MIC3201 High Brightness LED Driver with High-Side Current Sense General Description Features The MIC3201 is a hysteretic step-down, constant-current, High-Brightness LED (HB LED) driver capable of driving up to four, 1A LEDs. It provides an ideal solution for interior/exterior lighting, architectural and ambient lighting, LED bulbs, and other general illumination applications. The MIC3201 operates with an input voltage range from 6V to 20V. The hysteretic control gives good supply rejection and fast response during load transients and PWM dimming. The high-side current sensing and on-chip current sense amplifier delivers LED current with ±5% accuracy. An external high-side current sense resistor is used to set the output current. The MIC3201 offers a dedicated PWM input (DIM) which enables a wide range of pulsed dimming. A high switching frequency operation up to 1MHz allows the use of smaller external components minimizing space and cost. The MIC3201 operates over a junction temperature range of -40°C to +125°C and is available in an 8-pin ePAD SOIC package. Datasheets and support documentation can be found on Micrel’s web site at: www.micrel.com. • • • • • • • • • • • • • 6.0V to 20V input voltage range High efficiency (>90%) ± 5% LED current accuracy High-side current sense Dedicated dimming control input Hysteretic control (no compensation!) 1A internal power switch Up to 1MHz switching frequency Adjustable constant LED current 5V on board regulator Over temperature protection –40°C to +125°C junction temperature range Available in an 8-Pin ePAD SOIC package Applications • • • • • • Architectural, industrial, and ambient lighting LED bulbs Indicators and emergency lighting Street lighting Channel letters 12V lighting systems (MR-16 bulbs, under cabinet lighting, garden/pathway lighting) _________________________________________________________________________________________________________________________ Typical Application MIC3201 Step-down LED Driver Circuit Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com February 2011 M9999-021011-B Micrel, Inc. MIC3201 Ordering Information(1) Part Number Marking Junction Temp. Range Package Lead Finish MIC3201YME MIC3201YME -40°C to +125°C 8-Pin ePAD SOIC Pb-Free Note: ® 1. YME is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. Pin Configuration 8-Pin ePAD SOIC (ME) Pin Description Pin Number Pin Name 1 VCC 2 CS Current Sense Input. The CS pin provides the high-side current sense to set the LED current with an external sense resistor. 3 VIN Input Power Supply. VIN is the input supply pin to the internal circuitry and the positive input to the current sense comparator. Due to the high frequency switching noise, a 10µF ceramic capacitor is recommended to be placed as close as possible to VIN and the power ground (PGND) pin for bypassing. Please refer to layout recommendations. 4 AGND 5 EN Enable Input. The EN pin provides a logic level control of the output and the voltage has to be 2.0V or higher to enable the current regulator. The output stage is gated by the DIM pin. When the EN pin is pulled low, the regulator goes to off state and the supply current of the device is greatly reduced (below 1µA). In the off state, the output drive is placed in a "tri-stated" condition, where MOSFET is in an “off” or non-conducting state. Do not drive the EN pin above the supply voltage. 6 DIM PWM Dimming Input. The DIM pin provides the control for brightness of the LED. A PWM input can be used to control the brightness of LED. DIM high enables the output and its voltage has to be at least 2.0V or higher. DIM low disables the output, regardless of EN “high” state. 7 PGND Power Ground pin for Power FET. Power Ground (PGND) is the ground path for the high current hysteretic mode. The current loop for the power ground should be as small as possible and separate from the Analog ground (AGND) loop. Refer to the layout considerations for more details. 