LED6001

LED6001 PWM-dimmable single channel LED driver with integrated boost controller Datasheet - production data Applications • Indoor and architectural LED lighting • Emergency LED lighting • Off-grid LED street lighting • White goods HTSSOP-16 • Gaming/gambling machines Description Features • Switching controller section – 5.5 V to 36 V input voltage range – Very low shutdown current: ISHDN < 10 µA – Internal +5 V LDO for gate driver supply – Internal +3.3 V LDO for device supply – Fixed frequency peak current mode control – Adjustable (100 kHz to 1 MHz) switching frequency – External synchronization for multi-device applications – High performance external MOSFET driver – Cycle-by-cycle external MOSFET OCP – Fixed internal soft-start – Programmable output OVP – Boost, buck-boost and SEPIC topologies supported – Thermal shutdown with autorestart – Output short-circuit detection • LED control section – Up to 60 V output voltage – Constant current control loop – High-side output current sensing circuitry – 30 to 300 mV differential sensing voltage – ± 4% output current reference accuracy – Output overcurrent protection – Sensing resistor failure protection – PWM dimming with auxiliary series switch – Analog dimming February 2020 This is information on a product in full production. The LED6001 device is a LED driver that combines a boost controller and a high-side current sensing circuitry optimized for driving one string of high-brightness LEDs. The device is compatible with multiple topologies such as boost, SEPIC and floating load buck-boost. The brightness of the LEDs can be controlled through PWM dimming and analog dimming (10:1 ratio) by means of two independent pins. Enhanced PWM dimming can be obtained thanks to a MOSFET in series with the LED string and directly driven by a dedicated pin. The high-side current sensing, in combination with a P-channel MOSFET, provides an effective protection in case the positive terminal of the LED string is shorted to ground. The high precision current sensing circuitry allows a LED current regulation reference within ± 4% accuracy over the whole temperature range and production spread. A fault output (open-drain) informs the host system about faulty conditions: device overtemperature, output overvoltage (disconnected LED string) and LED overcurrent. Table 1. Device summary Order code Package Packaging LED6001 HTSSOP-16 (exposed pad) Tube LED6001TR DocID025575 Rev 4 Tape and reel 1/26 www.st.com Contents LED6001 Contents 1 Typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pin function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 Recommended operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.1 Device supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.2 Boost controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.2.1 Turn on and power-down sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.2.2 Boost controller operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.2.3 Boost converter stability and slope compensation . . . . . . . . . . . . . . . . . 14 7.2.4 Switching frequency oscillator and external synchronization . . . . . . . . . 16 7.3 LED current regulation and brightness control . . . . . . . . . . . . . . . . . . . . . 17 7.4 Device protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.4.1 Linear regulators undervoltage lockout . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.4.2 Power switch overcurrent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.4.3 Output overvoltage and OVFB pin disconnection . . . . . . . . . . . . . . . . . 20 7.4.4 Output rail disconnection detection or output short-circuit to ground . . . 