LM27961 Dual-Display White LED Driver with 3/2x Switched Capacitor Boost General Description Features The LM27961 is a charge-pump-based white-LED driver that is ideal for mobile phone display backlighting. It is intended to drive 4 LEDs for a main phone display backlight and 3 LEDs for a sub-display backlight. Regulated internal current sources deliver excellent current and brightness matching in all LEDs. n Drives 4 Individual Common-Anode LEDs with up to 20mA each for a Main Display Backlight n Drives 3 Individual Common-Cathode LEDs with up to 20mA each for a Sub-Display Backlight n Independent Resistor-Programmable Current Setting n Excellent Current and Brightness Matching n High-Efficiency 3/2x Charge Pump n Extended Li-Ion Input: 2.7V to 5.5V n PWM Brightness Control: 100Hz - 1kHz n 18-bump Thin Micro SMD Package: (2.1mm x 2.4mm x 0.6mm) The LED driver current sources are split into two independently controlled groups. The primary group (Group A) can be used to backlight a main phone display with up to 4 LEDs. The low-side current drivers of Group A accommodate common-anode-type LEDs. The second group (Group B) can backlight a secondary display with up to 3 LEDs. The high-side current drivers of Group B accommodate commoncathode-type LEDs. Both Group A and Group B can also drive standard two-terminal LEDs, and provide other general lighting functions (keypad lighting, fun lighting, etc). The brightness of the two LED groups can be adjusted independently with external resistors. The LM27961 works off an extended Li-Ion input voltage range (2.7V to 5.5V). Voltage boost is achieved with a highefficiency 3/2x-gain charge pump. The LM27961 is available in National’s chip-scale 18-bump micro SMD package. Applications n n n n Mobile Phone Display Lighting Mobile Phone Keypad Lighting PDAs General LED Lighting Typical Application Circuit 20127901 © 2004 National Semiconductor Corporation DS201279 www.national.com LM27961 Dual-Display White LED Driver with 3/2x Switched Capacitor Boost November 2004 LM27961 Connection Diagram 18-Bump Thin Micro SMD Package, Large Bump NS Package Number TLA18 20127902 Pin Description Pin #s Pin Names Pin Descriptions C1 VIN D2 GND Ground A3 POUT Charge pump output. Approximately 1.5xVIN A1, B2, A5, E1 C1+, C1-, C2+, C2- Flying capacitor connections. D6, E5, D4, E3 D1A, D2A, D3A, D4A LED Outputs - Group A C5, B4, C3 D1B, D2B, D3B LED Outputs - Group B B6 EN-A Enable for Group-A LEDs (current outputs). Logic input. High = Group-A LEDs ON. Low = Group A LEDs OFF. Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs. A7 EN-B Enable for Group-B LEDs (current outputs). Logic input. High = Group-B LEDs ON. Low = Group B LEDs OFF. Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs. E7 ISETA Placing a resistor (RSETA) between this pin and GND sets the LED current for Group A LEDs. LED Current = 100 x (1.25V ÷ RSETA). C7 ISETB Placing a resistor (RSETB) between this pin and GND sets the LED current for Group B LEDs. LED Current = 100 x (1.25V ÷ RSETB). Input voltage. Input range: 2.7V to 5.5V. Operational States ENA ENB L L Shutdown Mode of Operation H L Enabled. Group A LEDs ON. Group B LEDs OFF L H Enabled. Group B LEDs ON. Group A LEDs OFF H H Invalid for normal operation Ordering Information Order Information Package Supplied As LM27961TL TLA18 Micro SMD 250 Units, Tape & Reel LM27961TLX www.national.com 3000 Units, Tape & Reel 2 Operating Rating If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN pin voltage Input Voltage Range -0.3V to 7.1V ENA, ENB pin voltages -0.3V to (VIN+0.3V) w/ 6.0V max IDxx Pin Voltages Internally Limited Junction Temperature (TJ-MAX) 150oC Storage Temperature Range -65oC to +150o C Maximum Lead Temperature (Soldering, 10 sec.) 265oC ESD Rating (Note 4) Human Body Model - IDxx Pins: Human Body Model - All other Pins: Machine Model - IDxx