LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 LM3551 /LM3552 1A White LED Driver with Flash Timeout Protection Check for Samples: LM3551, LM3552 FEATURES DESCRIPTION * * * * * * * * * The LM3551 and LM3552 are fixed frequency, current mode step-up DC/DC converters with two integrated NFETs that can be used for precision LED brightness control. The devices are capable of driving loads up to 1A from a single-cell Li-Ion battery. 1 2 Up to 1A Total Drive Current Flash Timeout Protection Independent Torch/Flash/Shutdown Modes LED Disconnect in Shutdown Programmable Soft-Start Limits Inrush Current Over-Voltage Protection Wide Voltage Range 2.7 to 5.5V 1.25MHz Constant Switching Frequency Small, Low Profile Package, Non-Pullback WSON(4mm x 4mm) The LM3551 and LM3552 can drive one or more high current flash LEDs either in a high power Flash mode or a lower power Torch mode using the TORCH/FLASH pin. A programmable Timeout function on the FTO pin forces the internal NFETs to turn off after a certain user defined time. An external SD pin (LM3551) or EN pin (LM3552) is available to put the device into low power shutdown mode. During shutdown, the feedback resistors and the load are disconnected from the input to avoid leakage current paths to ground. APPLICATIONS * * * * * * White LED Camera Flash White LED Torch (Flashlight) DSC (Digital Still Camera) Flash Cellular Camera Phone Flash PDA Camera Flash Camcorder Torch (Flashlight) Lamp User programmable soft-start circuitry has been integrated to eliminate large inrush currents at startup. Over-voltage protection circuitry and a 1.25MHz switching frequency allow for the use of small, lowcost output capacitors with lower voltage ratings. The LM3551 and LM3552 are available in a low profile 14pin WSON package. Typical Application Circuits Sharp GM5BW05340A Flash LED D1 L1 VBAT + - RC CC SW VIN CIN FB VC FTO L1 SD/ T/F EN D1 SW SS CSS LUMILED LXCL-PWF1 Flash LED OVP + - FB CIN COUT RC CC RF FET-T FET-F CFTO VIN COUT RT LM3551/2 GND VBAT OVP VC FTO RT LM3551/2 RF FET-T FET-F CFTO SD/ EN T/F SS CSS 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 2005-2013, Texas Instruments Incorporated LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com Connection Diagram 14-Pin WSON Package 1 14 14 2 13 13 12 12 4 Die-Attach Pad(DAP) 11 5 GND 3 1 2 3 11 Die-Attach Pad(DAP) 10 10 GND 5 6 9 9 6 7 8 8 7 Top View 4 Bottom View Figure 1. Package Number NHL0014B PIN DESCRIPTIONS Pin Name 9 VIN Input Voltage. Input range: 2.7V to 5.5V. Function 13 T/F TORCH/FLASH Pin. Low = Torch Mode, High = Flash Mode 8 SW Switch Pin 10 OVP Over Voltage Protection Pin 3 VC 5 SD(LM3551) EN(LM3552) 12 FTO 11 SS Soft Start Pin 4 FB Feedback Pin 14 FET-T Torch FET Drain Flash FET Drain 2 FET-F 1,7,DAP GND 6 AGND Compensation network connection. Connected to the output of the voltage error amplifier. Shutdown pin logic input. High = Shutdown, Low = Enabled Enable pin logic input. High = Enabled, Low = Shutdown Flash Timeout. External capacitor determines max. duration allowed flash pulse Ground Analog Ground. Connect the ground of the compensation components, CFTO and soft start cap to AGND. AGND must be connected to the GND pin through a low impedance connection. These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. 2 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 Absolute Maximum Ratings (1) (2) (3) VIN pin: Voltage to GND 7.5V SW pin: Voltage to GND 21V FB pin: Voltage to GND 7V VC pin: Voltage to GND 1.26V 0.3V SD,T/F pins: Voltage to GND 7.5V FET-T, FET-F: Voltage to GND 6V Continuous Power Dissipation (4) Internally Limited Junction Temperature (TJ-MAX ) 150C Storage Temperature Range ESD Rating (5) (1) (2) (3) (4) (5) -65C to +150 Human Body Model 2.0kV Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is specified. Operating Ratings do not imply performance limits. For performance limits and associated test conditions, see the Electrical Characteristics tables. All voltages are with respect to the potential at the GND pin. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=140C (typ.) and disengages at TJ=120C (typ.). The human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin. (MIL-STD-883 3015.7) Operating Ratings (1) (2) Input Voltage Range SW Voltage Max. 2.7V to 5.5V (3) 20V Junction Temperature (TJ) Range -40C to +110C Ambient Temperature (TA) Range (4) (1) (2) (3) (4) -40C to +85C Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is specified. Operating Ratings do not imply performance limits. For performance limits and associated test conditions, see the Electrical Characteristics tables. All voltages are with respect to the potential at the GND pin. Maximum recommended SW pin voltage when the OVP pin is grounded. In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 110C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the part/package in the application (JA), as given by the following equation: TA-MAX = TJ-MAX-OP - (JA x PD-MAX). Thermal Properties Junction-to-Ambient Thermal Resistance (JA), NHL0014B Package (1) (1) 37.3C/W Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 3 LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com Electrical Characteristics (1) (2) Limits in standard typeface are for TJ = +25 C. Limits in boldface type apply over the full operating junction temperature range (-40C TJ +110C). Unless otherwise noted, specifications apply to the LM3551 and LM3552 Typical Application Circuit (pg. 1) with: VIN = 3.6V, V(SD) = 0V for LM3551 and V(EN) = VIN for LM3552, ILOAD = 0A (3) Symbol IQ Parameter Quiescent Current ISD Shutdown Current ICL (4) Switch Current Limit VFB Feedback Voltage IFB (6) Typ Max Units FB = VIN (Not Switching) Conditions Min 1.47 2.0 mA V(SD) = VIN, LM3551 2.55 5.0 V(EN) = 0V, LM3552 0.1 2.3 VIN = 3.0V (5) 2.1 1.2285 Feedback Pin Bias Current 1.265 A A 1.2915 V 50 nA 135 mho Error Amp Voltage Gain 135 V/V Maximum Duty Cycle 92.5 % gm Error Amp Transconductance AV DMAX fsw Switching Frequency ISDPIN Shutdown Pin Current (LM3551) IENPIN Enable Pin Current (LM3552) IT/FPIN T/F Pin Current IL-SW SW Pin Leakage Current RDSON-SW SW Pin RDSON IL-T I = 5A 0.9 1.25 1.6 MHz VSD = 0V 3.0 6 A VEN = 3.6V 3.0 6 A VT/F = 0V 26 VT/F = VIN 22 nA VL-SW = 20V 0.07 ISW = 0.5A 0.165 FET-T Leakage Current 0.1 A RDSON-T FET-T RDSON 0.98 IL-F FET-F Leakage Current 0.1 A RDSON-F FET-F RDSON 0.36 ThSD/EN Shutdown/Enable Pin Threshold ThT/F T/F Pin Threshold UVP Under Voltage Protection Thresholds On Threshold 2.25 2.48 2.70 Off Threshold 2.43 2.58 2.77 OVP Over Voltage Protection Thresholds On Threshold 11.3 12.4 14 Off Threshold 9.2 10.6 12 VFTO Flash Timeout trip-point 0.99 1.16 1.32 V IFTO Flash Timeout Current 1.12 1.4 1.68 A VSS Soft-Start Voltage 1.18 1.25 1.32 V ISS Soft-Start Current 10 11.5 13 A (1) (2) (3) (4) (5) (6) 4 Output High 1.2 Output Low Output High 8 0.3 1.2 Output Low 0.3 A V V V V All voltages are with respect to the potential at the GND pin. Min and Max limits are specified by design, test, or statistical analysis. Typical (Typ) numbers represent the most likely norm. Unless otherwise specified, conditions for Typ specifications are: VIN = 3.6V and TA = 25C. CIN and COUT,: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics Duty cycle affects current limit due to ramp generator. Current limit at 0% duty cycle. See TYPICAL PERFORMANCE section for Switch Current Limit vs. VIN Bias current flows into FB pin. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 Typical Performance Characteristics Unless otherwise specified: TA = +25C; VIN = 3.6V; L = 4.7H, (RC = 10k, CC = 4.7nF, CIN = COUT = 10F for Lumiled LED), (RC = 27k, CC = 10nF, CIN = 10F, COUT = 4.7F for Sharp LED), CFTO = 1F, CSS= 0.1F. ICL measure when VOUT = 95% x VOUT (nominal) Current Limit vs. Input Voltage VOUT = 5V Current Limit vs. Input Voltage VOUT = 10V Figure 2. Figure 3. ICL measure when VOUT = 95% x VOUT (nominal) Converter Efficiency vs. Input Voltage Lumiled Flash LED Converter Efficiency vs. Input Voltage Sharp Flash LED Figure 4. Figure 5. IOUT measured at 95%x VOUT (nominal) Maximum IOUT vs. Input Voltage VOUT = 5V Maximum IOUT vs. Input Voltage VOUT = 10V