21 7.4.5 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 8 Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2/26 DocID025575 Rev 4 LED6001 1 Typical application circuit Typical application circuit Figure 1. Basic application circuit schematic (boost topology) L BOOST DFW VIN CIN VOUT COUT ROVFBH VIN RGATE VLDO3 GATE VOVFB CLDO3 VLDO3 QSW CSNS RSLOPE LDO3 ROVFBL RSNS PGND VDR CVDR VFBP RVFB XFAULT LED6001 VFBN PWMI FSW VOVFB VLDO3 OVFB RFSW ADIM RCOMP PWMO QDIM COMP CCOMP SGND AM03411 DocID025575 Rev 4 3/26 26 Pin function 2 LED6001 Pin function Figure 2. Pin connection (through top view) PWMI 1 16 VFBP FS W 2 15 VFBN XFAU LT 3 14 VIN LDO3 4 13 VDR SGND 5 12 GATE COMP 6 11 PGND ADIM 7 10 PWMO OV FB 8 9 CSNS AM03412V1 4/26 DocID025575 Rev 4 LED6001 Pin function Table 2. Pin description N Pin Description 1 PWMI Device enable and PWM dimming control input. 2 FSW Switching frequency setting. A resistor between this pin and SGND sets the desired switching frequency. This pin is also used as synchronization input. If tied high (e.g. connected to LDO3 pin) a 600 kHz switching frequency is set. 3 XFAULT Fault indicator, open-drain output. This pin is tied low by the device in case of faulty condition. See Section 7.4 on page 20 for details. 4 LDO3 3.3 V linear regulator output and device supply. Connect a 1 μF (typ.) bypass MLCC between this pin and SGND as close as possible to the chip. 5 SGND Signal ground. Return for analog circuitry. All setting components must refer to this grounding pin. 6 COMP Boost controller loop compensation. A simple RC series must be connected between this pin and SGND for proper loop compensation. See Section 7.2.3 on page 14 for details. 7 ADIM Analog dimming control input. The current at the output is linearly controlled by the voltage applied to this pin (0.3 V to 1.2 V). When the device is set to operate in standalone mode, a partition of the LDO3 voltage must be applied to this pin through a resistor divider. 8 OVFB Output overvoltage protection feedback input. Connect to the central tap of a resistor divider at the output. 9 CSNS Boost controller power switch current sensing input. Connect to the source of the external power MOSFET for proper switch overcurrent protection. 10 PWMO PWM dimming control output. This pin provides a PWM output signal (in phase with the one applied to the PWMI pin) for direct control of a dimming N-channel MOSFET. 11 PGND Power ground. Return for the VDR linear regulator and the power switch gate drivers. Also used as reference for the power MOSFET current sensing circuitry. Connect to ground as close as possible to the quiet terminal of the power switch sensing resistor. 12 GATE Power switch gate driver output. Connect to the gate of the power MOSFET through a small value resistor. 13 VDR 5 V linear regulator output and gate driver supply. Connect a 1 μF (typ.) bypass MLCC between this pin and PGND as close as possible to the chip. 14 VIN Supply voltage input. Connect this pin to the supply power rail. A 1 μF (typ.) bypass MLCC must be connected between this pin and PGND as close as possible to the chip. 15 VFBN Output current differential sensing input, negative terminal. Connect to the hot terminal (load side) of the high-side sensing resistor. 16 VFBP Output current differential sensing input, positive terminal. Connect to the quiet terminal (output capacitor side) of the high-side sensing resistor. - TPAD Thermal pad. Connect to a suitable ground plane area in order to ensure proper heat dissipation. Electrically connected to PGND and SGND. DocID025575 Rev 4 5/26 26 Block diagram 3 LED6001 Block diagram Figure 3. Simplified block diagram VIN VDR 5 V LDO Slope compensation Ramp generator + UVLO detector EN Current sensing CSNS Boost converter control logic GATE + 3.3 V LDO + LDO3 _ PGND Sync. detector EN OSC Output current setting Soft start