MIC328916YD6 - Micrel, Inc. - Datasheet.Company

MIC3289

1.2MHz PWM White LED Driver with

Internal Schottky Diode and True 1-Wire

Digital Control

MicroLead Frame and MLF are registered trademarks of Amkor Technologies.

Micrel Inc. • 2180 Fort une Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel .com

June 2007 M9999-061807

(408) 944-0800

General Description

The MIC3289 is a PWM boost-switching regulator that is

optimized for constant-current white LED driver

applications. The MIC3289 features an internal Schottky

diode, allowing an efficient DC/DC solution that requires

only 4 external components.

The MIC3289 allows for a single wire simple digital

interface to control the dimming over 16 steps with a log

scale to give better resolution at the lower currents and to

better match the sensitivity of the human eye. The pre-

programming feature allows the user to select any one of

the 16 WLED current levels as the start-up brightness

level.

The feedback voltage of the MIC3289 is only 250mV,

allowing high efficiency while retaining excellent accuracy

for the white LED current.

The MIC3289 implements a constant frequency 1.2MHz

PWM control schem e. T he high frequency PWM operation

saves board space by reduc ing external com ponent si zes.

The 1.2MHz PWM scheme also reduces switching noise

and ripple to the input power source.

The 2.5V to 6.5V input voltage range of MIC3289 allows

direct operation from single cell Li Ion as well as 3- to 4-

cell NiCad/NiMH/Alkaline batteries. Battery life is

preserved with a low 1µA shutdown current.

The MIC3289 is available in a low profile Thin SOT23 6-

lead package and a 2mm × 2mm MLF®-8L package and

has a junction tem per ature r ange of –40°C to +125°C.

Data sheets and support documentation can be found on

Micrel’s web site at www.m ic rel.com.

Features

• Single wire combines 16 level logarithmic brightness &

shutdown control

• 16V / 24V OVP options supports up to 4 & 6 WLEDs

• Start-up in any one of 16 brightness levels

• Internal Schottky diode

• 2.5V to 6.5V input voltage

• 1.2 MHz PWM operation

• Over 500mA switch current

• 250mV reference voltage

• ±5% LED current accuracy

• <1µA shutdown current

• Over temperature protection

• UVLO

• Thin SOT23-6L package option

• 2mm × 2mm leadless MLF®-8L package option

• –40oC to +125oC junction temperature range

Applications

• White/Blue LED driver for backlighting

- Cell phones

- PDAs

- GPS systems

- Digital cameras

- Multimedia / MP3 players

• LED flashlights

• Constant current power supplies

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Typical Application

MIC3289

2mm×2mm MLF

0.27µF

Digital

Control

White LED Driver with OVP and Digital Control

Ordering Information

Part Number Marking

Code Output

Voltage Over Voltage

Protection Junction Temp.

Range Package

MIC3289-16YD6 WF16 Adjustable 16V -40°C to 125°C TSOT23-6

MIC3289-24YD6 WF24 Adjustable 24V -40°C to 125°C TSOT23-6

MIC3289-16YML WFA Adjustable 16V -40°C to 125°C 2x2 MLF®-8L

MIC3289-24YML WFB Adjustable 24V -40°C to 125°C 2x2 MLF®-8L

Pin Configuration

GND

OUT

VIN

1OUT

VIN

GND

8GND

TSOT23-6 (D) 2mm × 2mm 8-pin MLF®(ML)

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Pin Description

Pin Number

SOT23-6 Pin Number

8-pin MLF®

Pin Name Pin Name

6 1 OUT Output and Over Voltage Protection (output)

5 2 VIN Supply (Input): 2.5V to 6.5V for internal circuitry.

4 3 DC Single pin digital control. See diagrams.

- 5 N/C No connect (no internal connection to die)

3 6 FB Feedback (Input): Output voltage sense node. Connect the

cathode of the LED to this pin.

1 7 SW Switch Node (Input): Internal power BIPOLAR collector.

2 4,8 GND Ground (Return): Ground.

