MCP1664 High-Voltage Step-Up LED Driver with UVLO and Open Load Protection Features General Description • • • • The MCP1664 is a compact, space-efficient, fixed-frequency, non-synchronous step-up converter optimized to drive multiple strings of LEDs with constant current powered from two and three-cell alkaline or NiMH/NiCd as well as from one-cell Li-Ion or Li-Polymer batteries. • • • • • • • • • 36V, 400 m Integrated Switch Up to 92% Efficiency Drive LED Strings in Constant Current 1.8A Peak Input Current Limit: - ILED up to 200 mA at 3.3V VIN, 4 White LEDs - ILED up to 300 mA at 5.0V VIN, 4 White LEDs - ILED up to 150 mA at 4.2V VIN, 8 White LEDs Input Voltage Range: 2.4V to 5.5V Undervoltage Lockout (UVLO): - UVLO at VIN Rising: 2.3V, typical - UVLO at VIN Falling: 1.85V, typical Shutdown Current (EN = GND): 40 nA Typical PWM Operation: 500 kHz Switching Frequency Cycle-by-Cycle Current Limiting Internal Compensation Open Load Protection (OLP) in the event of: - Feedback Pin Shorted to GND (Prevent Excessive Current into LEDs) - Disconnected LED String (Prevent Overvoltage to the Converter’s Output and SW Pin) Overtemperature Protection Available Packages: - 5-Lead SOT-23 - 8-Lead 2x3 TDFN The device integrates a 36V, 400 m low-side switch, which is protected by the 1.8A cycle-by-cycle inductor peak current limit operation. The MCP1664 starts up without high inrush current or output overshoot. All compensation and protection circuitry is integrated to minimize the number of external components. The internal feedback (VFB) voltage is set to 300 mV for low power dissipation when sensing and regulating the LED current. A single resistor sets the LED current. The device features an UVLO which avoids start-up with low inputs or discharged batteries for two cell-powered applications. The MCP1664 features an open load protection (OLP) which turns off the operation in situations when the LED string is accidentally disconnected or the feedback pin is short-circuited to GND. While in Shutdown mode (EN = GND), the device stops switching, and consumes 40 nA typical of input current. Package Types MCP1664 SOT-23 Applications • Two and Three-Cell Alkaline or NiMH/NiCd White LED Driver for Backlighting Products • Li-Ion Battery LED Lightning Application • Camera Flash • LED Flashlights and Backlight Current Source • Medical Equipment • Portable Devices: - Hand-Held Gaming Devices - GPS Navigation Systems - LCD Monitors - Portable DVD Players 5 VIN SW 1 GND 2 VFB 3 4 EN MCP1664 2x3 TDFN* VFB 1 SGND 2 SW 3 NC 4 EP 9 8 EN 7 PGND 6 5 NC VIN * Includes Exposed Thermal Pad (EP); see Table 3-1. 2015 Microchip Technology Inc. DS20005408A-page 1 MCP1664 Typical Application D MBRM140 L 4.7 – 10 µH VOUT Max. 32V LED1 CIN 4.7 – 30 µF VIN 2.4V – 3.0V SW LED2 VIN + ALKALINE ILED = MCP1664 LED6 VFB ON ALAKLINE COUT 10 µF EN - + 0.3V RSET OFF GND VFB = 0.3V RSET 12 ILED = 25 mA - L = 4.7 µH for maximum 4 white LEDs L = 10 µH for 5 to 10 white LEDs CIN = 4.7 – 10 µF for VIN > 2.5V CIN = 20 – 30 µF for VIN < 2.5V Maximum LED Current in Regulation vs. Input Voltage, TA = +25°C 350 300 4 wLEDs, L = 4.7 µH IOUT (mA) 250 200 150 8 wLEDs, L = 10 µH 100 50 0 2 DS20005408A-page 2 2.5 3 3.5 4 VIN (V) 4.5 5 5.5 2015 Microchip Technology Inc. MCP1664 1.0 ELECTRICAL CHARACTERISTICS † Notice: Stresses above those listed under “Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operational sections of this specification is not intended. Exposure to maximum rating conditions for extended periods may affect device reliability. Absolute Maximum Ratings † VSW – GND .....................................................................+36V EN, VIN – GND...............................................................+6.0V VFB ...............................................................................+0.35V Power Dissipation ....................................... Internally Limited Storage Temperature ....................................-65°C to +150°C Ambient Temperature with Power Applied ....-40°C to +125°C Operating Junction Temperature...................-40°C to +150°C ESD Protection On All Pins: HBM ................................................................. 