View LM3500TL-16_1059399.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

Synchronous Step-up DC/DC Converter for White LED Applications
February 2005
LM3500 Synchronous Step-up DC/DC Converter for White LED Applications
General Description
The LM3500 is a fixed-frequency step-up DC/DC converter that is ideal for driving white LEDs for display backlighting and other lighting functions. With fully intergrated synchronous switching (no external schottky diode required) and a low feedback voltage (500mV), power efficiency of the LM3500 circuit has been optimized for lighting applications in wireless phones and other portable products (single cell Li-Ion or 3-cell NiMH battery supplies). The LM3500 operates with a fixed 1MHz switching frequency. When used with ceramic input and output capacitors, the LM3500 provides a small, low-noise, low-cost solution. Two LM3500 options are available with different output voltage capabilities. The LM3500-21 has a maximum output voltage of 21V and is typically suited for driving 4 or 5 white LEDs in series. The LM3500-16 has a maximum output voltage of 16V and is typically suited for driving 3 or 4 white LEDs in series (maximum number of series LEDs dependent on LED forward voltage). If the primary white LED network should be disconnected, the LM3500 uses internal protection circuitry on the output to prevent a destructive overvoltage event. A single external resistor is used to set the maximum LED current in LED-drive applications. The LED current can easily be adjusted using a pulse width modulated (PWM) signal on the shutdown pin. In shutdown, the LM3500 completely disconnects the input from output, creating total isolation and preventing any leakage currents from trickling into the LEDs.
Features
n Synchronous rectification, high efficiency and no external schottky diode required n Uses small surface mount components n Can drive 2-5 white LEDs in series (may function with more low-VF LEDs) n 2.7V to 7V input range n Internal output over-voltage protection (OVP) circuitry, with no external zener diode required LM3500-16: 15.5V OVP; LM3500-21: 20.5V OVP. n True shutdown isolation n Input undervoltage lockout n Requires only small ceramic capacitors at the input and output n Thermal Shutdown n 0.1A shutdown current n Small 8-bump thin micro SMD package
Applications
n n n n n LCD Bias Supplies White LED Backlighting Handheld Devices Digital Cameras Portable Applications
Typical Application Circuit
20065701
(c) 2005 National Semiconductor Corporation
DS200657
www.national.com
LM3500
Connection Diagram
Top View
20065702
8-bump micro SMD
Ordering Information
Maximum Output Voltage 16V 16V 21V 21V Order Number Package Type NSC Package Drawing TL08SSA TL08SSA TL08SSA TL08SSA Top Mark Supplied As
LM3500TL-16 LM3500TLX-16 LM3500TL-21 LM3500TLX-21
micro SMD micro SMD micro SMD micro SMD
S18 S18 S23 S23
250 Units, Tape and Reel 3000 Units, Tape and Reel 250 Units, Tape and Reel 3000 Units, Tape and Reel
Pin Description/Functions
Pin A1 B1 C1 C2 C3 B3 A3 A2 Name AGND VIN VOUT VSW GND FB NC SHDN Analog ground. Analog and Power supply input. PMOS source connection for synchronous rectification. Switch pin. Drain connections of both NMOS and PMOS power devices. Power Ground. Output voltage feedback connection. No internal connection made to this pin. Shutdown control pin. FB(pin B3): Output voltage feedback connection. Set the primary White LED network current with a resistor from the FB pin to GND. Keep the current setting resistor close to the device and connected between the FB and GND pins. NC(pin A3): No internal connection is made to this pin. The maximum allowable voltage that can be applied to this pin is 7.5V. SHDN(pin A2): Shutdown control pin. Disable the device with a voltage less than 0.3V and enable the device with a voltage greater than 1.1V. The white LED current can be controlled using a PWM signal at this pin. There is an internal pull down on the SHDN pin, the device is in a normally off state. Function
AGND(pin A1): Analog ground pin. The analog ground pin should tie directly to the GND pin. VIN(pin B1): Analog and Power supply pin. Bypass this pin with a capacitor, as close to the device as possible, connected between the VIN and GND pins. VOUT(pin C1): Source connection of internal PMOS power device. Connect the output capacitor between the VOUT and GND pins as close as possible to the device. VSW(pin C2): Drain connection of internal NMOS and PMOS switch devices. Keep the inductor connection close to this pin to minimize EMI radiation. GND(pin C3): Power ground pin. Tie directly to ground plane.
