LM3508 [NSC]

Synchronous Magnetic Constant Current White LED Driver; 同步磁场恒流白光LED驱动器
LM3508
型号: LM3508
厂家: National Semiconductor    National Semiconductor
描述:

Synchronous Magnetic Constant Current White LED Driver
同步磁场恒流白光LED驱动器

驱动器
文件: 总14页 (文件大小:1365K)
中文:  中文翻译
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April 2007  
LM3508  
Synchronous Magnetic Constant Current White LED Driver  
General Description  
Features  
The LM3508 is a synchronous boost converter (no external  
Schottky diode required) that provides a constant current out-  
put. It is designed to drive up to 4 series white LEDs at 30mA  
from a single-cell Li-Ion battery. A single low power external  
resistor is used to set the maximum LED current. The LED  
current can be adjusted by applying a PWM signal of up to  
100kHz to the DIM pin. Internal soft-start circuitry is designed  
to eliminate high in-rush current at start-up. For maximum  
safety, the device features an advanced short-circuit protec-  
tion when the output is shorted to ground. Additionally, over-  
voltage protection and an 850kHz switching frequency allow  
for the use of small, low-cost output capacitors with lower  
voltage ratings. During shutdown, the output is disconnected  
from the input preventing a leakage current path through the  
LEDs to ground. The LM3508 is available in a tiny 9-bump  
chip-scale micro-SMD package.  
Drives 4 Series White LEDs with up to 30mA  
>80% Peak Efficiency  
Up to 100kHz PWM Brightness Control  
Accurate ±5% LED Current Regulation across VIN range  
Internal Synchronous PFET (No Schottky Diode  
Required)  
True Shutdown Isolation  
Output Short-Circuit Protection  
17.5V Over-Voltage Protection  
Internal Soft-Start Eliminates Inrush Current  
Wide Input Voltage Range: 2.7V to 5.5V  
850kHz Fixed Frequency Operation  
Low Profile 9-Bump Micro-SMD Package (1.514mm x  
1.514mm x 0.6mm)  
Applications  
White LED Backlighting  
Handheld Devices  
Digital Cameras  
Portable Applications  
Typical Application Circuit  
30004201  
© 2007 National Semiconductor Corporation  
300042  
www.national.com  
Connection Diagram  
Top View  
30004202  
9-Bump (Large) µ-SMD (1.514mm x 1.514mm x 0.6mm) NS Package Number TLA09  
Ordering Information  
Part Number  
LM3508TL  
Package Type  
9-Bump micro SMD  
9-Bump micro SMD  
NSC Package Drawing Top Mark  
Supplied As  
TL09SDA  
TL09SDA  
D31  
D31  
250 Units, Tape and Reel  
3000 Units, Tape and Reel  
LM3508TLX  
Pin Descriptions/Functions  
Pin  
A1  
A2  
A3  
Name  
PGND  
SW  
Function  
Power Ground Connection.  
Inductor connection and drain connection for both NMOS and PMOS power devices.  
OUT  
Output capacitor connection, PMOS source connection for synchronous rectifier, and OVP  
sensing node.  
B1  
B2  
ILED  
DIM  
Regulated current source input.  
Current source modulation input. A logic low at DIM turns off the internal current source. A logic  
high turns the LEDs fully on (VSET=200mV). Apply a PWM signal at DIM for LED brightness control.  
B3  
C1  
IN  
Input voltage connection.  
SET  
Current sense connection and current source output. Connect a 1% resistor (RSET) from SET to  
PGND to set the maximum LED current (ILED = 200mV/RSET) .  
C2  
C3  
EN  
Enable input. A logic low at EN turns off the LM3508. A logic high turns the device on.  
Analog ground. Connect AGND to PGND through a low impedance connection.  
AGND  
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2
Absolute Maximum Ratings (Notes 1, 2)  
Operating Conditions (Notes 1, 2)  
If Military/Aerospace specified devices are required,  
please contact the National Semiconductor Sales Office/  
Distributors for availability and specifications.  