4 kV MM ..................................................................400V DC AND AC CHARACTERISTICS Electrical Specifications: Unless otherwise specified, all limits apply for typical values at ambient temperature TA = +25°C, VIN = 3.3V, VOUT loaded with 3 white LEDs (VF = 2.65V at IF = 100 mA), ILED = 20 mA, CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. Boldface specifications apply over the controlled TA range of -40°C to +125°C. Parameters Sym. Min. Typ. Max. Units VIN 2.4 — 5.5 V UVLOSTART — 2.3 — V VIN rising, ILED = 20 mA UVLOSTOP — 1.85 — V VIN falling, ILED = 20 mA Maximum Output Voltage VOUTmax — — 32 V Maximum Output Current IOUT — 150 — mA 4.2V VIN, 8 LEDs 200 — mA 3.3V VIN, 4 LEDs 300 — mA 5.0V VIN, 4 LEDs Input Voltage Range Undervoltage Lockout (UVLO) Conditions Note 1 Note 1 Feedback Voltage Reference VFB 275 300 325 mV Feedback Input Bias Current IVFB — 0.025 — µA Shutdown Quiescent Current IQSHDN — 0.04 — µA EN = GND NMOS Peak Switch Current Limit IN(MAX) — 1.8 — A Note 2 INLK — 0.4 — µA VIN = VSW = 5V; VOUT = 5.5V VEN = VFB = GND RDS(ON) — 0.4 — VIN = 5V, ILED = 100 mA, 4 series white LEDs Note 2 |(VFB/VFB)/VIN| — 0.5 1 %/V Maximum Duty Cycle DCMAX — 90 — % Note 2 Switching Frequency fSW 425 500 575 kHz ±15% EN Input Logic High VIH 85 — — % of VIN EN Input Logic Low VIL — — 7.5 % of VIN IENLK — 0.025 — µA NMOS Switch Leakage NMOS Switch ON Resistance Feedback Voltage Line Regulation EN Input Leakage Current Note 1: 2: VIN = 3.3V to 5V VEN = 5V Minimum input voltage in the range of VIN (VIN < 5.5V < VOUT) depends on the maximum duty cycle (DCMAX) and on the output voltage (VOUT), according to the boost converter equation: VINmin = VOUT x (1 – DCMAX). Output voltage is equal to the LED voltage plus the voltage on the sense resistor (VLED + V_RSET). Recommended (VOUT - VIN) > 1V. Determined by characterization, not production tested. 2015 Microchip Technology Inc. DS20005408A-page 3 MCP1664 DC AND AC CHARACTERISTICS (CONTINUED) Electrical Specifications: Unless otherwise specified, all limits apply for typical values at ambient temperature TA = +25°C, VIN = 3.3V, VOUT loaded with 3 white LEDs (VF = 2.65V at IF = 100 mA), ILED = 20 mA, CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. Boldface specifications apply over the controlled TA range of -40°C to +125°C. Sym. Min. Typ. Max. Units Start-Up Time Parameters tSS — 100 — s Thermal Shutdown Die Temperature TSD — 150 — °C Note 2 TSDHYS — 20 — °C Note 2 Die Temperature Hysteresis Note 1: 2: Conditions EN Low to High, 90% of ILED (Note 2, Figure 2-10) Minimum input voltage in the range of VIN (VIN < 5.5V < VOUT) depends on the maximum duty cycle (DCMAX) and on the output voltage (VOUT), according to the boost converter equation: VINmin = VOUT x (1 – DCMAX). Output voltage is equal to the LED voltage plus the voltage on the sense resistor (VLED + V_RSET). Recommended (VOUT - VIN) > 1V. Determined by characterization, not production tested. TEMPERATURE SPECIFICATIONS Electrical Specifications: Unless otherwise specified, all limits apply for typical values at ambient temperature TA = +25°C, VIN = 3.0V, IOUT = 20 mA, VOUT = 12V, CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. Boldface specifications apply over the air-forced TA range of -40°C to +125°C. Parameters Sym. Min. Typ. Max. Units Operating Junction Temperature Range TJ -40 — +125 °C Storage Temperature Range TA -65 — +150 °C Maximum Junction Temperature TJ — — +150 °C Thermal Resistance, 5L SOT-23 JA — 201.0 — °C/W Thermal Resistance, 8L 2x3 TDFN JA — 52.5 — °C/W Conditions Temperature Ranges Steady State Package Thermal Resistances DS20005408A-page 4 2015 Microchip Technology Inc. MCP1664 2.0 TYPICAL PERFORMANCE CURVES Note: The graphs and tables provided following this note are a statistical summary based on a limited number of samples and are provided for informational purposes only. The performance characteristics listed herein are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified operating range (e.g., outside specified power supply range) and therefore outside the warranted range. Note: Unless otherwise indicated: VIN = 3.3V, ILED = 20 mA, VOUT loaded (VF = 2.9V at IF = 100 mA), CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. 