www.national.com
2
LM3500
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN VOUT (LM3500-16)(Note 2) VOUT (LM3500-21)(Note 2) VSW(Note 2) FB, SHDN, and NC Voltages Maximum Junction Temperature Lead Temperature (Note 3) ESD Ratings (Note 4) Human Body Model Machine Model 2kV 200V -0.3V to 7.5V -0.3V to 16V -0.3V to 21V -0.3V to VOUT+0.3V -0.3V to 7.5V 150C 300C
Operating Conditions
Ambient Temperature (Note 5) Junction Temperature Supply Voltage -40C to +85C -40C to +125C 2.7V to 7V
Thermal Properties
Junction to Ambient Thermal Resistance (JA)(Note 6) 75C/W
Electrical Characteristics
Specifications in standard type face are for TA = 25C and those in boldface type apply over the Operating Temperature Range of TA = -10C to +85C. Unless otherwise specified VIN =2.7V and specification apply to both LM3500-16 and LM350021. Symbol IQ Parameter Quiescent Current, Device Not Switching Quiescent Current, Device Switching Shutdown VFB VFB ICL Feedback Voltage Feedback Voltage Line Regulation Switch Current Limit (LM3500-16) Conditions FB > 0.54V FB = 0V SHDN = 0V VIN = 2.7V to 7V VIN = 2.7V to 7V VIN = 2.7V, Duty Cycle = 80% VIN = 3.0V, Duty Cycle = 70% Switch Current Limit (LM3500-21) VIN = 2.7V, Duty Cycle = 70% VIN = 3.0V, Duty Cycle = 63% IB VIN RDSON DLimit FB Pin Bias Current Input Voltage Range NMOS Switch RDSON PMOS Switch RDSON Duty Cycle Limit (LM3500-16) Duty Cycle Limit (LM3500-21) FSW ISD Switching Frequency SHDN Pin Current (Note 10) SHDN = 5.5V SHDN = 2.7V SHDN = GND VIN = 2.7V, ISW = 300mA VOUT = 6V, ISW = 300mA FB = 0V FB = 0V 80 85 0.85 1.1 87 % 94 1.0 18 9 0.1 1.15 30 16 A MHz FB = 0.5V (Note 9) 2.7 0.47 Min (Note 7) Typ (Note 8) 0.95 1.8 0.1 0.5 0.1 275 255 420 450 400 400 640 670 45 Max (Note 7) 1.2 mA 2.5 2 0.53 0.4 480 530 mA 770 800 200 7.0 0.43 2.3 nA V A V %/V Units
3
www.national.com
LM3500
Electrical Characteristics
(Continued)
Specifications in standard type face are for TA = 25C and those in boldface type apply over the Operating Temperature Range of TA = -10C to +85C. Unless otherwise specified VIN =2.7V and specification apply to both LM3500-16 and LM350021. Symbol IL Parameter Switch Leakage Current (LM3500-16) Switch Leakage Current (LM3500-21) UVP OVP Input Undervoltage Lockout Output Overvoltage Protection (LM3500-16) Output Overvoltage Protection (LM3500-21) IVout VOUT Bias Current (LM3500-16) VOUT Bias Current (LM3500-21) IVL PMOS Switch Leakage Current (LM3500-16) PMOS Switch Leakage Current (LM3500-21) SHDN Threshold Conditions VSW = 15V VSW = 20V ON Threshold OFF Threshold ON Threshold OFF Threshold ON Threshold OFF Threshold VOUT = 15V, SHDN = VIN VOUT = 20V, SHDN = VIN VOUT = 15V, VSW = 0V VOUT = 20V, VSW = 0V 2.4 2.3 15 14 20 19 Min (Note 7) Typ (Note 8) 0.01 0.01 2.5 2.4 15.5 14.6 20.5 19.5 260 300 0.01 0.01 Max (Note 7) 0.5 2.0 2.6 2.5 16 15 21 20 400 A 460 3 A 3 V Units A
V