Pins: Machine Model - All Other Pins: Electrical Characteristics 2.7V to 5.5V Junction Temperature (TJ) Range -30˚C to +125˚C Ambient Temperature (TA) Range (Note 5) -30˚C to +85˚C Thermal Properties -0.3V to (VPOUT+0.3V) w/ 6.0V max Continuous Power Dissipation (Note 3) (Notes 1, 2) 100˚C/W Juntion-to-Ambient Thermal Resistance (θJA), (Note 6) 1.0kV 2.0kV 100V 200V (Notes 2, 7) Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: VIN = 3.6V; VDxA = 0.6V; VDxB = 3.6V; ENA = 1.5V and ENB = GND, or ENA = GND and ENB = 1.5V; RSETA = RSETB = 8.35kΩ; CIN, C1, C2 , and CPOUT = 1µF. Specifications related to output current(s) and current setting pins (IDxx and ISETx) apply to both Group A and Group B. (Note 8) Symbol Parameter Condition 3.0V ≤ VIN ≤ 4.2V, and VIN = 5.5V 0.45V ≤ VDxA ≤ 3.8V or 2.5V ≤ VDxB ≤ 3.8V; RSET = 8.35kΩ IDxx Output Current Regulation IDxx-MATCH Current Matching Between Any Two Group A Outputs or Group B Outputs Min Typ Max Units 13.5 (-10%) 15 16.5 (+10%) mA (%) 3.0V ≤ VIN ≤ 5.5V; 0.6V ≤ VDxA ≤ 3.8V or 2.5V ≤ VDxB ≤ 3.8V; RSET = 6.25kΩ 20 mA 3.0V ≤ VIN ≤ 5.5V; 0.3V ≤ VDxA ≤ 3.8V or 2.5V ≤ VDxB ≤ 3.8V; RSET = 12.5kΩ 10 mA 2.7V ≤ VIN ≤ 3.0V; 0.45V ≤ VDxA ≤ 3.8V or 2.5V ≤ VDxB ≤ 3.8V; RSET = 8.35kΩ 15 mA VIN = 3.0V (Note 9) 0.6 % IQ Quiescent Supply Current 2.7V ≤ VIN ≤ 4.2V; No Load Current, ENA or ENB = ON 4.4 6.75 mA ISD Shutdown Supply Current 2.7V ≤ VIN ≤ 5.5V, ENA and ENB = OFF 2.3 5 µA VSET ISET Pin Voltage 2.7V ≤ VIN ≤ 5.5V 1.25 IDxx/ISET Output Current to Current Set Ratio V 100 3 www.national.com LM27961 Absolute Maximum Ratings (Notes 1, 2) LM27961 Electrical Characteristics (Notes 2, 7) (Continued) Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: VIN = 3.6V; VDxA = 0.6V; VDxB = 3.6V; ENA = 1.5V and ENB = GND, or ENA = GND and ENB = 1.5V; RSETA = RSETB = 8.35kΩ; CIN, C1, C2 , and CPOUT = 1µF. Specifications related to output current(s) and current setting pins (IDxx and ISETx) apply to both Group A and Group B. (Note 8) Symbol Parameter Condition Min Typ Max Units ROUT Charge Pump Output Resistance VIN = 3.0V (Note 10) 2.7 Ω VHR Current Source Headroom Voltage Requirement (Note 11) IDxx = 95% X IDxx (nom) RSET = 8.35kΩ (IDxx (nom) ≈ 15mA) 320 mV fSW Switching Frequency 3.0V ≤ VIN ≤ 4.2V tSTART Start-up Time IDx = 90% steady state 350 µs 1.5x/1x Charge pump gain cross-over: Gain = 1.5 when VIN is below threshold. Gain = 1 when VIN is above threshold. 1.5x to 1x Threshold 4.75 V 1x to 1.5x Threshold 4.55 V 375 500 625 kHz Logic Pin Specifications: EN, ENA, ENB VIL Input Logic Low 2.7V ≤ VIN ≤ 5.5V 0 0.5 V VIH Input Logic High 2.7V ≤ VIN ≤ 5.5V 1.1 VIN V ILEAK Input Leakage Current VENx = 0V 0.1 VENx = 3V (Note 12) 10 µA Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 160˚C (typ.) and disengages at TJ = 120˚C (typ.). The thermal shutdown function is guaranteed by design. Note 4: The Human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly into each pin. MIL-STD-883 3015.7 Note 5: 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 = 125˚C), 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 x PD-MAX). Note 6: Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. Note 7: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. Note 8: CIN, CPOUT, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics Note 9: For the two groups of outputs on a part (Group A and Group B), the following are determined: the maximum output current in the group (MAX), the minimum output current in the group (MIN), and the average output current of the group (AVG). For each group, two matching numbers are calculated: (MAX-AVG)/AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the matching figure for the group. The matching figure for a given part is considered to be the highest matching figure of the two groups. The typical specification provided is the most likely norm of