160 80 RSET = 3ȍ 100 Efficiency (%) LED Current (mA) white LEDs 90 120 80 60 RSET = 6ȍ 40 VIN = 3.0V 70 VIN = 5.5V VIN = 4.0V 60 50 40 30 20 RSET = 15.2ȍ 20 10 0 2.3 2.7 3.1 FIGURE 2-1: VIN. 3.5 3.9 4.3 4.7 Input Voltage (V) 5.1 0 5.5 Four White LEDs, ILED vs. 0 50 100 FIGURE 2-4: vs. ILED. 160 150 200 ILED (mA) 300 350 Four White LEDs, Efficiency 90 VIN = 5.5V 80 RSET = 3ȍ 100 80 60 RSET = 6ȍ 40 Efficiency (%) 120 VIN = 4.0V 70 VIN = 3.0V 60 50 40 30 20 RSET = 15.2ȍ 20 10 0 -40 -25 -10 5 8 x wLED L = 10 µH 0 20 35 50 65 80 95 110 125 0 50 100 150 ILED (mA) Ambient Temperature (oC) FIGURE 2-2: Four White LEDs, ILED vs. Ambient Temperature. 8 x wLED, L = 10μH, VIN= 4.2V 140 RSET = 3ȍ 80 60 RSET = 6ȍ 40 RSET = 15.2ȍ 20 200 250 Eight White LEDs, Efficiency 400 RSET = 2.1ȍ 120 100 FIGURE 2-5: vs. ILED. 350 LED Current (mA) 160 250 100 RSET = 2.1ȍ 140 LED Current (mA) 4 100 RSET = 2.1ȍ 140 LED Current (mA) with 300 250 5 wLEDs, L = 10µH 200 4 wLEDs, L = 4.7µH 150 8 wLEDs, L = 10 µH 100 50 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 Ambient Temperature FIGURE 2-3: Eight White LEDs, ILED vs. Ambient Temperature. 2015 Microchip Technology Inc. 0 2.3 2.7 (oC) FIGURE 2-6: 3.1 3.5 3.9 4.3 Input Voltage (V) 4.7 5.1 5.5 Maximum ILED vs. VIN. DS20005408A-page 5 MCP1664 2.5 200 2.4 175 2.3 UVLO Start 2.2 2.1 2 UVLO Stop 1.9 1.8 1.7 Soft Start Time (µs) UVLO Thresholds (V) Note: Unless otherwise indicated: VIN = 3.3V, ILED = 20 mA, VOUT loaded (VF = 2.9V at IF = 100 mA), CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. 150 with 4 LEDs Blue Bars: ILED = 20 mA Red Bars: ILED = 40 mA COUT = 10 µF 125 100 75 50 25 1.6 1.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 Ambient Temperature (oC) FIGURE 2-7: Undervoltage Lockout (UVLO) vs. Ambient Temperature. 0 3 FIGURE 2-10: LED Number. 4 5 6 Number of LEDs 7 8 Start-Up Time vs. 50 3 wLEDs ILED 10 mA/div 40 Shutdown IQ (nA) white 30 20 EN 2V/div 10 VIN 2V/div 0 2.5 2.8 3.1 3.4 3.7 4.0 4.3 4.6 4.9 5.2 5.5 Input Voltage (V) FIGURE 2-8: Shutdown Quiescent Current, IQSHDN, vs. VIN (EN = GND). 80µs/div FIGURE 2-11: VIN = VENABLE. Start-Up When Switching Frequency (kHz) 550 3 wLEDs ILED 10 mA/div 525 500 EN 2V/div 475 450 -40 -25 -10 5 20 35 50 65 80 95 110 125 Ambient Temperature (°C) FIGURE 2-9: Switching Frequency, fSW vs. Ambient Temperature. DS20005408A-page 6 VIN 2V/div 80µs/div FIGURE 2-12: Start-Up After Enable. 2015 Microchip Technology Inc. MCP1664 Note: Unless otherwise indicated: VIN = 3.3V, ILED = 20 mA, VOUT loaded (VF = 2.9V at IF = 100 mA), CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. 3 wLEDs with 4 LEDs 3 wLEDs ILED = 20 mA ILED AC Coupled 2 mA/div ILED 10 mA/div white SW 5V/div SW 5V/div EN 2V/div FIGURE 2-13: 15% Duty Cycle. VOUT 5V/div 2 ms/div 100 Hz PWM Dimming, 3 wLEDs 1 µs/div FIGURE 2-16: Three White LEDs PWM Discontinuous Mode Waveforms. 3 wLEDs ILED = 145 mA ILED AC Coupled 10 mA/div ILED 10 mA/div SW 5V/div SW 5V/div EN 2V/div FIGURE 2-14: 85% Duty Cycle. VOUT 5V/div 2 ms/div 100 Hz PWM Dimming, 1 µs/div FIGURE 2-17: Three White LEDs PWM Continuous Mode Waveforms. Line Step 2.5V to 4.5V 3 wLEDs ILED = 20mA 3 wLEDs ILED 10 mA/div ILED SW 5V/div VIN 2V/div VFB 200mV/div AC Coupled 2 mA/div Step from 2.5V to 4.5V 10 ms/div FIGURE 2-15: Open Load (LED Fail or FB to GND) Response. 2015 Microchip Technology Inc. 1 ms/div FIGURE 2-18: Line Step Response. VIN steps from 2.5V to 4.5V. DS20005408A-page 7 MCP1664 NOTES: DS20005408A-page 8 2015 Microchip Technology Inc. MCP1664 3.0 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 3-1. TABLE 3-1: 3.1 PIN FUNCTION TABLE MCP1664 SOT-23 MCP1664 2x3 TDFN 3 1 VFB — 2 SGND Symbol Description Feedback Voltage Pin Signal Ground Pin (TDFN only) 1 3 SW Switch Node, Boost Inductor Pin — 4, 6 NC Not Connected Input Voltage Pin 5 5 VIN — 7 PGND Power Ground Pin (TDFN only) 4 8 EN Enable Control Input Pin — 9 EP Exposed Thermal Pad (EP); must be connected to Ground. (TDFN only) 2 — GND Ground Pin (SOT-23 only) Feedback Voltage Pin (VFB) The VFB pin is used to regulate the voltage across the RSET sense resistor to 300 mV to keep the output LED current in regulation. Connect the cathode of the LED to the VFB pin. 3.2 Signal Ground Pin (SGND) The signal ground pin is used as a return for the integrated reference voltage and error amplifier. 