Figure 6. Figure 7. IOUT measured at 95%x VOUT (nominal) Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 5 LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified: TA = +25C; VIN = 3.6V; L = 4.7H, (RC = 10k, CC = 4.7nF, CIN = COUT = 10F for Lumiled LED), (RC = 27k, CC = 10nF, CIN = 10F, COUT = 4.7F for Sharp LED), CFTO = 1F, CSS= 0.1F. 6 LED Torch Current vs. Input Voltage Lumiled Flash LED LED Flash Current vs. Input Voltage Lumiled Flash LED Figure 8. Figure 9. OVP Trip Voltage vs. Input Voltage Switching Frequency vs. Input Voltage Figure 10. Figure 11. Start-Up Waveform Sharp LED Start-Up Waveform Lumiled LED Figure 12. Ch1 = VSD, Ch3 = ILED, Ch4 = IIN Figure 13. Ch1 = VSD, Ch3 = ILED, Ch4 = IIN Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 Typical Performance Characteristics (continued) Unless otherwise specified: TA = +25C; VIN = 3.6V; L = 4.7H, (RC = 10k, CC = 4.7nF, CIN = COUT = 10F for Lumiled LED), (RC = 27k, CC = 10nF, CIN = 10F, COUT = 4.7F for Sharp LED), CFTO = 1F, CSS= 0.1F. Typical Switching Waveform Figure 14. Sharp LED in Flash Mode Ch1 = VSW, Ch3 = ILED, Ch4 = IL Block Diagram SS Load Current Measurement LM3551/2 PWM COMP FET-T Oscillator | + - ERROR AMP + - FB + SD / EN SW Duty Cycle Limit Set Reset Reset Drive LOGIC UVP OVP Thermal SD + - BG OVP COMP Bandgap Voltage Reference Thermal Shutdown FET-F Shutdown Comparator OVP VIN LM3551 Flash Timeout T/F LM3552 GND VC FTO AGND SD/EN OVP VIN GND Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 7 LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com Circuit Description OVERVIEW The LM3551/2 are high power white LED flash drivers capable of delivering up to 1A of output current. The devices utilize a highly efficient inductive DC/DC boost converter to achieve the required output voltage. A current-mode PWM control scheme regulates the output current over a wide input voltage range. Both the LM3551 and the LM3552 have two low-side load disconnect FET's allowing for a continuous low-power Torchmode and a high-power, short duration Flash-mode. Several application specific safety features are integrated into the LM3551/2 design. A flash timeout circuit is present on-chip to prevent a failure in the flash LED caused by a timing violation. Over-Voltage Protection protects the output capacitor, inductor and main power switch in the event of an open circuit condition. Other safety features include inductor current limit, thermal shutdown, and an undervoltage lockout. CIRCUIT COMPONENTS Inductive DC/DC Boost Converter In order to achieve the output voltages required to power high power white LEDs, the LM3551 and LM3552 utilize a highly efficient inductive DC/DC converter. The boost converter utilizes a current-mode controlled, constant frequency (1.25MHz.), PWM architecture. This architecture creates a predictable noise spectrum that allows for easy filtering and low noise. A very low on-resistance power NFET(RDSON = 0.165) and high value current limit (2.2A typ.) help efficiently provide a high power output (700mA@5V) over the entire lithium-ion voltage range. The feedback voltage for both the LM3551 and LM3552 is tightly regulated to 1.265V. SD/EN Pin The LM3551 and LM3552 provide two different options in regards to turn-on control logic. The LM3551 utilizes a shutdown pin (SD) that turns on the part when a voltage less than 0.3V is applied. An internal 1.2M pull-up to VIN is provided to place the LM3551 into shutdown when no control signal is provided. The LM3552 utilizes a enable pin (EN) that turns on the part when a voltage greater than 1.2V is applied. An internal 1.2M pull-down to GND is provided to place the LM3552 into shutdown when no control signal is provided. Low-side Load Disconnect FETs The LM3551 and LM3552 have two low-side load disconnect NFETs (FET-T and FET-F) that provide the physical mechanism of Torch Mode and Flash Mode. In Torch Mode, FET-T is enabled allowing current to flow through it. FET-T has an on-resistance of 0.98 and is capable of handling currents up to 200mA. In Flash Mode, both FET-T and FET-F are