TK65600B ADVANCED INFORMATION INDUCTIVE WHITE LED DRIVER WITH SYNCHRONOUS RECTIFER FEATURES APPLICATIONS n n n n n n n n n n n n n n n n Minimum External Components Efficiency as High as 80% LED Current Regulated Internal Synchronous Rectifer PWM Signal Intensity Control Can Drive Mulitple Strings of 3 WLED in Series 700 kHz PWM Operation Low Supply Current Enable Pin Short Circuit Protection Over Voltage Protection 8 Pin Flip Chip Package LCD Modules Cellular Telephone Battery Powered Systems Consumer Electronics The Enable pin can take a PWM signal provided by the user to reduce the display brightness. A PWM signal is prefered to pulse the LEDs with a regulated value of current and to maintain better consistency of chromaticity. TK65600B DESCRIPTION Top View Toko’s TK65600 White LED Driver IC has been optimized for battery controlled systems where power consumption and size are primary concerns. High efficiency has been optimized for this application. ENABLE A2 The miniature Flip Chip package device, together with the miniature Toko Coil D31FB or Low Profile D412F Coil, further helps system designers reduce the space required to drive the white LEDs. AGND A1 A3 N/C VDD B1 B3 FB C3 PGND VOUT C1 C2 IND The IC uses Current-mode PWM (Pulse Width Modulation) method of regulating the current through the string of LEDs. This time-proven method of regulation works at a fixed switching frequency which is preferred in RF systems, because the switching noise RF spectrum is more predictable. With a switching frequency of 700 kHz the operation of the IC should not disturb 455 kHz IF subsystem. ORDERING INFORMATION BLOCK DIAGRAM VDD IND B1 C2 C1 VOUT ENABLE A2 ENABLE GATE DRIVE TK65600B Tape/Reel Code Package Code OSC PWM SCP/OVP B3 FB VREF TAPE/REEL CODE PACKAGE CODE July 2, 2003 TOKO, Inc. A1 C3 AGND PGND Page 1 TK65600B ADVANCED INFORMATION ABSOLUTE MAXIMUM RATINGS All Pins except IND, VOUT and GND ........................... 6 V IND, and VOUT PINs ............................................... 16.5 V Storage Temperature Range ..................... -55 to +150 °C Operating Temperature Range ..................... -30 to +85 °C Junction Temperature TJMax (Note 3) ..................... 150 °C Package Power Dissipation TA = 25°C (Note 3) .... 560mW θJA Thermal Resistance (Note 3) ......................... 220°C/W TK65600B ELECTRICAL CHARACTERISTICS VDD = 3.7 V, TA = Tj = 25 °C, unless otherwise specified. Enable Pin Operation VDD Pin Operation SYMBOL PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 2.7 3.7 5.5 V 150 500 µA 2 µA VDD Input Supply Range IDD Quiescent Current in VDD PIN VEN ³ 1.2 V ISTB Standby Current VEN £ 0.3 V VEN(on) Enable Full On Voltage Output on 1.2 VDD +0.3 V VEN(off) Enable Off Voltage Output off -0.3 0.3 V IEN Enable Pin Current ILIM Boost FET Current Limit Setting µA -5 IND Pin Operation 400 TA = -30 to +85°C (Note 4) RDS(ON) Boost FET On Resistance VOUT Pin Operation OVP Ω 1.5 No Load FB Pin Operation mA 13.5 14.5 15.5 V Over Voltage Protection TA = -30 to +85°C (Note 4) RSYNCH Synchronous Rectifier on Resistance VFB Feedback Reference Voltage Ω 3.0 0.46 0.5 0.53 V 14 15 16 mA -1.5 ILED(SET) +1.5 % 0.161 mA/V TA = -30 to +85°C (Note4) ILED(SET) Average Current flowing through LED VEN ³ 1.2 V, (Sense resistor = 33.2Ω, 1%) ILED(VAR) Variation of Average Current through LED VEN ≥ 1.2V 2.7V < VIN < 5.5 V ILED(LINE) ILED LINE Regulation Page 2 VEN ≥ 1.2V 2.7V < VIN < 5.5 V ILED = 15 mA (Note 1) July 2, 2003 TOKO, Inc. TK65600B ADVANCED INFORMATION TK65600B ELECTRICAL CHARACTERISTICS VDD = 3.7 V, TA = Tj = 25 °C, unless otherwise specified. SYMBOL Boost Converter Operation FBOOST PARAMETER TEST CONDITIONS Boost Frequency MIN TYP MAX UNITS 575 700 825 kHz 85 95 % TA = -30 to +85°C (Note 4) DC(MAX) Boost Maximum Duty Cycle TA = -30 to +85°C (Note 4) ∆VOUT Output Voltage Ripple (Note 1) POUT MAX Maximum Power Output VIN = 3V 50 mV 300 mW TA = -30 to +85°C (Note4) EFF TSTART ILED =15mA (Note 1,2) L=27 µH D31FB 78 % ILED =15mA (Note 1,2) L=22 µH D3313FB 72 % 300 µs Boost Conver ter Efficiency Star t-Up Settling Time (Note 1) Note 1: When using test circuit below. Note 2: Converter efficiency is partly dependent upon the DC resistance of inductor L1. Higher DC resistances will result in lower converter efficiency. Note 