the matching figure for all parts. Note 10: Output resistance (ROUT) models all voltage losses in the charge pump. ROUT can be used to estimate the voltage at the charge pump output (POUT): VPout = (1.5 x VIN) – (ROUT x IOUT). In the equation, IOUT is the total output current: the sum of all active Dxx output currents and all current drawn from POUT. The equation applies when the charge pump is operating with a gain of 3/2 (VIN ≤ 4.75V typ.). Note 11: Headroom voltage: VHR = VPout – VLEDx . If headroom voltage requirement is not met, LED current regulation will be compromised. Note 12: There is a 300kΩ(typ.) pull-down resistor connected internally between each enable pin (ENA, ENB) and GND. www.national.com 4 Unless otherwise specified: VIN = 3.6V; VLEDxA = 3.6V; VLEDxB = 3.6V; ENA = VIN and ENB = GND, or ENA = GND and ENB = VIN; RSETA = RSETB = 8.35kΩ; CIN, C1, C2 , and CPOUT = 1µF. LED Current (D1A, D2A,D3A, D4A) vs. Input Voltage LED Current (DxA) vs. Input Voltage 20127904 20127905 Charge Pump Output Voltage vs. Output Current Quiescent Current vs. Input Voltage, 20127906 20127907 5 www.national.com LM27961 Typical Performance Characteristics LM27961 Typical Performance Characteristics Unless otherwise specified: VIN = 3.6V; VLEDxA = 3.6V; VLEDxB = 3.6V; ENA = VIN and ENB = GND, or ENA = GND and ENB = VIN; RSETA = RSETB = 8.35kΩ; CIN, C1, C2 , and CPOUT = 1µF. (Continued) Charge Pump Output Voltage vs. Output Current Charge Pump Output Voltage vs. Input Voltage (No Load Current) 20127910 20127908 Charge Pump Output Resistance vs Output Current Input Current vs. Input Voltage 20127911 20127909 www.national.com 6 = 3.6V; ENA = VIN and ENB = GND, or ENA = GND and ENB = VIN; RSETA = RSETB = 8.35kΩ; CIN, C1, C2 , and CPOUT = 1µF. (Continued) Charge Pump Switching Frequency vs. Input Voltage Diode Current (DxA) vs. Headroom Voltage (DxA) 20127913 20127912 Diode Current (DxB) vs. Headroom Voltage (DxB) Diode Current (DxA or DxB) vs. PWM Duty Cycle (ENA or ENB) 20127915 20127914 7 www.national.com LM27961 Typical Performance Characteristics Unless otherwise specified: VIN = 3.6V; VLEDxA = 3.6V; VLEDxB LM27961 Typical Performance Characteristics Unless otherwise specified: VIN = 3.6V; VLEDxA = 3.6V; VLEDxB = 3.6V; ENA = VIN and ENB = GND, or ENA = GND and ENB = VIN; RSETA = RSETB = 8.35kΩ; CIN, C1, C2 , and CPOUT = 1µF. (Continued) Diode Current (DxA) vs. RSETx Input Voltage (Top) and Output Voltage (Bottom) Waveforms 20127917 Vertical Scale = (100mV/div), Horizontal Scale = 1µs/div) 20127916 ENx Signal (Top) and Charge Pump Start-Up (Bottom) Waveforms 20127918 Vertical Scale = (2V/div), Horizontal Scale = 100µs/div) www.national.com 8 LM27961 Block Diagram 20127903 output voltage gain of the charge pump is 1.5, and the voltage at the output of the charge pump will be approximately 1.5x the input voltage (V(POUT) ≈ 1.5 * VIN ). When in the 1.5x mode, the charge pump provides the voltage boost that is required to drive white LEDs from a Li-Ion battery. (White LEDs typically have a forward voltage in the range of 3.3V to 4.0V. A Li-Ion battery typically is not considered to be fully discharged until the battery voltage falls to 3.0V (approx.) ) The charge pump operates in the 1x mode when the input voltage is above 4.75V (typ.). In these conditions, voltage boost is not required to drive the LEDs, so the charge pump merely passes the input voltage to POUT (V(POUT) ≈ VIN). This reduces the input current and the power dissipation of the LM27961 when the input voltage is high. Circuit Description OVERVIEW The LM27961 is primarily intended for Lithium-Ion battery driven white-LED drive applications, and is well suited to drive white LEDs that are used for backlighting small-format displays. The part has seven matched constant-current outputs, each capable of driving up to 20mA (or more) through white LEDs. The