Datasheet SP6683 Datasheet (Sipex)

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Page 1

SP6683

1.5x Charge Pump LED Driver for Parallel Configuration

FEATURES

■ 200mA Output Using 1µF Ceramic Caps

■ Drives up to 8 white LED's

■ 0.5µA Shutdown Current

■ 1x/1.5x Mode Charge Pump

■ +2.7V to +5.5V Input Voltage Range

■ Built-in 1.2MHz Oscillator

MODE

OUT

C1P

1 2

SP6683

10 Pin DFN

4 5

9 8 7 6

C2P C1N GND C2N EN/PWM

■ 0.5mA Quiescent Current

■ Programmable Output Current or Voltage

■ PWM Dimming Control via Enable Pin

■ Soft Start to limit In-Rush Current

■ Space Saving 10-pin 3 x 3mm DFN Package

■ Three Options for Optimizing Efficiency:

■ SP6683 - MOSFET discharge in shutdown

■ SP6683-03 - High Impedance in shutdown

■ SP6683-LV - Low Voltage (150mV)V

ence

Now Available in Lead Free Packaging

APPLICATIONS

■ Mobile Phone

■ Camera Flash Driver

■ PDA

■ Digital Still Camera

Refer-

■ Digital Camcorder

■ Color LCD Module

DESCRIPTION

The SP6683 is a high power current regulated charge pump ideal for converting a Li-Ion battery input for driving up to 8 white LED’s used in backlighting color displays. The SP6683 operates with an internal 1.2MHz clock, enabling the use of small external components. Output current can be accurately regulated by modulating the switcher between the charge pump and output capacitor. In shutdown mode, the SP6683 discharges the output to ground and draws less than 500nA current. The SP6683 utilizes 1µF capacitors to deliver up to 200mA current regulated WLED drive capability. The SP6683 family includes three options that allow the user to optimize LED driving circuit; SP6683-LV with low voltage reference, SP6683-03 with high impedance output in shutdown, and SP6683 with pulled down output in shutdown. The SP6683 is offered in 10-pin DFN package.

TYPICAL APPLICATION SCHEMATIC

SP6683

C2P C1N

GND

C2N

EN/PWM

10 9 8 7 6

C4 1µF

C5 1µF

White LED

1µF

R5 1M

Lithium-Ion

ENABLE/PWM DIMMING

C1 1µF

1 2 3 4 5

C3 1µF

V C1P V V FB

OUT

IN MODE

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ABSOLUTE MAXIMUM RATINGS

VIN, V Output Current (I Power Dissipation per Package - 10-pin DFN

(derate 8.84mW/°C above +70°C) ..................... 1.2W

Junction Temperature.................................... +125°C

Storage Temperature ...................... -65°C to +150°C

ESD Rating................................................. 2kV HBM

MODE

, V

and EN/PWM.................-0.3V to 6V

OUT

) ...................................... 300mA

OUT

These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.

ELECTRICAL CHARACTERISTICS

Unless otherwise specified: VIN = 3.6V, C1=C2=C4=C5=1.0µF (Ceramic, ESR=0.03 Ω) and T specifications which apply over full operating temperature range -40ºC to +85ºC.

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TUO

♦

TUO

♦

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V,V5.5-0.3=

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Aµ001=tuoI,V6.3

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Page 3

PIN DESCRIPTION

PIN NUMBER PIN NAME DESCRIPTION

OUT

Regulated charge pump output. 2 C1P Positive terminal to the charge pump flying capacitor C2. 3VINInput supply voltage. 4V

MODE

Charge pump mode program pin. When V

is greater than 1.25V,

MODE

a X1 charge pump is used. Otherwise, charge pump switches to X1.5

mode. A voltage divider shown in the typical application circuit

programs the VIN threshold for charge pump mode switching. 5FBThis is the feedback pin for output current or voltage regulation. The

voltage of this pin is compared with an internal 315mV reference. 6 EN/PWM Enable and PWM dimming control input. Pull this pin low to discon-

nect V

from VIN and shutdown the SP6683.V

OUT

is pulled to

OUT

ground in shutdown. 7 C2N Negative terminal to the charge pump flying capacitor, C4. 8 GND Ground reference. 9 C1N Negative terminal to the charge pump flying capacitor, C2.