enabled. FET-F has an on-resistance of 0.36 and is capable of handling currents up to 500mA. The total Flash current is equal to the sum total of the current flowing through FET-T and FET-F. See the CURRENT SET EQUATIONS in the Application Informations section for more information regarding setting LED current . In shutdown mode, the LM3551/2 provide a true load disconnect helping to keep the total shutdown current to a minimum. Over-Voltage Protection (OVP) The over voltage protection (OVP) is engaged when a failure mode occurs (FB pin grounded, Flash LED becomes open or disconnected, etc.). In the event of a failure, OVP prevents the output voltage from exceeding 12.4V (typ). When the OVP level is reached, the switch FET shuts off preventing the output voltage from climbing higher. Once the FET has shut off, the output will droop at a rate determined by the value of the output capacitor and current leakage through the OVP pin and any other leakage path. When the output voltage drops to 10.6V(typ), switching will resume. The LM3551 and LM3552 will go back into OVP if the failure is still present resulting in a pulsed output condition. NOTE To disable OVP, ground to OVP pin. CAUTION: The LM3551 and LM3552 may be damaged if an OVP condition occurs and OVP is disabled. 8 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 Under-Voltage Protection (UVP) Both the LM3551 and LM3552 have under-voltage protection circuitry (UVP). This protects the NMOS power device during startup and shutdown by preventing operation at voltages less than the minimum input voltage. The UVP protection is enabled at 2.48V(typ.) and will not disable until the input voltage rises above 2.58V(typ.) . Torch/Flash Pin (T/F) The TORCH/FLASH pin (T/F) controls whether the LM3551/2 is in continuous torch mode, or in flash mode. A logic '0' places the part into torch mode and a logic '1' places the part into flash mode. There are no pull-ups or pull-downs internally connected to T/F. When placed into torch mode, FET-T is enabled allowing the current set by RT to flow. In torch mode, FET-F is not enabled. Flash mode enables both FET-T and FET-F allowing the sum total of the current set by the two external resistors, RT and RF, to flow. Flash Timeout Protection (FTP) When SD is low(LM3551) or EN is high(LM3552), and T/F is high, a current is output to an external capacitor, CFTO. This causes the voltage on the capacitor to rise. If the voltage reaches Vtrip (1.16V(typ)), the timeout circuit forces the INTERNAL_EN signal to go low, which in turn shuts-off the low-side torch and flash FETs in addition to disabling the main power SW FET. At such time, the LED will be turned off. The part will remain disabled until SD is pulled high (LM3551) or EN is pulled low (LM3552) and/or T/F is pulled low. At that point, the part will return to normal operating mode. The diagram below shows a first pulse which exceeds the timeout period and internal_EN being driven low. The second FLASH pulse is shorter than the timeout period and therefore the voltage on CFTO never reaches Vtrip. For information on component selection, please see the FLASH TIMEOUT EQUATIONS below. TFTO = CFTO x (VFTO / IFTO) VFTO = 1.16V and IFTO= 1.4A TFTO = Desired Timeout Duration CFTO(F) = TFTO(sec.) x 1.21(A/V) (1) (2) (3) To disable the timeout function, ground the FTO pin. EXTERNAL/INTERNAL ITO INTERNAL EN CFTO FTO SD / EN SD / EN EN SD T/F VTRIP T/F VCFTO INTERNAL EN Figure 15. Flash Timeout Protection Diagram Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 9 LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com Soft-Start The LM3551 and LM3552 have a soft-start pin that can be used to limit the inductor inrush current on start-up. The external SS pin is used to tailor the soft-start for a specific application but is not required for all applications and can be left open when not needed. When used, a current source charges the external soft-start capacitor, CSS, forcing the internal reference to ramp-up at a user determined rate. Table 1. Typical Start-Up TimesVIN = 3.6V, TA = +25C CSS (F) 