FSW ADIM VFBP _ gm + COMP + 30 mV - 300 mV VFBN Thermal protection XFAULT Feedback/output disconnection and overload detection Control logic OVP + _ Fault management PWM detector Pow er-down watchdog timer EN OVFB 1.2 V VDR PWMO PWMI PGND SGND AM03413 6/26 DocID025575 Rev 4 LED6001 4 Absolute maximum ratings Absolute maximum ratings Table 3. Absolute maximum ratings Parameter Pin Min. Max. VIN to SGND -0.3 40 VFBP and VFBN to SGND 65 VDR to SGND -0.3 6 LDO3 to SGND -0.3 3.6 COMP, CSNS and OVFB to SGND -0.3 3.6 PGND to SGND -0.3 0.3 XFAULT, FSW, ADIM and GATE to SGND -0.3 6 PWMI and PWMO to SGND -0.3 6 HBM ESD susceptibility JEDEC JS001 All pins -2000 2000 VIN, VFBP, VFBN and ADIM ESD susceptibility VIN, VFBP, VFBN, ADIM to SGND -4000 4000 Corner pins -750 750 Non-corner pins -500 500 Typ. Max. Maximum pin voltage CDM ESD resistivity to SGND ANSI/ESD STM5.3.1 Unit V Table 4. Thermal characteristics Symbol Parameter TJ,OP Operating junction temperature -40 150 TSTG Storage temperature range -50 150 Thermal shutdown threshold 150 TSHDN Conditions Min. 160 Thermal shutdown hysteresis 20 XFAULT release hysteresis 40 Rth,JA(1) Junction to ambient thermal resistance Rth,JC Junction to case thermal resistance 1s0p 55 2s2p 45 175 Unit °C °C/W 37 1. The device mounted on a standard JESD51-5 test board. DocID025575 Rev 4 7/26 26 Recommended operating conditions 5 LED6001 Recommended operating conditions Table 5. Recommended operating conditions Symbol Parameter Conditions Min. Max. Unit DC characteristics VVIN Supply input voltage range VVDR VDR pin Input voltage range VVFBx Feedback input common mode voltage range VFB Feedback input differential mode voltage range VDR and VIN shorted together VFBP to VFBN 5.5 36 4.7 5.5 4.4 60 30 300 V mV AC characteristics 8/26 fsw Switching frequency 100 1000 fPWMI Dimming frequency 0.1 20 tPWMI,en Minimum PWMI pulse duration for device enable (turn on) PWMI input, fSW = 800 kHz 100 µs tPWMI,dim Minimum dimming on-time PWMI input, fSW = 1 MHz 6 µs DocID025575 Rev 4 kHz LED6001 6 Electrical characteristics Electrical characteristics VIN = 12 V, VVFBP = 12 V, VVFBN = 12 V and TJ =- 40 °C to 125 °C if not otherwise specified. Table 6. Electrical characteristics Symbol Parameter Conditions Min. Typ. Max. Unit Supply section Supply voltage range VVIN 5.5 PWMI turn on threshold PWMI turn off threshold PWMI pull-down resistor PMWI at 3.3 V tSHDN PWMI low to shutdown mode delay tSTART Start-up time VLDO3 VLDO3,ON VLDO3,OFF VVDR VVDR,ON VVDR,OFF 36 1.34 1.65 0.7 0.85 1.1 350 570 810 kΩ 10 15 22 ms 100 170 µs 3.3 3.4 V 20 CLDO3 = CVDR = 470 nF 3.3 V LDO output voltage 6 V ≤ VIN ≤ 36 V, ILDO3 = 0.5 mA, PWMI high 3.3 V LDO line regulation ILDO3 = 20 mA, PWMI high 6 V ≤ VIN ≤ 36 V 5 3.3 V LDO load regulation VIN = 6 V, PWMI high 0.5 mA ≤ ILDO3 ≤ 20 mA 90 100 3.2 V mV LDO3 undervoltage lockout upper threshold 2.2 2.8 3.0 LDO3 undervoltage lockout lower threshold 2.5 2.7 2.9 LDO3 undervoltage lockout hysteresis 50 200 400 mV V 3.3 V LDO current limit VLDO3 = 3.0 V 30 38 46 mA 5 V LDO output voltage 6 V ≤ VIN ≤ 36 V IVDR = 0.5 mA, PWMI high 4.8 5.0 5.2 V 5 V LDO line regulation IVDR = 40 mA, PWMI high 6 V ≤ VIN ≤ 36 V 10 40 5 V LDO load regulation VIN = 6 V, PWMI high 0.5 mA ≤ IVDR ≤ 40 mA 120 200 5 V LDO dropout voltage IVDR = 25 mA, VVIN = 4.8 V 150 300 VDR undervoltage lockout upper threshold 4.3 4.6 4.7 VDR undervoltage lockout lower threshold 4.25 4.4 4.55 20 150 300 50 75 100 VDR undervoltage lockout hysteresis 5 V LDO current limit VVDR = 4.5 V DocID025575 Rev 4 mV V mV mA 9/26 26 Electrical characteristics LED6001 Table 6. Electrical characteristics (continued) Symbol Parameter Conditions Min. Typ. Max. VIN = 16 V, PWMI low, -40 °C ≤ TJ ≤ 25 °C 1 4 10 VIN = 16 V, PWMI low, 25 °C ≤ TJ ≤ 125 °C 1 