3: The Absolute Maximum Power Dissipation depends upon the Ambient Temperature and can be calculated using the formula PDMAX =(TJMAX -TA) /θJA Note 4: Verified by design. TYPICAL APPLICATION AND TEST CIRCUIT ENABLE A2 VBATTERY AGND A1 A3 N/C V B1 DD B3 FB 1 µF TK65600B Top View 33 Ω V C1 OUT C3 PGND C2 IND L=D3313FB-22µH Coil 1 µF 22 µH July 2, 2003 TOKO, Inc. Page 3 TK65600B 502.5 502.5 502.0 502.0 501.5 501.5 Feedback Voltage (mV) Feedback Voltage (mV) Feedback Voltage vs. Supply Voltage 501.0 500.5 500.0 499.5 499.0 498.5 Feedback Voltage vs. Temperature 501.0 500.5 500.0 499.5 499.0 498.5 498.0 498.0 497.5 497.5 2.7 3.3 3.9 4.5 Supply Voltage (V) -50 -25 0 25 50 75 100 125 Temperature (°C) 5.1 Frequency vs. Supply Voltage Frequency vs. Temperature 700 700 680 660 Frequency (kHz) Frequency (kHz) 680 660 640 620 640 620 600 580 560 540 600 520 500 580 2.7 90.0 3.3 3.9 4.5 Supply Voltage (V) 5.1 Efficiency (22µH D3313FB Coil) vs. Supply Voltage 85.0 80.0 78.0 Efficiency @40 mA Efficiency @15 mA 65.0 Efficiency (%) Efficiency (%) 75.0 60.0 Efficiency @ 40 mA 74.0 72.0 70.0 Efficiency @ 15 mA 68.0 66.0 64.0 55.0 62.0 50.0 60.0 2.7 Page 4 Efficiency (22µH D3313FB coil) vs. Temperature 76.0 80.0 70.0 -50 -25 0 25 50 75 100 125 Temperature (°C) 3.3 3.9 4.5 Supply Voltage (V) 5.1 -50 -25 0 25 50 75 100 125 Temperature (°C) July 2, 2003 TOKO, Inc. TK65600B Quiescent Current vs. Supply Voltage 450 170.0 165.0 Quiescent Current (uA) Quiescent Current (mA) 400 350 300 250 200 150 100 50 160.0 155.0 150.0 145.0 140.0 135.0 130.0 0 2.7 3.3 3.9 4.5 Supply Voltage (V) -50 -25 0 25 50 75 100 125 Temperature (°C) 5.1 Standby Current vs. Supply Voltage 1.5 Standby Current vs. Temperature 4.0 3.5 Standby Current (uA) 1.4 Standby Current (µA) Quiescent Current vs. Temperature 1.3 1.2 1.1 1.0 0.9 0.8 3.0 2.5 2.0 1.5 1.0 0.5 0.7 0.0 0.6 2.7 3.3 3.9 4.5 Supply Voltage (V) 5.1 OVP Threshold vs. Supply Voltage OVP Threshold vs. Temperature Overvoltage Protection Threshold (V) Over Voltage Protection (V) 15.5 15.3 15.1 14.9 14.7 14.5 14.3 14.1 13.9 13.7 13.5 2.7 3.3 3.9 4.5 Supply Voltage (V) July 2, 2003 TOKO, Inc. 5.1 -50 -25 0 25 50 75 100 125 Temperature (°C) 15.5 15.3 15.1 14.9 14.7 14.5 14.3 14.1 13.9 13.7 13.5 -50 -25 0 25 50 75 100 125 Temperature (°C) Page 5 Output Power (mW) TK65600B Page 6 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 2.7 Maximum Output Power vs. Supply Voltage 3.0 3.3 3.6 3.9 Supply Voltage (V) 4.2 July 2, 2003 TOKO, Inc. TK65600B Supply Voltage Characteristics Channel 1 is Supply Voltage Channel 2 is the Feedback Voltage coming up to regulation. Channel 1 Supply Voltage turns off Channel 2 Feedback Voltage follows. Enable Characteristics Channel 1 is the Enable waveform Channel 1 is the Enable waveform to create a change in Channel 2 Output Voltage reacting to Enable signal intensity Channel 2 shows the Feedback Voltage reacting to the Enable signal. July 2, 2003 TOKO, Inc. Page 7 TK65600B Theory of Operation The TK65600 is an inductive white LED driver circuit. The input voltage is 2.7V up to 6V. The load is represented by white LED’s - one or more parallel strings of LED’s, each string consisting of two or more LED’s connected in series. The absolute maximum voltage allowed at the output pin is 16V, dictated by wafer process limits. The forward drop voltage of the LED’s dictates how many LED’s can be in a string, as the voltage at the output pin is the voltage across the LED’s in series in a string, plus the voltage drop across the feedback resistor. The feedback resistor appears in series with the load, connected between the bottom terminal of the LED string(s) and ground. The minimum input voltage of 2.7V and the maximum output voltage of about 15V requires this circuit to be a boost circuit - TK65600 is an inductive boost circuit. The circuit regulates the current in the load, as the light intensity of the LED’s depends on the current flowing through them. The LED current information is provided by a feedback resistor, connected between the load and ground. A classical current -mode control loop, using pulse width modulation (PWM) at a fixed frequency, regulates the boost circuit output, such as to maintain the current in the LED’s constant. As with any classical current -mode control loop PWM, the