0.1 0.47 1.0 10 Load (mA) Start-Up Time (msec.) Sharp LED @ 75mA Torch 3 Sharp LED @ 250mA Flash 8 Lumiled LED @ 200mA Torch 1.6 Lumiled LED @ 700mA Flash 6 Sharp LED @ 75mA Torch 12 Sharp LED @ 250mA Flash 35 Lumiled LED @ 200mA Torch 6 Lumiled LED @ 700mA Flash 35 Sharp LED @ 75mA Torch 25 Sharp LED @ 250mA Flash 75 Lumiled LED @ 200mA Torch 30 Lumiled LED @ 700mA Flash 70 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 APPLICATION INFORMATION LM3551 AND LM3552 FUNCTIONALITY TRUTH TABLE SD (LM3551) or EN (LM3552) T/F LM3551 Result LM3552 Result 1 0 Shut-down Torch Mode 1 1 Shut-down Flash Mode 0 0 Torch Mode Shut-down 0 1 Flash Mode Shut-down The LM3551 has a 1.2M pull-up to VIN on SD and the LM3552 has a 1.2M pull-down to GND on EN. CURRENT SET EQUATIONS The LM3551/2 utilize inline resistors to set the Torch and Flash LED currents. The Torch-Mode current (continuous) and the Flash-Mode current (pulsed) are programmed by placing the appropriately selected resistors between the feedback pin (FB) and FET-T (torch FET) and FET-F (flash FET) pins. Torch-mode is set by utilizes the current through one resistor while Flash-mode is set by utilizes the currents though both current set resistors. The following equations are used to set the LED currents. RTORCH = (1.265V / ITORCH) - RDSON-T RFLASH = (1.265V / (IFLASH- ITORCH)) - RDSON-F RDSON-T= 0.98 and RDSON-F = 0.36 (4) (5) (6) NOTE Flash LEDs from different manufacturers can have very different continuous and pulse current ratings. See the manufacturers datasheets to ensure that the proper current levels are used to avoid damaging the flash LED. INDUCTOR SELECTION Special care must be taken when selecting an inductor for use in LM3551/2 applications. The inductor should have a current saturation rating that is larger than the worst case peak inductor current of the application to ensure proper operation. Using an inductor with a lower saturation current rating than is required can cause a dramatic drop in the inductance and can derate the maximum output current levels severely. It is worth noting that the output voltage ripple is also affected by the total ripple current in the inductor. The following equations can help give a good approximation as to what the peak inductor current will be for a given application at room temperature (TA = +25C). IL(average) = [ILED x VOUT-MAX] / [VIN-MIN x Eff.] IL = [VIN x D] / [L x FSW] IL(peak) = IL(ave) + [IL / 2] (7) (8) (9) VOUT-MAX Maximum Output Voltage. Maximum output voltage over temperature with OVP used is 11V (12.4V typically). VIN-MIN Minimum Input Voltage. Recommended minimum input voltage is 3.0V. The LM3551/2 will work down to 2.7V however, use at lower input voltages will required an inductor with a higher saturation current rating. Eff. Converter Efficiency (approx. 85% over input voltage range). D Duty Cycle = 1 - [VIN / VOUT] L Inductance. Recommended inductance value is 4.7H. FSW Switching Frequency = 1.25MHz Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 11 LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com DIODE SELECTION The output diode for a boost regulator must be chosen correctly depending on the output voltage and output current. The output diode must have a reverse voltage rating equal to or greater than the output voltage used. The average current rating must be greater than the maximum load current expected, and the peak current rating must be greater than the peak inductor current. Using Schottky diodes with lower forward voltage drop will decrease power dissipation and increase efficiency. CAPACITOR SELECTION Input Capacitor An input capacitor is required to reduce the input ripple and noise for proper operation of the regulator. The size used is dependant on the application and board layout. If the regulator will be loaded uniformly, with very little load changes, and at lower current outputs, the input capacitor size can often be reduced. The size can also be reduced if the input of the regulator is very close to the source output. The size will generally need to be larger for