National Semiconductor LM3410 Technical data

April 8, 2008
LM3410 PowerWise® 525kHz/1.6MHz, Constant Current Boost and SEPIC LED Driver with Internal Compensation
LM3410 PowerWise
Internal Compensation

General Description

The LM3410 constant current LED driver is a monolithic, high frequency, PWM DC/DC converter in 5-pin SOT23, 6-pin LLP, & 8-pin eMSOP packages. With a minimum of external com­ponents the LM3410 is easy to use. It can drive 2.8A typical peak currents with an internal 170 m NMOS switch. Switch­ing frequency is internally set to either 525 kHz or 1.60 MHz, allowing the use of extremely small surface mount inductors and chip capacitors. Even though the operating frequency is high, efficiencies up to 88% are easy to achieve. External shutdown is included, featuring an ultra-low standby current of 80 nA. The LM3410 utilizes current-mode control and in­ternal compensation to provide high-performance over a wide range of operating conditions. Additional features include dimming, cycle-by-cycle current limit, and thermal shutdown.

Typical Boost Application Circuit

Features

Space Saving SOT23-5 & 6-LLP Package
Input voltage range of 2.7V to 5.5V
Output voltage range of 3V to 24V
2.8A Typical Switch Current
High Switching Frequency
525 KHz (LM3410-Y)
1.6 MHz (LM3410-X)
170 m NMOS Switch
190 mV Internal Voltage Reference
Internal Soft-Start
Current-Mode, PWM Operation
Thermal Shutdown

Applications

LED Backlight Current Source
LiIon Backlight OLED & HB LED Driver
Handheld Devices
LED Flash Driver
®
525kHz/1.6MHz, Constant Current Boost and SEPIC LED Driver with
30038501
30038502
© 2008 National Semiconductor Corporation 300385 www.national.com

Connection Diagrams

LM3410
Top View
5–Pin SOT23
30038503
Top View
6-Pin LLP
Top View
30038504
8-Pin eMSOP

Ordering Information

Order Number Frequency Package Type Package Drawing Supplied As
LM3410YMF
LM3410YMFX 3000 units Tape & Reel
LM3410YMFE 250 units Tape & Reel
LM3410YSD
LM3410YSDX 4500 units Tape & Reel
LM3410YSDE 250 units Tape & Reel
LM3410YMY
LM3410YMYX 3500 units Tape & Reel
LM3410YMYE 250 units Tape & Reel
LM3410XMF
LM3410XMFX 3000 units Tape & Reel
LM3410XMFE 250 units Tape & Reel
LM3410XSD
LM3410XSDX 4500 units Tape & Reel
LM3410XSDE 250 units Tape & Reel
LM3410XMY
LM3410XMYX 3500 units Tape & Reel
LM3410XMYE 250 units Tape & Reel
525 kHz
1.6 MHz
SOT23-5 MF05A
LLP-6 SDE06A
eMSOP-8 MUY08A
SOT23-5 MF05A
LLP-6 SDE06A
eMSOP-8 MUY08A
1000 units Tape & Reel
1000 units Tape & Reel
1000 units Tape & Reel
1000 units Tape & Reel
1000 units tape & reel
1000 units Tape & Reel
30038505
www.national.com 2

Pin Descriptions - 5-Pin SOT23

Pin Name Function
1 SW Output switch. Connect to the inductor, output diode.
2 GND
3 FB Feedback pin. Connect FB to external resistor divider to set output voltage.
4 DIM
5 VIN Supply voltage pin for power stage, and input supply voltage.
Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin.
Dimming & shutdown control input. Logic high enables operation. Duty Cycle from 0 to 100%. Do not allow this pin to float or be greater than VIN + 0.3V.

