPERATING FREQUENCY

The operating frequency of the oscillator is programmed between 30KHz to 300KHz.

2.5 x 1010

fosc=

RF

ENABLE

PT6901 can be turned off by pulling the PWMD to GROUND. When disabled, PT6901 draws quiescent current of less than 0.5mA.

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High Brightness LED Driver Reference PT6901

AC/DC OFF-LINE APPLICATIONS

PT6901 is a low-cost buck converter control IC that designs for driving multi-LED strings or arrays. It can operate from either universal AC line or DC voltage via the change of application current. PT6901 can drive up to hundreds of HB LEDs.

LED+R168KΩR268KΩD4U14PWMDVDD15OkΩD6BYV26BC7120pF300VR9GD333ΩL14.7mHLED-ACF1U2DF04SVINC168uF250VD2FR1G-13D1FR1G-13D3FR1G-131N4148J1R3R410kΩ5PWMD6VDDQ1IRF840PT6901CSLDRF8GND2C33.3nF400VC268uF250VD59VC410uFC56.8nF71220ΩR5C66.8nFR70KΩR71ΩR82.2ΩGNDFigure 1. Typical AC application for a string of 16 HB LEDs

POWER FACTOR CORRECTION

When the input power to the LED driver does not exceed 25W, a simple passive power factor

correction (PFC) circuit can be added to the application circuit of figure 1. A simple circuit consists of PFC to improve the line current harmonic distortion and to achieve a power factor greater than 0.85.

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High Brightness LED Driver Reference PT6901

DC/DC LOW VOLTAGE APPLICATIONS

BUCK CONVERTER OPERATION

When the LED string voltage is needed to be lower than the input supply voltage, the buck power conversion topology can be used. The basic design procedure for a buck LED driver outline in the previous chapter, but the application of the output voltage must be maintain lower than two times of the input voltage. With this limitation, PT6901 buck converter enables to operate at a duty cycle less than 0.5 to avoiding an oscillation of the output current at a sub-harmonic of the switching frequency.

12VVINPWMDPT6901VDDLDB140220uHVN3205LEDHB LED 900mAGDCS10uF0.24RFGND270kFigure 2. PT6901 Buck Driver for a Single 900mA HB LEDs

Inductor Design

Referring to figure 2, when the nominal current ILED is 900mA with one 5W LED, the peak-to-peak current is 20% of average current. So, the sense resistor is:

240mV240mV

RCS==≈0.24Ω

IAVG+IPP/2900mA+900mA*0.2/2

When the ILED is 900mA, the forward drop voltage of LED is about 4.5V. Knowing the nominal input voltage is 12V, the switching duty cycle is :

V4.5

≈0.38 D=LED=

VIN12

If the oscillation frequency is 100KHz, the required off-time of MOSFET transistor can be calculated: TOFF=(1−D)/fosc=(1−0.38)/100k=6.2uS The required value inductor is given by

L=(VLED+VD)⋅TOFF/IPP=(4.5+0.4)×6.2u/(0.2×900m)≈170uH

The nominal application is 220μH, because the value of inductor is greater than the calculation.

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High Brightness LED Driver Reference PT6901

TYPICAL APPLICATION

R1220KΩR2220KΩD2F1U2DF04SLED+D1BYV26BC6U1PWMDVDD15OkΩL14.7mH1N4148ACJ1R3R410kΩ4VIN5PWMD6VDD100pF1kVR9GD333ΩLED-Q1IRF840PT6901SACSLDROSC8GND2C14.7uFC23.3nFD39VC310uFC46.8nF71220ΩR5C56.8nFR70KΩR71ΩR82.2ΩGND

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High Brightness LED Driver Reference PT6901

ABSOLUTE MAXIMUM RATINGS

Parameter

VIN to GND CS to GND

LD, PWMD to GND OSC to GND VDD to GND

Operating temperature Storage temperature

Symbol Rating Unit

-0.3 ~ +20 V -0.3 ~ VDD+0.3 V -0.3 ~ VDD+0.3 V -0.3 ~ VDD+0.3 V -0.3 ~7 V

℃ Topr -40 ~ +85 ℃ Tstg -65 ~ +150 PT6901 REF2.0 - 9 - Nov, 2006

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High Brightness LED Driver Reference PT6901

ELECTRICAL CHARACTERISTICS

(Unless otherwise specified, Ta=25℃)