Input Voltage Range  
2.7V to 5.5V  
Ambient Temperature Range  
(Note 5)  
Junction Temperature Range  
−30°C to +85°C  
−30°C to +105°C  
VIN  
−0.3V to 6V  
−0.3V to 22V  
−0.3V to 22V  
VOUT  
Thermal Properties  
Junction to Ambient Thermal  
VSW  
VILED, VSET, VDIM, VEN  
−0.3V to 6V  
64.7°C/W  
Resistance (θJA)(Note 6)  
Continuous Power Dissipation  
(Note )  
Internally Limited  
Junction Temperature  
Lead Temperature  
(Note 4)  
Storage Temperature Range  
ESD Rating(Note 9)  
Human Body Model  
+150°C  
ESD Caution Notice  
National Semiconductor recommends that all integrated cir-  
cuits be handled with appropriate ESD precautions. Failure to  
observe proper ESD handling techniques can result in dam-  
age to the device.  
+300°C  
-65°C to +150°C  
2kV  
Electrical Characteristics  
Specifications in standard type face are for TA = 25°C and those in boldface type apply over the Operating Temperature Range  
of TA = −30°C to +85°C. Unless otherwise specified VIN =3.6V.(Note 7)  
Symbol  
Parameter  
LED Current  
Regulation  
Conditions  
RSET = 10Ω  
Min  
Typ  
20  
Max  
Units  
ID  
mA  
RSET = 6.67Ω  
30  
VSET  
VILED  
VHR  
Voltage at SET Pin  
Voltage at ILED Pin  
3.0V < VIN < 5.5V  
190  
200  
500  
210  
mV  
mV  
Current Sink  
Headroom Voltage  
Where ILED = 95% of  
nominal, RSET = 20Ω  
ISW = 100mA  
400  
0.5  
mV  
RDSON  
NMOS Switch On  
Resistance  
PMOS Switch On  
Resistance  
VOUT = 10V, ISW = 65mA  
2.2  
ICL  
NMOS Switch  
Current Limit  
370  
500  
0.01  
620  
nA  
µA  
ILSW  
SW Leakage Current VSW = VIN = 5.5V, OUT  
Floating, VEN = PGND  
IOUT_SHUTDOWN  
Outout Pull-Down  
Resistance in  
Shutdown  
VEN = 0V  
630  
VOVP  
Output Over-Voltage ON Threshold (VOUT rising)  
17.5  
715  
19.8  
18.6  
21.8  
Protection  
V
OFF Threshold (VOUT  
falling)  
Switching Frequency 3.0V < VIN < 5.5V  
Maximum Duty Cycle  
fSW  
850  
91  
1150  
MHz  
%
DMAX  
VSC  
Output Voltage  
Threshold for Short  
Circuit Detection  
VOUT Falling  
VOUT Rising  
0.93×VIN  
0.95×VIN  
V
VEN_TH  
VDIM_TH  
IDIM  
EN Threshold  
Voltage  
On Threshold  
Off Threshold  
On Threshold  
Off Threshold  
VDIM = 1.8V  
1.1  
1.1  
0.5  
0.5  
V
V
DIM Threshold  
Voltage  
DIM Bias Current  
(Note 8)  
4.7  
µA  
3
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Symbol  
Parameter  
Conditions  
VEN = 1.8V  
Min  
Typ  
Max  
Units  
IEN  
EN Bias Current  
(Note 8)  
4.7  
µA  
IOUT  
OUT Bias Current  
VOUT = 16V, device not  
switching  
420  
630  
µA  
ROUT_SHUTDOWN  
Output Pull-Down  
Resistance in  
Shutdown  
VEN = 0V, VOUT < VIN  
IQ  
Quiescent Current  
Device Not Switching  
VILED > 0.5V, 3.0V < VIN  
5.5V, SW Floating  
<
0.18  
0.01  
825  
0.3  
0.5  
mA  
VEN = 0V, 3.0V < VIN < 5.5V  
IQ_SW  
Switching Supply  
Current  
µA  
µs  
tSTART_UP  
From EN Low to High VOUT = 17V, ILED = 20mA  
to Inductor Current  
470  
Steady State  
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: All voltages are with respect to PGND.  
Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown enagaes at TJ = +150°C (typ.) and disengages at  
TJ = +140°C (typ.).  
Note 4: 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 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 (θJA), as given by the  
following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).  
Note 6: Junction-to-ambient thermal resistance (θJA) is taken from thermal modeling performed under the conditions and guidelines set forth in the JEDEC  
standard JESD51-7. The test board is a 4-layer FR-4 board mesuring (102mm × 76mm × 1.6mm) with a 2 × 1 array of thermal vias. The ground plane on the  
board is (50mm × 50mm). Thickness of copper layers are (36µm/18µm/18µm/36µm) (1.5oz/1oz/1oz/1.5oz copper). Ambient temperature in simulation is +22°C,  
still air. Power dissipation is 1W.  
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.  