SHDN Low 0.65 0.3 V SHDN High 1.1 0.65 Specifications in standard type face are for TJ = 25C and those in boldface type apply over the full Operating Temperature Range (TJ = -40C to +125C). Unless otherwise specified VIN =2.7V and specification apply to both LM3500-16 and LM350021. Symbol Parameter Quiescent Current, Device Not Switching Quiescent Current, Device Switching Shutdown Conditions FB > 0.54V FB = 0V SHDN = 0V VIN = 2.7V to 7V VIN = 2.7V to 7V VIN = 3.0V, Duty Cycle = 70% VIN = 3.0V, Duty Cycle = 63% FB = 0.5V (Note 9) 2.7 VIN = 2.7V, ISW = 300mA VOUT = 6V, ISW = 300mA FB = 0V FB = 0V 0.8 1.1 87 % 94 1.0 1.2 MHz 0.47 Min (Note 7) Typ (Note 8) 0.95 1.8 0.1 0.5 0.1 400 mA 670 45 200 7.0 0.43 2.3 nA V Max (Note 7) 1.2 mA 2.5 2 0.53 0.4 A V %/V Units
IQ
VFB VFB ICL
Feedback Voltage Feedback Voltage Line Regulation Switch Current Limit (LM3500-16) Switch Current Limit (LM3500-21)
IB VIN RDSON DLimit
FB Pin Bias Current Input Voltage Range NMOS Switch RDSON PMOS Switch RDSON Duty Cycle Limit (LM3500-16) Duty Cycle Limit (LM3500-21)
FSW
Switching Frequency
www.national.com
4
LM3500
Electrical Characteristics
(Continued)
Specifications in standard type face are for TJ = 25C and those in boldface type apply over the full Operating Temperature Range (TJ = -40C to +125C). Unless otherwise specified VIN =2.7V and specification apply to both LM3500-16 and LM350021. Symbol ISD Parameter SHDN Pin Current (Note 10) Conditions SHDN = 5.5V SHDN = 2.7V SHDN = GND IL Switch Leakage Current (LM3500-16) Switch Leakage Current (LM3500-21) UVP OVP Input Undervoltage Lockout Output Overvoltage Protection (LM3500-16) Output Overvoltage Protection (LM3500-21) IVout VOUT Bias Current (LM3500-16) VOUT Bias Current (LM3500-21) IVL PMOS Switch Leakage Current (LM3500-16) PMOS Switch Leakage Current (LM3500-21) SHDN Threshold SHDN Low SHDN High 1.1 VSW = 15V VSW = 20V ON Threshold OFF Threshold ON Threshold OFF Threshold ON Threshold OFF Threshold VOUT = 15V, SHDN = VIN VOUT = 20V, SHDN = VIN VOUT = 15V, VSW = 0V VOUT = 20V, VSW = 0V 2.4 2.3 15 14 20 19 Min (Note 7) Typ (Note 8) 18 9 0.1 0.01 0.01 2.5 2.4 15.5 14.6 20.5 19.5 260 300 0.01 0.01 0.65 0.65 0.5 2.0 2.6 2.5 16 15 21 20 400 A 460 3 A 3 0.3 V V A Max (Note 7) 30 16 A Units
V
Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: This condition applies if VIN < VOUT. If VIN > VOUT, a voltage greater than VIN + 0.3V should not be applied to the VOUT or VSW pins. Note 3: For more detailed soldering information and specifications, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale Package (AN-1112), available at www.national.com. Note 4: The human body model is a 100 pF capacitor discharged through a 1.5 k resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin. 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 = 125oC), 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). Note 6: Junction-to-ambient thermal resistance (JA) is highly application and board-layout dependent. The 75oC/W figure provided was measured on a 4-layer test board conforming to JEDEC standards. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues when designing the board layout. Note 7: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are production tested, guaranteed through statistical analysis or guaranteed by design. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Note 8: Typical numbers are at 25C and represent the most likely norm. Note 9: Feedback current flows out of the pin. Note 10: Current flows into the pin.