- Pad GND Ground (Return): Backside pad.

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Absolute Maximum Ratings(1)

Suppl y voltag e (VIN).....................................................7.5V

Switch voltage (VSW).....................................–0.3V to 27V

Digital Control Voltage (VDC)..............................–0.3 to VIN

FB Voltage (VFB) .............................................................6V

Switch Current (ISW)........................................................2A

Ambient Storage Temperature (TS).........–65°C to +150°C

ESD Rating, Note 3.....................................................2KV

Operating Ratings(2)

Suppl y Voltag e (VIN) …………………..…… ..... 2.5V to 6.5V

Output Volta ge (V OUT) …………….…................(VIN to VOVP)

Junction Temperature Range (TJ) ……......-40°C to +125°C

Package Thermal Impedance

θJA 2mm × 2mm MLF®-8L..................................93°C/W

θJA TSOT23-6 ..................................................235°C/W

Electrical Characteristics(4)

TA=25oC, VIN = 3.6V, VOUT = 10V, I OUT = 20mA, unless otherwise noted. Bold values indicate -40°C ≤ TJ ≤ 125°C.

Symbol Parameter Condition Min Typ Max Units

VIN Supply Voltage Range 2.5 6.5 V

VUVLO Under-voltage Lockout 1.8 2.1 2.4 V

IVIN Quiescent Current VFB >500m V 1.4 5 mA

ISD Shutdown Current (DC pin

low ) VDC = 0V for > 2ms. 0.01 1 µA

VFB Feedback Voltage (+/-5%) 237 250 263 mV

IFB Feedback Input Current VFB = 250mV 450 nA

Line Regulation 2.5V ≤ VIN ≤ 4.5V 0.5 %

Load Regulation 5mA ≤ IOUT ≤ 20mA 0.5 %

DMAX Ma ximum Duty Cycle 85 90 %

ISW Switch Current Limit VIN = 3.6V 500 750 1200 mA

VDC DC pin thresholds High

Low 1.1

0.4 V

DC Pin Hysteresis 20 mV

IDC DC Pin Current VDC = 3.6V 5 10 µA

tshutdown Shutdown Pulse Width VIN = 2.8V to 5.5V

VDC = Low 1260 µs

tMODE_UP Count UP mode pulse width VIN = 2.8V to 5.5V

VDC = Low 100 160 µs

tMODE_DO

WN Count Down mode pulse

width VIN = 2.8V to 5.5V

VDC = Low 420 500 µs

tstart_up Turn-on Delay Time VIN = 2.8V to 5.5V 140 µs

tprog_low Programming pulse width

low VIN = 2.8V to 5.5V 1 32 µs

tprog_high Programming pulse width

high VIN = 2.8V to 5.5V 1 32 µs

tdelay Minimum Delay for mode

change VIN = 2.8V to 5.5V

VDC = High 140 µs

Tprog_setup First Pulse Window for

Preprogramming VIN = 2.8V to 5.5V 35 50 µs

fSW Oscillator Frequency 1 1.2 1.35 MHz

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Symbol Parameter Condition Min Typ Max Units

VD Schottky Forward Drop ID = 150mA 0.8 1 V

IRD Schottky Leakage Current VR = 30V 4

µA

VOVP Over Voltage Protection 3289- 16 only (nominal voltage) 13 14 16 V

3289- 24 only (nominal voltage) 21 22.5 24 V

Tj Over-Temperature

Threshold Shutdown 150

°C

Notes:

1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating

the device outside of its operati ng rati ngs. The maximum allowable power dissipat i on is a function of the maxim um juncti on tem p erature, TJ(Max), the

juncti on-to-ambi ent t herm al resis t ance, θ JA, and the ambient temperature, TA. The maximum allowable power dissipation will res ult in excessive die

temperature, and the regulator will go into thermal shutdown.