Parameter

Input DC supply voltage Internal regulated voltage VDD source current RF voltage

Active supply current Shut-down supply current VIN start voltage VIN under voltage lockout hysteresis

Pin PWMD input low voltage Pin PWMD input high voltage Pin PWMD pull-down resistance Current sense threshold voltage GD high output voltage GD low output voltage Oscillator frequency

Maximum oscillator PWM duty cycle

Linear dimming pin voltage range Current sense blanking internal GD output rise time GD output fall time

SymbolVIN

Conditions Min. Typ. Max.UnitDC input voltage 8 12 18 V VIN=8~18V, IDD(ext)=0,

VDD 4.6 5 5.4 V pin GD open

=12V IVDD VIN 10 mA ===Ω VRF 1.18 1.21 1.24 V VIN=8~18V,RRF=270k=IIN VIN8~18V 0.4 0.6 mA Pin PWMD to GND,

IINsd 0.3 0.5 mA VIN=12V =VST VIN 6.9 7.5 V =rising 6.3 VIN falling 500 700 900 mV =

==8~18V VENL VIN 0.5 V VENH VIN8~18V 1.5 V KΩ REN VPWMD5V 70 100 130 Ta=-40~+85℃ 220 240 260 mV VCS

=VGDH IOUT10mA VDD-0.2 V VGDL IOUT 0.2 V =10mA RF=270KΩ fosc 80 100 120 KHz FPWM=100KHz,

DMAX 100 % at CS to GND

VLD VIN12V 0 240 mV TBLANK VCS0.55VLD, VLDVDD200 400 600 ns TRISE CGD560pF 30 50 ns TFALL CGD560pF 30 50 ns VHYS

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High Brightness LED Driver Reference PT6901

ORDER INFORMATION

Valid Part Number

PT6901-S PT6901-S (L)

Package Type 8 Pins, SOP 8 Pins, SOP

Top Code PT6901-S PT6901-S

Notes:

1. (L), (C) or (S) = Lead Free.

2. The Lead Free mark is put in front of the date code.

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High Brightness LED Driver Reference PT6901

PACKAGE INFORMATION

8 PINS, SOP, 150MIL

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High Brightness LED Driver Reference PT6901

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High Brightness LED Driver Reference PT6901 Symbol Min. Typ. Max. A 1.35 - 1.75 A1 0.10 - 0.25 A2 1.25 - 1.65 b 0.31 - 0.51 b1 0.28 - 0.48 c 0.17 - 0.25 c1 0.17 - 0.23 D 4.90 BSC. E 6.00 BSC. E1 3.90 BSC. e 1.27 BSC. L 0.40 - 1.27 L1 1.04 REF. L2 0.25 BSC. R 0.07 - - R1 0.07 - h 0.25 - 0.50 θ 0° - 8° θ1 5° - 15° θ2 0° - -

Notes

1. Dimensioning and tolerancing per ANSI Y 14.5M-1994 2. Controlling Dimension: MILLIMETERS.

3. Dimension D does not include mold flash protrusions or gate burrs. Mold flash, protrusions or

gate burrs shall not exceed 0.15 mm (0.006 in) per end. Dimension E1 does not include

interlead flash or protrusion. Interlead flash or protrusion shall not exceed 0.25mm per side. D and E1 dimensions are determined at datum H.

4. The package top may be smaller than the package bottom. Dimensions D and E1 are

determined at the outermost extremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but including any mismatch between the top and bottom of the plastic body.

5. Datums A & B to be determined at datum H. 6. N is the number of terminal positions. (N=8)

7. The dimensions apply to the flat section of the lead between 0.10 to 0.25mm from the lead tip.8. Dimension “b” does not include dambar protrusion. Allowable dambar protrusion shall be

0.10mm total in excess of the “b” dimension at maximum material condition. The dambar cannot be located on the lower radius of the foot.

9. This chamfer feature is optional. If it is not present, then a pin 1 identifier must be located within

the index area indicated.

10. Refer to JEDEC MS-012, Variation AA. JEDEC is the registered trademark of JEDEC SOLID STATE TECHNOLOGY ASSOCIATION.

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High Brightness LED Driver Reference PT6901

REVISION HISTORY

Date

June, 26, 2006

Revision # -

Reference # PT6901 REF1.0

Remarks Request #:

PT6901 REF2.0 - 15 - Nov, 2006