5
www.national.com
LM3500
Typical Performance Characteristics
Switching Quiescent Current vs VIN Non-Switching Quiescent Current vs VIN
20065755
20065756
2 LED Efficiency vs LED Current L = Coilcraft DT1608C-223, Efficiency = 100*(PIN/(2VLED*ILED))
2 LED Efficiency vs LED Current L = TDK VLP4612T-220MR34, Efficiency = 100*(PIN/(2VLED*ILED))
20065757
20065779
3 LED Efficiency vs LED Current L = Coilcraft DT1608C-223, Efficiency = 100*(PIN/(3VLED*ILED))
3 LED Efficiency vs LED Current L = TDK VLP4612T-220MR34, Efficiency = 100*(PIN/(3VLED*ILED))
20065758
20065780
www.national.com
6
LM3500
Typical Performance Characteristics
4 LED Efficiency vs LED Current L = Coilcraft DT1608C-223, Efficiency = 100*(PIN/(4VLED*ILED))
(Continued) 4 LED Efficiency vs LED Current L = TDK VLP4612T-220MR34, Efficiency = 100*(PIN/(4VLED*ILED))
20065759
20065781
2 LED Efficiency vs VIN L = Coilcraft DT1608C-223, Efficiency = 100*(PIN/(2VLED*ILED))
3 LED Efficiency vs VIN L = Coilcraft DT1608C-223, Efficiency = 100*(PIN/(3VLED*ILED))
20065769
20065770
4 LED Efficiency vs VIN L = Coilcraft DT1608C-223, Efficiency = 100*(PIN/(4VLED*ILED))
SHDN Pin Current vs SHDN Pin Voltage
20065773
20065761
7
www.national.com
LM3500
Typical Performance Characteristics
Output Power vs VIN: LM3500-16 (L = Coilcraft DT1608C-223)
(Continued) Output Power vs Temperature: LM3500-16 (L = Coilcraft DT1608C-223)
20065784
20065785
Switch Current Limit vs VIN: LM3500-16
Switch Current Limit vs Temperature LM3500-16, VOUT=8V
20065762
20065763
Switch Current Limit vs Temperature LM3500-16, VOUT=12V
Switch Current Limit vs VIN: LM3500-21
20065776
20065791
www.national.com
8
LM3500
Typical Performance Characteristics
Switch Current Limit vs Temperature LM3500-21, VOUT=8V
(Continued) Switch Current Limit vs Temperature LM3500-21, VOUT=12V
20065792
20065793
Switch Current Limit vs Temperature LM3500-21, VOUT=18V
Oscillator Frequency vs VIN
20065794 20065764
VOUT DC Bias vs VOUT Voltage: LM3500-16
VOUT DC Bias vs VOUT Voltage: LM3500-21
20065765
20065795
9
www.national.com
LM3500
Typical Performance Characteristics
FB Voltage vs Temperature
(Continued) FB Voltage vs VIN
20065766
20065767
NMOS RDSON vs VIN (ISW = 300mA)
PMOS RDSON vs Temperature
20065774
20065775
Typical VIN Ripple
Start-Up: LM3500-16
20065768
20065771
LM3500-16, 3 LEDs, RLED = 22, VIN = 3.0V 1) SW, 10V/div, DC 3) IL, 100mA/div, DC 4) VIN, 100mV/div, AC T = 250ns/div
3 LEDs, RLED = 22, VIN = 3.0V 1) SHDN, 1V/div, DC 2) IL, 100mA/div, DC 3) ILED, 20mA/div, DC T = 100s/div
www.national.com
10
LM3500
Typical Performance Characteristics
Start-Up: LM3500-21
(Continued) SHDN Pin Duty Cycle Control Waveforms
20065796
20065772
3 LEDs, RLED = 22, VIN = 3.0V 1) SHDN, 1V/div, DC 4) IL, 100mA/div, DC 2) VOUT, 10/div, DC T = 200s/div VCONT = 2.7V
LM3500-16, 3 LEDs, RLED = 22, VIN = 3.0V, SHDN frequency = 200Hz 1) SHDN, 1V/div, DC 2) IL, 100mA/div, DC 3) ILED, 20mA/div, DC 4) VOUT, 10V/div, DC T = 1ms/div
Typical VOUT Ripple, OVP Functioning: LM3500-16
Typical VOUT Ripple, OVP Functioning: LM3500-21
20065782
20065797
VOUT open circuit and equals approximately 15V DC, VIN = 3.0V 3) VOUT, 200mV/div, AC T = 1ms/div
VOUT open circuit and equals approximately 20V DC, VIN = 3.0V 1) VOUT, 200mV/div, AC T = 400s/div
11
www.national.com
LM3500
Operation
20065704
