LM3551SDX

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 © 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 © 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 ) 150°C Storage Temperature Range ESD Rating (5) (1) (2) (3) (4) (5) -65°C 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=140ºC (typ.) and disengages at TJ=120ºC (typ.). The human body model is a 100pF capacitor discharged through a 1.5kΩ 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 -40°C to +110°C Ambient Temperature (TA) Range (4) (1) (2) (3) (4) -40°C to +85°C 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 = 110ºC), 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 (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX). Thermal Properties Junction-to-Ambient Thermal Resistance (θJA), NHL0014B Package (1) (1) 37.3°C/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 © 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 (-40°C ≤ TJ ≤ +110°C). 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 µA A 1.2915 V 50 nA 135 µmho 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 ΔI = 5µA 0.9 1.25 1.6 MHz VSD = 0V 3.0 6 µA VEN = 3.6V 3.0 6 µA VT/F = 0V 26 VT/F = VIN 22 nA VL-SW = 20V 0.07 ISW = 0.5A 0.165 Ω FET-T Leakage Current 0.1 µA RDSON-T FET-T RDSON 0.98 Ω IL-F FET-F Leakage Current 0.1 µA RDSON-F FET-F RDSON 0.36 Ω 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 µA VSS Soft-Start Voltage 1.18 1.25 1.32 V ISS Soft-Start Current 10 11.5 13 µA (1) (2) (3) (4) (5) (6) 4 Output High 1.2 Output Low Output High 8 0.3 1.2 Output Low 0.3 µA 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 = 25ºC. 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 © 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 = +25°C; VIN = 3.6V; L = 4.7µH, (RC = 10kΩ, CC = 4.7nF, CIN = COUT = 10µF for Lumiled LED), (RC = 27kΩ, CC = 10nF, CIN = 10µF, COUT = 4.7µF for Sharp LED), CFTO = 1µF, CSS= 0.1µF. ICL measure when VOUT = 95% × 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% × 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%× VOUT (nominal) Maximum IOUT vs. Input Voltage VOUT = 5V Maximum IOUT vs. Input Voltage VOUT = 10V Figure 6. Figure 7. IOUT measured at 95%× VOUT (nominal) Submit Documentation Feedback Copyright © 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 = +25°C; VIN = 3.6V; L = 4.7µH, (RC = 10kΩ, CC = 4.7nF, CIN = COUT = 10µF for Lumiled LED), (RC = 27kΩ, CC = 10nF, CIN = 10µF, COUT = 4.7µF for Sharp LED), CFTO = 1µF, CSS= 0.1µF. 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 © 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 = +25°C; VIN = 3.6V; L = 4.7µH, (RC = 10kΩ, CC = 4.7nF, CIN = COUT = 10µF for Lumiled LED), (RC = 27kΩ, CC = 10nF, CIN = 10µF, COUT = 4.7µF for Sharp LED), CFTO = 1µF, CSS= 0.1µF. 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 © 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 = 0.165Ω) 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 1.2MΩ 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 1.2MΩ 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 0.98Ω 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 0.36Ω 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 © 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 × (ΔVFTO ÷ IFTO) ΔVFTO = 1.16V and IFTO= 1.4µA TFTO = Desired Timeout Duration CFTO(µF) = TFTO(sec.) × 1.21(µA/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 © 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 = +25°C CSS (µF) 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 © 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 1.2MΩ pull-up to VIN on SD and the LM3552 has a 1.2MΩ 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= 0.98Ω and RDSON-F = 0.36Ω (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 = +25°C). IL(average) = [ILED × VOUT-MAX] ÷ [VIN-MIN × Eff.] ΔIL = [VIN × D] ÷ [L × FSW] IL(peak) = IL(ave) + [ΔIL ÷ 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 4.7µH. FSW Switching Frequency = 1.25MHz Submit Documentation Feedback Copyright © 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 10µF should be used under normal operating condtions while a 10-22µF 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 4.7µF (Sharp LED) and 10µF (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: ΔVOUT ≊ 2 × ΔIL× 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