10 C2P Positive terminal to the charge pump flying capacitor C4.

FUNCTIONAL DIAGRAM

EN/PWM

MODE

1.25V

MODE COMP

Voltage

Reference

315mV

OUT

COMP

1.2 MHz Clock

Manager

Mode Control

Start-up

and

Charge

Pump

Switches

C1P

C1N

C2P

C2N

OUT

GND

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TYPICAL PERFORMANCE CHARACTERISTICS (25ºC)

200

150

100

Iout (mA)

3.0 3.5 4.0 4.5 5.0

200

150

100

Iout (mA)

3.0 3.5 4.0 4.5 5.0

100

Efficiency (%)

3.0 3.5 4.0 4.5 5.0

Iout vs. Vin @ 60mA

Vf = 3.0V Vf = 3.3V Vf = 3.6V Vf = 3.9V Vf = 4.2V

Vin (V)

Iout vs. Vin @ 100mA

Vf = 3.0V Vf = 3.3V Vf = 3.6V Vf = 3.9V Vf = 4.2V

Vin (V)

Efficiency vs Vin (Iout = 60mA)

Vf = 3.0V Vf = 3.3V Vf = 3.6V Vf = 3.9V Vf = 4.2V

Vin (V)

300

250

200

150

Iout (mA)

100

3.0 3.5 4.0 4.5 5.0

400

350

300

250

200

Iout (mA)

150

100

3.0 3.5 4.0 4.5 5.0

100

Efficiency (%)

3.0 3.5 4.0 4.5 5.0

Iout vs. Vin @ 200mA

Vin (V)

Iout vs. Vin @ 300mA

Vin (V)

Efficiency vs Vin (Iout = 200mA)

Vf = 3.0V Vf = 3.3V Vf = 3.6V Vf = 3.9V

Vin (V)

Vf = 3.0V Vf = 3.3V Vf = 3.6V Vf = 3.9V

Vf = 3.0V Vf = 3.3V

Vf = 3.6V

100

Efficiency (%)

3.0 3.5 4.0 4.5 5.0

Efficiency vs Vin (Iout = 100mA)

Vf = 3.0V Vf = 3.3V Vf = 3.6V Vf = 3.9V Vf = 4.2V

Vin (V)

100

Efficiency (%)

3.0 3.5 4.0 4.5 5.0

Efficiency vs Vin (Iout = 300mA)

Vf = 3.0V

Vf = 3.3V Vf = 3.6V

Vin (V)

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General Overview

OPERATION

The SP6683 is a current regulated charge pump ideal for converting a Li-Ion battery input for driving white LEDs used in backlighting color displays in cellular phones, PDAs, digital cameras and MP3 players. The SP6683 is able to efficiently drive up to eight 20mA white LEDs in parallel and maintain a constant brightness over a very wide operating voltage range (2.7V to 5.5V). The SP6683 operates with an internal

1.2MHz clock, enabling the use of small external components. Other features of SP6683 include PWM dimming control as well as complete input/output disconnect in shutdown. In shut down mode the IC typically draws 500nA current. The output regulation is achieved by sensing the voltage at the feedback pin and modulating the switch between the charge pump and output capacitor.

Theory of Operation

The SP6683 regulated charge pump block diagram consists of four main blocks (Voltage Reference, Mode Control, Clock Manager, Startup and Charge-Pump Switches) and two comparators (V

Comparator and V

MODE

OUT

Com-

parator).

1) Voltage Reference. This block provides the 315mV and 1.25V reference voltages needed for the two comparators.

2) Mode Control. An external voltage divider connected to the V

pin will define an input

MODE

voltage to the mode comparator which sets the logic state of the mode selection outputs to the X1 or X1.5 modes. V

is compared to a

MODE

1.25V bandgap voltage. For example, if one makes a 158K/100K divider, the mode will change at 2.58 x 1.25 V =3.23V. A comparatorbased cycle by cycle regulation ensures that no mode change occurs during cycles.

3) Clock Manager. An internal 1.2MHz clock is generated in this block. Depending on the mode control, the appropriate clock phasing is generated here and sent to the start-up and charge-pump switches block.