3.3 Switch Node Pin (SW) Connect the inductor from the input voltage to the SW pin. The SW pin carries inductor current and has a typical value of 1.8A. The integrated N-Channel switch drain is internally connected to the SW node. 3.4 Not Connected (NC) This is an unconnected pin. 3.5 3.7 Enable Pin (EN) The EN pin is a logic-level input used to enable or disable device switching and lower quiescent current while disabled. A logic high (>85% of VIN) will enable the regulator output. A logic low (<7.5% of VIN) will ensure that the regulator is disabled. 3.8 Exposed Thermal Pad (EP) There is no internal electrical connection between the Exposed Thermal Pad (EP) and the SGND and PGND pins. They must be connected to the same potential on the Printed Circuit Board (PCB). 3.9 Ground Pin (GND) The ground or return pin is used for circuit ground connection. The length of the trace from the input cap return, the output cap return and the GND pin must be as short as possible to minimize noise on the GND pin. The SOT-23 5-lead package uses a single ground pin. Power Supply Input Voltage Pin (VIN) Connect the input voltage source to VIN. The input source should be decoupled from GND with a 4.7 µF minimum capacitor. 3.6 Power Ground Pin (PGND) The power ground pin is used as a return for the high-current N-Channel switch. The PGND and SGND pins are connected externally. The signal ground and power ground must be connected externally in one point. 2015 Microchip Technology Inc. DS20005408A-page 9 MCP1664 NOTES: DS20005408A-page 10 2015 Microchip Technology Inc. MCP1664 4.0 DETAILED DESCRIPTION 4.1 Device Overview The MCP1664 is a fixed-frequency, synchronous step-up converter, with a low voltage reference of 300 mV, optimized to keep the output current constant by regulating the voltage across the feedback resistor (RSET). The MCP1664 integrates a peak current mode architecture and delivers high-efficiency conversion for LED lightning applications while being powered by two-cell and three-cell Alkaline, Ultimate Lithium, NiMH, NiCd and single-cell Li-Ion battery inputs. The maximum input voltage, VINmax is 5.5V. A high level of integration lowers total system cost, eases implementation and reduces board area. The conventional boost converter with a high voltage reference has a high voltage drop across the LED series current limit resistor. The power dissipated in this resistor, which is usually in series with the LED string, reduces the total efficiency conversion of an LED driver solution. Therefore, the voltage drop on the sense resistor (RSET) used to regulate the LED current must be low. In the case of MCP1664, the VFB value is 300 mV. The device features controlled start-up voltage (UVLOSTART = 2.3V) and an open load protection in case the LED fails or short circuit of the VFB pin to GND. Once the VFB voltage drops below 50 mV, the device stops switching and the output voltage will be equal to the input voltage (minus a diode drop voltage). This feature prevents damage to the device and LEDs in case of an accidental event like the one previously described. The 400 m, 36V integrated switch is protected by the 1.8A cycle-by-cycle inductor peak current limit operation. When the Enable pin is pulled to ground (EN = GND), the device stops switching, enters in Shutdown mode and consumes less than 50 nA of input current (Figure 2-8). 2015 Microchip Technology Inc. DS20005408A-page 11 MCP1664 4.2 Functional Description Figure 4-1 describes the functional block diagram of the MCP1664. It incorporates a current mode control scheme in which the PWM ramp signal is derived from the NMOS power switch current (VSENSE). A slope compensation signal (VRAMP) is added to the current sense signal (VSENSE) and compared to the output of the error amplifier (VERROR) to control the ON-time of the power switch. The MCP1664 is a compact, high-efficiency, fixed 500 kHz frequency, step-up DC-DC converter that operates as a constant current generator for applications powered by either two-cell or three-cell alkaline or Lithium Energizer; three-cell NiCd or NiMH; or one-cell Li-Ion or Li-Polymer batteries. SW VIN Internal Bias UVLO_COMP VBIAS VUVLO_REF VIN_OK Overcurrent Comparator Gate Drive and Shutdown VEXT Control Logic EN OCRef + + - VSENSE + VRAMP S + Slope Compensation Oscillator VLIMIT - GND CLK VPWM - Logic SR Latch + QN VERROR EA 300 mV VFB + Open Load Comparator VOLP_REF + - VFB_FAULT VFB VOUT_OK Power Good Comparator and Delay Thermal Shutdown FIGURE 4-1: DS20005408A-page 12 Rc 300 mV Cc VOLP_REF VUVLO_REF VFB VIN_OK Bandgap EN MCP1664 Simplified Block Diagram. 