applications where the regulator is supplying nearly the maximum rated output or if large load steps are expected. A minimum value of 10F should be used under normal operating condtions while a 10-22F capacitor may be required for higher power and dynamic loads. Larger values and/or lower ESR may be needed if the application requires very low ripple on the input source voltage. Output Capacitor A minimum output capacitor value of 4.7F (Sharp LED) and 10F (Lumiled) is recommended and may be increased to a larger value. The ESR of the output capacitor is important because it determines the peak to peak output voltage ripple according to the approximate equation: VOUT 2 x ILx RESR (in Volts) (10) After choosing the output capacitor you can determine a pole-zero pair introduced into the control loop by the following equations: fP1 = 1 2S>RESR + (VOUT/ILED)]COUT fZ1 = Hz 1 Hz 2SRESRCOUT (11) The zero created by the ESR of the output capacitor is generally at a very high frequency if the ESR is small. If low ESR capacitors are used it can be neglected. The output capacitor pole information is useful in selecting the proper compensation components and is discussed in the Compensation Components section of the datasheet. Capacitor Properties Surface-mount multi-layer ceramic capacitors are recommended for both the input and output capacitors. These capacitors are small, inexpensive and have very low equivalent series resistance (ESR <20m typ.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are not recommended for use with the LM3551/2 due to their high ESR, as compared to ceramic capacitors. For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with the LM3551/2. These capacitors have tight capacitance tolerance (as good as 10%) and hold their value over temperature (X7R: 15% over -55C to 125C; X5R: 15% over -55C to 85C). Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with the LM3551/2. Capacitors with these temperature characteristics typically have wide capacitance tolerance (+80%, 20%) and vary significantly over temperature (Y5V: +22%, -82% over -30C to +85C range; Z5U: +22%, -56% over +10C to +85C range). Under some conditions, a nominal 1F Y5V or Z5U capacitor could have a capacitance of only 0.1F. Such deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum capacitance requirements of the LM3551/2. The minimum voltage rating acceptable for the input capacitor is 6.3V (10V recommended) and 16V for the output capacitor. In applications that have DC operating points near the maximum voltage rating of the ceramic capacitor, larger capacitor values may be required to compensate for capacitance loss due to capacitor voltage coefficient. See the capacitor manufacturer's datasheet for DC bias performance. 12 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 COMPENSATION DC Gain and Open-Loop Gain Since the control stage of the converter forms a complete feedback loop with the power components, it forms a closed-loop system that must be stabilized to avoid positive feedback and instability. A value for open-loop DC gain will be required, from which you can calculate, or place, poles and zeros to determine the crossover frequency and the phase margin. A high phase margin (greater than 45) is desired for the best stability and transient response. For the purpose of stabilizing the LM3551/2, choosing a crossover point well below where the right half plane zero is located will ensure sufficient phase margin. To ensure a bandwidth of 1/2 or less of the frequency of the RHP zero, calculate the open-loop DC gain, ADC. After this value is known, you can calculate the crossover visually by placing a -20dB/decade slope at each pole, and a +20dB/decade slope for each zero. The point at which the gain plot crosses unity gain, or 0dB, is the crossover frequency. If the crossover frequency is less than 1/2 the RHP zero, the phase margin should be high enough for stability. The equation for ADC is given below with additional equations required for the calculation: ADC(DB) = 20log10 2fs Zc # nD' Leff = (R RFB2 FB1 + RFB2 gmROD' )R {[(ZcLeff)// RL]//RL} (in dB) DSON (12) (in rad/s) (13) L (D')2 (14) 2mc (no unit) n = 1+ m1 (15) (16) mc 0.072 x fs (in V/s) m1 # VINRDSON L (in V/s) (17) where RL is the minimum load resistance, fs is the switching frequency, VIN is the minimum input voltage, gm is the error amplifier transconductance and RDSON-S is the power switch on-resistance. The value for gm and RDSON-S are found in the Electrical Characteristics table. Right Half Plane Zero A current mode control boost regulator has an inherent right half plane zero (RHP zero). This zero has the effect of a zero in the gain plot, causing an imposed +20dB/decade on the rolloff, but has the effect of a pole in the phase, subtracting another 90 in the phase plot. This can cause undesirable effects if the control loop is influenced by this zero. To ensure the RHP zero does not cause instability issues, the control loop should be designed to have a bandwidth of less than 1/2 the frequency of the RHP zero. This zero occurs at a frequency of: RHPzero = VOUT(D')2 (in Hz) 2S,LOADL (18) where ILOAD is the maximum load current. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 13 LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com Compensation Components The LM3551 and LM3552 provide a compensation pin (VC) to customize the voltage loop feedback. It is recommended that a series combination of RC and CC be used for the compensation network, as shown in the typical application circuit. For any given application, there exists a unique combination of RC and CC that will optimize the performance of the LM3551/2 circuit in terms of its transient response. The series combination of RC and CC introduces a pole-zero pair. The frequency of the pole created is determined by the equation: fPC = 1 Hz 2S(RC + RO)CC (19) where RO is the output impedance of the error amplifier, approximately 900k. Since RC is generally much less than RO, it has little effect on the above equation and can be neglected until a value is chosen to set the zero fZC. fZC is created to cancel the pole created by the output capacitor, fP1. The output capacitor pole will shift with different load currents as shown by the equation, so setting the zero is not exact. Determine the range of fP1 over the expected loads and then set the zero fZC to a point approximately in the middle. The frequency of this zero is determined by: fZC = 1 Hz 2SRCCC (20) Now RC can be chosen with the selected value for CC. Check to make sure that the pole fPC is still in the 10Hz to 500Hz range, and change each value slightly if needed to ensure both component values are in the recommended range. For both typical applications circuits shown on the front page, the Recommended value for CC is 4.7nF and RC = 10k for Lumiled applications. 10nF and 27k are recommended for Sharp applications. RECOMMENDED MINIMUM COMPONENT SPECIFICATIONS Component Value Ratings L1 4.7H 2.0A 30% ISAT Rating CIN COUT CFTO CC RC 4.7F (Sharp) 10F (Lumiled) 4.7F (Sharp) 10uF (Lumiled) User Determined 4.7nF (Lumiled) 10nF (Sharp) 10V X5R or X7R 16V X5R or X7R 6.3V X5R or X7R 6.3V X5R or X7R 10k (Lumiled) 27k (Sharp) RFLASH User Determined Application Specific RTORCH User Determined Application Specific CSS User Determined 6.3V X5R or X7R Torch and Flash Resistor ratings are dependent upon the current through each resistor. The minimum ratings will vary depending upon the current selected on an applicaiton by application basis. Power Rating Minimum = (Desired Current)2 x Resistor Value.See the CURRENT SET EQUATIONS section to determine torch and flash currents. 