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S P6 6 9 9 STEP UP WHITE LED CONVERTER
FEATURES High Output Voltage: Up to 27V
Drives 2 to 5 LEDs @ 20mA High Efficiency up to 84%
Integrated Schottky Diode Fast 1.0MHz Switching Frequency 200mV Feedback Voltage PWM Dimming Capability up to 1KHz Over Output Voltage Protection Internal Soft Start Circuit Small SOT23-6 Package APPLICATIONS Cellular Phones LCD Modules Keypad Backlighting Digital Cameras GPS Receivers Portable Media Players DESCRIPTION
The SP6699 is an inductor-based DC/DC converter designed to drive up to five white LEDs in series for LCD modules and keypad backlighting functions. Only one feedback resistor is needed to control the LED current and obtain the desired brightness. A 1.0MHz constant frequency PWM control scheme is used, enabling the usage of small external components. A typical application needs a 1mm tall inductor and a 0.22F output capacitor. Additionally, the boost circuit Schottky diode is integrated, further reducing the overall foot print. A logic controlled enable pin allows this device to be placed in a low current consumption mode of a few microamps. Furthermore, the SP6699 is equipped with an over voltage output protection circuit which clamps the output voltage to 27 volts when any LED fails or in other abnormal conditions.
TYPICAL APPLICATION CIRCUIT
Rev. E - 01/21/2008
SP6699 Step-Up White LED Converter 1/10
(c) 2008 Exar Corporation
BLOCK DIAGRAM
Figure 1: SP6699 Block Diagram
PIN DESCRIPTION
SOT23-6
Figure 2: SP6699 Pin Out
Pin Number 1 2 3 4
Name SW GND FB CTRL Ground signal pin
Description Switch pin. Connect external inductor Voltage Feedback. Reference voltage is 200mV Shutdown and dimming pin. VCTRL>1.8V: Device Enabled 50mV< VCTRL <1.8V:Linear dimming VCTRL<50mV: Device Disabled Output Pin. Connected to the cathode of the internal Schottky diode Input supply pin. Must be locally bypassed
5 6
VOUT VIN
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(c) 2008 Exar Corporation
ELECTRICAL CHARACTERISTICS
Absolute Maximum Ratings
These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground.
Input Voltage VIN ...................................... 20V SW Voltage.............................................. 27V FB Voltage ............................................... 20V CTRL Voltage ........................................... 20V Thermal Resistance (junction to Atm.) RJA .................................................265C/W
Operating Junction Temperature ..............150C Storage Temp. Range TSTG .........-65C to 150C Lead Temperature (sold. 10s) TLEAD ..........260C ESD Ratings - Human Body Model .......... 2000V ESD Ratings - Machine Model ................... 250V
Recommended Operating Conditions
Operating Temperature TOP .........-40C to 85 C Input voltage VIN ........................... 2.5V to 16V
VIN=3V, VCTRL =3V, TA=25C, unless otherwise specified. Parameter Symbol Conditions Min 2.5 16 IOUT=20mA, 4 LEDs TA=-40C to 85C VFB=VIN, not switching VCTRL=0V 188 200 35 1.3 2.0 0.7 90 TA=25C, D=40% TA=25C, D=80% ISW=250mA VSW=5V VCTRL High Low 40 CTRL Pin Bias Current Schottky Forward Drop Schottky Leakage Current Soft Start Time t ICTRL VDROP TA=85C TA=-40C ID=150mA VR=23V VR=27V 300 55 50 75 0.7 0.1 4 150 1.8 0.05 72 2.0 3.2 1.0 93 500 350 360 0.01 5 212 100 2.7 5.0 1.3 Typ. Max Unit V V mV nA mA A MHz % mA mA mV A V V A A A V A A s
CTRL Voltage VCTRL ....................................16V
Minimum Operating Voltage VIN(min) Maximum Operating Voltage VIN(max) Feedback Voltage FB Pin Bias Current Supply Current Supply Current Switching Frequency Maximum Duty Cycle Switch Current Limit (Note 1) Switch VCE Saturation Voltage Switch Leakage Current CTRL Pin Voltage VFB IFB ICC IQ f DMAX ILIMIT VCESAT
Note 1: The Switch Current Limit is related to the Duty Cycle. Please refer to figure 15 for details.
Rev. E - 01/21/2008
SP6699 Step-Up White LED Converter 3/10
(c) 2008 Exar Corporation
ELECTRICAL CHARACTERISTICS
Typical Characteristics
VIN=3.6V, EN=VIN, RSET=24k, CIN=1F, TA=25C, unless otherwise noted.