2015 Microchip Technology Inc. MCP1664 4.2.1 INTERNAL BIAS The MCP1664 gets its bias from VIN. The VIN bias is used to power the device and drive circuits over the entire operating range. The maximum VIN is 5.5V. 4.2.2 START-UP The MCP1664 is capable of starting from two alkaline cells. The MCP1664 starts switching at approximately 2.3V typical for a light load current. Once started, the device will continue to operate under normal load conditions down to 1.85V typical. The start-up time is dependent on the LED’s current, the number of the LEDs connected at output and on the output capacitor value (see Figure 2-10). Output capacitor value increases the start-up time. When the device is powered, the output capacitor charges to a value close to the input voltage (VIN minus a Schottky diode voltage drop). To avoid high inrush currents that occur when charging the output capacitor during start-up, the switch peak current is limited to 1.8A. Once the voltage on the output capacitor reaches the sum of the forward voltages of all LEDs, the MCP1664 enters in constant current operation. Due to the direct path from input to output, in the case of dimming applications (EN voltage switches from low to high), the output capacitor is already charged and the output starts from a value close to the input voltage. In this particular situation the device starts faster. The internal oscillator has a delayed start to let the output capacitor be completely charged to the input voltage value. 4.2.3 UNDERVOLTAGE LOCKOUT (UVLO) The MCP1664 features an UVLO that prevents fault operation below 1.85V typical, which is close to the value of two discharged alkaline batteries. Essentially, there is a comparator, which monitors VIN and a reference voltage derived from the bandgap. The device starts its normal operation at 2.3V typical input. A hysteresis is set for the comparator to avoid input transients (temporary VIN drop) which might trigger the lower UVLO threshold and restart the device. When the input voltage is below the UVLOSTART threshold, the device is operating with limited specification. 4.2.4 ENABLE PIN The MCP1664 enables switching when the EN pin is set high. The device is put into Shutdown mode when the EN pin is set low. To enable the boost converter, the EN voltage level must be greater than 85% of the VIN voltage. To disable the boost converter, the EN voltage must be less than 7.5% of the VIN voltage. 4.2.4.1 Shutdown Mode. Input-to-Output Path (EN = GND) In Shutdown mode, the MCP1664 stops switching and all internal control circuitry is switched off. The input voltage will be bypassed to output through the inductor and the Schottky diode. While the device stops switching, VOUT is equal to the output capacitor voltage, which slowly discharges on the leak path (from VOUT to a value close to VIN) after the LEDs have been turned off. In Shutdown mode, the current consumed by the MCP1664 from batteries is very low, below 50 nA. 4.2.5 PWM MODE OPERATION The MCP1664 operates as a fixed-frequency, non-synchronous converter. The switching frequency is maintained with a precision oscillator at 500 kHz. Lossless current sensing converts the inductor’s peak current signal to a voltage (VSENSE) and adds it to the internal slope compensation (VRAMP). This summed signal is compared to the voltage error amplifier output (VERROR) to provide a peak current control signal (VPWM) for the PWM. The slope compensation signal depends on the input voltage. Therefore, the converter provides the proper amount of slope compensation to ensure stability. The peak limit current is set to 1.8A. 2015 Microchip Technology Inc. DS20005408A-page 13 MCP1664 4.2.6 INTERNAL COMPENSATION 4.2.9 OUTPUT SHORT-CIRCUIT CONDITION The error amplifier, with its associated compensation network, completes the closed-loop system by comparing the output voltage to a reference at the input of the error amplifier and by feeding the amplified and inverted signal to the control input of the inner current loop. The compensation network provides phase leads and lags at appropriate frequencies to cancel excessive phase lags and leads of the power circuit. All necessary compensation and slope compensation components are integrated. Like all non-synchronous boost converters, the MCP1664 inductor current will increase excessively during a short circuit on the converter’s output. Short circuit on the output will cause the diode rectifier to fail and the inductor’s temperature to rise or even to fail. When the diode fails, the SW pin becomes a high-impedance node; it remains connected only to the inductor and the excessive resulted ringing may cause damage to the MCP1664. 