Unless otherwise specified, conditions for typical specifications are VIN = 3.6V, TA = +25°C.  
Note 8: There is a typical 383kpull-down on this pin.  
Note 9: The human body model is a 100pF capacitor discharged through 1.5kresistor into each pin. (MIL-STD-883 3015.7).  
Typical Performance Characteristics VIN = 3.6V, RSET = 10Ω, L = TDK VLF3012AT-220MR33 (22µH),  
LEDs are OSRAM (LW M67C), COUT = CIN = 1µF, TA = +25°C, unless otherwise noted.  
4 LED Efficiency vs ILED  
3 LED Efficiency vs ILED  
(L = TDK VLF3012AT-220MR33, RL = 0.66Ω)  
(L = TDK VLF3012AT-220MR33, RL = 0.66Ω)  
30004242  
30004241  
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2 LED Efficiency vs ILED  
Converter Output Voltage vs LED Current  
(L = TDK VLF3012AT-220MR33, RL = 0.66Ω)  
30004243  
30004258  
Efficiency vs VIN (ILED = 20mA)  
Efficiency vs VIN (ILED = 30mA)  
30004260  
30004261  
Peak Current Limit vs VIN  
Switching Frequency vs VIN  
30004214  
30004213  
5
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Maximum Duty Cycle vs VIN  
Quiescent Current vs VIN  
(EN = GND)  
30004215  
30004217  
Quiescent Current vs VIN  
(Device Not Switching, VIN = VSW  
Quiescent Current vs VIN  
(Device Switching)  
)
30004216  
30004218  
SET Voltage vs DIM Frequency  
(50% Duty Cycle at DIM)  
SET Voltage vs VIN  
30004259  
30004219  
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6
SET Voltage vs DIM Duty Cycle  
NFET On-Resistance vs VIN  
(ISW = 250mA)  
30004262  
30004224  
PFET On-Resistance vs Temperature  
(VSW = 10.4V, VOUT = 10V)  
Over Voltage Limit vs VIN  
(VOUT Rising)  
30004225  
30004227  
Over Voltage Limit vs VIN (VOUT Falling)  
Start-Up Waveform  
30004257  
4 LEDs, ILED = 30mA, VIN = 3.6V  
Channel 1: VOUT (10V/div)  
Channel 2: EN (2V/div)  
Channel 4: IIN (200mA/div)  
Time Base: 100µs/div  
30004228  
7
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Over-Voltage Protection Function  
Line-Step Response  
30004237  
30004255  
VIN = 3.6V, VOUT = 18.86V  
VIN = 3.6V, 4 LEDs  
Channel 1: VOUT (1V/div)  
Channel 4: IIN (500mA/div)  
Time Base: 400µs/div  
Channel 1: VOUT (AC Copupled, 1V/div)  
Channel 3: VIN (AC Coupled, 500mV/div)  
Channel 4: ILED (DC Coupled, 5mA/div)  
Time Base: 200µs/div  
Output Short-Circuit Response  
Typical Operating Waveforms (DIM High)  
30004256  
30004229  
VIN = 3.6V, ILED = 30mA  
Channel 1: VOUT (10V/div)  
Channel 2: IIN (100mA/div)  
Time Base: 200µs/div  
VIN = 3.6V, 4 LEDs, ILED = 30mA, VOUT = 15.8V  
Channel 1: VOUT (AC Coupled, 100mV/div)  
Channel 2: VSW (DC Coupled, 10V/div)  
Channel 4: IL (DC Coupled, 100mA/div)  
Time Base: 400ns/div  
Typical Operating Waveforms (DIM With 20kHz Square  
Wave)  
DIM Operation (ILED changing from 30mA to 15mA)  
30004238  
30004230  
VIN = 3.6V  
VIN = 3.6V, 4 LEDs, ILED = 15mA  
Channel 4: ILED (DC Coupled, 10mA/div)  
Channel 2: VOUT (AC Coupled, 2V/div)  
Channel 1: DIM (DC Coupled, 2V/div, 20kHz, 50% duty cycle)  
Channel 3: IIN (DC Coupled, 200mA/div)  
Time Base: 400µs/div  
Channel 1: VOUT (AC Coupled, 200mV/div)  
Channel 3: VIN (AC Coupled, 100mV/div)  
Channel 2: IL (DC Coupled, 100mA/div)  
Channel 4: DIM (DC Coupled, 2V/div)  
Time Base: 10µs/div  
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8
Operation  
30004203  
FIGURE 1. LM3508 Block Diagram  
The LM3508 utilizes a synchronous step-up current mode  
PWM controller and a regulated current sink to provide a  
highly efficient and accurate LED current for white LED bias.  