Unit Power consumption IVIN,SHDN IVIN,Q IVIN,ON Shutdown current μA 9 25 1.7 Quiescent current VIN = 16 V, PWMI to LDO3, -40 °C ≤ TJ ≤ 125 °C switching off-time 1 Operating current VIN = 16 V, PWMI high, fSW = 200 kHz, CL = 3.3 nF 5 7 Pulse skipping mode 140 180 ns • kΩ mA Boost controller tON,min Minimum switching on-time KFSW Switching frequency constant Adjustable switching frequency Fixed switching frequency fSW Synchronization signal frequency capture range FSW synchronization input high level FSW synchronization input low level Synchronization input high level pulse width RGATE Power switch gate driver output resistance tr,GATE Power switch gate driver rise time (20 to 80%) tf,GATE Power switch gate driver fall time (80 to20%) tSS Internal soft-start duration KS Slope compensation constant 45 50 55 RFSW = 500 kΩ 90 100 110 RFSW = 250 kΩ 180 200 220 RFSW = 50 kΩ 900 1000 1100 FSW pin high (LDO3) 500 600 tCLK,H = 250 ns, VCLK,L = 0.8 V, VCLK,H = 3.0 V 100 fCLK = 100 kHz to 1 MHz, tCLK,H = 250 ns fCLK = 100 kHz to 1 MHz, VCLK,L = 0.5 V, VCLK,H = 2.8 V MHz kHz 700 1000 2.8 0.5 250 V ns Pull-up 3 6 Pull-down 1 3 VVDR = 5 V, CL = 3.3 nF 15 30 Ω ns VCSNS,OCP Power switch OCP detection threshold 10/26 RFSW = 250 kΩ CSNS pin to PGND DocID025575 Rev 4 7 14 2.9 3.5 4.5 ms 3 5 7 A/s 300 360 400 mV LED6001 Electrical characteristics Table 6. Electrical characteristics (continued) Symbol Parameter Conditions Min. Typ. Max. VADIM = 0.3 V 20 30 40 VADIM = 0.6 V 110 120 130 VADIM = 1.2 V 280 300 304 VADIM to LDO3 288 300 308 ADIM pin voltage turn off threshold 260 270 280 ADIM pin voltage turn off hysteresis 5 10 20 Unit Output current sensing section VFB Feedback voltage (VVFBP - VVFBN differential current sensing voltage) Feedback reference voltage accuracy VADIM,OFF IVFBP Feedback positive input current VVFBP = 12.0 V VVFBN = 11.7 V -32 -25 -18 IVFBN Feedback negative input current VVFBP = 12.0 V VVFBN = 11.7 V -7 -5 -4 Pull-up 14 22 Pull-down 3 8 VVDR = 5 V, CL = 3.3 nF 50 120 30 60 mV μA PWM dimming control RPWMO PWMO gate driver output resistance tr,PWMO PWMO gate driver rise time (20 to 80%) tf,PWMO PWMO gate driver fall time (80 to 20%) Ω ns Fault management section VOVFB,th XFAULT output low level IXFAULT = 4 mA 0.12 0.2 V XFAULT high level leakage current VXFAULT = 5 V 1 4 µA OVFB input overvoltage detection threshold 1.14 1.20 1.25 V OVFB input overvoltage detection hysteresis 70 100 130 mV VOVFB = 1 V 0.7 1 1.2 µA (VVFBP - VVFBN) -190 -120 -80 OVFB pull-up current Open load/VFBP pin disconnection detection threshold (differential) mV Overload /VFBN pin disconnection detection threshold (differential) VFBx undervoltage detection threshold VVFBx respect to SGND DocID025575 Rev 4 550 600 650 3.0 3.5 4.0 V 11/26 26 Device description 7 LED6001 Device description The LED6001 device is a LED driver that integrates a boost controller, a high-side current sensing circuitry and a gate driver for an external dimming switch. It has been specifically designed for driving a single string of high-brightness LEDs. The device can support boost, floating buck-boost and SEPIC topologies in order to cover most of applications. A single pin, PWMI, combines both the device enable and PWM dimming control functions. The brightness of the LED string can be controlled through PWM modulation, analog control of the output current level (by means of a dedicated pin) or a combination of the two. 7.1 Device supply The LED6001 device integrates two low dropout linear regulators to derive the + 3.3 V (typ.) main supply and the +5 V supply for the gate drivers. The VIN pin is the input terminal for both linear regulators. Both the linear regulators are enabled when a PWM signal is applied to the PMWI pin. If the PWMI pin is held low for more than 10 ms (min.), the shutdown mode is automatically entered and both the LDOs are turned-off for minimum power consumption. An undervoltage lockout (UVLO) protection is associated to each linear regulator: in case the output voltage of LDO3 and VDR is below their respective nominal value, the device is no allowed to operate and the XFAULT pin is tied low. When an external +5 V rail is available, the related internal LDO can be bypassed by connecting together the VIN and VDR pins: in this case the VDR pin is used as supply input. 