4.2.7 4.2.10 OPEN LOAD PROTECTION (OLP) An internal VFB fault signal turns off the PWM signal (VEXT) when output goes out of regulation in the event of: • open load (LED string fails) or • short circuit of the feedback pin to GND. In any of the above events, for a regular integrated circuit (IC) without any protection implemented, the VFB voltage drops to ground potential, its N-channel transistor is forced to switch at full duty cycle and VOUT rises. This fault event may cause the SW pin to exceed its maximum voltage rating and may damage the boost regulator IC, its external components and the LEDs. To avoid these, the MCP1664 features an open load protection (OLP) which turns off PWM switching when such a condition is detected. There is an overvoltage comparator with 50 mV reference which monitors the VFB voltage. OVERTEMPERATURE PROTECTION Overtemperature protection circuitry is integrated into the MCP1664. This circuitry monitors the device junction temperature and shuts the device off if the temperature exceeds +150°C. The device will automatically restart when the junction temperature drops by 20°C. The OLP is disabled during an overtemperature condition. If the OLP event occurs with the input voltage below the UVLOSTART threshold and VFB remains under 50 mV due to weak input (discharged batteries) or an overload condition, the device latches its output; it resumes after power-up. The OLP comparator is disabled during start-up sequences and thermal shutdown. 4.2.8 OVERCURRENT LIMIT The MCP1664 uses a 1.8A cycle-by-cycle input current limit to protect the N-channel switch. There is an overcurrent comparator which resets the drive latch when the peak of the inductor current reaches the limit. In current limitation, the output voltage and load current start dropping. DS20005408A-page 14 2015 Microchip Technology Inc. MCP1664 5.0 APPLICATION INFORMATION 5.1 Typical Applications The MCP1664 non-synchronous boost LED current regulator operates over a wide output range up to 32V, which allows it to drive up to 10 LEDs in series connection. The input voltage ranges from 2.4V to 5.5V. The device operates down to 1.85V with limited specification. The UVLO typical thresholds are set to 2.3V typical when VIN is ramping and to 1.85V when VIN is falling. Output current capability increases with the input voltage and is limited by the 1.8A typical peak input current limit. Typical characterization curves in this data sheet are presented to display the typical output current capability. 5.2 5.2.1 LED Brightness Control CONSTANT CURRENT CALCULATIONS To calculate the resistor value for setting the LED current, use Equation 5-1, where RSET is connected to VFB and GND. The reference voltage, VFB, is 300 mV. The calculated current does not depend on the number of LEDs in the string. EQUATION 5-1: VFB I LED = -----------R SET 5.2.2 PWM DIMMING LED brightness can also be controlled by setting the maximum current for the LED string (using Equation 5-1) and by lowering this current in small steps, with a variable duty cycle PWM signal applied to the EN pin. The maximum frequency for dimming is limited by the MCP1664’s start-up time, which varies with the LED current. By varying the duty cycle of the signal applied on the EN pin (from 0 to 100%), the LED current is changing linearly. 