Pin Descriptions - 6-Pin LLP

Pin Name Function
1 PGND Power ground pin. Place PGND and output capacitor GND close together.
2 VIN Supply voltage for power stage, and input supply voltage.
3 DIM
4 FB Feedback pin. Connect FB to external resistor divider to set output voltage.
5 AGND
6 SW Output switch. Connect to the inductor, output diode.
DAP GND
Dimming & shutdown control input. Logic high enables operation. Duty Cycle from 0 to 100%. Do not allow this pin to float or be greater than VIN + 0.3V.
Signal ground pin. Place the bottom resistor of the feedback network as close as possible to this pin & pin
4.
Signal & Power ground. Connect to pin 1 & pin 5 on top layer. Place 4-6 vias from DAP to bottom layer GND plane.
LM3410

Pin Descriptions - 8-Pin eMSOP

Pin Name Function
1 - No Connect
2 PGND Power ground pin. Place PGND and output capacitor GND close together.
3 VIN Supply voltage for power stage, and input supply voltage.
4 DIM
5 FB Feedback pin. Connect FB to external resistor divider to set output voltage.
6 AGND Signal ground pin. Place the bottom resistor of the feedback network as close as possible to this pin & pin 5
7 SW Output switch. Connect to the inductor, output diode.
8 - No Connect
DAP GND
Dimming & shutdown control input. Logic high enables operation. Duty Cycle from 0 to 100%. Do not allow this pin to float or be greater than VIN + 0.3V.
Signal & Power ground. Connect to pin 2 & pin 6 on top layer. Place 4-6 vias from DAP to bottom layer GND plane.
3 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
LM3410
please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.
V
IN
SW Voltage -0.5V to 26.5V FB Voltage -0.5V to 3.0V DIM Voltage -0.5V to 7.0V ESD Susceptibility (Note 4) Human Body Model 2kV Junction Temperature (Note 2) 150°C
-0.5V to 7V
Storage Temp. Range -65°C to 150°C Soldering Information Infrared/Convection Reflow (15sec) 220°C

Operating Ratings (Note 1)

V
IN
V
(Note 5) 0V to V
DIM
V
SW
Junction Temperature Range -40°C to 125°C Power Dissipation
(Internal) SOT23-5 400 mW
2.7V to 5.5V
3V to 24V
IN

Electrical Characteristics Limits in standard type are for T

= 25°C only; limits in boldface type apply over the
J
junction temperature (TJ) range of -40°C to 125°C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. VIN = 5V, unless otherwise indicated under the Conditions column.
Symbol Parameter Conditions Min Typ Max Units
V
FB
ΔVFB/V
I
FB
F
SW
D
MAX
D
MIN
R
DS(ON)
I
CL
Feedback Voltage 178 190 202 mV
Feedback Voltage Line Regulation
IN
VIN = 2.7V to 5.5V
- 0.06 - %/V
Feedback Input Bias Current - 0.1 1 µA
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
Switch On Resistance
LM3410-X 1200 1600 2000
LM3410-Y 360 525 680
LM3410-X 88 92 -
LM3410-Y 90 95 -
LM3410-X - 5 -
LM3410-Y - 2 -
SOT23-5 and eMSOP-8 - 170 330
LLP-6 190 350
Switch Current Limit 2.1 2.80 - A
kHz
%
%
m
SU Start Up Time - 20 - µs
I
Q
Quiescent Current (switching)
Quiescent Current (shutdown)
UVLO Undervoltage Lockout
V
DIM_H
I
SW
I
DIM
Shutdown Threshold Voltage - - 0.4
Enable Threshold Voltage 1.8 - -
Switch Leakage
Dimming Pin Current Sink/Source - 100 - nA
LM3410-X VFB = 0.25
LM3410-Y VFB = 0.25
All Options V
DIM
= 0V
VIN Rising
VIN Falling
VSW = 24V
- 7.0 11
- 3.4 7
- 80 - nA
- 2.3 2.65
1.7 1.9 -
- 1.0 - µA
mA
V
V
www.national.com 4
Symbol Parameter Conditions Min Typ Max Units
θ
JA
θ
JC
T
SD
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but does not guarantee specific performance limits. For guaranteed specifications and conditions, see the Electrical Characteristics.
Note 2: Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device.
Note 3: Applies for packages soldered directly onto a 3” x 3” PC board with 2oz. copper on 4 layers in still air.
Note 4: The human body model is a 100 pF capacitor discharged through a 1.5 k resistor into each pin. Test method is per JESD22-A114.
Note 5: Do not allow this pin to float or be greater than VIN +0.3V.
Junction to Ambient 0 LFPM Air Flow (Note 3)
Junction to Case (Note 3)
Thermal Shutdown Temperature (Note 2) - 165 - °C
LLP-6 and eMSOP-8 Package - 80 -
SOT23-5 Package - 118 -
LLP-6 and eMSOP-8 Package - 18 -
SOT23-5 Package - 60 -
°C/W
°C/W
LM3410
5 www.national.com

