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MIC3289
1.2MHz PWM White LED Driver with Internal Schottky Diode and True 1-Wire Digital Control PRELIMINARY INFORMATION
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 to better match the sensitivity of the human eye 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 scheme. The high frequency PWM operation saves board space by reducing external component sizes. 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 4cell NiCad/ NiMH/Alkaline batteries. Battery life is preserved with a low 1A shutdown current. The MIC3289 is available in a low profile Thin SOT23 6(R) lead package and a 2mm x 2mm MLF -8L package and has a junction temperature range of -40C to +125C. Data sheets and support documentation can be found on Micrel's web site at www.micrel.com.
Features
* * * * * * * * * * * * * * * 2.5V to 6.5V input voltage Output voltage up to 24V 16V & 24V OVP options Single wire combines 16 level logarithmic brightness & shutdown control Internal Schottky diode 1.2 MHz PWM operation Over 500mA switch current Programmable 5% current control <1% line and load regulation <1A shutdown current Over temperature protection UVLO Thin SOT23-6L package option (R) 2mm x 2mm leadless MLF -8L package option o o -40 C to +125 C 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 ___________________________________________________________________________________________________________
MicroLead Frame and MLF are registered trademarks of Amkor Technologies. Micrel Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel +1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com
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M9999-030407 (408) 944-0800
Micrel, Inc.
MIC3289
Typical Application
MIC3289 2mmx2mm MLF
Digital Control
0.27F
2mmx2mm 8-lead MLF White LED Driver with OVP and Digital Control
(R)
Ordering Information
Part Number MIC3289-16YD6 MIC3289-24YD6 MIC3289-16YML MIC3289-24YML Marking Code WF16 WF24 WFA WFB Output Voltage Adjustable Adjustable Adjustable Adjustable Over Voltage Protection 16V 24V 16V 24V Junction Temp. Range -40C to 125C -40C to 125C -40C to 125C -40C to 125C Package TSOT23-6 TSOT23-6 2x2 MLF -8L 2x2 MLF -8L
(R) (R)
Pin Configuration
OUT 1 2 3 4 8 7 6 5
(R)
GND SW FB NC
SW 1 GND 2 FB 3
6 OUT 5 VIN 4 DC
VIN DC GND
TSOT23-6 (D)
2mm x 2mm 8-pin MLF (ML)
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MIC3289
Pin Description
Pin Number SOT23-6 Pin Number 8-pin MLF
(R)
Pin Name
Pin Name
6 5 4 3 1 2
1 2 3 5 6 7 4,8 Pad
OUT VIN DC N/C FB SW GND GND
Output and Over Voltage Protection (output) Supply (Input): 2.5V to 6.5V for internal circuitry. See diagrams No connect (no internal connection to die) Feedback (Input): Output voltage sense node. Connect the cathode of the LED to this pin. Switch Node (Input): Internal power BIPOLAR collector. Ground (Return): Ground. Ground (Return): Backside pad.
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MIC3289
Absolute Maximum Ratings(1)
Supply voltage (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) .........-65C to +150C ESD Rating, Note 3 ..................................................... 2KV
Operating Ratings(2)
Supply Voltage (VIN) ............................. ..... 2.5V to 6.5V Output Voltage (VOUT) ......................VIN to (VSW(MAX) - 4V) or VIN to VOVP (for options with over voltage protection) Junction Temperature Range (TJ) ............-40C to +125C Package Thermal Impedance (R) JA 2mm x 2mm MLF -8L ..................................93C/W JA TSOT23-6 ..................................................235C/W
Electrical Characteristics(4)
TA=25 C, VIN = 3.6V, VOUT = 10V, IOUT = 20mA, unless otherwise noted. Bold values indicate -40C TJ 125C.
Symbol Parameter Condition Min Typ Max Units
o
VIN VUVLO IVIN ISD VFB IFB
Supply Voltage Range Under-voltage Lockout Quiescent Current Shutdown Current (DC pin low ) Feedback Voltage Feedback Input Current Line Regulation Load Regulation VFB >500mV VDC = 0V for > 2ms. (+/-5%) VFB = 250mV 2.5V VIN 4.5V 5mA IOUT 20mA
2.5 1.8 2.1 1.4 0.01 237 250 450 0.5 0.5 85 VIN = 3.6V High Low VDC = 3.6V VIN = 2.8V to 5.5V VDC = Low VIN = 2.8V to 5.5V VDC = Low VIN = 2.8V to 5.5V VDC = Low VIN = 2.8V to 5.5V VIN = 2.8V to 5.5V VIN = 2.8V to 5.5V VIN = 2.8V to 5.5V VDC = High VIN = 2.8V to 5.5V 1260 100 420 140 1 1 140 35 1 1.2 500 1.1 90 750
6.5 2.4 5 1 263
V V mA A mV nA % % %
DMAX ISW VDC
Maximum Duty Cycle Switch Current Limit DC pin thresholds DC Pin Hysteresis
1200 0.4
mA V mV
20 5 10
IDC tshutdown tMODE_UP tMODE_DO
WN
DC Pin Current Shutdown Pulse Width Count UP mode pulse width Count Down mode pulse width Turn-on Delay Time Programming pulse width low Programming pulse width high Minimum Delay for mode change First Pulse Window for Preprogramming Oscillator Frequency
A s s s s
160 500
tstart_up tprog_low tprog_high tdelay Tprog_setup fSW
32 32
s s s
50 1.35
s MHz
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Symbol Parameter Condition Min Typ Max
MIC3289
Units
VD IRD VOVP
Schottky Forward Drop Schottky Leakage Current Over Voltage Protection Over-Temperature Threshold Shutdown
ID = 150mA VR = 30V 3289- 16 only (nominal voltage) 3289- 24 only (nominal voltage) 13 21
0.8 14 22.5 150
1 4 16 24
V A V V C
Tj
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 operating ratings. The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(Max), the junction-to-ambient thermal resistance, JA, and the ambient temperature, TA. The maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. This device is not guaranteed to operate beyond its specified operating rating. IC devices are inherently ESD sensitive. Handling precautions required. Specification for packaged product only.