2. This device is not guaranteed to operate beyond its specified operating rating.

3. IC devices are inherently ESD sensitive. Handling precautions requi red.

4. Specificat i on for pack aged product only.

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Typical Characteris t ics

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Functional Characteristics

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Functional Diagram

MIC3289 Block Diagram

Functional Description

The MIC3289 is a constant frequency, PWM current

mode boost regulator. It is composed of an oscillator,

slope compensation ramp generator, current amplifier,

gm error amplifier, PWM generator, bipolar output

transistor, digital interface with D/A converter and

Schottky rectifier diode. It features true one-wire digital

control that may be used to vary the brightness of the

output LEDs and to place the device into shutdown

mode. The oscillator generates a 1.2MHz clock which

triggers the PWM generator that turns on the output

transistor and resets the slope compensation ramp

generator. The current amplifier is used to measure the

switch current by amplifying the voltage signal from the

internal sense resistor. The output of the current

amplifier is summed with the output of the slope

compensation ramp generator. This summed current-

loop signal is fed to one of the inputs of the PWM

generator.

MIC3289 Block Diagram

The gm error amplifier measures the LED current

through the external sense resistor and amplifies the

error between the detected signal and the reference

voltage indicated by the digital interface. The output of

the gm error amplifier provides the voltage-loop signal

that is fed to the other input of the PWM generator.

When the current-loop signal exceeds the voltage-loop

signal, the PWM generator turns off the bipolar output

transistor. The next clock period initiates the next

switching cycle, maintaining the constant frequency

current-mode PWM control. The LED current level at

maximum brightness is set by the feedback resistor:

LEDR

250mV

ILED =

MIC3289 Digital Interface

The MIC3289 incorporates an easy to use single-wire,

serial programming interface allowing users to set LED

brightness to one of 16 levels spaced in a logarithmic

manner. In contrast to other solutions requiring a PWM

drive signal to maintain LED brightness, the MIC3289 is

“set and f orget”, r eli evin g the c ontroll ing pr ocess or of the

constant bur den of suppl ying a dri ve signal. Addit ionally,

brightness levels can be preset so that LEDs can be

turned on at a particular br i ghtn es s level .

State Diagram

The MIC3289 logic state flow is depicted in Figure 1

below. Brightness level changes are negative edge

triggered while all other state changes require a logic

high or low be a pplied t o the DC pi n for a s pecif ic leng th

of time.

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Figure 1. MIC3289 Logic State Diagram

W ith an input s upp l y vo lta g e bet ween 2.5V and 6.5 V a nd

a logic-level LOW applied to the DC pin, the MIC3289

will enter State 0, shutdown, and remain there

consuming less than 1µA.

Start Up

Presuming no presetting brightness command is issued

(discussed in a later section), the MIC3289 will start-up

in its def ault state ap proxim ately 140µs (tSTART_UP) after a

logic level high has been applied and maintained at the

DC pin. In the default state the LED drive current is at

the maximum brightness level of 15 and brightness

counter is set to count down mode. Any falling edges

during the tPROG_SETUP period will cause the initial

brightness level of the LEDs to be below the maximum

brightness level. This is discussed in more detail in the

Presett ing Bri ghtn es s section.

Figure 2. Typical Start-Up Timing

Shutdown

Whenever a logic-level LOW is applied to the DC input

pin for a period greater than or equal to

tSHUTDOWN(1260µs), the MIC3289 will return to State 0

entering its power saving shutdown mode.

Figure 3. Shutdown Timing

Once the device is shutdown, the boost supply is

disabled and the LEDs are turned off. Brightness level

information stored in the MIC3289 prior to shutdown will

be lost.

Programming Pulse Counter Modes

Referring to the state diagram in Figure 1, notice that

there are two programming pulse counting modes. At

power up the MIC3289 defaults to State 1, the Count

Down Mode. The counting mode can be changed to

State 2, the Count Up Mode, by pulling the DC pin low

for a period equal to tMODE_UP (100µs to 160µs). The

device will remain in Count Up Mode until its state is

changed to Count Down Mode or by disabling the

MIC3289.