5.2.3 OUTPUT CURRENT CAPABILITY. MINIMUM INPUT VOLTAGE The maximum device output current is dependent upon the input and output voltage. As there is a 1.8A inductor peak current limit, output current can go out of regulation before reaching the maximum duty cycle. (Note that, for boost converters, the average inductor current is equal to the input current.) Characterization graphs show device limits. The maximum number of LEDs (nLED in Equation 5-2) that can be placed in series and be driven is dependent on the maximum LED forward voltage (VFmax) and LED current set by the RSET resistor. The maximum voltage at the output of the MCP1664 should be 32V. Consider that VFmax has some variation over the operating temperature range and that the LED data sheet must be reviewed for the correct data to be introduced in Equation 5-2. A maximum of 10 white LEDs in series connection can be driven safely. EQUATION 5-2: EXAMPLE 1: VFB = 300 mV VFmax nLED + V FB 32V ILED = 100 mA RSET = 3 EXAMPLE 2: VFB = 300 mV ILED = 200 mA RSET = 1.5 The power dissipated on the RSET resistor is low and equal to VFB x ILED. For ILED = 100 mA, the power dissipated on the sense resistor is 30 mW and the efficiency of the conversion is high. 2015 Microchip Technology Inc. Characterization graphs show the maximum current the device can supply according to the numbers of LEDs at the output. For example, to ensure a 150 mA load current for five LEDs (output equal to approximately 15V), a minimum of 3V input voltage is necessary. If an application is required to drive eight LEDs and is powered by one Li-Ion battery (VIN from 3.6V to 4.2V), the minimum LED current the MCP1664 can regulate is close to 125 mA (Figure 2-6). DS20005408A-page 15 MCP1664 5.2.4 OPEN LOAD PROTECTION The MCP1664 features an open load protection (OLP) in case the LED is disconnected from the output line. If the voltage on the VFB pin drops below 50 mV, the device stops switching and prevents overvoltage on the output and SW pin as well as excessive current into LEDs. OLP is not enabled during start-up and thermal shutdown events. 5.3 Input Capacitor Selection The boost input current is smoothened by the boost inductor, reducing the amount of filtering necessary at the input. Some capacitance is recommended to provide decoupling from the source and to ensure that the input does not drop excessively during switching transients. Because the MCP1664 is rated to work at an ambient temperature of up to +125°C, low ESR X7R ceramic capacitors are well suited since they have a low temperature coefficient and small size. For use within a limited temperature range of up to +85°C, a X5R ceramic capacitor can be used. For light load applications, 4.7 µF of capacitance is sufficient at the input. For high-power applications that have high source impedance or long leads, using a 10 µF – 20 µF input capacitor is recommended. When the device is working below a 3.0V input with high LED current, additional input capacitance can be added to provide a stable input voltage (3 x 10 µF or 33 µF) due to high input current demand. The input capacitor must be rated at a minimum of 6.3V. For MLCC ceramic capacitors and X7R or X5R capacitors, capacitance varies over the operating temperature or the DC bias range. Usually, there is a drop down to 50% of capacitance. Review the capacitor manufacturer data sheet to see how rated capacitance varies over these conditions. Table 5-1 contains the recommended range for the input capacitor value. DS20005408A-page 16 5.4 Output Capacitor Selection The output capacitor helps provide a stable output voltage and smooth load current during sudden load transients and reduces the LED current ripple. Ceramic capacitors are well suited for this application (X5R and X7R). The output capacitor ranges from 4.7 µF in case of light loads and dimming applications and up to 20 µF for hundreds of mAmps LED current applications. Extra output capacitor value is recommended when device drives higher output currents and with small boost ratios (input voltage close to the output voltage). As mentioned in Section 5.3, Input Capacitor Selection X7R or X5R capacitance varies over the operating temperature or the DC bias range. With a voltage applied at the maximum DC rating, capacitance might drop down to half. This might affect the stability or limit the output power. Capacitance drop over the entire temperature range is less than 20%. Users must carefully select the DC voltage rating (DCVRATE) for the output capacitor according to Equations 5-3 and 5-4: EQUATION 5-3: DCV RATE V Fmax nLED + V FB or EQUATION 5-4: DCV RATE V OUTmax Table 5-1 contains the recommended range for the input and output capacitor value. TABLE 5-1: CAPACITOR VALUE RANGE CIN COUT Minimum 4.7 µF 4.7 µF Maximum — 47 µF 2015 Microchip Technology Inc. MCP1664 5.5 Inductor Selection 5.6 The MCP1664 is designed to be used with small surface mount inductors; the inductance value can range from 4.7 µH to 10 