7.2 Boost controller 7.2.1 Turn on and power-down sequences The LED6001 is turned on and off by acting on the PWMI pin. This digital input combines two functions at the same time: device turn on/off and PWM dimming control. When a high pulse having a 100 µs (typ.) minimum duration appears at the PWMI pin, the LDOs are turned on and, after the VDR has reached its nominal value, a soft-start sequence on the boost controller takes place. The output voltage is smoothly increased by releasing in steps the current limit of the boost converter within a fixed 3 ms (typ.) period, unless the feedback voltage reaches 75% of the nominal value in advance. 12/26 DocID025575 Rev 4 LED6001 Device description Figure 4. Turn-on and turn-off waveforms tSHDN PWMI LDO3 VDR tSS tSTART VOUT ILED AM03414 Suddenly after the pulse detection at the PWMI pin, an internal timer is enabled and cleared. The timer starts counting down on every subsequent falling edge. If the PWMI pin is held low for more than 10 ms (typ.), the timer is allowed to expire and the LED6001 automatically turns off minimizing the current consumption. The start-up time, defined as the delay between the rising edge at the PWMI pin and the first pulse at the GATE pin, clearly depends on the bypass capacitors connected on both LDO3 and VDR pins. With a typical 1 µF MLCC for both pins, the start-up time is in the order of 100 µs. 7.2.2 Boost controller operation The boost controller of the LED6001 device is based on peak current mode control architecture and can easily support boost, floating buck-boost and SEPIC topologies. The switching frequency of the converter is set through the FSW pin (external clock source or setting resistor toward ground) while the switching duty cycle is modulated by the control loop in order to keep the output (LED) current constant. As a consequence, the output voltage of the boost converter is determined by the LED string. DocID025575 Rev 4 13/26 26 Device description LED6001 Figure 5. Simplified output regulation circuitry L VIN VOUT CIN COUT QSW S GATE Q EN RSLOPE R + _ PGND RSNS Sync. detector + FSW ISL Current ramp generator CSNS OSC ISL RFSW 50 μA VFBP EN + CCOMP _ gm VFBN + RCOMP VADIM RVFB - COMP ADIM 30mV 300mV Feedback reference setting EN PWMI Enable detector and auto-shutdown counter PWMO QDIM AM03415 The boost controller regulates the output (LED) current by measuring the voltage across the external sensing resistor. The internal circuitry related to the two pins connected to the sensing resistor (VFBP and VFBN) has been designed to implement a high-side sensing scheme and can sustain a relatively high voltage. The voltage drop across the sensing resistor is the actual feedback voltage for the boost regulator control loop and it can be linearly varied by means of the ADIM pin (see Section 7.3: LED current regulation and brightness control on page 17 for details). The COMP pin is the output of the transconductance amplifier involved in the regulation loop and a simple RC series must be connected between this pin and SGND to ensure proper loop stability. 