Figure 4. Mode Change to Count Up

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To change the state b ack to Co unt Down Mod e, pull t he

DC pin low for a period equal to tMODE_DOWN (420µs to

500µs). Now the internal circuitry will remain in Count

Down Mode until changed to Count Up as described

previously.

Figure 5. Mode Change to Count Down

Programming the Brightness Level

MIC3289 is designed to start driving the output LEDs

(tSTART_UP) in 140µs at the maximum brightness level of

15. After start up, the internal control logic is ready to

decrease the LED brightness upon receiving

program m ing pulses (neg ativ e edges app lied to DC p in).

Since MIC3289 starts in Count Down Mode, the

brightness level is decreased one level by applying two

programming pulses, as shown in Figure 6. Each

programming pulse has a high (tPROG_HIGH) and a low

(tPROG_LOW) pulse width that must be between 1µs to

32µs. Note that n+1 number of pulses are needed to

decrease brightness by n level(s) since the first clock

pulse is ignored. Ignoring the first clock pulse is

necessary in order that Mode Change (tMODE_UP,

tMODE_DOWN) pulses do not result in adjustments to the

brightness level. The MIC3289 internal circuit can be

changed f rom Count Down Mode t o Count U p Mode a nd

vice versa. The user may elect to send a Mode Change

as shown in Figure 4 to set the MIC3289 to step up the

brightness level with subsequent programming pulses.

For proper operation, ensure the DC pin has remained

high for at least tDELAY(140µs) before issuing a mode

change command.

Figure 6. Brightness Programming Pulses

Brightness programming pulses are not restricted to j ust

one pair at a time. Multiple level changes can be set as

shown in Figure 7 below. When issuing multiple

brightness level adjustment commands to the DC pin,

ensure both tPROG_LOW and tPROG_HIGH are within 1µs and

32µs.

To maintain operation at the current brightness level

simply maintain a logic level high signal at the DC pin.

Figure 7. Decreasing Brightness Several Levels

As m entioned, MIC3 289 ca n be program med to s et LED

drive current to produce one of 16 distinct brightness

levels. The internal logic keeps track of the brightness

level with an Up/Down counter circuit. The following

section explains how the brightness counter functions

with continued programming edges.

Counter Roll-Over

The MIC3289 internal up/down counter contains

registers from 0 to 15. When the brightness level is at 0

and a programming pulse forces the brightness to step

down, then the counter will roll-over to level 15. This is

illustrated in Figure 8 below.

DC:

OUTPUT

LEVEL

DOWN

COUNT 3 2 1 0 151413 12665

Edge Ignore d

Figure 8. Down Counter Roll-over

Similar l y, when the coun ter m ode is set to C ount Up and

a programming pulse forces the brightness level to step

up from level 15, then the counter will ro ll-over to leve l 0

as illustrated in figure 9.

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DC:

OUTPUT

LEVEL

COUNT 13 14 15 0 1 2 3 410 10 11

Edge Ignored

Figure 9. Up Counter Roll-over

One-Step Brightness Changes

For applications where a keypad button press is to be

translated into a brightness level change, the following

method of decreasing the brightness level may be

useful. This “One-Step” brightness change procedure

relieves the user from keeping track of the MIC3289’s

up/down counter state. It combines a counter mode

change with a programming pulse, therefore a one-step

decrease in brightness is assured no matter what the

previous up/down counter mode was.

Figure 10. One-Step Brightness Decrease

This method is quite simple and the only requirement is

that the first DC low period be equal to the tMODE_DOWN

(420µs to 500µs) and immediately followed by a falling

edge within tPROG_HIGH (1µs to 32µs) as shown in Figure

10 for One-Step Brightness Decrease. Similarly a one-

step increase can be assured by first generating a DC

down pulse whose period i s equal to the tMODE_UP (100µs

to 160µs) and immediately followed by a falling edge

within tPROG_HIGH (1µs to 32µs). Figure 11 illustrates the

proper timing for execution of a One-Step Brightness

Increase.