4) V

Comparator and Output Control. A

OUT

315mV reference voltage is compared to feedback voltage to control the Vout needed for the application. Output current is set by a bias resistor from the FB pin to the GND pin chosen by the relationship:

FB FB

OUT

where VFB = 315mV.

Configuring the SP6683 as Voltage or Current Source

The white LED load configuration used by customers can be discrete white LEDs or a white LED module. Inside the white LED module, there may or may not be resistors in series with the white LEDs. According to the different application requirements, the SP6683 can be configured as either a voltage source or a current source to provide solutions for these different applications, as shown in figures 9-12. Figure 9 shows the SP6683 driving discrete white LEDs as a current source.

OUT

SP6683

GND

Figure 9. Driving discrete white LEDs as current source

1uF

The current in one white LED current is set by the ratio of the feedback pin voltage (315mV) and the bias resistor RB. To set the operating current, RB can be selected by:

RB = I

LED

The current of the remaining white LEDs is set according to the similarity of the white LEDs. 3wire white LED modules with internal series

Page 6

OPERATION

Anode

SP6683

Cathode

OUT

1uF

2-wire W-LED module

GND

resistors (as shown in figure 10) can also be driven in this way.

Fig 10. 3-wire white LED module

Anode

3-wire W-LED module

GND

In figure 11, SP6683 was used to drive a 2-wire white LED module (without internal series resistors) as a current source. The bias resistor R is selected to regulate the total current of the white LED module instead of the current of a single LED as in figure 9.

Anode

Cathode

SP6683

GND

OUT

2-wire W-LED module

In this application, the bias resistor can be selected by:

LED (TOTAL)

is the total operating current

where I

LED(TOTAL)

of all the white LEDs. To use SP6683 as a voltage source for fixed

voltage applications, a voltage divider is need to program the output voltage, as shown in figure 12.

The output voltage is set by the ratio of the two resistors and the feedback control voltage as shown by:

OUT

= ( 1 +

) • V

Figure 11. Driving 2-wire white LED module as current source

Figure 12. Driving 2-wire white LED module as voltage source

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Programming The Operating Mode

The SP6683 can automatically change from X1 mode to X1.5 to maximize efficiency. To use this feature, divider resistors should be chosen according to the specific application, as shown in figure 13.

APPLICATION INFORMATION

Which can be expressed as R

R1 = [(VTH/1.25) - 1] R

Figure 13. Programming the Vmode Resistors

SP6683

MODE

GND

The guideline for divider resistor selections is as follows. For high input voltage, the SP6683 will work in X1 mode. When the input voltage drops to Vth threshold voltage, it will switch to X1.5 mode automatically. The Vth threshold voltage for mode change can be calculated by:

VTH = (VF + 0.315 + m • I

LED

• R

OUT

)

Where VF and m are the forward voltage and number of the white LEDs, Rout is the output resistance of the SP6683.

The equation for the voltage divider R1 and R with V

MODE

= 1.25V is:

VTH = 1.25V • (1+R1/R2)

For the typical SP6683 application, using VF =

3.6V, m = 8, I

LED =

15mA, R

OUT

= 6Ω, V

be 4.63V, Select R2 = 100kΩ, then R1 = 270kΩ

Capacitor Selection

Ceramic capacitors are recommended for their inherently low ESR, which will help produce low peak to peak output ripple, and reduce high frequency spikes.

The fly capacitor controls the strength of the charge pump. Selection of the fly capacitor is a trade-off between the output voltage ripple and the output current capability. Decreasing the fly capacitor will reduce the output voltage ripple because less charge will be delivered to the output capacitor. However, a smaller fly capacitor leads to larger output resistance, thus decreasing the output current capability and the circuits efficiency. Increasing the value of the input and output capacitors could further reduce the input and output ripple. For peak performance, place all capacitors as close to the SP6683

as possible.