The internal synchronous rectifier increases efficiency and  
eliminates the need for an external diode. Additionally, inter-  
nal compensation eliminates the need for external compen-  
sation components resulting in a compact overall solution.  
LED’s. At the end of the clock period the PWM controller is  
again set and the process repeats itself. This action regulates  
ILED to 500mV.  
The second stage of the LM3508 consists of an internal cur-  
rent source powered by the ILED voltage and providing a  
regulated current at SET. The regulated LED current is set by  
connecting an external resistor from SET to PGND. VSET is  
adjusted from 0 to 200mV by applying a PWM signal of up to  
typically 100kHz at DIM (see Typical Performance Charac-  
teristic of SET voltage vs DIM frequency). The PWM signal at  
DIM modulates the internal 200mV reference and applies it to  
an internal RC filter resulting in an adjustable SET voltage and  
thus an adjustable LED current.  
Figure 1 shows the detailed block diagram of the LM3508.  
The output of the boost converter (OUT) provides power to  
the series string of white LED’s connected between OUT and  
ILED. The boost converter regulates the voltage at ILED to  
500mV. This voltage is then used to power the internal current  
source whose output is at SET.  
The first stage of the LM3508 consists of the synchronous  
boost converter. Operation is as follows: At the start of each  
switching cycle the oscillator sets the PWM controller. The  
controller turns the low side (NMOS) switch on and the syn-  
chronous rectifier (PMOS) switch off. During this time current  
ramps up in the inductor while the output capacitor supplies  
the current to the LED’s. The error signal at the output of the  
error amplifier is compared against the sensed inductor cur-  
rent. When the sensed inductor current equals the error sig-  
nal, or when the maximum duty cycle is reached, the NMOS  
switch turns off and the PMOS switch turns on. When the  
PMOS turns on, the inductor current ramps down, restoring  
energy to the output capacitor and supplying current to the  
Start-Up  
The LM3508 features a soft-start to prevent large inrush cur-  
rents during start-up that can cause excessive voltage ripple  
on VIN. During start-up the average input current is ramped  
up at a controlled rate. For the typical application circuit, driv-  
ing 4LED’s from a 3.6V lithium battery at 30mA, when EN is  
driven high the average input current ramps from zero to 160-  
mA in 470µs. See plot of Soft Start functionality in the Typical  
Performance Characteristics.  
9
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figure 1) will be fully on, appearing as a 5resistor between  
ILED and SET.  
DIM Operation  
DIM is the input to the gate of an internal switch that accepts  
a logic level PWM waveform and modulates the internal  
200mV reference through an internal RC filter. This forces the  
current source regulation point (VSET) to vary by the duty cycle  
Output Short Circuit Protection  
The LM3508 provides a short circuit protection that limits the  
output current if OUT is shorted to PGND. During a short at  
OUT when VOUT falls to below VIN × 0.93, switching will stop.  
The PMOS will turn into a current source and limit the output  
current to 35mA. The LM3508 can survive with a continuous  
short at the output. The threshold for OUT recovering from a  
short circuit condition is typically VIN × 0.95.  
(D) of the DIM waveform making ILED = D × 200mV / RSET  
.
The cutoff frequency for the filter is approximately 500Hz. DIM  
frequencies higher than 100kHz cause the LED current to  
drastically deviate from their nominal set points. The graphs  
of SET voltage vs DIM frequency, SET voltage vs VIN and SET  
voltage vs DIM duty cycle (see Typical Performance Charac-  
teristics) show the typical variation of the current source set  
point voltage.  
Output Over-Voltage Protection  
When the load at the output of the LM3508 goes high  
impedance the boost converter will raise VOUT to try and  
maintain the programmed LED current. To prevent over-volt-  
age conditions that can damage output capacitors and/or the  
device, the LM3508 will clamp the output at a maximum of  
21.8V. This allows for the use of 25V output capacitors avail-  
able in a tiny 1.6mm × 0.8mm case size.  
Enable Input and Output Isolation  
Driving EN high turns the device on while driving EN low  
places the LM3508 in shutdown. In shutdown the supply cur-  
rent reduces to less than 1µA, the internal synchronous PFET  
turns off as well as the current source (N2 in figure 1). This  
completely isolates the output from the input and prevents  
leakage current from flowing through the LED’s. In shutdown  
the leakage current into SW and IN is typically 400nA. EN has  
an internal 383kpull-down to PGND.  