well-matched current sources ensure the current through all the LEDs is virtually identical. This keeps brightness of all LEDs matched to near perfection so that they can provide a consistent backlight over the entire display. CHARGE PUMP The core of the LM27961 is a 1.5x/1x dual-mode charge pump. The input of the charge pump is connected to the VIN pin. The recommended input voltage range of the LM27961 is 2.7V to 5.5V. The output of the charge pump is the POUT pin (“Pump OUTput”). The output voltage of the charge pump is unregulated and varies with input voltage and load current. The charge pump operates in the 1.5x mode when the input voltage is below 4.75V (typ.). In this mode, the input-to- REGULATED CURRENT OUTPUTS The matched current outputs are generated with a precision current mirror that is biased off the charge pump output. Matched currents are ensured with the use of tightly matched internal devices and internal mismatch cancellation circuitry. There are seven regulated current outputs. These seven outputs are split into two groups, a group of 4 common 9 www.national.com LM27961 Circuit Description VPOUT = 1.5xVIN – NxILEDxROUT (eq. 2) kHR – Headroom constant. This parameter models the minimum voltage required to be present across the current sources for them to regulate properly. This minimum voltage is proportional to the programmed LED current, so the constant has units of mV/mA. The typical kHR of the LM27961 is 22mV/mA. In equation form: (eq. 3) (VPOUT – VLED) > kHRxILED The "ILED-MAX" equation (eq. 1) is obtained from combining the ROUT equation (eq. 2) with the kHR equation (eq. 3) and solving for ILED. Maximum LED current is highly dependent on minimum input voltage and LED forward voltage. Output current capability can be increased by raising the minimum input voltage of the application, or by selecting an LED with a lower forward voltage. Excessive power dissipation may also limit output current capability of an application. (Continued) anode outputs and a group of 3 common cathode outputs. There is an ON/OFF control pin for each group (ENA and ENB). The DC current through the LEDs is programmed with an external resistor. Changing currents on-the-fly can be achieved with the use of digital pulse (PWM) signals. ENABLE PINS: ENA, ENB The LM27961 has 2 enable pins. Both are active-high logic (HIGH = ON). There are internal pull-down resistors (300kΩ typ.) that are connected internally between each of the enable pins and GND. ENA and ENB can both enable and disable the part. When the voltage on both pins are low ( < 0.5V), the part is in shutdown mode. All internal circuitry is OFF and the part consumes very little supply current when the LM27961 is shutdown. When the voltage on either ENx pin is high ( > 1.1V), the part is active. The charge pump is ON, and the corresponding output current drivers are active. PARALLEL Dx OUTPUTS FOR INCREASED CURRENT CAPABILITY Outputs D1A through D4A, or D1B through D3B may be connected together in any combination to drive higher currents through fewer LEDs. For example in Figure 1, outputs D1A and D2A are connected together to drive one LED. D3A and D4A are connected to drive a second LED. ENA and ENB are used to turn the output currents ON and OFF. ENA activates/deactivates the four GroupA outputs (D1A-D4A). ENB activates/deactivates the three GroupB outputs (D1B-D3B). SETTING LED CURRENTS The output currents of the LM27961 can be set to a desired value simply by connecting an appropriately sized resistor (RSETx) between the ISETx pins of the LM27961 and GND. RSETA sets the current for the GroupA outputs and RSETB sets the current for the GroupB outputs. The output currents (LED currents) are proportional to the current that flows out of the ISETx pins. The output currents are a factor of 100 greater than the ISETx current. The feedback