Refer to table 1 for some suggested low ESR capacitors.

will

Table: 1

SUGGESTED LOW ESR CAPACITORS

Manufacturers/ Website Part Number Capacitance/

TDK/www.tdk.com C1005X5R0J105M 1uF/6.3V 0402/X5R/0.5mm 0.03

TDK/www.tdk.com C1608X5R0J225K 2.2uF/6.3V 0603/X5R/0.9mm 0.02 Murata/www.murata.com GRM155R60J105KE19B 1uF/6.3V 0402/X5R/0.55mm 0.03 Murata/www.murata.com GRM188R61A225KE34B 2.2uF/6.3V 0603/X5R/0.9mm 0.02

Volta

Capacitor

Size/Type/Thickness

ESR at

100KHz

Page 8

Brightness Control Using PWM

Dimming control can be achieved by applying a PWM control signal to the EN/PWM pin. The brightness of the white LEDs are controlled by increasing and decreasing the duty cycle of the PWM signal. While operating frequency range is from 60Hz to 700Hz, the recommended maximum brightness frequency range is from 60Hz to 200Hz. A repetition rate of at least 60Hz is required to prevent flicker.

Brightness Matching

For white LEDs, the forward voltage drop is a function of the operating current. However, for a given current, the forward voltage drop across each LED does not always match exactly. This can cause uneven brightness in the white LEDs.

In figure 14, assuming high-precision bias resistors were used, the operating current ratio of two different branches can be easily derived as shown by:

APPLICATION INFORMATION

Since the brightness of the white LED is proportional to the operating current, for better brightness matching, a higher output voltage could be used. This could be done by using a larger resistor, as shown in figure 14. Rb2 is used to bias the operating current of the white LED, Rb1 is use to increase the output voltage. Better brightness matching was achieved at the cost of the power wasted on the bias resistor.

Power Efficiency

The efficiency of driving the white LEDs can be calculated by

VF • IF

Vi •Ii

VF • IF

≈

Vi • (n • IF + IQ)Vi • n

Where Vi, Ii are input voltage and current; VF, I are the forward voltage and operating current of the White LED; IQ is quiescent current, which is considered small compared with IF.

- V

I2 V

OUT

- V

where I1 I2 are the operating current of the white LEDs, where VF1,VF2 are the forward voltage of the white LEDs.

OUT

SP6683

GND

Figure 14. Improving brightness matching

Rb1

Rb2

VF2

VFnVF1

Three Options for Optimization

The SP6683 family includes three options that allow the user to optimize the LED driving circuit. The SP6683 includes an on-board discharge switch that ensures that V

is completely dis-

OUT

charged in shutdown. This feature is very useful in systems using PWM dimming, when the SP6683 is periodically turned on and off. The discharge switch ensures that the falling and rising edges of the LED current have similar durations.

The SP6683-03 has the discharge MOSFET disabled ensuring that the output node is at high impedance during shutdown. This can be useful if the system is feeding LED current from another source while the SP6683 is in shutdown.

The SP6683-LV offers a lower reference voltage that allows to reduce efficiency loss occurring in the current sense resistor. This part is ideal for driving single LEDs for Flash applications.

Page 9

PACKAGE: 10 PIN DFN

Top View

D/2

E/2

Side View

10 Pin DFN

(JEDEC MO-229,

VEED-5 VARIATION)

DIMENSIONS

(mm)

SYMBOL MIN NOM MAX

A A1 A3

b D D2

Bottom View

e E

0.80 0.90 1.00

0.02 0.05

0.20 REF

0.18

0.25 0.30

3.00 BSC

2.20

0.50

PITCH

2.70

3.00 BSC

1.40

1.75

0.20

0.30 0.40 0.50

Page 10

ORDERING INFORMATION

Part Number Operating Temperature Range Package Type

SP6683ER .................................................. -40°C to +85°C ........................................................... 10 Pin DFN

SP6683ER/TR ............................................ -40°C to +85°C ........................................................... 10 Pin DFN

SP6683-03ER............................................. -40°C to +85°C ........................................................... 10 Pin DFN

SP6683-03ER/TR....................................... -40°C to +85°C ........................................................... 10 Pin DFN

*Contact factory for availability of the following parts

SP6683LVER.............................................. -40°C to +85°C ........................................................... 10 Pin DFN

SP6683LVER/TR........................................ -40°C to +85°C ........................................................... 10 Pin DFN

Available in lead free packaging. To order add "-L" suffix to part number. Example: SP6683ER/TR = standard; SP6683ER-L/TR = lead free

/TR = Tape and Reel Pack quantity is 3000 for DFN.

Corporation

ANALOG EXCELLENCE

Sipex Corporation Headquarters and

Sales Office

233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600

Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.