Typical Performance Characteristics All curves taken at V

= 5.0V with configuration in typical
IN
application circuit shown in Application Information section of this datasheet. TJ = 25C, unless otherwise specified.
LM3410
LM3410-X Efficiency vs VIN (R
SET
= 4Ω)
LM3410-X Start-Up Signature
30038502
4 x 3.3V LEDs 500 Hz DIM FREQ D = 50%
30038508
Current Limit vs Temperature
DIM Freq & Duty Cycle vs Avg I-LED
R
vs Temperature
DSON
30038507
30038509
30038510
www.national.com 6
30038511
LM3410
Oscillator Frequency vs Temperature - "X"
30038512
VFB vs Temperature
Oscillator Frequency vs Temperature - "Y"
30038513
30038580
7 www.national.com

Simplified Internal Block Diagram

LM3410

FIGURE 1. Simplified Block Diagram

Application Information

THEORY OF OPERATION

The LM3410 is a constant frequency PWM, boost regulator IC. It delivers a minimum of 2.1A peak switch current. The device operates very similar to a voltage regulated boost con­verter except that it regulates the output current through LEDs. The current magnitude is set with a series resistor. This series resistor multiplied by the LED current creates the feed­back voltage (190 mV) which the converter regulates to. The regulator has a preset switching frequency of either 525 kHz or 1.60 MHz. This high frequency allows the LM3410 to op­erate with small surface mount capacitors and inductors, resulting in a DC/DC converter that requires a minimum amount of board space. The LM3410 is internally compen­sated, so it is simple to use, and requires few external com­ponents. The LM3410 uses current-mode control to regulate the LED current. The following operating description of the LM3410 will refer to the Simplified Block Diagram (Figure 1) the simplified schematic (Figure 2), and its associated wave­forms (Figure 3). The LM3410 supplies a regulated LED current by switching the internal NMOS control switch at con­stant frequency and variable duty cycle. A switching cycle
30038514
begins at the falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output con­trol logic turns on the internal NMOS control switch. During this on-time, the SW pin voltage (VSW) decreases to approx­imately GND, and the inductor current (IL) increases with a linear slope. IL is measured by the current sense amplifier, which generates an output proportional to the switch current. The sensed signal is summed with the regulator’s corrective ramp and compared to the error amplifier’s output, which is proportional to the difference between the feedback voltage and V output switch turns off until the next switching cycle begins. During the switch off-time, inductor current discharges through diode D1, which forces the SW pin to swing to the output voltage plus the forward voltage (VD) of the diode. The regulator loop adjusts the duty cycle (D) to maintain a regu­lated LED current.
. When the PWM comparator output goes high, the
REF
www.national.com 8
30038515

FIGURE 2. Simplified Boost Topology Schematic

LM3410

Design Guide

SETTING THE LED CURRENT

30038517
FIGURE 4. Setting I
LED
The LED current is set using the following equation:
where R
is connected between the FB pin and GND.
SET

DIM PIN / SHUTDOWN MODE

The average LED current can be controlled using a PWM signal on the DIM pin. The duty cycle can be varied between 0 & 100% to either increase or decrease LED brightness. PWM frequencies in the range of 1 Hz to 25 kHz can be used. For controlling LED currents down to the µA levels, it is best to use a PWM signal frequency between 200-1 kHz. The maximum LED current would be achieved using a 100% duty cycle, i.e. the DIM pin always high.

LED-DRIVE CAPABILITY

When using the LM3410 in the typical application configura­tion, with LEDs stacked in series between the VOUT and FB pin, the maximum number of LEDs that can be placed in se­ries is dependent on the maximum LED forward voltage (VF
).
MAX
(VF
x N
MAX
When inserting a value for maximum VF voltage variation over the operating temperature range
) + 190 mV < 24V
LEDs
the LED forward
MAX
should be considered.
30038516

FIGURE 3. Typical Waveforms

CURRENT LIMIT

The LM3410 uses cycle-by-cycle current limiting to protect the internal NMOS switch. It is important to note that this cur­rent limit will not protect the output from excessive current during an output short circuit. The input supply is connected to the output by the series connection of an inductor and a diode. If a short circuit is placed on the output, excessive cur­rent can damage both the inductor and diode.