During output open circuit conditions when the output voltage  
rises to the over voltage protection threshold (VOVP = 19.8V  
typical) the OVP circuitry will shut off both the NMOS and  
PMOS switches. When the output voltage drops below 18.6V  
(typically) the converter will begin switching again. If the de-  
vice remains in an over voltage condition the cycle will be  
repeated resulting in a pulsed condition at the output. See  
waveform for OVP condition in the Typical Performance Char-  
acteristics.  
Peak Current Limit/Maximum  
Output Current  
The LM3508 boost converter provides a peak current limit.  
When the peak inductor current reaches the peak current limit  
the duty cycle is terminated. This results in a limit on the max-  
imum output power and thus the maximum output current the  
LM3508 can deliver. Calculate the maximum LED current as  
a function of VIN, VOUT, L and IPEAK as:  
Light Load Operation  
During light load conditions when the inductor current reaches  
zero before the end of the switching period, the PFET will turn  
off, disconnecting OUT from SW and forcing the converter  
into discontinuous conduction. At the beginning of the next  
switching cycle, switching will resume. (see plot of discontin-  
uous conduction mode in the Typical Performance Charac-  
teristics graphs).  
Boost converters that operate in the discontinuous conduc-  
tion mode with fixed input to output conversion ratios (VOUT  
/
VIN) have load dependent duty cycles, resulting in shorter  
switch on-times as the load decreases. As the load is de-  
creased the duty cycle will fall until the converter hits its  
minimum duty cycle (typically 15%). To prevent further de-  
creases in the load current altering the VOUT/VIN ratio, the  
LM3508 will enter a pulsed skip mode. In pulse skip mode the  
device will only switch as necessary to keep the LED current  
in regulation.  
and fSW = 850kHz. Efficiency and IPEAK can be found in the  
efficiency and IPEAK curves in the Typical Performance Char-  
acteristics.  
Output Current Accuracy  
The LM3508 provides highly accurate output current regula-  
tion of ±5% over the 3V to 5.5V input voltage range. Accuracy  
depends on various key factors. Among these are; the toler-  
ance of RSET, the frequency at DIM (ƒDIM), and the errors  
internal to the LM3508 controller and current sink. For best  
accuracy, use a 1% resistor for RSET and keep ƒDIM between  
1kHz and 100kHz. Refer to the Typical Performance Char-  
acteristics for VSET vs VIN, VSET vs ƒDIM, and VSET vs DIM duty  
cycle.  
Thermal Shutdown  
The LM3508 provides a thermal shutdown feature. When the  
die temperature exceeds +150°C the part will shutdown, turn-  
ing off both the NMOS and PMOS FET’s. The part will start-  
up again with a soft-start sequence when the die temperature  
falls below +115°C.  
Applications Information  
Voltage Head Room at ILED  
BRIGHTNESS ADJUSTMENT  
If the LED current is increased to a point where the peak in-  
ductor current is reached, the boost converter's on-time is  
terminated until the next switching cycle. If the LED current is  
further increased the 500mV regulated voltage at ILED begins  
to drop. When VILED drops below the current sink headroom  
voltage (VHR = 400mV typ.) the current sink FET (see N2 in  
A logic high at DIM forces SET to regulate to 200mV. Adjust  
the maximum LED current by picking RSET (the resistor from  
SET to GND) such that:  
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10  
input capacitor, the output voltage ripple is composed of two  
parts, the ripple due to capacitor discharge (delta VQ) and the  
ripple due to the capacitors ESR (delta VESR). Most of the time  
the LM3508 will operate in continuous conduction mode. In  
this mode the ripple due to capacitor discharge is given by:  
Once ILED_MAX is set, the LED current can be adjusted from  
ILED_MAX down to ILED_MIN by applying a logic level PWM signal  
to DIM. This results in:  
The output voltage ripple component due to the output ca-  
pacitors ESR is found by:  
where D is the duty cycle of the PWM pulse applied to DIM.  
The LM3508 can be brought out of shutdown while a signal  
is applied to DIM, allowing the device to turn on into a low LED  
current mode. A logic low at DIM will shut off the current  
source making ILED high impedance however, the boost con-  
verter continues to operate. Due to an offset voltage at SET  
(approximately +/-2mV) the LED’s can faintly illuminate even  
with DIM pulled to GND. If zero LED current is required then  
pulling EN low will shutdown the current source causing the  
LED current to drop to zero. DIM has an internal 383kpull  
down to PGND.  