Fig. 3. Efficiency vs Junction Temperature
Fig. 4. Efficiency vs Input Voltage
Fig. 5. Efficiency vs LED Number
Fig. 6. Schottky Forward Current vs Schottky Forward Drop
Fig. 7. Shutdown Quiescent Current vs Input Voltage
Fig. 8. Supply Current vs Input Voltage
Rev. E - 01/21/2008
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(c) 2008 Exar Corporation
ELECTRICAL CHARACTERISTICS
Fig. 9. Output Clamp Voltage vs Input Voltage
Fig. 10. Input Current in Output Open Circuit vs Input Voltage
Fig. 11. Switching Frequency vs Junction Temperature
Fig. 12. Feedback Voltage vs Junction Temperature
Fig. 13. Schottky Forward Drop vs Junction Temperature
Fig. 14. Schottky Leakage Current vs Junction Temperature
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(c) 2008 Exar Corporation
ELECTRICAL CHARACTERISTICS
Fig. 15. Switch Current Limit vs Duty Cycle
Fig. 16. Switch Saturation Current vs Switch Current
Fig. 17. Feedback Voltage vs CTRL Pin Voltage
Rev. E - 01/21/2008
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(c) 2008 Exar Corporation
THEORY OF OPERATION
Detailed Description The SP6699 is a boost DC-DC converter which uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Figure 1. At the start of each oscillator cycle, the SR latch is set and the switch Q1 turns on. The switch current will increase linearly. The voltage on sense resistor is proportional to the switch current. The output of the current sense amplifier is added to a stabilizing ramp and the result is fed into the non-inversion input of the PWM comparator A2. When this voltage exceeds the output voltage level of the error amplifier A1, the SR latch is reset and the switch is turned off. It is clear that the voltage level at non-inversion input of A2 sets the peak current level to keep the output in regulation. This voltage level is the output signal of error amplifier A1, and is the amplified signal of the voltage difference between feedback voltage and reference voltage of 200mV. So, a constant output current can be provided by this operation mode. The relation for R1 and LED current can be expressed as below: R1=200mV/ILED Over Voltage Protection The SP6699 has an internal open-circuit protection circuit. When the LEDs are disconnected from the circuit or fail open, the output voltage is clamped at 27V. The SP6699 will switch at a low frequency, and minimize input current. Soft Start The SP6699 has an internal soft start circuit to limit the inrush current during startup. The startup delay is controlled by internal soft start capacitor. Please refer to Figure 19.
Fig. 19: Soft Start Waveform VIN=3.6V, 4 LEDs, ILED=20mA
Dimming Control
Fig. 18: R1 Selection Typical Application Circuit
LED Current Control Refer to Figure 18, the LED current is controlled by the feedback resistor R1. LEDs' current accuracy is determined by the regulator's feedback threshold accuracy and is independent of the LED's forward voltage variation. So the precise resistors are preferred. The resistance of R1 is in inverse proportion to the LED current since the feedback reference is fixed at 200mV.
Rev. E - 01/21/2008
Two typical types of dimming control circuit are present. First, controlling the CTRL Pin voltage to change operation state is a good choice. Second, changing the feedback voltage to get appropriate duty and luminous intensity is also useful. 1. Adding a Control Signal to CTRL Pin There are three methods to control CTRL pin signal. First, adding a PWM Signal to the CTRL pin directly. The SP6699 is turned on or off by the PWM signal when it is applied on the CTRL pin. The typical frequency of this
(c) 2008 Exar Corporation
SP6699 Step-Up White LED Converter 7/10
THEORY OF OPERATION
PWM signal is 200Hz to 1KHz. Please refer to figure 20. the DC voltage can get appropriate luminous intensity. Comparing with all kinds of PWM signal control, this method features a stable output voltage and LEDs current. Please refer Figure 23.
Fig. 20: Dimming Control Using a PWM Signal on CTRL Pin
Secondly, adding a constant DC voltage through a resistor divider to CTRL pin can control the dimming. The FB voltage is indirectly adjusted when the CTRL pin voltage is between 50mV to 1.8V, which can be used as dimming control. Please refer Figure 21.
Fig. 23: Dimming Control Using a DC Voltage
Second, using a filtered PWM signal can do it. The filtered PWM signal can be considered as a varying and adjustable DC voltage.
Fig. 21: Dimming Control Using a DC Voltage on CTRL Pin
Thirdly, using a filtered PWM signal added to the CTRL pin can achieve dimming control. The filtered PWM signal can be considered as an adjustable DC voltage. It will change the FB voltage indirectly and achieve dimming control. The circuit is shown in Figure 22.
Fig. 24: Dimming Control Using a Filtered PWM Voltage
Third, using a logic signal to change the feedback voltage. For example, the FB pin is connected to the GND through a MOSFET and a resistor. And this MOSFET is controlled by a logic signal. The luminous intensity of LEDs will be changed when the MOSFET turns on or off.
Fig. 22: Dimming Control Using a Filtered PWM Signal Voltage on CTRL Pin
2. Changing the Effective Feedback Voltage There are three methods to change the effective feedback voltage. First, adding a constant DC voltage through a resistor divider to FB pin can control the dimming. Changing the DC voltage or resistor between the FB Pin and
Rev. E - 01/21/2008
Fig. 25: Dimming Control Using Logic Signal
SP6699 Step-Up White LED Converter 8/10
(c) 2008 Exar Corporation
TYPICAL APPLICATIONS
Four White LED Driver
C: X5R or X7R Dielectric L: SUMIDA CDRH5D28R-100NC or Equivalent For use over the full operating temperature range
Five White LED Driver
C: X5R or X7R Dielectric L: SUMIDA CDRH5D28R-220NC or Equivalent For use over the full operating temperature range
Rev. E - 01/21/2008
SP6699 Step-Up White LED Converter 9/10
(c) 2008 Exar Corporation
PACKAGE
SOT23-6L Unit: mm (inch)
ORDERING INFORMATION
Operating Temperature Range -40C to +85C Packing Quantity 3,000/T&R
Part Number SP6699EK-L/TR "WW" = Work Week
Package SOT23-6
Marking PBWW
Exar Corporation Headquarters and Sales Offices 48720 Kato Road Fremont, CA 94538 - USA Tel.: +1 (510) 668-7000 Fax: +1 (510) 668-7030 www.exar.com
Rev. E - 01/21/2008
SP6699 Step-Up White LED Converter 10/10
(c) 2008 Exar Corporation

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