loop of an internal amplifier sets the voltage of the ISETx pin to 1.25V (typ.). Placing a resistor between ISETx and GND programs the ISETx current, and thus the LED currents. The statements above are simplified in the equations below: IDxx = 100 x (VSETx / RSETx) RSETx = 100 x (1.25V / IDxx) 20127919 FIGURE 1. Two Parallel Connected LEDs MAXIMUM OUTPUT CURRENT, MAXIMUM LED VOLTAGE, MINIMUM INPUT VOLTAGE The LM27961 can drive 4 LEDs at 15mA each from an input voltage as low as 2.7V, so long as the LEDs have a forward voltage of 3.5V or less (room temperature). The statement above is a simple example of the LED drive capabilities of the LM27961. The statement contains the key application parameters that are required to validate an LEDdrive design using the LM27961: LED current (ILEDx), number of active LEDs (N), LED forward voltage (VLED), and minimum input voltage (VIN-MIN). The equation below can be used to estimate the total output current capability of the LM27961: ILED_MAX = ((1.5 x VIN) - VLED) / ((N x ROUT) + kHR) (eq. 1) ILED_MAX = ((1.5 x VIN ) - VLED) / ((N x 2.7Ω) + 22mV/mA) ROUT – Output resistance. This parameter models the internal losses of the charge pump that result in voltage droop at the pump output POUT. Since the magnitude of the voltage droop is proportional to the total output current of the charge pump, the loss parameter is modeled as a resistance. The output resistance of the LM27961 is typically 2.7Ω (VIN = 3.0V, TA = 25˚C). In equation form: www.national.com With this configuration, two parallel current sources of equal value provide current to one of the LEDs. RSET should therefore be chosen so that the current through each output is programmed to 50% of the desired current through the parallel connected LED. For example, if 40mA is the desired drive current for the parallel connected LED, RSETx should be selected so that the current through each of the outputs is 20mA. Other combinations of parallel outputs may be implemented in similar fashions, such as in Figure 2. 10 LM27961 Circuit Description (Continued) Neglecting IQ will result in a slightly higher efficiency prediction, but this impact will be no more than a few percentage points when several LEDs are driven at full power. ADJUSTING LED BRIGHTNESS (PWM control) Perceived LED brightness can be adjusted using a PWM control signal to turn the LM27961 current sources ON and OFF at a rate faster than perceptible by the eye. When this is done, the total brightness perceived is proportional to the duty cycle (D) of the PWM signal (D = the percentage of time that the LED is on in every PWM cycle). A simple example: if the LEDs are driven at 15mA each with a PWM signal that has a 50% duty cycle, perceived LED brightness will be about half as bright as compared to when the LEDs are driven continuously with 15mA. A PWM signal thus provides brightness (dimming) control for the solution. 20127920 The minimum recommended PWM frequency is 100Hz. Frequencies below this may be visibly noticeable as flicker or blinking. The maximum recommended PWM frequency is 1kHz. Frequencies above this may cause interference with internal current driver circuitry. In cases where a PWM signal must be connected to the ENx pins, measures can be taken to reduce the magnitude of the charge-pump turn-on voltage spikes. More input capacitance, series resistors and/or ferrite beads may provide benefits. If the current and voltage spikes can be tolerated, connecting the PWM signal to the EN pin does provide a benefit: lower supply current when the PWM signal is active. When the PWM signal is low, the LM27961 will be shutdown and input current will only be a few micro-amps. This results in a lower time-averaged input current. FIGURE 2. One Parallel Connected LED Connecting outputs in parallel does not affect internal operation of the LM27961 and has