Table 1. Recommended Output Capacitor Manufacturers  
Manufact  
urer  
Part  
Number  
Value  
Case Size Voltage  
Rating  
INPUT CAPACITOR SELECTION  
Choosing the correct size and type of input capacitor helps  
minimize the input voltage ripple caused by the switching ac-  
tion of the LM3508’s boost converter. For continuous inductor  
current operation the input voltage ripple is composed of 2  
primary components, the capacitor discharge (delta VQ) and  
the capacitor’s equivalent series resistance (delta VESR). The  
ripple due to strictly to the capacitor discharge is:  
GRM39X5  
R105K25  
D539  
1µF  
0603  
25V  
Murata  
TDK  
C1608X5  
R1E105M  
1µF  
0603  
25V  
INDUCTOR SELECTION  
The LM3508 is designed to operate with 10µH to 22µH  
inductor’s. When choosing the inductor ensure that the in-  
ductors saturation current rating is greater than  
The ripple due to strictly to the capacitors ESR is:  
Additionally, the inductor’s value should be large enough such  
that at the maximum LED current, the peak inductor current  
is less than the LM3508’s peak switch current limit. This is  
done by choosing L such that  
In the typical application circuit, a 1µF ceramic input capacitor  
works well. Since the ESR in ceramic capacitors is typically  
less than 5mand the capacitance value is usually small, the  
input voltage ripple is primarily due to the capacitive dis-  
charge. With larger value capacitors such as tantalum or  
aluminum electrolytic the ESR can be greater than 0.5. In  
this case the input ripple will primarily be due to the ESR.  
Output Capacitor Selection  
In a boost converter such as the LM3508, during the on time,  
the inductor is disconnected from OUT forcing the output ca-  
pacitor to supply the LED current. When the PMOS switch  
(synchronous rectifier) turns on the inductor energy supplies  
the LED current and restores charge to the output capacitor.  
This action causes a sag in the output voltage during the on  
time and a rise in the output voltage during the off time.  
Values for IPEAK and efficiency can be found in the plot of peak  
current limit vs. VIN in the Typical Performance Characteris-  
tics graphs.  
The LM3508’s output capacitor is chosen to limit the output  
ripple to an acceptable level and to ensure the boost converter  
is stable. For proper operation use a 1µF ceramic output ca-  
pacitor. Values of 2.2µF or 4.7µF can be used although start-  
up current and start-up time will be increased. As with the  
11  
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Table 2. Recommended Inductor Manufacturers  
1, Use a separate ground plane for power ground (PGND)  
and analog ground (AGND).  
MANUFACT  
URER  
L
Part  
Number  
Size  
Saturation  
Current  
2, Keep high current paths such as SW and PGND connec-  
tions short.  
TDK  
TDK  
Toko  
22µ VLF3010 2.6mm×2.  
AT-220M 8mm×1m  
R33  
22µ VLF3012 2.6mm×2.  
AT-220M 8mm×1.2  
R33 mm  
22u D3313FB 3.3mm×3.  
(1036FB- 3mm×1.3  
220M) mm  
330mA  
330mA  
350mA  
3, Connect the return terminals for the input capacitor and the  
output capacitor together at a single point as close as possible  
to PGND.  
H
m
4, Connect PGND and AGND together as close as possible  
to the IC. Do not connect them together anywhere else.  
H
5, Connect the input capacitor (CIN) as close as possible to  
IN.  
6, Connect the output capacitor (COUT) as close as possible  
to OUT.  
H
7, Connect the positive terminal of RSET as close as possible  
to ILED and the negative terminal as close as possible to  
PGND. This ensures accurate current programming.  
LAYOUT CONSIDERATIONS  
Proper layout is essential for stable, jitter free operation, and  
good efficiency. Follow these steps to ensure a good layout.  
www.national.com  
12  
Physical Dimensions inches (millimeters) unless otherwise noted  
9-Bump Micro SMD Package (TL09AAA)  
For Ordering, Refer to Ordering Information Table  
NS Package Number TLA09AAA  
X1 = 1.514mm (±0.03mm), X2 = 1.514mm (±0.03mm), X3 = 0.6mm (±0.075mm)  
13  
www.national.com  
Notes  
THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION  
(“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY  
OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO  
SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS,  
IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS  
DOCUMENT.  
TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT  
NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL  
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Life support devices or systems are devices 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  
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