2. 3. 4.
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MIC3289
Typical Characteristics
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MIC3289
Functional Characteristics
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MIC3289
Functional Diagram
VIN FB OUT
OVP SW gm PWM Generator
DC
Digital I/F
1.2MHz Oscillator
Ramp Generator
GND
MIC3289 Block Diagram
Functional Description
The MIC3289 is a constant frequency, PWM current mode boost regulator. The MIC3289 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 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:
ILED =
250mV RLED
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 forget", relieving the controlling processor of the constant burden of supplying a drive signal. Additionally, brightness levels can be preset so that LEDs can be turned on at a particular brightness level.
State Diagram The MIC3289 logic state flow is depicted in Figure 1 below. State changes are asynchronous and are edge triggered, with the exception of Start Up and Shutdown, which are level triggered.
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MIC3289
Figure 1. MIC3289 Logic State Diagram
With an input supply voltage between 2.5V and 6.5V and a logic-level LOW applied to the DC pin, the MIC3289 will enter State 0, Shutdown, and remain there consuming less than 1A until a logic level high is applied to the DC pin.
Start Up Applying a logic-level HIGH to the DC pin initiates the start-up sequence. After the tSTART_UP period the MIC3289 will transition to State 1, the boost drive will turn on and begin regulating LED drive current at maximum brightness level 15, and DC pin programming pulses will cause the brightness level to decrease.
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 once again 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. Subsequent programming pulses will then increase the LED brightness one level for each pair of programming pulses. Figure 4 shows the timing for the mode change.
Figure 2. 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, the MIC3289 will return to State 0 entering its power saving
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MIC3289 as tPROG_LOW and tPROG_HIGH are not exceeded. To maintain operation at the current brightness level simply maintain a logic level high signal at the DC pin.
Figure 4. Mode Change to Count Up
To return the programming pulse counter to the CountDown Mode, apply a negative going pulse to the DC pin with a period equal to tMODE_DOWN. Now each pair of programming pulses will cause the LED brightness to decrease one level.
Figure 7. Decreasing Brightness Several Levels
tMODE_DOWN DC
MODE
COUNT DOWN
Figure 5. Mode Change to Count Down
As mentioned, the MIC3289 can be programmed to set LED drive current to produce one of 16 distinct brightness levels. The MIC3289s internal logic keeps track of the brightness level with an Up/Down counter circuit. The following section explains how the MIC3289s brightness counter functions with continued programming pulses.
Counter Roll-Over The MIC3289 internal up/down counter counts from 0 to 15. When counting DOWN, and brightness level 0 is reached, the counter will roll-over to level 15. This is illustrated in Figure 8 below.
Programming the Brightness Level When it is powered up and the DC pin is at a logic level high for greater than tSTART_UP, the MIC3289 will begin regulating LED drive current at the maximum brightness level (Level 15). The internal control logic is set to decrease the LED brightness upon receiving programming pulses (falling edges of the DC input pin). Applying a pair of clock signals as shown in Figure 6 below, decreases the brightness one level. Notice that the first clock pulse is ignored. This is done so that Mode Change pulses do not produce brightness changes. The user may also elect to send a Mode Change as shown in Figure 4 to set the MIC3289 to increment the brightness level with subsequent programming pulses.
tPROG_LOW
tPROG_HIGH
Figure 8. Down Counter Roll-over
DC
LEVEL n + 1 LEVEL n LEVEL n - 1
When the counter Mode is set to count Up and brightness level 15 is reached, the counter will roll-over to level 0. Figure 9 shows that continuing to send programming pulses will cause the brightness level to start over at level zero.
BRIGHTNESS LEVEL
PULSE IGNORED
Figure 6. Brightness Programming Pulses
Brightness programming pulses are not restricted to just one pair at a time. Multiple level changes can be set as shown in Figure 7 below. Just remember that the first falling edge of the DC input clock will be ignored so long March 2007 10
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Figure 11. One-Step Brightness Increase 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.
Presetting Brightness The brightness level can be preset by sending a series of programming pulses via the DC pin within the tPROG_SETUP period. This pre-programming window starts at 35s after the DC pin is driven high and ends 15s later. Although the MIC3289s does not drive current into the load until DC pin is kept high for tstart_up, preprogramming must begin somewhere with the 15s window or the MIC3289 may continue to start at the full (default) brightness level.
Figure 10. One-Step Brightness Decrease
Figure 12. Pre-programming Timing
This method is quite simple and the only requirement is that the first DC down clock period be equal to the tMODE_DOWN period. Similarly a one-step increase can be assured by generating a first DC down pulse whose period is equal to the tMODE_UP period followed by one DC falling edge.
Figure 12 shows the correct pre-programming 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, to insure that the part has enter the power saving shutdown state, then the DC pin is driven high and a number of programming pulses are sent. Notice that when using the pre-programming feature the first programming pulse is not ignored. This is because the counter's default mode is count down. The MIC3289 does not drive current into the load until the DC pin has remained high for time period tstart_up from the last programming activity. Note that the same limits on programming timing in normal operation also apply in pre-programming.
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MIC3289
Package Information
6-Pin TSOT23 (D)
March 2007
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Micrel, Inc.
MIC3289
8-Pin MLFTM (ML)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
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 responsibility 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 for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2007 Micrel, Incorporated.
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