no impact on the Electrical Characteristics and limits previously presented. The available diode output current, maximum diode voltage, and all other specifications provided in the Electrical Characteristics table apply to parallel output configurations, just as they do to the standard application circuit on pg1 of the datasheet. SOFT START The LM27961 contains internal soft-start circuitry to limit input inrush currents when the part is enabled. Soft start is implemented with a controlled turn-on of the internal voltage reference. During soft start, the current through the LED outputs rise at the rate of the reference voltage ramp. Due to the soft-start circuitry, turn-on time of the LM27961 is approximately 350µs (typ.). CAPACITOR SELECTION The LM27961 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance (ESR < 20mW typ.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are not recommended for use with the LM27961 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 LM27961. These capacitors have tight capacitance tolerance (as good as ± 10%) and hold their value over temperature (X7R: ± 15% over -55˚C to 125˚C; X5R: ± 15% over -55˚C to 85˚C). Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with the LM27961. Capacitors with these temperature characteristics typically have wide capacitance tolerance (+80%, -20%) and vary significantly over temperature (Y5V: +22%, -82% over -30˚C to +85˚C range; Z5U: +22%, -56% over +10˚C to +85˚C range). Under some conditions, a nominal 1µF Y5V or Z5U capacitor could have a capacitance of only 0.1µF. Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum capacitance requirements of the LM27961. THERMAL PROTECTION Internal thermal protection circuitry disables the LM27961 when the junction temperature exceeds 160˚C (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 120˚C (typ.). It is important that the board layout provides good thermal conduction. This will help to keep the junction temperature within specified operating ratings. Applications Information POWER EFFICIENCY Efficiency of LED drivers is commonly taken to be the ratio of power consumed by the LEDs (PLED) to the power drawn at the input of the part (PIN). With a 1.5x charge pump, the input current is approximately 1.5x the output current (total LED current). For a simple approximation, the current consumed by internal circuitry can be neglected and the efficiency of the LM27961 can be predicted as follows: 11 www.national.com LM27961 Applications Information MICRO SMD MOUNTING The LM27961 is an 18-bump micro SMD with a bump size of approximately 300 micron diameter. The micro SMD package requires specific mounting techniques detailed in National Semiconductor Application Note 1112 (AN-1112). (Continued) The voltage rating of the output capacitor should be 10V or more. All other capacitors should have a voltage rating at or above the maximum input voltage of the application. CIRCUIT BOARD LAYOUT For optimal, low-noise performance, all capacitors (CIN, CPOUT, C1, C2) should be placed very close to the LM27961. A solid ground plane should be used for IC and component GND connections. Refer to the LM27961 Evaluation Board for an example layout. www.national.com 12 inches (millimeters) unless otherwise noted TLA18EHA: 18-Bump Thin Micro SMD, Large Bump X1 = 2.098 ± 0.030mm X2 = 2.403mm ± 0.030 X3 = 0.600mm ± 0.075mm National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. National Semiconductor Americas Customer Support Center Email: [email protected] Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: [email protected] Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: [email protected] National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: [email protected] Tel: 81-3-5639-7560 LM27961 Dual-Display White LED Driver with 3/2x Switched Capacitor Boost Physical Dimensions