boost converter has the feature of pulse by pulse current limiting. On the TK65600 that current loop limit is set to about 400mA. Therefore, the inductor, which is to be used with the TK65600, should have an Isat above 400mA. There are a few additional functions the circuit incorporates: · Disable - allows the circuit to be turned on and off by an external enable signal (off for Venable<0.3V, on for Venable>1.2V) · Over-Voltage Protection (OVP) - shuts off the power FET’s if the output voltage rises above a predetermined threshold (14V). This is intended to prevent damage to the circuit for an open load condition, for instance, by not allowing the output voltage to rise above the preset limit. · Short-Circuit Protection (SCP) - if the output sees an unusually high load or a short-circuit, there is circuitry provided that will cut off the current path to the output, wait a predetermined amount of time, then attempt to restart. If the output short-circuit or heavy loading condition at the output disappeared, the circuit will start and function normally. If the short-circuit condition persists, the circuit will wait again the predetermined amount of time, then it will attempt to restart again. The high load or short-circuit condition is identified, for the purpose of this feature, by a low output voltage (less than 1.2V). In order to provide for start-up condition (when the output voltage is inherently low), the SCP circuitry waits for a little while, before asserting the short circuit condition signal. That little while is set now at sixteen (16) clock cycles, while the reset time, that is, the time before the circuit attempts to restart, it is set now at (512) clock cycles. With a clock of 600kHz, these times are approximately 27us for asserting the short circuit condition signal and about 853us between attempts to restart the boost circuit. Page 8 July 2, 2003 TOKO, Inc. TK65600B Theory of Operation Cont. A classic boost configuration is not able to provide short circuit protection, as the input voltage source can provide current to the load, through the inductor and diode, even if the circuit is disabled. A synchronous rectifier is required, in order to be able to provide short circuit protection. The synchronous rectifier (Msr) is replacing the diode found in classic boost circuits. The main advantage is eliminating the need for an external component. The second important advantage is the potential for less voltage drop across this device. A serious drawback is the fact that a FET is a non-directional device, unlike the diode it replaces, so, while the diode operated by itself, careful control of the synchronous rectifier operation is required. The synchronous rectifier must be off , at all times when the inductor switch is on - otherwise, shoot-through current from the boost capacitor, through the synchronous rectifier and through the inductor switch, to the ground, can occur - this cannot be allowed to happen, because of its effect on efficiency. A second issue to consider when driving the synchronous rectifier is the fact that, the FET being a non-directional device, the drive circuitry must ensure that the synchronous rectifier is on only when the boost voltage (output) is smaller than the voltage at the inductor node - otherwise, the boost (output) capacitor will discharge through the synchronous rectifier FET and inductor, to the input voltage source (Vdd). When the inductor switch is off and the synchronous rectifier it is held off because the inductor voltage is smaller than the boost voltage, both power FET’s (Mind and Msr) are off. When this happens, the remaining energy in the inductor may be enough to start ringing, using the inductor and whatever parasitic capacitance can find (both Mind and Msr are large devices, with large parasitic capacitance). The resulting oscillations can be large enough to trigger the hysteresis comparator in the internal synchronous rectifier driver circuitry. Also, this ringing oscillation may cause noise in other parts of the application’s system. To avoid these effects, a snubber circuit is used, to short the inductor node not to ground (that would be a loss of energy), but back to Vdd (charging back the source). The snubber circuit must carefully select the moment when Mind and