Figure 11. One-Step Brightness Increase

Presetting Brightness

The brightness level can be preset before the MIC3289

begins to drive the LEDs by sending a series of

programming edges via the DC pin during the tSTART_UP

(140µs) per iod and within 35µs to 50µs after the DC pin

is pulled high. The 15µs timeframe between 35µs and

50µs is the tPROG_SETUP period. The MIC3289 does not

drive current into the load until DC pin is kept high for

tSTART_UP (140µs) after presetting has concluded in order

to grant the user sufficient time to preset LED

brightness. The first presetting pulse edge must occur

somewhere bet wee n the tim efram e of 35µs to 50µs after

DC pin is first pulled HIGH otherwise the MIC3289 may

continue to start at the full (default) brightness level.

Figure 12. Presetting Timing

Figure 12 shows the correct presetting sequence to set

the MIC3289 brightness to level 6 prior to start up. The

sequence is initiated by driving the DC pin low for a

period exceeding tSHUTDOWN (1260µs) to insure that the

part has entered the power saving shutdown state

erasing all br ight ness le vel st ate and m ode s etting. T hen

the DC pin is driven high and the first presetting pulse

edge is entered within the tPROG_SETUP window. Notice

that when using the presetting feature the first

programming pulse is not ignored. This is because the

counter’s default mode is Count Down and a Mode

Change cannot be performed in the presetting mode.

(Note that the same timing requirements of standard

brightness programming also apply during presetting

brightness.)

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External Component Selection

The MIC3289 can be used across a wide range of

applications. The table below shows recommended

inductor and output capacitor values for applications

driving 3-6 LEDs in series assuming a 20mA maximum

drive current from Li-Ion battery source.

Series LEDs L Manufacturer Min COUT Manufacturer

LQH43MN220K03 (Murata) 0603YD225MAT2A (AVX)

22µH NLC453232T-220K (TDK) 2.2µF GRM188R61C225KE15D (Murata)

LQH43MN100K03 (Murata) 0603YD334MAT2A (AVX)

10µH NLCV32T-100K-PFR (TDK) 0.33µF GRM188RT1C224KA01D (Murata)

LQH43MN4R7K03 (Murata)

4.7µH NLCV32T-4R7M-PFR (TDK) 0.22µF 06036ZD224MAT2A (AVX)

LQH43MN220K03 (Murata) 0805YD105MAT (AVX)

22µH NLC453232T-220K (TDK) 1.0µF GRM188R61E105KA12D (Murata)

LQH43MN100K03 (Murata) 06033D334MAT2A (AVX)

10µH NLCV32T-100K-PFR (TDK) 0.33µF GRM21BR71E334KA01L (Murata)

LQH43MN4R7K03 (Murata)

4.7µH NLCV32T-4R7M-PFR (TDK) 0.27µF VJ0805Y274KXAAT (Vishay)

LQH43MN220K03 (Murata) 06033D334MAT2A (AVX)

22µH NLC453232T-220K (TDK) 0.33µF GRM21BR71E334KA01L (Murata)

LQH43MN100K03 (Murata)

10µH NLCV32T-100K-PFR (TDK) 0.27µF VJ0805Y274KXAAT (Vishay)

LQH43MN4R7K03 (Murata)

5,6

4.7µH NLCV32T-4R7M-PFR (TDK) 0.22µF 06036ZD224MAT2A (AVX)

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Layout Recommendations

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Bottom

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Package Information

6-Pin TSOT23 (D)

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8-Pin MLF™ (ML)

MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 US

TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com

The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no respons i bili ty is assumed by Micrel for its

use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.

Micrel Products are not designed or authorized f or use as components in life support appliances, devices or systems where malfunction of a product

can reasonably be expected to result i n personal injury. Lif e support devices or systems are devices or systems th at (a) are intended for surgical implan

into the body or (b) support or sustain li f e, and whose failure to perform can be reasonably expected to result in a significan t injury to the user. A

Purchas er’s use or sal e of Micrel Products for use in life support applianc es, devic es or sys tems is a Purchaser’s own risk and Purchaser agrees to fully

indemnify Micrel for any damages result i ng from such use or sale.