8 LX Drain of Internal Power MOSFET. The LX pin connects directly to the inductor and provides the switching current necessary to operate in hysteretic mode. Due to the high frequency switching and high voltage associated with this pin, the switch node should be routed away from sensitive nodes. EP GND February 2011 Pin Function Voltage Regulator Output. The VCC pin supplies the power to the internal circuitry. The VCC in the output of a linear regulator which is powered from VIN. A 1µF ceramic capacitor is recommended for bypassing and should be placed as close as possible to the VCC and AGND pins. Do not connect to an external load. Ground pin for analog circuitry. Internal signal ground for all low power sections. Connect to PGND. 2 M9999-021011-B Micrel, Inc. MIC3201 Absolute Maximum Ratings(1) Operating Ratings(2) VIN, VCS to PGND/AGND ................................ -0.3V to +22V VDIM, VEN to PGND/AGND ..................................-0.3V to VIN VLX to PGND/AGND ................................. -0.3V to VIN+1.0V VCC to PGND/AGND ..................................... -0.3V to +7.0V VCS to VIN ...................................................................... 0.3V VPGND to VAGND ............................................... -0.3V to +0.3V Storage Temperature (Ts).........................–60°C to +150°C Lead Temperature (Soldering, 10sec) ....................... 260°C ESD Ratings (HBM)(3) ...... ................................………..2kV (MM)(3)......................... ...........................100V Supply Voltage (VIN).......................................... 6.0V to 20V Junction Temperature (TJ) .........................-40°C to +125°C Junction Thermal Resistance SOIC (θJA) ..........................................................41°C/W SOIC (θJC).......................................................14.7°C/W Electrical Characteristics(4) VIN = 12V, VDIM = VEN = VIN, CVCC = 1µF, bold values indicate –40°C≤ TJ ≤ +125°C, unless noted. Typical values are at TA = +25°C. Symbol Parameter VIN Operating Input Voltage Range IS Supply Current LX open ISD Shut Down Supply Current VEN = 0V VCS(MAX) Sense Voltage Threshold High VIN - VCS 206 VCS(MIN) Sense Voltage Threshold Low VIN - VCS 171 VHYS Current Sense Hysteresis Current Sense Response Time CS Pin Input Current RDSON Internal Switch RON FMAX Maximum Switching Frequency VCC VCC Regulator ENHI EN Input Voltage High ENLO EN Input Voltage Low LX Pin Leakage Current 224 mV 189 mV ns 3 VIN - VCS = 200mV 300 mΩ 1.0 MHz 6 V V 30 0.4 V 50 µA 1 µA 2.0 V 22 VIN - VCS ≥ 250mV VLX=VIN From EN Pin going high, DIM = 12V, CVCC = 1µF µA 550 2.0 Over-Temperature Shutdown Hysteresis Start-up Time µA ns VDIM =12V Over-Temperature Shutdown mA 1 60 VDIM= 0V TLIM 1.75 100 DIM Input Leakage Low Maximum DIM Frequency V VCS Falling DIM Input Current High FDIM Units 20.0 VCS Rising VEN = 0V DIM Input Voltage Low 1.2 TA = 25ºC Max mV EN Input Leakage Low DIM Input Voltage High Typ 35 VEN =12V DIMLO Min 6.0 EN Input Current High DIMHI TLIMHYS Condition 0.4 V 30 µA 1 µA 20 kHz 5 µA 165 ºC 20 ºC 300 µs Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. 4. Specification for packaged product only. February 2011 3 M9999-021011-B Micrel, Inc. MIC3201 Typical Characteristics 1 LED Efficiency vs. Input Voltage 90 1A 80 1000 80 350mA 50 40 30 20 1A 70 350mA 60 50 40 30 20 10 10 15 20 400 2 LED Current vs. Input Voltage 1200 10 20 15 5 600 400 350mA 200 5 10 15 Shutdown Current vs. Input Voltage 0.050 1.2 1.0 0.8 0.6 0.4 TA = 25°C 0.2 0.045 0.040 0.035 0.030 0.025 0.020 0.015 0.010 TA = 25°C 0.005 0.000 5 20 20 Supply Current vs. Input Voltage 0.0 0 15 INPUT VOTLAGE (V) SHUTDOWN CURRENT (uA) SUPPLY CURRENT (mA) 1A 800 10 INPUT VOTLAGE (V) 1.4 1000 350mA 0 5 INPUT VOTLAGE (V) 10 15 20 5 10 15 INPUT VOTLAGE (V) INPUT VOLTAGE (V) INPUT VOLTAGE (V) Switching Frequency vs. Input Voltage Enable Threshold vs. Input Voltage VCC vs. Input Voltage 1.6 7.0 700 1.4 6.0 1.2 5.0 600 500 400 300 RCS = 0.2Ω L = 22µH TA = 25°C 200 100 0 1.0 VCC (V) ENABLE THRESHOLD (V) 800 0.8 0.6 TA = 25°C 0.2 10 15 20 10 15 VCS(Max) 200 VCC (V) VCS(Min) 100 7.0 350 6.0 300 4.0 3.0 TA = 25°C 1.0 0.0 0 20 0 5 10 ICC (mA) INPUT VOLTAGE (V) February 2011 4 15 20 Switch Voltage vs. Switch Current 2.0 50 10 INPUT VOLTAGE (V) 5.0 15 5 20 VCC vs. ICC 250 10 TA = 25°C INPUT VOLTAGE (V) Current Sense Voltage vs. Input Voltage 5 3.0 0.0 5 INPUT VOLTAGE (V) 150 4.0 1.0 0.0 5 20 2.0 0.4 SWITCH VOLTAGE (mV) ILED (mA) 600 0 5 SWITCHING FREQUENCY (kHz) 800 200 10 0 CURRENT SENSE (mV) ILED (mA) EFFICIENCY (%) 60 1 LED Current vs. Input Voltage 1200 1A 90 70 EFFICIENCY (%) 2 LED Efficiency vs. Input Voltage 100 15 20 250 200 150 100 TA = 25°C 50 0 0 0.25 0.5 0.75 1 SWITCH CURRENT (A) M9999-021011-B Micrel, Inc. MIC3201 180 350 250 200 150 100 IOUT = 1A @ 25°C 50 OFF 120 100 80 60 40 20 0 10 15 10 SUPPLY CURRENT (mA) TCASE (ºC) 50 1 LED 30 20 10 15 10 15 -40 -20 1.8 1.4 1.6 1.4 VIN = 12V 1.2 1.0 0.8 0.6 0.4 0.2 -40 -20 VIN = 12V 25 20 15 10 5 20 40 60 40 60 VIN = 12V 1.0 CURRENT SENSE (mV) 2.0 0.2 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) 600 500 400 300 12V Input RCS = 0.2Ω L = 22µH 200 100 0 Low-Side MOSFET RDS(ON) vs. Temperature VIN = 12V 350 300 250 200 150 100 50 0 0 20 40 60 80 100 120 Current Sense Voltage vs. Temperature 3.0 0.4 400 VCC vs. Temperature 4.0 0.6 450 TEMPERATURE (°C) 5.0 0.8 0.0 80 100 120 TEMPERATURE (°C) 6.0 80 100 120 OFF 1.0 500 250 60 1.2 700 -40 -20 7.0 40 ON 800 80 100 120 20 Enable Threshold vs. Temperature Switching Frequency vs. Temperature 0 0 20 TEMPERATURE (°C) SWITCHING FREQUENCY (kHz) 35 0 0 TEMPERATURE (°C) 2.0 20 Shutdown Current vs. Temperature -40 -20 1.0 1.6 INPUT VOTLAGE (V) 30 2.0 20 0.0 0 5 3.0 Supply Current vs. Temperature T CASE @ 1.0A vs. Input Voltage 40 OFF 4.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 60 5.0 0.0 5 20 ENABLE THRESHOLD (V) 5 SHUTDOWN CURRENT (uA) ON 140 0 VCC (V) 6.0 R DS(ON) (mΩ) RDS(ON) (mΩ) 300 UVLO Threshold vs. Temperature ON 160 THERMAL SHUTDOWN (°C) 400 Thermal Shutdown vs. Input Voltage UVLO THRESHOLD (V) RDSON vs. Input Voltage -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) VC(Max) 200 VCS(Min) 150 100 50 VHYS 0 0.0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) February 2011 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) 5 M9999-021011-B Micrel, Inc. MIC3201 Functional Characteristics February 2011 6 M9999-021011-B Micrel, Inc. February 2011 MIC3201 7 M9999-021011-B Micrel, Inc. MIC3201 Functional Diagram Figure 1. MIC3201 Block Diagram The frequency of operation depends upon input voltage, total LEDs voltage drop, LED current and temperature. The calculation for frequency of operation is given in application section. The MIC3201 has an on board 5V regulator which is for internal use only. Connect a 1µF capacitor on VCC pin to analog ground. The MIC3201 has an EN pin which gives the flexibility to enable and disable the output with logic high and low signals. The MIC3201 also has a DIM pin which can turn on and off the LEDs if EN is in HIGH state. This DIM pin controls the brightness of the LED by varying the duty cycle from 1% to 99%. Functional Description The MIC3201 is a hysteretic step-down regulator which regulates the LED current over wide input voltage range and capable of driving up to four, 1A LEDs in series. The device operates from a 6V to 20V input voltage range, and includes an integrated 1.0A power switch. When the input voltage approaches 6V, the internal 5V VCC is regulated and the integrated MOSFET is turned on if EN pin and DIM pin are high. The inductor current builds up linearly. When the CS pin voltage hits the VCS(MAX) with respect to VIN, the internal MOSFET turns off and the Schottky diode takes over and returns the current to VIN. Then the current through inductor and LEDs starts decreasing. When CS pin hits VCS(MIN), the internal MOSFET turns on and the cycle repeats. February 2011 8 M9999-021011-B Micrel, Inc. MIC3201 Application Information The MIC3201 is a hysteretic step-down constant-current High-Brightness LED (HB LED) driver. The internal block diagram is shown in Figure 1. The MIC3201 is composed of a current sense comparator, voltage and current reference, 5V regulator, MOSFET driver, and a MOSFET. Hysteretic mode control, also called bangbang control, is the topology that does not employ an error amplifier, and instead uses an error comparator. The inductor current is controlled within a hysteretic window. If the inductor current is too small, the power MOSFET is turned on; if the inductor current is large enough, the power MOSFET is turned off. It is a simple control scheme with no oscillator and no loop compensation. Since the control scheme does not need loop compensation, it makes a design easy, and avoids problems of instability. Transient response to load and line variation is very fast and only depends on propagation delay. This makes the control scheme very popular for certain applications. LED Current and RCS The main feature in MIC3201 is to control the LED current accurately within ± 5% of set current. Choosing a high-side RCS resistor helps for setting constant LED current irrespective of wide input voltage range. The following equation gives the RCS value: R CS = dI dt L is the inductance, dI is fixed (the value of the hysteresis) VCS(MAX ) − VCS(MIN) dI = R CS VL = L VL voltage across inductor L which varies by supply. For current rising (MOSFET is ON): tr = L VL_RISE = VIN – ILED·RCS - VLED For current falling (MOSFET is OFF): tf = L I2R (W) Size (SMD) 2.00 0.1 0.0200 0402 1.00 0.2 0.0400 0402 0.63 0.3 0.0567 0402 0.56 0.35 0.0691 0603 0.50 0.4 0.0800 0603 0.40 0.5 0.1000 0805 0.33 0.6 0.1188 0805 0.28 0.7 0.1372 0805 0.24 0.8 0.1536 0805 0.22 0.9 0.1782 0805 0.20 1.0 0.2000 1206 Table 1. Selecting RCS for LED Current VCS(MIN) refer to the electrical dI VL _ FALL where: VL_FALL = VD + ILED·RCS + VLED T = t r + t f , FSW = FSW = ILED (A) For VCS(MAX) and characteristic table. dI VL _ RISE where: 1 VCS(MAX) + VCS(MIN) ( ) 2 ILED RCS (Ω) February 2011 Frequency of Operation To calculate the frequency spread across input supply: 1 T (VD + ILED⋅ RCS + VLED) • (VIN −ILED⋅ RCS − VLED) L ⋅ dI⋅ (VD + VIN) Where VD is Schottky diode forward drop VLED is total LEDs voltage drop VIN is input voltage ILED is average LED current: According to the above equation, choose the inductor to make the operating frequency no higher than 1MHz. Free Wheeling Diode The free wheeling diode should have the reverse voltage rating to accommodate the maximum input voltage. The forward voltage drop should be small to get the lowest conduction dissipation for high efficiency. The forward current rating has to be at least equal to LED current. A Schottky diode is recommended. LED Ripple Current The LED current is the same as inductor current. If LED ripple current needs to be reduced then place a 10µF capacitor across LED. 9 M9999-021011-B Micrel, Inc. PCB Layout Guideline Warning!!! To minimize EMI and output noise, follow these layout recommendations. PCB Layout is critical to achieve reliable, stable and efficient performance. A ground plane is required to control EMI and minimize the inductance in power, signal and return paths. The following guidelines should be followed to insure proper operation of the MIC3201 regulator. IC Use fat traces to route the input and output power lines. The exposed pad (EP) on the bottom of the IC must be connected to the ground. Use four via to connect the EP to the ground plane. Signal and power grounds should be kept separate and connected at only one location. Input Capacitor Place the input capacitors on the same side of the board and as close to the IC as possible. Keep both the VIN and PGND connections short. Place several vias to the ground plane close to the input capacitor ground terminal, but not between the input capacitors and IC pins. Use either X7R or X5R dielectric input capacitors. Do not use Y5V or Z5U type capacitors. Do not replace the ceramic input capacitor with any other type of capacitor. Any type of capacitor can be placed in parallel with the input capacitor. If a Tantalum input capacitor is placed in parallel with the input capacitor, it must be recommended for switching regulator applications and the operating voltage must be derated by 50%. In “Hot-Plug” applications, a Tantalum or Electrolytic bypass capacitor must be placed in parallel to ceramic capacitor to limit the over-voltage spike seen on the input supply with power is suddenly applied. In this case, an additional Tantalum or Electrolytic bypass input capacitor of 22µF or higher is required at the input power connection if necessary. MIC3201 Output Capacitor If LED ripple current needs to be reduced then place a 10µF capacitor across LED. The capacitor must be placed as close to the LED as possible. Diode Place the Schottky diode on the same side of the board as the IC and input capacitor. The connection from the Schottky diode’s Anode to the IC LX pin must be as short as possible. The diode’s Cathode connection to the RCS must be keep as short as possible. RC Snubber If a RC snubber is needed, place the RC snubber on the same side of the board and as close to the Schottky diode as possible. RCS (Current Sense Resistor) VIN pin and CS pin must be as close as possible to RCS. Make a Kelvin connection to the VIN and CS pin respectively for current sensing. Trace Routing Recommendation Keep the power traces as short and wide as possible. One current flowing loop is during the MOSFET ON time, the traces connecting the input capacitor CIN, RCS, LEDs, Inductor, the MIC3201 LX and PGND pin and back to CIN. The other current flowing loop is during the MOSFET OFF time, the traces connecting RCS, LED, inductor, free wheeling diode and back to RCS. These two loop areas should kept as small as possible to minimize the noise interference, Keep all analog signal traces away from the LX pin and its connecting traces. Inductor Keep the inductor connection to the switch node (LX) short. Do not route any digital lines underneath or close to the inductor. To minimize noise, place a ground plane underneath the inductor. February 2011 10 M9999-021011-B Micrel, Inc. MIC3201 Ripple Measurements To properly measure ripple on either input or output of a switching regulator, a proper ring in tip measurement is required. Standard oscilloscope probes come with a grounding clip, or a long wire with an alligator clip. Unfortunately, for high frequency measurements, this ground clip can pick-up high frequency noise and erroneously inject it into the measured output ripple. The standard evaluation board accommodates a home made version by providing probe points for both the input and output supplies and their respective grounds. This requires the removing of the oscilloscope probe sheath and ground clip from a standard oscilloscope probe and wrapping a non-shielded bus wire around the oscilloscope probe. If there does not happen to be any non-shielded bus wire immediately available, the leads from axial resistors will work. By maintaining the shortest possible ground lengths on the oscilloscope probe, true ripple measurements can be obtained. February 2011 Figure 2. Low Noise Measurement 11 M9999-021011-B Micrel, Inc. MIC3201 Evaluation Board Schematic February 2011 12 M9999-021011-B Micrel, Inc. MIC3201 Bill of Materials Item Part Number 12103D106KAT2A C1, C2 C3 C4 D1 L1 R1 Manufacturer Description (1) AVX Qty. 10µF/25V, Ceramic Capacitor, X5R, Size 0805 (2) Murata 10µF/25V, Ceramic Capacitor, X7R, Size 0805 C3225X7R1E106M TDK(3) 10µF/25V, Ceramic Capacitor, X7R, Size 0805 08053D105KAT2A AVX(1) 1µF/25V, Ceramic Capacitor, X5R, Size 0805 GRM32DR71E106KA12L GRM216R61E105KA12D (2) Murata C2012X7R1E105K TDK 08055A271JAT2A AVX(1) GQM2195C1H271JB01D SS24-TP MCC(4) Fairchild(5) CDRH8D43NP-220NC SUMIDA(6) 1 1µF/25V, Ceramic Capacitor, X7R, Size 0805 Murata(2) SS24 CSR 1/2 0.2 1% I 1µF/25V, Ceramic Capacitor, X5R, Size 0805 (3) 2 Stackpole Electronics Inc (8) (7) 270pF/50V, Ceramic Capacitor NPO, Size 0805 1 40V, 2A, SMA, Schottky Diode 1 22µH, 2.6A, SMT, Power Inductor 1 0.2Ω Resistor, 1/2W, 1%, Size 1206 1 R2, R3 CRCW08051003FKEA Vishay 100kΩ Resistor, 1% , Size 0805 2 R4 CRCW08052R20FKEA Vishay(8) 2.2 Ohms Resistor, 1%, Size 0805 1 U1 MIC3201YME High-Brightness LED Driver with High-Side Current Sense 1 Micrel, Inc.(9) Notes: 1. AVX: www.avx.com 2. Murata: www.murata.com 3. TDK: www.tdk.com 4. MCC: www.mccsemi.com 5. Fairchild: www.fairchildsemi.com 6. Sumida Tel: www.sumida.com 7. Stackpole Electronics: www.seielect.com 8. Vishay: www.vishay.com 9. Micrel, Inc.: www.micrel.com February 2011 13 M9999-021011-B Micrel, Inc. MIC3201 PCB Layout Recommendations Top Assembly Top Layer Bottom Layer February 2011 14 M9999-021011-B Micrel, Inc. MIC3201 Package Information 8-Pin ePAD SOIC (ME) February 2011 15 M9999-021011-B Micrel, Inc. MIC3201 Recommended Landing Pattern 8-Pin ePAD SOIC 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 Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and 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. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. 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. © 2009 Micrel, Incorporated. February 2011 16 M9999-021011-B