FIGURE 1. LM3500 Block Diagram The LM3500 utilizes a synchronous Current Mode PWM control scheme to regulate the feedback voltage over almost all load conditions. The DC/DC controller acts as a controlled current source ideal for white LED applications. The LM3500 is internally compensated preventing the use of any external compensation components providing a compact overall solution. The operation can best be understood referring to the block diagram in Figure 1. At the start of each cycle, the oscillator sets the driver logic and turns on the NMOS power device conducting current through the inductor and turns off the PMOS power device isolating the output from the VSW pin. The LED current is supplied by the output capacitor when the NMOS power device is active. During this cycle, the output voltage of the EAMP controls the current through the inductor. This voltage will increase for larger loads and decrease for smaller loads limiting the peak current in the inductor minimizing EMI radiation. The EAMP voltage is compared with a voltage ramp and the sensed switch voltage. Once this voltage reaches the EAMP output voltage, the PWM COMP will then reset the logic turning off the NMOS power device and turning on the PMOS power device. The inductor current then flows through the PMOS power device to the white LED load and output capacitor. The inductor current recharges the output capacitor and supplies the current for the white LED branches. The oscillator then sets the driver logic again repeating the process. The Duty Limit Comp is always operational preventing the NMOS power switch from being on more than one cycle and conducting large amounts of current. The LM3500 has dedicated protection circuitry active during normal operation to protect the IC and the external components. The Thermal Shutdown circuitry turns off both the NMOS and PMOS power devices when the die temperature reaches excessive levels. The LM3500 has a UVP Comp that disables both the NMOS and PMOS power devices when battery voltages are too low preventing an on state of the power devices which could conduct large amounts of current. The OVP Comp prevents the output voltage from increasing beyond 15.5V(LM3500-16) and 20.5V(LM350021) when the primary white LED network is removed or if there is an LED failure, allowing the use of small (16V for LM3500-16 and 25V for LM3500-21) ceramic capacitors at the output. This comparator has hysteresis that will regulate the output voltage between 15.5V and 14.6V typically for the LM3500-16, and between 20.5V and 19.5V for the LM350021. The LM3500 features a shutdown mode that reduces the supply current to 0.1uA and isolates the input and output of the converter.
www.national.com
12
LM3500
Application Information
ADJUSTING LED CURRENT The White LED current is set using the following equation:
The LED current can be controlled using a PWM signal on the SHDN pin with frequencies in the range of 100Hz (greater than visible frequency spectrum) to 1kHz. For controlling LED currents down to the A levels, it is best to use a PWM signal frequency between 200-500Hz. The LM3500 LED current can be controlled with PWM signal frequencies above 1kHz but the controllable current decreases with higher frequency. The maximum LED current would be achieved using the equation above with 100% duty cycle, ie. the SHDN pin always high. LED-DRIVE CAPABILITY The maximum number of LEDs that can be driven by the LM3500 is limited by the output voltage capability of the LM3500. When using the LM3500 in the typical application configuration, with LEDs stacked in series between the VOUT and FB pins, the maximum number of LEDs that can be placed in series (NMAX) is dependent on the maximum LED forward voltage (VF-MAX), the voltage of the LM3500 feedback pin (VFB-MAX = 0.53V), and the minimum output overvoltage protection level of the chosen LM3500 option (LM3500-16: OVPMIN = 15V; LM3500-21: OVPMIN = 20V). For the circuit to function properly, the following inequality must be met: (NMAX x VF-MAX) + 0.53V OVPMIN When inserting a value for maximim LED VF, LED forward voltage variation over the operating temperature range should be considered. The table below provides maximum LED voltage numbers for the LM3500-16 and LM3500-21 in the typical application circuit configuration (with 3, 4, 5, 6, or 7 LEDs placed in series between the VOUT and FB pins). # of LEDs (in series) 3 4 5 6 7 Maximum LED VF LM3500-16 4.82V 3.61V 2.89V X X LM3500-21 6.49V 4.86V 3.89V 3.24V 2.78V