7.2.3 Boost converter stability and slope compensation As visible in Figure 5, the difference between the feedback voltage and the programmed is converted into an error current by the transconductance amplifier. This current, provided at the COMP pin, is turned into a voltage across the compensation network externally connected to the same pin. This voltage, in turn, determines the trip current for the following error amplifier. When the boost converter operates in continuous conduction mode (CCM) and the switching duty cycle is higher than 50%, sub-harmonic instability may occur. In order to prevent this, the trip current has to be properly shaped by summing a negative sawtooth ramp voltage (slope compensation) with the amplified error voltage. 14/26 DocID025575 Rev 4 LED6001 Device description In LED6001 the slope compensation is achieved by injecting a sawtooth current into the CSNS pin. Therefore the voltage across the CSNS pin is given by: Equation 1 vCSNS (t) = iMOS (t) • RSHUNT + iSL (t) • RCSNS The RSNS resistor is usually designed so that the peak voltage is about 15% of the overcurrent threshold at the CSNS pin in order to have a good S/N ratio, while the RSLOPE resistor is calculated for the desired slope compensation amount (typically at least half the downslope of the inductor current during the switching off-time): Equation 2 50mV R SNS ≅ -------------------I L, PEAK Equation 3 V OUT – V IN, min R SNS R SLOPE ≥ ---------------------------------------- • -------------f SW • L I SL Where ISL = 50 µA is the maximum current injected by the slope compensation circuitry in the CSNS pin. Figure 6. Power switch current sensing scheme VIN ISL 50μA GATE ISL CSNS + OCP RSLOPE VSC 360mV _ VSNS RSNS AM03416 DocID025575 Rev 4 15/26 26 Device description 7.2.4 LED6001 Switching frequency oscillator and external synchronization The switching frequency of the boost controller is simply set by connecting a resistor between the FSW pin and ground. The resistor can be calculated according to Equation 4: Equation 4 K FSW R = --------------fSW Where KFSW = 5 • 1010 Hz • Ω (typ.) and 100 kHz ≤ fSW ≤ 1 MHz. Figure 7. Switching frequency vs. setting resistor at the FSW pin 1000 900 800 fSW (kHz) 700 600 500 400 300 200 100 0 0 50 100 150 200 250 300 R FSW 350 400 450 500 550 ) AM03417 If the FSW pin is tied high (e.g. connecting it to LDO3), a 600 kHz (typ.) default switching frequency is set. In case the boost controller of the LED6001 has to be externally synchronized, the FSW pin can be used as synchronization clock input. In this case the external clock must have a frequency in the 100 kHz - 1 MHz range and a 250 ns minimum pulse duration in order to ensure internal oscillator locking. 16/26 DocID025575 Rev 4 LED6001 Device description Figure 8. External synchronization signal timing diagram V FSW 250 ns 3V 0.8 V t AM03418 7.3 LED current regulation and brightness control The brightness of the LEDs connected at the output of the LED6001 can be controlled by applying the desired PWM signal at the PWMI pin. The boost controller is turned on and off according to the duty cycle of the PWMI control signal. When the PWMI is high (and the soft-start has been completed), the output (LED) current is regulated by keeping constant the voltage drop across the external sensing resistor connected between the VFBP and VFBN pins. A buffered replica of PWMI is available at the PWMO for driving a dimming N-channel MOSFET when superior dimming performance is required. In some applications a high-side dimming switch could be desirable (e.g.: protection against output short-circuit to ground or LED strings using the chassis as return) and a P-channel MOSFET can be used as shown in Figure 9. Some additional components may be needed to avoid excessive voltage between the gate and the source of such MOSFET. DocID025575 Rev 4 17/26 26 Device description LED6001 Figure 9. High-side dimming control by using