THERMAL SHUTDOWN

Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature exceeds 165°C. After thermal shutdown occurs, the output switch doesn’t turn on until the junction temperature drops to ap­proximately 150°C.

INDUCTOR SELECTION

The inductor value determines the input ripple current. Lower inductor values decrease the physical size of the inductor, but increase the input ripple current. An increase in the inductor value will decrease the input ripple current.
9 www.national.com
LM3410
From the previous equations, the inductor value is then ob­tained.
30038519

FIGURE 5. Inductor Current

The Duty Cycle (D) for a Boost converter can be approximat­ed by using the ratio of output voltage (V (VIN).
) to input voltage
OUT
Therefore:
Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the voltage drop across the inductor resistance (R losses must be included to calculate a more accurate duty
) and switching
DCR
cycle (See Calculating Efficiency and Junction Tempera- ture for a detailed explanation). A more accurate formula for calculating the conversion ratio is:
Where η equals the efficiency of the LM3410 application. Or:
Therefore:
Where
1/TS = f
SW
One must also ensure that the minimum current limit (2.1A) is not exceeded, so the peak current in the inductor must be calculated. The peak current (Lpk I) in the inductor is calcu­lated by:
I
= IIN + ΔIL or I
Lpk
Lpk
= I
OUT
/D' + Δi
L
When selecting an inductor, make sure that it is capable of supporting the peak input current without saturating. Inductor saturation will result in a sudden reduction in inductance and prevent the regulator from operating correctly. Because of the speed of the internal current limit, the peak current of the in­ductor need only be specified for the required maximum input current. For example, if the designed maximum input current is 1.5A and the peak current is 1.75A, then the inductor should be specified with a saturation current limit of >1.75A. There is no need to specify the saturation or peak current of the in­ductor at the 2.8A typical switch current limit.
Because of the operating frequency of the LM3410, ferrite based inductors are preferred to minimize core losses. This presents little restriction since the variety of ferrite-based in­ductors is huge. Lastly, inductors with lower series resistance (DCR) will provide better operating efficiency. For recom­mended inductors see Example Circuits.

INPUT CAPACITOR

An input capacitor is necessary to ensure that VIN does not drop excessively during switching transients. The primary specifications of the input capacitor are capacitance, voltage, RMS current rating, and ESL (Equivalent Series Inductance). The recommended input capacitance is 2.2 µF to 22 µF de­pending on the application. The capacitor manufacturer specifically states the input voltage rating. Make sure to check any recommended deratings and also verify if there is any significant change in capacitance at the operating input volt­age and the operating temperature. The ESL of an input capacitor is usually determined by the effective cross sec­tional area of the current path. At the operating frequencies of the LM3410, certain capacitors may have an ESL so large that the resulting impedance (2πfL) will be higher than that required to provide stable operation. As a result, surface mount capacitors are strongly recommended. Multilayer ce­ramic capacitors (MLCC) are good choices for both input and output capacitors and have very low ESL. For MLCCs it is recommended to use X7R or X5R dielectrics. Consult capac­itor manufacturer datasheet to see how rated capacitance varies over operating conditions.
Inductor ripple in a LED driver circuit can be greater than what would normally be allowed in a voltage regulator Boost & Sepic design. A good design practice is to allow the inductor to produce 20% to 50% ripple of maximum load. The in­creased ripple shouldn’t be a problem when illuminating LEDs.
www.national.com 10

OUTPUT CAPACITOR

The LM3410 operates at frequencies allowing the use of ce­ramic output capacitors without compromising transient re­sponse. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple. The output ca­pacitor is selected based upon the desired output ripple and transient response. The initial current of a load transient is provided mainly by the output capacitor. The output impedance will therefore determine the maximum voltage perturbation. The output ripple of the converter is a function
Loading...
+ 22 hidden pages