In the event that the primary LED network is disconnected from the LM3500-21, the output voltage will increase and be limited to 20.5V (typ.). There is a 1V hysteresis associated with this circuitry which will cause the output to fluctuate between 20.5V and 19.5V (typ.) if the primary network is disconnected. In the event that the network is reconnected regulation will begin at the appropriate output voltage. The 20.5V limit allows the use of 25V 1F ceramic output capacitors. RELIABILITY AND THERMAL SHUTDOWN The maximum continuous pin current for the 8 pin thin micro SMD package is 535mA. When driving the device near its power output limits the VSW pin can see a higher DC current than 535mA (see INDUCTOR SELECTION section for average switch current). To preserve the long term reliability of the device the average switch current should not exceed 535mA. The LM3500 has an internal thermal shutdown function to protect the die from excessive temperatures. The thermal shutdown trip point is typically 150C. There is a hysteresis of typically 35C so the die temperature must decrease to approximately 115C before the LM3500 will return to normal operation. INDUCTOR SELECTION The inductor used with the LM3500 must have a saturation current greater than the cycle by cycle peak inductor current (see Typical Peak Inductor Currents table below). Choosing inductors with low DCR decreases power losses and increases efficiency. The minimum inductor value required for the LM3500-16 can be calculated using the following equation:
The minimum inductor value required for the LM3500-21 can be calculated using the following equation:
For the LM3500 to operate properly, the output voltage must be kept above the input voltage during operation. For most applications, this requires a minimum of 2 LEDs (total of 6V or more) between the FB and VOUT pins. OUTPUT OVERVOLTAGE PROTECTION The LM3500 contains dedicated circuitry for monitoring the output voltage. In the event that the primary LED network is disconnected from the LM3500-16, the output voltage will increase and be limited to 15.5V (typ.). There is a 900mV hysteresis associated with this circuitry which will cause the output to fluctuate between 15.5V and 14.6V (typ.) if the primary network is disconnected. In the event that the network is reconnected regulation will begin at the appropriate output voltage. The 15.5V limit allows the use of 16V 1F ceramic output capacitors creating an overall small solution for white LED applications.
13
For both equations above, L is in H, VIN is the input supply of the chip in Volts, RDSON is the ON resistance of the NMOS power switch found in the Typical Performance Characteristics section in ohms and D is the duty cycle of the switching regulator. The above equation is only valid for D greater than or equal to 0.5. For applications where the minimum duty cycle is less than 0.5, a 22H inductor is the typical recommendation for use with most applications. Bench-level verification of circuit performance is required in these special cases, however. The duty cycle, D, is given by the following equation:
where VOUT is the voltage at pin C1.