a P-channel MOSFET L BOOST DFW VOUT VIN COUT CIN VIN RGATE VLDO3 QSW GATE CLDO3 ROVFBH VOVFB CSNS LDO3 ROVFBL RSLOPE VDR RSNS PGND CVDR VFBP XFAULT RVFB LED6001 VFBN PWMI RGL RGH QDIMH VOVFB FSW DZ VLDO3 RFSW OVFB ADIM RCOMP PWMO QDIML COMP CCOMP SGND AM03419 The regulation loop continuously compares the differential voltage drop with an internal reference and adjusts the switching duty cycle accordingly. In order to provide design flexibility and analog dimming capability, the internal feedback reference can be changed through the ADIM pin. As visible in Figure 10, the reference voltage is proportional to the voltage at the ADIM pin within a limited range. Equation 5 18/26 DocID025575 Rev 4 LED6001 Device description Figure 10. Differential feedback reference voltage vs. ADIM pin voltage VREF 300 mV 30 mV 300 mV 260 mV 1.2 V VADIM AM03420 In case a fixed output (LED) current is needed or simple PWM dimming is used, the ADIM pin must be connected to the central tap of a resistor divider (supplied by the LDO3 pin) for the desired LED current level. Because of the best LED current accuracy overtemperature is obtained at full scale, a voltage higher than 1.2 V should be applied at the ADIM pin in case the analog dimming is not needed. If an analog dimming control is required, the voltage at the ADIM pin can be changed runtime within its functional range. A simple way to perform an analog dimming is easily achieved by extracting the average value of a PWM signal through a simple RC low-pass filter (Figure 10). Figure 11. Simple ADIM pin voltage control through a filtered PWM signal LED6001 PWMI Rf ADIM Cf SGND AM03421 If the voltage at the ADIM pin is lower than 260 mV, both the PWMO and GATE pins are forced low and the boost converter is temporary disabled. As soon as the ADIM pin voltage is driven inside the operating range, normal operation is resumed. DocID025575 Rev 4 19/26 26 Device description LED6001 7.4 Device protections 7.4.1 Linear regulators undervoltage lockout Both the 5 V and 3.3 V linear regulators of the LED6001 are equipped with an undervoltage lockout (UVLO) protection. The UVLO protections avoid improper device operation in case at least one of the two outputs (VDR and LDO3) is below the allowed level. In particular, the LED6001 performs the soft-start sequence only after both VDR and LDO3 cross their respective upper UVLO threshold. 7.4.2 Power switch overcurrent The current flowing through the external power MOSFET is monitored, cycle-by-cycle, by sensing the voltage across the shunt resistor in series with its source. If the voltage drop exceeds the overcurrent protection (OCP) level, the ongoing switching cycle is suddenly terminated (cycle-by-cycle power MOSFET OCP). Normal operation is automatically resumed once the root cause has been removed. The XFAULT pin is not affected by OCP. As explained in Section 7.2 on page 12 the slope compensation is added by injecting a sawtooth current at the CSNS pin. As a consequence, the OCP threshold depends on both the slope compensation amount and the boost converter's operating point: Equation 6 VCSNS, OCP – D • I SL • R SLOPE I MOS, OCP = ---------------------------------------------------------------------------------R SNS Where VCSNS,OCP = 360 mV (typ.), ISL = 50 µA (typ.) and D is the switching duty cycle. 