Msr are off, following the current ramp-up in the inductor, and NOT preceding it. The state machine inside the snubber does that. There is another moment when both Mind and Msr are off at the same time - when the inductor switch is cut off, after ramping the current in the inductor, but the synchronous rectifier, Msr, is not yet on (due to delays in circuitry, etc.). At this point in time, the inductor node voltage is highest and no snubber effect is acceptable. July 2, 2003 TOKO, Inc. Page 9 TK65600B PIN DESCRIPTION Pin No. Symbol Description A1 AGND Analog Ground pin. This pin provides return current path to low power circuits supplied current through the VDD pin. In the circuit board connect to PGND pin at ground plane. A2 ENABLE Enable input pin. This pin turns on the IC to start switching action. Set the Enable Pin higher that 1.2V to enable the IC. Set the Enable pin below 0.3V to disable the IC. Do not leave this pin floating. A3 N/C No Connection B1 VDD Power Supply pin. This pin supplies power to low voltage (<6V) control circuits in the IC. B3 FB Feedback Voltage Regulation Input pin. A low voltage input that is regulated to 500mV C1 VOUT Output Voltage pin. This pin supplies the voltage to drive the White LEDs. It is a high voltage pin (<16.5V) which is protected by an over voltage protect circut, which stops the IC switching if this pin reaches about 14.5V C2 IND Inductor Connection pin. This pin is also a high voltage pin and is connected to the internal boost N-channel MOSFET C3 PGND Power Ground pin. This pin provides return current path to high currents flowing to ground through the IND and VOUT pins. In the circuit board connect to AGND pin through ground plane. Page 10 July 2, 2003 TOKO, Inc. TK65600B APPLICATION NOTES As wtih all switching power converters, care should be given to the circuit board layout. The bolded lines, on the schematic below, show where the high current paths of switched currents are in the circuit. The circuit board traces for these paths should be short and wide to minimize the power losses and electromagnetic interference generated from the switching currents. Therefore CIN, L and COUT should be located close to the IC in the circuit board layout. Also, the circuit board layout should keep the sense resistor close to the IC such that there is no voltage differences in the ground references. The (AGND) Analog Ground and the Power Ground (PGND) should short as close to the device as possible. L=D3313FB-22µH Coil VBATTERY 22 µH 1 µF VDD B1 IND C2 ENABLE C1 A2 ENABLE VOUT GATE DRIVE 1 µF ON/OFF ILED OSC PWM SCP/OVP B3 FB VREF 33 Ω C3 A1 AGND July 2, 2003 TOKO, Inc. PGND Page 11 TK65600B ADVANCED INFORMATION PACKAGE OUTLINE (FLIP CHIP) X 0.60 ± 0.02 Marking Information Pin Mark A2 CL Marking 0.220 ± 0.015 0.5 Bump (Note 1) A3 Y 0.5 A1 B3 B1 CL C3 C1 C2 Silicon 8 Bumps 0.300mm ± 0.010 Diameter Bumps .5mm Pitch Between Bumps x = 1.500mm y = 1.500mm Bottom View Note 1: Sn/Pb Eutectic Solder Bump Toko America, Inc. Headquarters 1250 Feehanville Drive, Mount Prospect, Illinois 60056 Tel: (847) 297-0070 Fax: (847) 699-7864 TOKO AMERICA REGIONAL OFFICES Midwest Regional Office Toko America, Inc. 1250 Feehanville Drive Mount Prospect, IL 60056 Tel: (847) 297-0070 Fax: (847) 699-7864 Semiconductor Technical Support Toko Design Center 4755 Forge Road Colorado Springs, CO 80907 Tel: (719) 528-2200 Fax: (719) 528-2375 Visit our Internet site at http://www.toko.com The information furnished by TOKO, Inc. is believed to be accurate and reliable. However, TOKO reserves the right to make changes or improvements in the design, specification or manufacture of its products without further notice. TOKO does not assume any liability arising from the application or use of any product or circuit described herein, nor for any infringements of patents or other rights of third parties which may result from the use of its products. No license is granted by implication or otherwise under any patent or patent rights of TOKO, Inc. TOKO’s products are not authorized for use as critical components in life support devices or systems without the express written approval of the president of Toko, Incorporated. Page 12 © 1999 Toko, Inc. All Rights Reserved July 2, 2003 TOKO, Inc. IC-xxx-TK65600 0798O0.0K Printed in the USA