14 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 THERMAL PROTECTION Internal thermal protection circuitry disables the LM3551/2 when the junction temperature exceeds +140C (typ.). This feature protects the device from being damaged by high die temperatures that might otherwise result from excessive power dissipation. The device will recover and operate normally when the junction temperature falls below +120C (typ.). It is important that the board layout provide good thermal conduction to keep the junction temperature within the specified operating ratings. PCB LAYOUT CONSIDERATIONS The WSON is a leadframe based Chip Scale Package (CSP) with very good thermal properties. This package has an exposed DAP (die attach pad) at the center of the package measuring 2.6mm x 3.0mm. The main advantage of this exposed DAP is to offer lower thermal resistance when it is soldered to the thermal land pad on the PCB. For PCB layout, Texas Instruments highly recommends a 1:1 ratio between the package and the PCB thermal land. To further enhance thermal conductivity, the PCB thermal land may include vias to a ground plane. For more detailed instructions on mounting WSON packages, please refer to Application Note AN-1187 (SNOA401) Application Examples TYPICAL CONFIGURATIONS + 4.7 H - VBAT CIN VIN SW 10 F 10V VC OVP FB COUT RT LM3551/2 RC CC LUMILED LXCL-PWF1 Flash LED D1 RF 10 F 16V FTO CFTO FET-T SD/ GND EN FET-F T/F SS CSS RC = 10 k CC= 4.7 nF Figure 16. LUMILED LXCL-PWF1 RT = 5.6, RF = 2.2 ITORCH = 200mA, IFLASH = 700mA Sharp GM5BW05340A Flash LED 4.7 PH + VBAT D1 SW - CIN 10 PF 10V VIN RC FTO CC OVP FB COUT VC CFTO RC = 27 k: RT LM3551/2 GND SD/EN RF 4.7 PF 16V FET-T FET-F T/F SS CSS CC= 10 nF Figure 17. SHARP GM5BW05340A RT = 17, RF = 6.5 ITORCH = 75mA, IFLASH = 250mA Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 15 LM3551, LM3552 SNVS371D - AUGUST 2005 - REVISED MAY 2013 www.ti.com DUAL-MODE CONFIGURATION (1) D1 L1 SW R1 OVP VIN + - VBAT VOUT = 5V FB CIN COUT VC RC FTO R2 LM3551/2 RF FET-T CFTO FET-F CC GND SD/EN T/F SS Figure 18. R1 = 29.5k,R2 = 10k RF = 3 IFLASH = 500mA Using the Dual-Mode configuration with either the LM3551/2, a 5V, high current rail (approx. 700mA total) can be created while still allowing for a high flash with a true load disconnect. R1 and R2 setup the +5V following the equation:VOUT = 1.265 x (1 + R1/R2) . When the LM3551/2 is on, and the T/F pin is low (logic '0'), the part will provide a regulated output voltage that can be used to provide a voltage rail within a system. By setting the T/F pin high, the LM3551/2 will allow the current to flow through the flash LED while still maintaining the fixed output voltage rail. The flash current is set by RF using the equation RF = [(VOUT - VLED) / ILED] - 0.36 , and should not exceed 500mA. The total usable output current is dependent upon the output voltage selected. If the dual-mode configuration is used, the FTO pin should be grounded to prevent the voltage rail from being shutdown at an unwanted time. (1) 16 Please refer to the RECOMMENDED MINIMUM COMPONENT SPECIFICATIONS section of the datasheet for more information. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 LM3551, LM3552 www.ti.com SNVS371D - AUGUST 2005 - REVISED MAY 2013 REVISION HISTORY Changes from Revision C (May 2013) to Revision D * Page Changed layout of National Data Sheet to TI format .......................................................................................................... 16 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM3551 LM3552 17 PACKAGE OPTION ADDENDUM www.ti.com 16-Oct-2015 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (C) Device Marking (4/5) LM3551SD/NOPB LIFEBUY WSON NHL 14 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 L3551SD LM3552SD/NOPB LIFEBUY WSON NHL 14 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 L3552SD (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 16-Oct-2015 In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 2-Sep-2015 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LM3551SD/NOPB WSON NHL 14 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 LM3552SD/NOPB WSON NHL 14 1000 178.0 12.4 4.3 4.3 1.3 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 2-Sep-2015 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM3551SD/NOPB WSON NHL 14 1000 210.0 185.0 35.0 LM3552SD/NOPB WSON NHL 14 1000 210.0 185.0 35.0 Pack Materials-Page 2 MECHANICAL DATA NHL0014B SDA14B (Rev A) www.ti.com IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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