7.4.3 Output overvoltage and OVFB pin disconnection The output overvoltage fault detection is achieved by comparing the voltage at the OVFB pin with an internal threshold. Because of this fault can potentially damage both the device and the external components, a latched turn off condition is triggered once this event has been detected. A resistor divider connected to the output of the boost converter sets the desired OVP threshold. The OVFB is internally pulled-up in order to protect the device against an OVFB pin disconnection fault: if the pin is left floating, the OVP is suddenly triggered regardless of the output voltage level. This small pull-up current (IOVFB,PU) must be taken into account when designing an OVP output divider involving high resistance values. Equation 7 allows setting the desired output OVP level (ROVPH and ROVPL are the two resistors of the output divider whose central tap is connected to the OVFB pin of LED6001): Equation 7 R OVPH + R OVPL V OUT, OVP = ------------------------------------------- V TH, OVFB – R OVPL • I OVFB, PU R OVPL Where VTH,OVFB = 1.2 V (typ.) and IOVFB,PU = 1 µA (typ.). Once the OVP faulty condition is detected, the LED6001 device suddenly stops switching. Both GATE and PWMO are forced low and the XFAULT pin is lowered. The condition is 20/26 DocID025575 Rev 4 LED6001 Device description latched and normal operation is resumed by toggling the PWMI pin (PWMI has to be low for more than 10 ms) after the root cause has been removed. 7.4.4 Output rail disconnection detection or output short-circuit to ground If the connection between the output rail and the output sensing resistor is lost, the voltage of both the VFBP and VFBN pins falls down to zero. The LED6001 detects this faulty condition by comparing the absolute voltage of both VFBP and VFBN pins with an internal 3.3 V threshold and latches-off as a consequence (the GATE and PWMO pins forced low, XFAULT pin lowered). Normal operation is resumed by toggling the PWMI pin (PWMI has to be low for more than 10 ms) after the root cause has been removed. When the LED6001 is operating with a boost topology, a similar condition occurs in case of output-to-ground short-circuit. Of course, because of the inherent path between input and output, a real protection against this faulty condition can be achieved only if the device is capable of disconnecting the boost output by means of the dimming switch (e.g. in case a P-channel MOSFET is used as a high-side dimming switch). Figure 12. Load disconnection (1 and 5), open feedback (2 and 3) and open OVFB faulty conditions L BOOST DFW VOUT VIN COUT CIN VIN QSW 1 CSNS VDR VLDO3 RGATE GATE CVDR RSLOPE RSNS LDO3 PGND CLDO3 LED6001 2 VFBP XFAULT VFB PWMI 3 RVFB VFBN VLDO3 VOUT RADIMH RADIML 4 ADIM OVFB ROVFBH VOVFB RFSW ROVFBL FSW PWMO COMP CCOMP RCOMP SGND 5 QDIM AM03422 DocID025575 Rev 4 21/26 26 Device description 7.4.5 LED6001 Thermal shutdown The LED6001 implements an autorestarting thermal protection in order to avoid damages due to excessive die temperature. Once the chip temperature reaches the upper overtemperature protection (OTP) threshold, the ongoing operation is suddenly stopped, both the PWMO and XFAULT pins are held low and the 5 V linear regulator (VDR pin) is turned off. As soon as the die temperature drops below the autorestarting threshold, a new soft-start sequence takes place if the PWMI pin is still high and a 1 ms (typ.) deglitch delay has expired. The XFAULT pin goes low as soon as the OTP threshold is crossed and it is released once the device temperature drops below a third threshold, lower than the restart one, in order to provide a stable information to the host system. Table 7. Faulty conditions management summary Faulty condition Detection mechanism 1 Output rail/load disconnection VVFBx 1.2 V (internal pull-up) Device turning-off (latched condition). GATE, PWMO and XFAULT pins are forced low. VOVFB > 1.2 V Output overvoltage Power switch overcurrent IC overtemperature VCSNS > 360 mV Ongoing switching cycle terminated TJ > 160 °C (typ.) Device turning-off (VDR off, LDO3 active). GATE, PWMO and XFAULT pins are forced low. Autorestart if TJ < 140 °C (typ.) and PWMI still high. XFAULT pin is released If TJ