MAQ3203 High-Brightness LED Driver Controller with High-Side Current Sense General Description The MAQ3203 is a hysteretic, step-down, constantcurrent, High-Brightness LED (HB LED) driver. It provides an ideal solution for interior/exterior lighting, architectural and ambient lighting, LED bulbs, and other general illumination applications. The MAQ3203 is well suited for lighting applications requiring a wide-input voltage range. 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 currentsense resistor is used to set the output current. The MAQ3203 offers a dedicated PWM input (DIM) which enables a wide range of pulsed dimming. A high-frequency switching operation up to 1.5MHz allows the use of smaller external components minimizing space and cost. The MAQ3203 offers frequency dither feature for EMI control. The MAQ3203 operates over a junction temperature from −40°C to +125°C and is available in an 8-pin SOIC package. The MAQ3203 is AEC-Q100 qualified for automotive applications. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. Features • • • • • • • • • • • • AEC-Q100 qualified 4.5V to 42V input voltage range High efficiency (>90%) ±5% LED current accuracy Dither enabled for low EMI High-side current sense Dedicated dimming control input Hysteretic control (no compensation!) Up to 1.5MHz switching frequency Adjustable constant LED current Over-temperature protection −40°C to +125°C junction temperature range Applications • Automotive lighting • Industrial lighting Typical Application MAQ3203 Step-Down LED Driver Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com April 20, 2015 Revision 1.2 Micrel, Inc. MAQ3203 Ordering Information (1) Part Number Marking Junction Temperature Range Package PWM MAQ3203YM MAQ3203YM −40°C to +125°C 8-Pin SOIC Dither Note: 1. YM is a GREEN RoHS-compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. Pin Configuration 8-Pin SOIC (M) (Top View) Pin Description Pin Number Pin Name Pin Function 1 VCC Voltage Regulator Output. The VCC pin supplies the power to the internal circuitry. The VCC is 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. 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 Ground pin for analog circuitry. Internal signal ground for all low power sections. 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, during this period 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 for the high-current switching with 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. DRV Gate-Drive Output. Connect to the gate of an external N-channel MOSFET. The drain of the external MOSFET 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. 8 April 20, 2015 2 Revision 1.2 Micrel, Inc. MAQ3203 Absolute Maximum Ratings(2) Operating Ratings(3) VIN to PGND .................................................. −0.3V to +45V VCC to PGND ................................................ −0.3V to +6.0V CS to PGND ........................................ −0.3V to (VIN + 0.3V) EN to AGND ........................................ −0.3V to (VIN + 0.3V) DIM to AGND ...................................... −0.3V to (VIN + 0.3V) DRV to PGND .................................... −0.3V to (VCC + 0.3V) PGND to AGND........................................... −0.3V to + 0.3V Junction Temperature ................................................ 150°C Storage Temperature Range .................... −60°C to +150°C Lead Temperature (soldering, 10s) ............................ 260°C (4) ESD Ratings HBM ...................................................................... 1.5kV MM ......................................................................... 200V Supply Voltage (VIN) .......................................... 4.5V to 42V Enable Voltage (VEN) .............................................. 0V to VIN Dimming Voltage (VDIM) ................................................................. 0V to VIN Junction Temperature (TJ) ........................ −40°C to +125°C Junction Thermal Resistance SOIC (θJA) ....................................................... 98.9°C/W SOIC (θJC) ....................................................... 48.8°C/W Electrical Characteristics(5) VIN = VEN = VDIM = 12V; CVCC = 1.0µF; TJ = 25°C, bold values indicate −40°C ≤ TA ≤ +125°C; unless noted. Symbol Parameter Condition Min. Typ. Max. Units 42 V 3 mA 1 µA 4.5 V Input Supply 4.5 VIN Input Voltage Range (VIN) IS Supply Current DRV = open ISD Shutdown Current VEN = 0V UVLO VIN UVLO Threshold VIN rinsing UVLOHYS VIN UVLO Hysteresis 1 3.2 4 500 mV VCC Supply VCC VCC Output Voltage VIN = 12V, ICC = 10mA 4.5 5 5.5 201.4 212 222.6 199 212 225 168 177 186 165 177 189 V Current Limit VCS(MAX) Current Sense Upper Threshold VCS(MAX ) = VIN − VCS VCS(MIN) Sense Voltage Threshold Low VCS(MIN ) = VIN − VCS VCSHYS VCS Hysteresis Current Sense Response Time CS Input Current 35 VCS Rising 50 VCS Falling 70 VIN − VCS = 220mV 0.5 mV mV mV ns 10 µA Notes: 2. Exceeding the absolute maximum ratings may damage the device. 3. The device is not guaranteed to function outside its operating ratings. 4. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF. 5. Specification for packaged product only. April 20, 2015 3 Revision 1.2 Micrel, Inc. MAQ3203 Electrical Characteristics(5) (Continued) VIN = VEN = VDIM = 12V; CVCC = 1.0µF; TJ = 25°C, bold values indicate −40°C ≤ TA ≤ +125°C; unless noted. Symbol Parameter Condition Min. Typ. Max. Units 1.5 MHz Frequency FMAX Switching Frequency Dithering VDITH FDITHER VCS Hysteresis Dithering Range Frequency Dithering Range (6) (6) % of switching frequency ±6 mV ±12 % Enable Input ENHI EN Logic Level High ENLO EN Logic Level Low EN Bias Current Start-Up Time 2.0 V 0.4 V VEN = 12V 60 µA VEN = 0V 1 µA From EN going high to DRV going high 30 µs Dimming Input DIMHI DIM Logic Level High DIMLO DIM Logic Level Low DIM Bias Current DIM Delay Time FDIM 2.0 V 0.4 20 VDIM = 0V 50 1 From DIM going high to DRV going high 450 Maximum Dimming Frequency V µA ns 20 kHz External FET Driver DRV On-Resistance DRV Transition Time Pull Up, ISOURCE = 10mA 2 Pull Down, ISINK = -10mA 1.5 Rise Time, CLOAD = 1000pF 13 Fall Time, CLOAD = 1000pF 7 Ω ns Thermal Protection TLIM Over-Temperature Shutdown TLIMHYS Over-Temperature Shutdown Hysteresis TJ Rising 160 20 °C Note: 6. Guaranteed by design. April 20, 2015 4 Revision 1.2 Micrel, Inc. MAQ3203 Typical Characteristics Efficiency vs Input Voltage Efficiency vs Input Voltage 100 100 90 90 Normalized LED Currents vs Input Voltage 1.03 4LED 6LED 80 8LED 10LED 70 4LED 6LED 80 8LED 10LED 70 L=150µH ILED=1A 5 10 15 20 25 30 35 40 45 0 5 10 INPUT VOLTAGE (V) 20 25 30 35 40 1 1LED 0.99 6LED 0.98 10LED 8LED 15 20 25 30 35 40 4LED 200 2LED 150 100 1LED 50 45 0 5 10 15 20 25 30 35 40 25 INPUT VOLTAGE (V) April 20, 2015 5 35 40 45 10 15 20 25 30 35 40 45 35 40 45 Supply Current vs. Input Voltage 75 8LED 1LED 2LED 4LED 6LED 50 25 0 30 10LED INPUT VOLTAGE (V) L=68µH ILED=1A 0 8LED 1.4 L=150µH ILED=1A 25 1LED 200 0 SUPPLY CURRENT (mA) DUTY CYCLE (%) 4LED 6LED 20 2LED 300 45 10LED 8LED 15 45 400 6LED 10LED 75 10 40 100 8LED 100 5 35 4LED Duty Cycle vs Input Voltage 100 0 500 INPUT VOLTAGE (V) 50 30 0 Duty Cycle vs. Input Voltage 1LED 25 L=68µH ILED=1A 600 250 INPUT VOLTAGE (V) 2LED 20 Frequency vs. Input Voltage 0 10 15 10LED 0.97 5 10 700 6LED 0 5 INPUT VOLTAGE (V) FREQUENCY (kHz) 1.01 4LED L=150µH ILED=1A 0 45 L=150µH ILED=1A 300 FREQUENCY (kHz) LED CURRENTS (A) 15 350 L=68µH ILED=1A 8LED 0.99 Frequency vs. Input Voltage 1.03 2LED 1LED 6LED 1 INPUT VOLTAGE (V) Normalized LED Currents vs. Input Voltage 1.02 4LED 2LED 0.97 60 0 10LED 1.01 0.98 L=68µH ILED=1A 60 DUTY CYCLE (%) LED CURRENTS (A) EFFICIENCY (%) EFFICIENCY (%) 1.02 1.2 1.0 TA = 25°C ILED = 0A 0.8 0.6 0.4 0.2 0.0 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 5 35 40 45 0 5 10 15 20 25 30 INPUT VOLTAGE (V) Revision 1.2 Micrel, Inc. MAQ3203 Typical Characteristics (Continued) VCC vs. Input Voltage Enable Threshold vs. Input Voltage Current-Sense Voltage vs. Input Voltage 6.0 250 1.8 3.0 2.0 1.0 0.0 1.6 200 1.4 1.2 5 10 15 20 25 30 35 40 1.0 0.8 100 0.6 TA=25°C 1LED ILED=1A 0.4 0.2 L=100µA ILED=1A 50 0 45 0 5 INPUT VOLTAGE (V) 10 15 20 25 30 35 40 45 0 5 10 INPUT VOLTAGE (V) 15 20 25 30 35 40 45 40 45 100 120 INPUT VOLTAGE (V) Enable Current vs. Enable Voltage Shutdown Current vs. Input Voltage ICC Limit vs. Input Voltage 160 40 200 140 30 25 20 15 10 TA=25°C ILED=0A 5 0 180 160 120 ICC LIMIT (mA) 35 ENABLE CURRENT (µA) SHUTDOWN CURRENT (µA) VCS_MIN 150 0.0 0 VCS_MAX CURRENT SENSE VOLTAGE (mV) TA = 25°C ILED = 0A ICC = 0A 4.0 VCC (V) ENABLE THRESHOLD (V) 5.0 100 80 60 40 0 5 10 15 20 25 30 35 40 100 80 60 TA=25°C VCC=4.2V ILED=0A 40 20 0 0 45 120 TA=25°C 20 -5 140 0 5 INPUT VOLTAGE (V) 10 15 20 25 30 35 40 0 45 5 10 ENABLE VOLTAGE (V) Supply Current vs. Temperature 15 20 25 30 35 INPUT VOLTAGE (V) VCC vs. Temperature Enable Threshold vs. Temperature 2.0 1.2 6.0 1.0 5.0 ENABLE THRESHOLD (V) 0.8 4.0 VCC (V) SUPPLY CURRENT (mA) 1.8 0.6 0.4 3.0 2.0 VIN=12V ILED=0A 0.2 VIN=12V ILED=0A ICC=0A 1.0 0.0 -20 0 20 40 60 80 TEMPERATURE (°C) April 20, 2015 100 120 ON 1.4 1.2 OFF 1.0 0.8 0.6 1LED ILED=1A 0.4 0.2 0.0 -40 1.6 0.0 -40 -20 0 20 40 60 80 TEMPERATURE (°C) 6 100 120 -40 -20 0 20 40 60 80 TEMPERATURE (°C) Revision 1.2 Micrel, Inc. MAQ3203 Typical Characteristics (Continued) VIN Shutdown Current vs. Temperature 0.3 250 50 EN = 0V VIN = 12V 0.2 0.15 0.1 0.05 200 40 35 25 -25 0 25 50 75 TEMPERATURE (°C) April 20, 2015 100 125 1LED ILED=1A 100 20 15 10 D_VCS 50 VIN=12V VEN=VIN 0 -50 VCS_MIN 150 30 5 0 VCS_MAX CURRENT SENSE VOLTAGE (mV) 45 0.25 ENABLE CURRENT (uA) VIN SHUTDOWN CURRENT (uA) Current-Sense Voltage vs. Temperature Enable Current vs. Temperature 0 -40 -20 0 20 40 60 80 TEMPERATURE (°C) 7 100 120 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) Revision 1.2 Micrel, Inc. MAQ3203 Functional Characteristics April 20, 2015 8 Revision 1.2 Micrel, Inc. MAQ3203 Functional Characteristic (Continued) April 20, 2015 9 Revision 1.2 Micrel, Inc. MAQ3203 Functional Diagram Functional Description 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 MAQ3203 is a hysteretic step-down driver which regulates the LED current over wide input voltage range. The device operates from a 4.5V to 42V input MOSFET voltage range and provides up to 0.5A source and 1A sink drive capability. When the input voltage reaches 4.5V, the internal 5V VCC is regulated and the DRV pin is pulled high to turn on an external MOSFET 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 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 MOSFET turns on and the cycle repeats. April 20, 2015 The MAQ3203 has an on board 5V regulator which is for internal use only. Connect a 1µF capacitor on VCC pin to analog ground. The MAQ3203 has an EN pin which gives the flexibility to enable and disable the output with logic high and low signals. The MAQ3203 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 of DIM from 1% to 99%. 10 Revision 1.2 Micrel, Inc. MAQ3203 Frequency of Operation Refer to Equation 2 to calculate the frequency spread across input supply. Application Information The internal block diagram of the MAQ3203 is shown in the Functional Diagram. The MAQ3203 is composed of a current-sense comparator, voltage and current reference, 5V regulator and MOSFET driver. Hysteretic mode control – also called bang-bang control – is a topology that does not employ an error amplifier, using an error comparator instead. VL = L 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. Eq. 2 L is the inductance; ∆IL is fixed (the value of the hysteresis): ∆IL = 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. VCS(MAX ) - VCS(MIN) R CS Eq. 3 VL is the voltage across inductor L which varies by supply. LED Current and RCS The main feature in MAQ3203 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. Equation 1 gives the RCS value: RCS ΔI L Δt For current rising (MOSFET is ON): tr = L ∆IL VL _ RISE Eq. 4 where: 1 VCS(MAX ) + VCS(MIN) = x( ) 2 ILED Eq. 1 VL_RISE = VIN − ILED × RCS − VLED For current falling (MOSFET is OFF): Table 1. RCS for LED Current ∆IL RCS (Ω) ILED (A) I R (W) Size (SMD) 1.33 0.15 0.03 0603 0.56 0.35 0.07 0805 0.4 0.5 0.1 0805 where: 0.28 0.7 0.137 0805 VL_FALL = VD + ILED × RCS + VLED 0.2 1.0 0.2 1206 0.13 1.5 0.3 1206 0.1 2.0 0.4 2010 0.08 2.5 0.5 2010 0.068 3.0 0.6 2010 2 For VCS(MAX) and VCS(MIN), refer Characteristics section. April 20, 2015 to the tf = L VL _ FALL T = t r + t f , FSW = FSW = Eq. 5 1 T ( VD + ILED × RCS + VLED ) × ( VIN - ILED × RCS - VLED ) L × ΔIL × ( VD + VIN ) where : Electrical • • • • 11 VD is Schottky diode forward drop VLED is total LEDs voltage drop VIN is input voltage ILED is average LED current Revision 1.2 Micrel, Inc. MAQ3203 Given an inductor value, the size of the inductor can be determined by its RMS and peak current rating. Inductor According to the above equation, choose the inductor to make the operating frequency no higher than 1.5MHz. Table 2, Table 3, and Table 4 give a reference inductor value and corresponding frequency for a given LED current. For space-sensitive applications, smaller inductor with higher switching frequency could be used but efficiency of the regulator will be reduced. VCS(MAX ) - VCS(MIN) ∆IL = 2× = 0.18 IL VCS(MAX ) + VCS(MIN) IL(RMS) = IL2 + Table 2. Inductor for VIN = 12V, 1 LED RCS (Ω) ILED (A) L (µH) FSW (kHz) 1.33 0.15 220 474 0.56 0.35 100 439 0.4 0.5 68 461 0.28 0.7 47 467 0.2 1.0 33 475 0.13 1.5 22 463 0.1 2.0 15 522 0.08 2.5 12 522 0.068 3.0 10 533 IL(PK ) = IL + 1 2 ∆I ≈ IL 12 L 1 ∆IL = 1.09IL 2 where: IL is inductor average current. Select an inductor with saturation current rating at least 30% higher than the peak current. MOSFET MOSFET selection depends upon the maximum input voltage, output LED current and switching frequency. The selected MOSFET should have 30% margin on maximum voltage rating for high reliability requirements. Table 3. Inductor for VIN = 24V, 4 LEDs The MOSFET channel resistance RDSON is selected such that it helps to get the required efficiency at the required LED currents as well as meets the cost requirement. RCS (Ω) ILED (A) L (µH) FSW (kHz) 1.33 0.15 470 474 0.56 0.35 220 426 0.4 0.5 150 447 0.28 0.7 100 470 0.2 1.0 68 493 0.13 1.5 47 463 0.1 2.0 33 507 0.08 2.5 27 496 2 PLOSS(CON) = IRMS × R DSON (FET ) 0.068 3.0 22 517 IRMS(FET ) = ILED × D Logic level MOSFETs are preferred as the drive voltage is limited to 5V. The MOSFET power loss has to be calculated for proper operation. The power loss consists of conduction loss and switching loss. The conduction loss can be found by: D= Table 4. Inductor for VIN = 36V, 8 LEDs RCS (Ω) ILED (A) L (µH) FSW (kHz) 1.33 0.15 470 495 0.56 0.35 220 446 0.4 0.5 150 467 0.28 0.7 100 490 0.2 1.0 68 515 0.13 1.5 47 485 0.1 2.0 33 530 0.08 2.5 27 519 0.068 3.0 22 541 April 20, 2015 Eq. 6 12 Eq. 7 VTOTAL _ LED VIN Revision 1.2 Micrel, Inc. MAQ3203 The switching loss occurs during the MOSFET turn-on and turn-off transition and can be found by: V ×I ×F PLOSS( TRAN) = IN LED SW × (Qgs2 + Qgd ) IDRV IDRV = VDRV RGATE Proper snubber design requires the parasitic inductance and capacitance be known. A method of determining these values and calculating the damping resistor value is outlined below: 1. Measure the ringing frequency at the switch node which is determined by parasitic LP and CP. Define this frequency as f1. Eq. 8 2. Add a capacitor CS (normally at least 3 times as big as the COSS of the diode) across the diode and measure the new ringing frequency. Define this new (lower) frequency as f2. LP and CP can now be solved using the values of f1, f2 and CS. where: RGATE is total MOSFET resistance, Qgs2 and Qgd can be found in a MOSFET manufacturer datasheet. 3. Add a resistor RS in series with CS to generate critical damping. If the snubber resistance is equal to the characteristic impedance of the resonant circuit (1/sqrt(LPCP)), the resonant circuit will be critically damped and have no ringing. The total power loss is: PLOSS( TOT ) = PLOSS(CON) + PLOSS( TRAN) Eq. 9 Step 1: First measure the ringing frequency on the switch node voltage when the high-side MOSFET turns on. This ringing is characterized by the equation: The MOSFET junction temperature is given by: TJ = PLOSS( TOT ) × R θJA + TA Eq. 10 1 f1 = The TJ must not exceed maximum junction temperature under any conditions. 2π LP × CP Eq. 11 where: Snubber A RC voltage snubber is used to damp out highfrequency ringing on the switch node caused by parasitic inductance and capacitance. The capacitor is used to slow down the switch node rise and fall time and the resistor damps the ringing. Excessive ringing can cause the MAQ3203 to operate erratically by prematurely tripping its current limit comparator circuitry. CP and LP are the parasitic capacitance and inductance. Step 2: Add a capacitor, CS, in parallel with the Schottky diode. The capacitor value should be approximately 3 times the COSS of D1. Measure the frequency of the switch node ringing, f2. The snubber is connected across the Schottky diode as shown in the evaluation board schematic. Capacitor CS (C4) is used to block the DC voltage across the resistor, minimizing the power dissipation in the resistor. This capacitor value should be between two to five times the parasitic capacitance of the MOSFET COSS and the Schottky diode junction capacitance Cj. A capacitor that is too small will have high impedance and prevent the resistor from damping the ringing. A capacitor that is too large causes unnecessary power dissipation in the resistor, which lowers efficiency. f2 = 1 2π LP × (C S + CP ) Eq. 12 Define f’ as: f' = f1 f2 Eq. 13 The snubber components should be placed as close as possible to the Schottky diode. Placing the snubber too far from the diode or using an etch that is too long or too thin adds inductance to the snubber and diminishes its effectiveness. April 20, 2015 13 Revision 1.2 Micrel, Inc. MAQ3203 Freewheeling Diode The diode provides a conduction path for the inductor current during the switch off time. The reverse voltage rating of the diode should be at least 1.2 times the maximum input voltage. A Schottky diode is recommend for highest efficiency. Combining the equations for f1, f2 and f’ to derive CP, the parasitic capacitance: CS CP = , 2 2 × (f ) − 1 Eq. 14 The Schottky diode can be the major source of power loss, especially at the maximum input voltage. The current through the diode is equal to the LED current with a duty cycle of (VIN – VLED)/VIN. LP is solved by re-arranging the equation for f1: The diode dissipation is given by: LP = 1 (2π )2 × CP × (f1 )2 Eq. 15 PD = ILED × (VIN − VLED ) × Vf VIN Eq. 18 Step 3: Calculate the damping resistor. Critical damping occurs at Q = 1: Q= 1 RS LP =1 C S + CP Vf is the forward voltage of the diode at ILED. A Schottky diode forward voltage is typically 0.6V at its full rated current. It is normal design practice to use a diode rated at 1.5 to 2 times output current to maintain efficiency. This derating allows Vf to drop to approximately 0.5V. When calculating the “worst case” power dissipation, use the maximum input voltage and the actual diode forward voltage drop at the maximum operating temperature; otherwise the calculated power dissipation will be artificially high. The forward voltage drop of a diode decrease as ambient temperature is increased, at a rate of −1.0mV/°C. Eq. 16 Solving for RS: RS = LP C S + CP Eq. 17 Input Capacitor The ceramic input capacitor is selected by voltage rating and ripple current rating. To determine the input current ripple rating, the RMS value of the input capacitor can be found by: The snubber capacitor, CS, is charged and discharged each switching cycle. The energy stored in CS is dissipated by the snubber resistor, RS, two times per switching period. This power is calculated in the equation below: PSNUBBER = fS × C S × VIN 2 ICIN(RMS) = ILED × D × (1 − D ) Eq. 19 Eq. 18 The power loss in the input capacitor is: where: PLOSS(CIN) = I2 CIN(RMS) × CINESR fS is the switching frequency for each phase. VIN is the DC input voltage. An alternate method to reduce the switch node ringing is to place a 2.2Ω resistor in series with the n-channel MOSFETs gate pin. This will slow down both the rising and falling edge of the switch node waveform. April 20, 2015 Eq. 20 The input capacitor current rating can be considered as ILED/2 under the worst condition D = 50%. 14 Revision 1.2 Micrel, Inc. MAQ3203 LED Ripple Current The LED current is the same as inductor current. If LED ripple current needs to be reduced then place a 4.7µF/50V ceramic capacitor across LED. Frequency Dithering The MAQ3203 is designed to reduce EMI by dithering the switching frequency ±12% in order to spread the frequency spectrum over a wider range. This lowers the EMI noise peaks (see Figure 1) generated by the switching regulator. Output Voltage Frequency Spectrum with Dither 100 90 Amplitude (dBµV) 80 70 60 50 40 30 20 10 0 100 1000 10000 Frequency (kHz) Figure 1. Output Voltage Frequency Spectrum with Dither Switching regulators generate noise by their nature and they are the main EMI source to interference with nearby circuits. If the switching frequency of a regulator is modulated via frequency dithering, the energy of the EMI is spread among many frequencies instead of concentrated at fundamental switching frequency and its harmonics. The MAQ3203 modulates the VCS(MAX) with amplitude ±6mV by a pseudo random generator to generate the ±12% of the switching frequency dithering to reduce the EMI noise peaks. April 20, 2015 15 Revision 1.2 Micrel, Inc. MAQ3203 PCB Layout Guidelines Warning!!! To minimize EMI and output noise, follow these layout recommendations. Output Capacitor • If LED ripple current needs to be reduced then place a 4.7µF/50V capacitor across LED. The capacitor must be placed as close to the LED as possible. 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. MOSFET • Place the MOSTET as close as possible to the MAQ3203 to avoid the trace inductance. Provide sufficient copper area on MOSFET ground to dissipate the heat. The following guidelines should be followed to insure proper operation of the MAQ3203 regulator: IC • Use thick traces to route the input and output power lines. • Signal and power grounds should be kept separate and connected at only one location. 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 switching node must be as short as possible. • The diode’s Cathode connection to the RCS must be keep as short as possible. 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 traces as short as possible. • 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. 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 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 MOSFET and back to CIN. The other current flowing loop is during the MOSFET OFF time, the traces connecting RCS, LED, inductor, freewheeling 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 switching node and its connecting traces. Inductor • Keep the inductor connection to the switch node (MOSFET drain) short. • Do not route any digital lines underneath or close to the inductor. • To minimize noise, place a ground plane underneath the inductor. April 20, 2015 16 Revision 1.2 Micrel, Inc. MAQ3203 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 homemade 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. Figure 2. Low-Noise Measurement April 20, 2015 17 Revision 1.2 Micrel, Inc. MAQ3203 Evaluation Board Schematic April 20, 2015 18 Revision 1.2 Micrel, Inc. MAQ3203 Bill of Materials Item C1, C5 Part Number 12105C475KAZ2A GRM32ER71H475KA88L 12105C475KAZ2A C2 GRM32ER71H475KA88L C3225X7S1H475M 08053D105KAT2A C3 C4 D1 GRM21BR71E105KA99L Manufacturer AVX Murata (8) Murata TDK AVX Murata (Open) 08055A271JAT2A AVX (Open) GRM2165C2A271JA01D Murata SK36-TP MCC L1 SLF10145T-680M1R2 M1 FDS5672 R1 CSR 1/2 0.2 1% I 4.7µF/50V, Ceramic Capacitor, X7R, Size 1210 2 4.7µF/50V, Ceramic Capacitor, X5R, Size 1210 1 1µF/25V, Ceramic Capacitor, X5R, Size 0805 1 1µF/25V, Ceramic Capacitor, X7R, Size 0805 1 270pF/50V, Ceramic Capacitor NPO, Size 0805 1 60V, 3A, SMC, Schottky Diode 1 68µH, 1.2A, 0.14Ω, SMT, Power Inductor 1 MOSFET, N-CH, 60V, 12A, SO-8 1 0.2Ω Resistor, 1/2W, 1%, Size 1206 1 100kΩ Resistor, 1% , Size 0805 2 (9) TDK SK36-7-F Qty. AVX C2012X7R1E105K SK36 Description (7) (10) Fairchild (11) Semiconductor Diodes, Inc. (12) TDK Fairchild Semiconductor Stackpole Electronics, (13) Inc. (14) R2, R3 CRCW08051003FKEA R4 CRCW08050000FKEA Vishay 0Ω Resistor, 1%, Size 0805 1 R5 (Open) CRCW08052R20FKEA Vishay 2.2Ω Resistor, 1%, Size 0805 1 R6 CRCW08051002FKEA Vishay 10kΩ Resistor, 1% , Size 0805 1 High-Brightness LED Driver Controller with HighSide Current Sense 1 U1 MAQ3203YM Vishay (15) Micrel, Inc. Notes: 7. AVX: www.avx.com. 8. Murata: www.murata.com. 9. TDK: www.tdk.com. 10. MCC: www.mcc.com. 11. Fairchild Semiconductor: www.fairchildsemi.com. 12. Diodes, Inc.: www.diodes.com. 13. Stackpole Electronics, Inc.: www.seielect.com. 14. Vishay: www.vishay.com. 15. Micrel, Inc.: www.micrel.com. April 20, 2015 19 Revision 1.2 Micrel, Inc. MAQ3203 PCB Layout Recommendations Top Assembly Top Layer April 20, 2015 20 Revision 1.2 Micrel, Inc. MAQ3203 PCB Layout Recommendations (Continued) Bottom Layer April 20, 2015 21 Revision 1.2 Micrel, Inc. MAQ3203 Package Information and Recommended Landing Pattern(16) 8-Pin SOIC (M) Note: 16. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. April 20, 2015 22 Revision 1.2 Micrel, Inc. MAQ3203 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, Inc. is a leading global manufacturer of IC solutions for the worldwide high performance linear and power, LAN, and timing & communications markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products. Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network of distributors and reps worldwide. Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. 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. © 2011 Micrel, Incorporated. April 20, 2015 23 Revision 1.2