www.national.com
LM3500
Application Information
VIN (V) 2.7 # LEDs (in series) 2 3 4 5 3.3 2 3 4 5 4.2 2 3 4 5
(Continued)
Coilcraft DT1608C series Coilcraft DO1608C series TDK VLP4612 series 60 mA 234 352 X X 198 290 X X 162 246 318 456 TDK VLP5610 series TDK VLF4012A series CAPACITOR SELECTION Choose low ESR ceramic capacitors for the output to minimize output voltage ripple. Multilayer X7R or X5R type ceramic capacitors are the best choice. For most applications, a 1F ceramic output capacitor is sufficient. Local bypassing for the input is needed on the LM3500. Multilayer X7R or X5R ceramic capacitors with low ESR are a good choice for this as well. A 1F ceramic capacitor is sufficient for most applications. However, for some applications at least a 4.7F ceramic capacitor may be required for proper startup of the LM3500. Using capacitors with low ESR decreases input voltage ripple. For additional bypassing, a 100nF ceramic capacitor can be used to shunt high frequency ripple on the input. Some recommended capacitors include but are not limited to: TDK C2012X7R1C105K Taiyo-Yuden EMK212BJ105 G LAYOUT CONSIDERATIONS The input bypass capacitor CIN, as shown in Figure 1, must be placed close to the device and connect between the VIN and GND pins. This will reduce copper trace resistance which effects the input voltage ripple of the IC. For additional input voltage filtering, a 100nF bypass capacitor can be placed in parallel with CIN to shunt any high frequency noise to ground. The output capacitor, COUT, should also be placed close to the LM3500 and connected directly between the VOUT and GND pins. Any copper trace connections for the COUT capacitor can increase the series resistance, which directly effects output voltage ripple and efficiency. The current setting resistor, RLED, should be kept close to the FB pin to minimize copper trace connections that can inject noise into the system. The ground connection for the current setting resistor should connect directly to the GND pin. The AGND pin should connect directly to the GND pin. Not connecting the AGND pin directly, as close to the chip as possible, may affect the performance of the LM3500 and limit its current driving capability. Trace connections made to the inductor should be minimized to reduce power dissipation, EMI radiation and increase overall efficiency. It is good practice to keep the VSW routing away from sensitive pins such as the FB pin. Failure to do so may inject noise into the FB pin and affect the regulation of the device. See Figure 2 and Figure 3 for an example of a good layout as used for the LM3500 evaluation board.
Typical Peak Inductor Currents (mA) LED Current 15 mA 82 118 142 191 76 110 132 183 64 102 122 179 20 mA 100 138 174 232 90 126 158 216 76 116 146 206 30 mA 134 190 244 319 116 168 212 288 96 148 186 263 40 mA 160 244 322 413 136 210 270 365 116 180 232 324 50 mA 204 294 X X 172 250 320 446 142 210 272 388
CIN = COUT = 1 F L = 22 H, 160 m DCR max. Coilcraft DT1608C-223 2 and 3 LED applications: LM3500-16 or LM3500-21; LED VF = 3.77V at 20mA; TA = 25C 4 LED applications: LM3500-16 or LM3500-21; LED VF = 3.41V at 20mA; TA = 25C 5 LED applications: LM3500-21 only; LED VF = 3.28V at 20mA; TA = 25C
The typical cycle-by-cycle peak inductor current can be calculated from the following equation:
where IOUT is the total load current, FSW is the switching frequency, L is the inductance and is the converter efficiency of the total driven load. A good typical number to use for is 0.8. The value of can vary with load and duty cycle. The average inductor current, which is also the average VSW pin current, is given by the following equation:
The maximum output current capability of the LM3500 can be estimated with the following equation:
where ICL is the current limit. Some recommended inductors include but are not limited to:
www.national.com
14
LM3500
Application Information
(Continued)
20065777
FIGURE 2. Evaluation Board Layout (2X Magnification) Top Layer
20065778
FIGURE 3. Evaluation Board Layout (2X Magnification) Bottom Layer (as viewed from the top)
15
www.national.com
LM3500
Application Information
(Continued)
20065709
FIGURE 4. 2 White LED Application
20065754
FIGURE 5. Multiple 2 LED String Application
www.national.com
16
LM3500
Application Information
(Continued)
20065783
FIGURE 6. Multiple 3 LED String Application
20065790
FIGURE 7. LM3500-21 5 LED Application
17
www.national.com
Synchronous Step-up DC/DC Converter for White LED Applications
Physical Dimensions
unless otherwise noted
inches (millimeters)
8-Bump Micro SMD Package (TL) For Ordering, Refer to Ordering Information Table NS Package Number TLA08SSA X1 = 1.92mm (0.03mm), X2 = 1.92mm (0.03mm), X3 = 0.6mm (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. BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that 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: new.feedback@nsc.com Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Francais Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: ap.support@nsc.com National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560
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.
WWW..COM
Copyright (c) Each Manufacturing Company. All Datasheets cannot be modified without permission.
This datasheet has been download from : www..com
100% Free DataSheet Search Site. Free Download. No Register. Fast Search System. www..com

▲Up To Search▲

Price & Availability of LM3500TL-16

	To Download LM3500TL-16 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .