MP3378GY-Z

MP3378 24 V, 4-Channel WLED Controller Plus High-Efficiency Buck Converter DESCRIPTION The MP3378 is a one-chip solution designed for monitor applications. It includes a step-up controller with 4 current channels for backlighting and a high-efficiency buck converter for internal bus voltage or standby power. The 4-string WLED controller drives an external MOSFET to boost up the output voltage from the input supply. It regulates the current in each LED string to the programmed value set by an external current-setting resistor. It supports both analog and PWM dimming independently to meet the special dimming mode request. In addition, rich protection modes are integrated including OCP, OTP, UVP, OVP, LED short/open protection, and inductor/diode short protection. The high-efficiency buck converter operates in current mode with a built in MOSFET and synchronous rectifier. It offers a very compact solution to achieve excellent load and line regulation. Full protection features include OCP and thermal shutdown. The MP3378 is available in SOIC28 and TSSOP28EP package. FEATURES WLED Controller:  4-String, Max 350 mA/String WLED Controller Up to 24 V Input Voltage Range 2.5% Current Matching Accuracy Programmable Switching Frequency PWM and Analog Dimming Mode Open and Short LED Protection Programmable Over-Voltage Protection Recoverable Thermal Shutdown Protection Over-Current Protection Over-Temperature Protection Inductor/Diode Short Protection           Buck Converter:  144 mΩ/58 mΩ Low Rds(on) Internal Power MOSFETs Low Quiescent Current Fixed 235 kHz Switching Frequency Frequency Sync from 250 kHz to 2 MHz External Clock AAM Power-Save Mode Internal Soft Start OCP and Hiccup Over-Temperature Protection Output Adjustable from 0.8 V         APPLICATIONS    Desktop LCD Flat Panel Displays Flat Panel Video Displays 2D/3D LCD TVs and Monitors All MPS parts are lead-free, halogen-free, and adhere to the RoHS directive. For MPS green status, please visit the MPS website under Quality Assurance. “MPS” and “The Future of Analog IC Technology” are registered trademarks of Monolithic Power Systems, Inc. MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 1 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER TYPICAL APPLICATION L1 D1 VIN C2 C1 M1 24 C3 25 GATE VIN1 ISENSE VCC1 R11 23 R10 22 R2 2 4 28 R4 3 15 VIN C4 22 µF 21 EN OVP OSC LED1 ADIM LED2 PWM LED3 MP3378 ISET LED4 VIN2 BST SW SYNC 8 7 6 5 20 R6 47 Ω 16 C7 0.1µF GATE 14 C6 0.1 µF R7 R5 75 k AAM L2 10 µH R8 40.2 k 5V C5 66 µF FB 51 k 13 MP3378 Rev. 1.01 5/26/2017 12 VCC2 String 4 9 String 3 27 C4 GND1 COMP String 1 R3 1 String 2 R1 26 GND2 AGND 19 R9 7.5 k 17, 18 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 2 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER ORDERING INFORMATION Part Number MP3378GY MP3378GF Package SOIC-28 TSSOP-28 EP Top Marking See Below See Below * For Tape & Reel, add suffix –Z (e.g. MP3378GY–Z); * For Tape & Reel, add suffix –Z (e.g. MP3378GF–Z); TOP MARKING (MP3378GY) MPS: MPS prefix YY: Year code WW: Week code MP3378: Product code of MP3378GY LLLLLLLLL: Lot number TOP MARKING (MP3378GF) MPS: MPS prefix YY: Year code WW: Week code MP3378: Product code of MP3378GF LLLLLLLLL: Lot number MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 3 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER PACKAGE REFERENCE TOP VIEW GND1 1 28 PWM OSC 2 27 EN ISET 3 26 COMP ADIM 4 25 VCC1 LED4 5 24 VIN1 LED3 6 23 GATE LED2 7 22 ISENSE LED1 8 21 OVP 9 20 NC 10 19 NC 11 18 PWM OSC 2 27 EN ISET 3 26 COMP ADIM 4 25 VCC1 LED4 5 24 VIN1 6 23 GATE 7 22 ISENSE SYNC LED1 8 21 SYNC BST OVP 9 20 BST AGND NC 10 19 AGND GND2 NC 11 18 GND2 FB 12 17 GND2 AAM 13 16 SW VCC2 14 15 VIN2 17 GND2 AAM 13 16 SW 15 28 LED3 12 14 1 LED2 FB VCC2 GND1 VIN2 SOIC28 Exposed Pad Connect to GND TSSOP28EP ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance WLED Driver VIN1 ........................................... -0.3 V to + 28 V VLED1 to VLED4 ............................... -1 V to + 55 V VGATE, VCC1, VISENSE .................. -0.3 V to + 6.5 V All other pins ............................. –0.3 V to VCC1 Buck Converter VIN2, VSW ..................................... –0.3 V to 28 V VBST .................................................... VSW + 6 V All other pins ................................. –0.3 V to 6 V (2) Continuous power dissipation (TA = 25°C) SOIC-28 ......................................................2 W TSSOP-28 EP .......................................... 3.9 W Junction temperature ............................... 150°C Lead temperature .................................... 260°C SOIC-28…………………..……62.5……30....°C/W TSSOP-28 EP……………...…32…….…6....°C/W Recommended Operating Conditions (4) θJA θJC NOTES: 1) Exceeding these ratings may damage the device. The voltage is measured with a 20 MHz bandwidth limited oscilloscope. 2) The maximum allowable power dissipation is a function of the maximum junction temperature TJ (MAX), the junction-toambient thermal resistance θJA, and the ambient temperature TA. The maximum allowable continuous power dissipation at any ambient temperature is calculated by PD (MAX) = (TJ (MAX)-TA)/θJA. Exceeding the maximum allowable power dissipation produces an excessive die temperature, causing the regulator to go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. 3) The device is not guaranteed to function outside of its operating conditions. 4) Measured on JESD51-7, 4-layer PCB. (3) Supply voltage (VIN1, VIN2) ................ 5 V to 24 V Operating junction temp. (TJ). .. -40°C to +125°C MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 4 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER ELECTRICAL CHARACTERISTICS (5) VIN1 = VIN2 = 12 V, VEN = 5 V, TA = 25°C, unless otherwise noted. Parameters Symbol Condition Min Typ Max Units 1.2 1.35 1.5 mA 1 μA WLED controller section Supply current (quiescent) IQ1 Supply current (shutdown) IST LDO output voltage VCC1 UVLO threshold VCC1 VCC1_UVLO VIN1 = 12 V, VEN = 5 V, no load without switching, buck disabled VEN = 0 V, VIN = 12 V, buck disabled VEN = 5 V, 7 V < VIN1 < 28 V, 0 < IVCC1 < 10 mA Rising edge 5.4 6 6.6 V 3.6 4 4.4 V VCC1 UVLO hysteresis 200 EN high voltage VEN_HIGH VEN rising EN low voltage VEN_LOW VEN falling STEP-UP CONVERTER Gate driver impedance (sourcing) Gate driver impedance (sinking) mV 1.8 VCC1 = 6 V, VGATE = 6 V VCC1 = 6 V, IGATE = 10 mA V 0.6 V 4.1 7 Ω 3 5 Ω ROSC = 115 kΩ 470 530 590 kHz ROSC = 374 kΩ 150 180 210 kHz 1.20 1.23 1.26 V Switching frequency fSW1 OSC voltage VOSC Maximum duty cycle Cycle-by-cycle ISENSE current limit COMP source current limit DMAX1 ICOMP SOLI 1 V < COMP < 1.9 V 70 μA COMP sink current limit ICOMP SILI 1 V < COMP < 1.9 V 17 μA ΔICOMP = ±10 μA 440 μA/V COMP transconductance 93 Max duty cycle GCOMP 145 180 % 230 mV CURRENT DIMMING PWM input low threshold VPWM_LO VPWM falling PWM input high threshold Analog dimming input low threshold Analog dimming input high threshold LED CURRENT REGULATION ISET voltage VPWM_HI VPWM rising LEDX average current Current matching ILED (5) VCC max current limit LED FET resistance MP3378 Rev. 1.01 5/26/2017 VISET RISET = 30.5 kΩ 0.75 1.25 V 0.38 0.41 0.44 V 1.44 1.49 1.54 V 1.20 1.225 1.25 V 31.4 32 34.2 mA 2.5 % 100 mA Ω ILED = 32 mA ICC1_Limit R_LED 50 ILED = 10 mA V 75 1.7 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 5 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN1 = VIN2 = 12 V, VEN = 5 V, TA = 25°C, unless otherwise noted. Parameters Symbol LEDX regulation voltage VLEDX PROTECTION OVP (over-voltage protection) threshold OVP (over-voltage protection) threshold HYS OVP UVLO threshold LEDX UVLO threshold LEDX over-voltage threshold VOVP_OV Condition ILED = 60 mA 260 mV Rising edge Step-up converter fails VLEDX_OV VLMT Thermal protection threshold TST Units mV VOVP_UV VLEDX_UV Latch-off current limit Max 800 HYS T_LED_OV Typ ILED = 330 mA VOVP_HYS LED short fault cycles Min 1.20 1.23 1.26 65 V mV 20 120 57 190 100 260 mV mV 5.8 6.3 6.8 V 720 mV 4096 600 Thermal protection hysteresis 660 150 °C 25 °C Buck converter section Supply current (quiescent) VIN2 under-voltage threshold VIN2 under-voltage threshold-hysteresis VCC2 regulator lockout IQ2 VIN2_UVLO VFB = 1 V, AAM = 0.5 V, WLED controller disabled 150 200 250 μA Rising edge 3.7 3.9 4.1 V 550 650 750 mV 4.65 4.9 5.15 0 1 3 lockout VCC2 VCC2 load regulation ICC2 = 5 mA V % HS switch on resistance HSRDS-ON VBST-SW = 5 V 144 mΩ LS switch on resistance LSRDS-ON VCC2 = 5 V 58 mΩ Current limit ILIMIT Duty cycle = 40% 4.8 6 7.2 A Oscillator frequency fSW2 VFB = 750 mV 190 235 280 kHz Foldback frequency fFB VFB = 200 mV Maximum duty cycle DMAX2 VFB = 750 mV Minimum on time (5) TON_MIN Sync frequency range fSYNC Feedback voltage VFB TA = 25ºC Feedback current IFB VFB = 820 mV Soft-start period TSS 10% to 90% AAM source current IAAM MP3378 Rev. 1.01 5/26/2017 90 0.5 fSW2 95 % 90 ns 0.25 2 MHz 791 803 mV 10 50 nA 0.8 1.5 2.2 ms 5.6 6.2 6.8 uA 779 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 6 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN1 = VIN2 = 12 V, VEN = 5 V, TA = 25°C, unless otherwise noted. Parameters Symbol SYNC high threshold VSYNC_HI SYNC low threshold VSYNC_LO Condition Min Typ Max 1.8 Units V 0.6 V Thermal shutdown 150 ˚C Thermal hysteresis 20 ˚C NOTE: 5) Matching is defined as the difference between the maximum to minimum current divided by 2 times the average currents. MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 7 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS WLED Controller Section: VIN = 16 V, 10 LEDs in series, 4 strings parallel, 120 mA/string, TA = 25°C, unless otherwise noted. MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 8 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS Buck Converter Section: VIN = 16 V, VOUT = 5 V, L2 = 10 μH, TA = 25°C, unless otherwise noted. MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 9 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER PIN FUNCTIONS Pin # Name Description 1 GND1 2 OSC 3 ISET 4 ADIM 5 LED4 6 LED3 7 LED2 8 LED1 9 OVP 10,11 NC 12 FB 13 AAM Ground for WLED controller. Switching frequency set. Connect a resistor between OSC and GND to set the step-up converter switching frequency. The voltage at OSC is regulated to 1.23 V. The clock frequency is proportional to the current sourced from OSC. LED current set. Tie a current-setting resistor from ISET to ground to program the current in each LED string. ISET voltage is regulated to 1.225 V. The LED current is proportional to the current through the ISET resistor. Input for analog brightness control. The LED current amplitude is determined by ADMIN. The input signal can be either a PWM signal or a DC voltage signal. An internal RC filter (10 MΩ resistor and 100 pF capacitor) is integrated to ADMIN. If a PWM signal is applied to ADMIN, a >20 kHz frequency is recommended. This obtains a better PWM signal filtering performance and ensures the amplitude voltage is higher than 1.5 V and the low-level voltage is less than 0.4 V. For a DC signal input, please apply a DC input signal range from 0.41 V to 1.49 V to set linearly the LED current from minimum to full scale. If ADMIN is floated, pull internally to GND. LED string 4 current input. LED4 is the open-drain output of an internal dimming control switch. Connect the LED string 4 cathode to LED4. LED string 3 current input. LED3 is the open-drain output of an internal dimming control switch. Connect the LED string 3 cathode to LED3. LED string 2 current input. LED2 is the open-drain output of an internal dimming control switch. Connect the LED string 2 cathode to LED2. LED string 1 current input. LED1 is the open-drain output of an internal dimming control switch. Connect the LED string 1 cathode to LED1. Over-voltage protection input. Connect a resistor divider from the output to OVP to program the OVP threshold. No connection. Buck converter feedback. An external resistor divider from the output to AGND (tapped to FB) sets the output voltage. To prevent current-limit runaway during a short-circuit fault condition, the frequency foldback comparator lowers the oscillator frequency when the FB voltage is below 400 mV. AAM mode setting for buck converter. Connect a resistor from AAM to ground to set the AAM voltage and force the buck converter into non-synchronous mode when the load is small. Driving AAM high (=VCC2) forces the buck converter into CCM. MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 10 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER PIN FUNCTIONS (continued) Pin # Name 14 VCC2 15 VIN2 16 SW 17,18 19 GND2 AGND 20 BST 21 SYNC 22 ISENSE 23 GATE 24 VIN1 25 VCC1 26 COMP 27 28 EN PWM MP3378 Rev. 1.01 5/26/2017 Description Bias supply for buck converter. Decouple with a 0.1 μF-0.22 μF capacitor. The capacitance should be no more than 0.22 μF. Supply voltage input for buck converter. A ceramic capacitor is needed to decouple the input rail. Use a wide PCB trace to make the connection. Switch output for buck converter. Use a wide PCB trace to make the connection. Ground for buck converter. Analog ground for buck converter. Bootstrap for buck converter. A capacitor and a 47 Ω resistor connected between SW and BST are required to form a floating supply across the high-side switch driver. Synchronization for buck converter. Apply a clock signal with a frequency higher than 250 KHz; the frequency of the buck converter can be synchronized by the external clock. The internal clock’s rising edge is synchronized to the external clock’s falling edge. Current sense input for WLED controller. During normal operation, ISENSE senses the voltage across the external inductor current-sensing resistor (RSENSE) for peakcurrent–mode control. Also, it limits the inductor current during every switching cycle. Power switch gate output for WLED controller. GATE drives the external power N-channel MOSFET. Supply input for WLED controller. The internal 6 V linear regulator output for WLED controller. VCC1 provides a power supply for the external MOSFET switch gate driver and the internal control circuitry. Bypass VCC1 to GND with a ceramic capacitor. Error amplifier output of WLED controller. Connect a capacitor and resistor in series to stabilize the boost converter loop. Enable input for WLED controller. Input signal for PWM brightness control. If PWM is floated, pull internally to GND. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 11 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER FUNCTIONAL BLOCK DIAGRAM VCC1 VIN1 Regulator GND1 - Control Logic + PWM Comparator GATE Current-Sense Amplifier + 200 ns Blank Time ISENSE - OV Comparator OVP + OSC Oscillator - 100 ns Blanking + - ILIMIT PWM STOP + - COMP - UP_ CLAMP Short-String Protection 1.23 V 6.3 V + Max - Min EA Feedback Control + Ref EN Enable Control LED1-4 1 Current Control + 1. 225 V ADIM - PWM ISET VIN2 VCC2 RSEN VCC Regulator BST LDO HS Driver AAM 1 pF SYNC Rference 50 pF 400 k On-Time Current-Limit Control Logic Comparator SW VCC LS Driver FB Error Amplifier GND2 AGND Figure 1—Functional block diagram MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 12 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER OPERATION WLED CONTROLLER SECTION: The WLED controller employs a programmable constant frequency, peak-current–mode, stepup converter with 4 channel regulated current sources to drive an array of up to 4 strings of white LEDs. Internal 6 V Regulator When VIN1 is greater than 6.5 V, VCC1 outputs a 6 V power supply to the external MOSFET switch gate driver and the internal control circuitry. The VCC1 voltage drops to 0 V when the WLED controller shuts down. System Start-Up When enabled, the WLED controller checks the topology connection first. The WLED controller monitors the over-voltage protection (OVP) pin to see if the Schottky diode is connected or if the boost output is shorted to GND. An OVP voltage of less than 57 mV disables the WLED controller . Once all the protection tests pass, the WLED controller starts boosting the step-up converter with an internal soft-start. It is recommended that the enable signal occurs after the establishment of the input voltage and PWM dimming signal during the start-up sequence to avoid large inrush current. Step-Up Converter The converter operating frequency is programmable by an external resistor on OSC. 300 kHz to 500 kHz is recommended as an operating frequency. This optimizes efficiency and the size of external components. At the beginning of each switching cycle, the internal clock turns on the external MOSFET (In normal operation, the minimum turn-on time is 200 ns.) A stabilizing ramp added to the output of the current sense amplifier prevents subharmonic oscillations for duty cycles greater than 50 percent. This result is fed into the PWM comparator. When this voltage reaches the output voltage of the error amplifier (VCOMP) the external MOSFET turns off. The output voltage of the internal error amplifier is an amplified signal of the difference between the reference voltage and the feedback voltage. MP3378 Rev. 1.01 5/26/2017 The converter chooses automatically the lowest active LEDX voltage to provide a bus voltage high enough to power all the LED arrays. If the feedback voltage drops below the reference, the output of the error amplifier increases. This results in more current flowing through the MOSFET, thus increasing the power delivered to the output. This forms a closed loop that regulates the output voltage. Under light-load operation (especially in the case of VOUT1 ≈ VIN1), the converter runs in pulse-skipping mode where the MOSFET turns on for a minimum on-time of approximately 200 ns, and then the converter discharges the power to the output for the remaining period. The external MOSFET remains off until the output voltage needs to be boosted again. Dimming Control The MP3378 allows two dimming methods: PWM and analog dimming mode. For PWM dimming, apply a PWM signal to PWM. The LED current is chopped by this PWM signal, and the average LED current is equal to ISET*DDIM; where DDIM is the duty cycle of PWM dimming signal, and ISET is the LED current amplitude. For analog dimming, either a PWM signal or DC signal can be applied to ADIM. When a PWM signal is applied to ADIM, the signal is filtered by the internal RC filter. The LED current amplitude is equal to ISET * DDIM; where DDIM is the duty cycle of the PWM dimming signal, and ISET is the LED current amplitude. A PWM signal of 20 kHz or higher is recommended to achieve better filtering performance. When a DC signal is applied to ADIM, the voltage range (0.41 V to 1.49 V) sets directly the LED current linearly from minimum to full scale. Open-String Protection Open-string protection is achieved through the OVP pin and LEDX pins (1 to 4). If one or more strings are open, the respective LEDX pins are pulled to ground, and the WLED controller keeps charging the output voltage until it reaches the over-voltage protection www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 13 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER (OVP) threshold. If the OVP point has been triggered for >4 µs, the WLED controller stops switching and marks off the strings that have an LEDX voltage lower than 190 mV. Once marked off, the remaining LED strings force the output voltage back into tight regulation. The string with the largest voltage drop determines the output regulation. If all strings are open, the WLED controller shuts down until the WLED controller re-sets. Short-String Protection The WLED controller monitors the LEDX voltages to determine if a short-string fault has occurred. If one or more strings are shorted, the respective LEDX pins tolerate high-voltage stress. If an LEDX pin voltage is higher than 6.3 V, this condition triggers the detection of a short string. When a short-string fault (LEDX over-voltage fault) remains for 4096 switching clocks, the fault string is marked off and disabled. Once a string is marked off, it disconnects from the output voltage loop. The marked LED strings shut off completely until the boost part re-starts. In order to prevent mis-triggering short LED protection when opening an LED string or sharp ADIM, the short LED protection function is disabled when the Vledxs of all the used LED channels are higher than 1.5 V. across the sense resistor (connected between MOSFET and GND) hits VLMT limit value and lasts for 4 switching cycles, the WLED controller turns off and latches. Thermal Shutdown Protection To prevent the WLED controller from operating at exceedingly high temperatures, thermal shutdown detects the die temperature. When the die temperature exceeds the upper threshold (150°C), the WLED controller shuts down. The controller resumes normal operation when the die temperature drops below the lower threshold. Typically, the hysteresis value is 25°C. Inductor/Diode Short Protection To prevent damage to the WLED controller and external MOSFET when the external inductor/diode is shorted, the protection mode operates in the following ways: 1. When the inductor/diode is shorted, the output cannot maintain enough energy to load the LED, causing the output voltage to drop. Thus, the COMP (the error amplifier output) voltage tends to rise until it is clamped high. If it lasts longer than 512 switching cycles, the WLED controller turns off and latches. 2. However, in some cases the COMP voltage cannot be clamped high when the inductor/diode is shorted, so the WLED controller provides the protection mode by detecting the current flowing through the power MOSFET. In this mode, when the current sense voltage MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 14 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER Buck Converter Section: The step-down, switch-mode converter has built in internal power MOSFETs and offers a very compact solution. It operates in a fixed frequency, peak-current-control mode to regulate the output voltage. A PWM cycle is initiated by the internal clock. The integrated high-side power MOSFET is turned on and remains on until its current reaches the value set by the COMP_BUCK voltage. (COMP_BUCK is one of the buck’s internal control voltages; it is not the COMP pin.) When the power switch is off, it remains off until the next clock cycle starts. If the current in the power MOSFET does not reach the COMP_BUCK set current value within 95 percent of one PWM period, the power MOSFET is forced off. Internal Regulator Most of the internal circuitries are powered from the 5 V internal regulator. This regulator takes the VIN2 input and operates in the full VIN2 range. When VIN2 is greater than 5.0 V, the output of the regulator is in full regulation. When VIN2 is lower than 5.0 V, the output decreases; a 0.1 uF ceramic capacitor for decoupling is required. Error Amplifier The error amplifier compares the FB voltage with the internal 0.8 V reference (REF) and outputs a COMP_BUCK voltage, which is used to control the power MOSFET current. The optimized internal compensation network minimizes the external component count and simplifies the control loop design. AAM Operation MP3378 has advanced asynchronous modulation (AAM) power-save mode for light load. Connect a resistor from AAM to GND to set the AAM voltage. Under a heavy-load condition, the VCOMP_BUCK is higher than VAAM. When the clock goes high, the high-side power MOSFET turns on and remains on until VILsense reaches the value set by the COMP_BUCK voltage. The internal clock re-sets every time VCOMP_BUCK is higher than VAAM. MP3378 Rev. 1.01 5/26/2017 Under a light-load condition, the value of VCOMP_BUCK is low. When VCOMP_BUCK is less than VAAM and VFB is less than VREF, VCOMP_BUCK ramps up until it exceeds VAAM. During this time, the internal clock is blocked. This causes the device to skip pulses for pulse frequency modulation (PFM) mode, achieving the lightload power save (see Figure 2). CLOCK 1.1 pF HS_driver VAAM Q VOUT2 50 pF 400 K S R1 RT R R2 VCOMP_BUCK VREF VIL_SENSE Figure 2—Simplified AAM control logic SYNC Control The buck converter can be synchronized through SYNC to an external clock range from 250 kHz to 2 MHz. The internal clock’s rising edge is synchronized to the external clock’s falling edge. The synchronized logic high voltage should be higher than 1.8 V. The synchronized logic low voltage should be lower than 0.6 V. The frequency of the external clock should be higher than the frequency of the internal clock. Otherwise the internal clock may pulse high and turn on the high-side MOSFET again. Under-Voltage Lockout (UVLO) Under-voltage lockout (UVLO) protects the buck converter from operating at an insufficient supply voltage by monitoring the output voltage of the internal regulator (VCC2). The UVLO rising threshold is about 3.9 V while its falling threshold is a consistent 3.25 V. Internal Soft Start (SS) Soft start is implemented to prevent the converter output voltage from overshooting during start up. When the chip starts up, the internal circuitry generates a soft-start voltage (SS) ramping up from 0 V. The soft-start period lasts until the voltage on the soft-start capacitor exceeds the reference voltage of 0.8 V. At this point, the reference voltage takes over. The soft-start time is set internally at around 1.5 ms. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 15 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER Over-Current Protection (OCP) and Hiccup The cycle-by-cycle over-current limit is implemented when the inductor current peak value exceeds the set current-limit threshold. Meanwhile, the output voltage starts to drop until FB is below the under-voltage (UV) threshold (50 percent below the reference, typically). Once a UV is triggered, the buck converter enters hiccup mode to re-start the part periodically. This protection mode is useful when the output is dead shorted to ground. The average short-circuit current is reduced greatly to alleviate thermal issues and protect the regulator. The buck converter exits hiccup mode once the over-current condition is removed. Thermal Shutdown Thermal shutdown prevents the chip from operating at exceedingly high temperatures. When the die temperature is higher than 150°C, it shuts down the buck converter. When the temperature is lower than its lower threshold (130°C, typically) the buck converter is enabled again. Floating Driver and Bootstrap Charging The floating power MOSFET driver is powered by an external bootstrap capacitor. This floating driver has its own UVLO protection. The UVLO’s rising threshold is 2.2 V with a hysteresis of 150 mV. The bootstrap capacitor voltage is regulated internally by VIN2 through DB, R6, C7, L2, and C5 (see Figure 3). If VIN2-VSW is more than 5 V, U1 regulates MB to maintain a 5 V BST voltage across C7. MP3378 Rev. 1.01 5/26/2017 DB VIN2 MB BST 5V R6 U1 C7 L2 SW VOUT2 C5 Figure 3—Internal bootstrap charging circuit start-up and shutdown If VIN2 is higher than its appropriate thresholds, the buck converter starts up. The reference block starts first, generating stable reference voltage and currents and then the internal regulator is enabled. The regulator provides a stable supply for the remaining circuitries. Two events can shut down the buck converter: VIN2 UVLO and thermal shutdown. During the shutdown procedure, the signaling path is blocked first to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 16 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER APPLICATION INFORMATION WLED CONTROLLER SECTION: Selecting the Switching Frequency The switching frequency of the step-up converter is recommended from 300 kHz to 500 kHz for most applications. An oscillator resistor on OSC sets the internal oscillator frequency for the stepup converter according to Equation (1): FSW1 KHz   67320 Rosc KΩ  Choose an inductor that does not saturate under the worst-case load conditions. Select the minimum inductor value to ensure that the boost converter works in continuous conduction mode (CCM) with high efficiency and good EMI performance. Calculate the required inductance value using Equation (3): L1  (1) For ROSC = 224 kΩ, the switching frequency is set to 300 kHz. Setting the LED Current Each LED string current is set through the current-setting resistor on ISET. See Equation (2): ILED(mA)  795  1.23 RSET KΩ  (2) For RSET = 8.06 kΩ, the LED current is set to 120 mA. Please do NOT leave ISET open. Selecting the Input Capacitor The input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. The input capacitor impedance at the switching frequency should be less than the input source impedance to prevent the high-frequency switching current from passing through to the input. Use ceramic capacitors with X5R or X7R dielectrics for their low ESR and small temperature coefficients. For most applications, use a 4.7 μF ceramic capacitor in parallel with a 220 µF electrolytic capacitor. η  VOUT1  D  (1  D)2 2  fSW1  ILOAD1 D  1 VIN1 VOUT1 (3) Where VIN1 and VOUT1 are the input and output voltages, fSW1 is the switching frequency, ILOAD1 is the LED load current, and η is the efficiency. Usually the switching current is used for peakcurrent-mode control. In order to avoid hitting the current limit, the voltage across the sensing resistor (RSENSE) must be less than 80% of the worst-case current-limit voltage (VSENSE). See Equation (4): RSENSE  IL1(PEAK)  0.8  VSENSE IL1(PEAK) VOUT1  ILOAD1 VIN1  (VOUT1  VIN1 )  ηVIN1 2  L1 FSW1  VOUT1 (4) Where IL1(PEAK) is the peak value of the inductor current. VSENSE is shown in Figure 4. Selecting the Inductor and Current-Sensing Resistor A larger value inductor results in less ripple current and lower peak inductor current, reducing stress on the N-channel MOSFET. However, the larger value inductor has a larger physical size, a higher series resistance, and a lower saturation current. Figure 4—VSENSE vs. duty cycle MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 17 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER Selecting the Power MOSFET The critical parameters for the selection of a MOSFET are as follows: 1. Maximum drain-to-source voltage, VDS(MAX) 2. Maximum current, ID(MAX) 3. On-resistance, RDS(ON) 4. Gate-source charge (QGS) and gate-drain charge (QGD) 5. Total gate charge, QG Ideally, the off-state voltage across the MOSFET is equal to the output voltage. Considering the voltage spike when it turns off, VDS(MAX) should be greater than 1.5 times the output voltage. The maximum current through the power MOSFET occurs at the minimum input voltage and the maximum output power. The maximum RMS current through the MOSFET is given by Equation (5): IRMS(MAX)  IIN1(MAX)  DMAX , where: DMAX  VOUT1  VIN1(MIN) VOUT1 (5) The current rating of the MOSFET should be greater than 1.5 x IRMS. The on resistance of the MOSFET determines the conduction loss, which is given by Equation (6): Pcond  IRMS 2  R DS (on)  k (6) Where k is the temperature coefficient of the MOSFET. The switching loss is related to QGD and QGS1, which determine the commutation time. QGS1 is the charge between the threshold voltage and the plateau voltage when a driver charges the gate (see the chart of VGS vs. QG of the MOSFET datasheet). QGD is the charge during the plateau voltage. These two parameters are needed to estimate turn-on and turn-off losses. See Equation (7): PSW  Q GS1  R G  VDS  I IN1  f SW1  VDR  VTH Q GD  R G  VDS  I IN1  f SW1 VDR  VPLT MP3378 Rev. 1.01 5/26/2017 (7) Where VTH is the threshold voltage, VPLT is the plateau voltage, RG is the gate resistance, and VDS is the drain-source voltage. Please note that calculating the switching loss is the most difficult part in the loss estimation. Equation (7) provides a simplified equation. For more accurate estimates, the equation becomes much more complex.The total gate charge (QG) is used to calculate the gate drive loss. See Equation (8) PDR  QG  VDR  fSW1 (8) Where VDR is the drive voltage. Selecting the Output Capacitor The output capacitor keeps the output voltage ripple small and ensures feedback loop stability. The output capacitor impedance must be low at the switching frequency. Ceramic capacitors with X7R dielectrics are recommended for their low ESR characteristics. For most applications, a 4.7 μF ceramic capacitor in parallel with a 22 μF electrolytic capacitor will suffice. Setting the Over-Voltage Protection Open-string protection detects the voltage on OVP. In some cases, an LED string failure results in the feedback voltage equaling zero. The part then keeps boosting the output voltage higher and higher. If the output voltage reaches the programmed OVP threshold, the protection is triggered. To ensure the chip functions properly, select resistor values for the OVP resistor divider to provide an appropriate set voltage. The recommended OVP point is about 1.1 to 1.2 times higher than the output voltage for normal operation. See Equation (9): VOVP  1.23  (1  RHIGH ) RLOW (9) Selecting Dimming Control Mode Two different dimming methods are provided: 1. Direct PWM Dimming An external PWM dimming signal is employed to achieve PWM dimming control. Apply a PWM dimming signal (in the range of 100 Hz to 20 kHz) to PWM. The minimum recommended amplitude of the PWM signal is 1.5 V, and the low-level amplitude should be less than 0.4 V (see Table 1). www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 18 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER Table 1—The range of PWM dimming duty fPWM(Hz) Dmin Dmax 0.30% 100% 100 < f  200 0.75% 100% 200 < f  500 1.50% 100% 500 < f  1 k 3.00% 100% 1k65% VIN2 In these cases, an external BST diode is recommended from VCC2 to BST (see Figure 8). The recommended external BST diode is IN4148, and the BST capacitor is 0.1 μF ─1μF. RBST BST External BST Diode 1N4148 VCC2 CBST MP3378 0.1µF-1μF SW L2 + COUT Figure 8—Add optional external bootstrap diode to enhance efficiency VOUT2 V 1  (1  OUT2 )  (R ESR  ) FSW2  L2 VIN2 8  FSW2  C 5 (17) MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 21 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER PCB Layout Guidelines Efficient PCB layout is critical to reduce EMI noise. For best results, refer to Figure 9 (boost driver layout) and Figure 10 (buck converter layout) and follow the guidelines below: Boost Driver Layout (see Figure 9) 1) Make the loop from the external MOSFET (M1), through the output diode (D1) and the output capacitors (C2, C3) as small and short as possible as they carry a high-frequency pulse current. Figure 9—Recommended boost driver layout 2) Separate the power ground and signal ground and then connect PGND and GND together as all logic signals refer to the signal ground. This reduces the noise affection. Buck Converter Layout (see Figure 10) 1) Keep the connection of the input ground and GND2 (PGND) as short and wide as possible. 2) Keep the connection of the input capacitors (C16, C16A, and C17) and VIN2 as short and wide as possible. 3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. Figure 10—Recommneded buck converter layout 4) Route SW away from sensitive analog areas such as FB. 5) Connect a resistor (R23) to AGND as SYN is sensitive to noise. Otherwise SCP may fail, and the buck converter may be damaged. 6) Connect GND1 and GND2 together by a single point. MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 22 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER TYPICAL APPLICATION CIRCUITS Figure 11—4 string, 10 LED in series, 120 mA/string plus 5 V output application MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 23 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER PACKAGE INFORMATION TSSOP-28 EP 5.90 TYP 9.60 9.80 0.65 BSC 0.40 TYP 28 15 1.60 TYP 4.30 4.50 PIN 1 ID 3.20 TYP 6.20 6.60 5.80 TYP 14 1 TOP VIEW RECOMMENDED LAND PATTERN 0.80 1.05 1.20 MAX SEATING PLANE 0.19 0.30 0.65 BSC 0.00 0.15 0.09 0.20 SEE DETAIL "A" FRONT VIEW SIDE VIEW GAUGE PLANE 0.25 BSC 5.70 6.10 0o-8o 0.45 0.75 DETAIL “A” 2.60 3.10 BOTTOM VIEW MP3378 Rev. 1.01 5/26/2017 NOTE: 1) ALL DIMENSIONS ARE IN MILLIMETERS. 2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSION OR GATE BURR. 3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSION. 4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.10 MILLIMETERS MAX. 5) DRAWING CONFORMS TO JEDEC MO-153, VARIATION AET. 6) DRAWING IS NOT TO SCALE. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 24 MP3378 – 4-CHANNEL WLED CONTROLLER PLUS BUCK CONVERTER SOIC-28 NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP3378 Rev. 1.01 5/26/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 25