µH. An inductance value of 4.7 µH is recommended for output voltages below 15V (4 or 5 LEDs in series connection). For higher output voltages, up to 32V (from 5 to maximum 10 LEDs), an inductance value of 10 µH is optimum. TABLE 5-2: MCP1664 RECOMMENDED INDUCTORS FOR BOOST CONVERTER Value (µH) DCR (typ) ISAT (A) Size WxLxH (mm) MSS6132-472 4.7 0.043 2.84 6.1x6.1x3.2 XFL4020-472 4.7 0.0574 2.7 4.3x4.3x2.1 LPS5030-472 4.7 0.083 2.0 5.0x5.0x3.0 LPS6235-103 10 0.100 2.4 6.2x6.2x3.5 Part Number Rectifier Diode Selection Schottky diodes are used to reduce losses. The diode’s average and peak current rating must be greater than the average output current and the peak inductor current, respectively. The diode’s reverse breakdown voltage must be higher than the internal switch maximum rating voltage of 36V. The converter’s efficiency will be improved if the voltage drop across the diode is lower. The forward voltage (VF) rating is forward-current dependent, which is equal in particular to the load current. For high currents and high ambient temperatures, use a diode with good thermal characteristics. TABLE 5-3: Coilcraft RECOMMENDED SCHOTTKY DIODES Type VOUTmax TA PMEG2010 18V < +85°C STPS120 18V < +125°C Wurth® Elektronik Group MBRM120 18V < +125°C 7440530047 WE-TPC 4.7 32V < +85°C 74404042047 WE-LQS 74438335047 WE-MAPI XAL4040-103 10 0.092 1.9 4.3x4.3x4.1 0.07 2.2 5.8x5.8x2.8 PMEG4010 4.7 0.03 2.0 4.0x4.0x1.6 UPS5819 32V < +85°C 4.7 0.141 2.0 3.0x3.0x1.5 MBRM140 32V < +125°C 744778610 WE-PD2 10 0.074 1.8 5.9x6.2x4.9 74408943100 WE-SPC 10 0.082 2.1 4.8x4.8x3.8 TDK EPCOS B82462G4472 4.7 0.04 1.8 6.3x6.3x3.0 LTF5022-4R7 4.7 0.073 2.0 5.2x5.0x2.2 VLCF4024-4R7 4.7 0.075 1.76 4.0x4.0x2.4 SLF7055-100 10 0.039 2.5 7.0x7.0x5.5 Several parameters are used to select the correct inductor: maximum rated current, saturation current and copper resistance (DCR). For boost converters, the inductor current is much higher than the output current. The average inductor current is equal to the input current. The inductor’s peak current is much higher than the average. The lower the inductor DCR, the higher the efficiency of the converter, a common trade-off in size versus efficiency. Peak current is the maximum or limit value and saturation current typically specifies a point at which the inductance has rolled off a percentage of the rated value. This can range from a 20% to 40% reduction in inductance. As inductance rolls off, the inductor ripple current increases, as does the peak switch current. It is important to keep the inductance from rolling off too much, causing switch current to reach the peak limit. 2015 Microchip Technology Inc. 5.7 Thermal Calculations The MCP1664 is available in two different packages (5-lead SOT-23 and 8-lead 2x3 TDFN). By calculating the power dissipation and applying the package thermal resistance (JA), the junction temperature is estimated. The maximum operating junction temperature rating (steady state) for the MCP1664 is +125°C. To quickly estimate the internal power dissipation for the switching boost regulator, an empirical calculation using measured efficiency can be used. Given the measured efficiency, the internal power dissipation is estimated by Equation 5-5. EQUATION 5-5: V OUT I OUT ------------------------------------- – V I = P Efficiency OUT OUT Dis The difference between the first term, input power, and the second term, power delivered, is the internal power dissipation of the MCP1664. This is an estimate, assuming that most of the power lost is internal to the MCP1664 and not CIN, COUT, the rectifier diode and the inductor. There is some percentage of power lost in the boost inductor and the rectifier diode, with very little loss in the input and output capacitors. For a more accurate estimation of internal power dissipation, subtract the IINRMS2 x LDCR and ILED x VF power dissipation (where IINRMS is the average input current, LDCR is the inductor series resistance and VF is the diode voltage drop). Another source of power losses for the LED driver, that is external to the MCP1664, is the sense resistor. The losses for the sense resistor can be approximated by VFB x ILED. DS20005408A-page 17 MCP1664 5.8 PCB Layout Information should be used. Therefore, it is important that the input and output capacitors be placed as close as possible to the MCP1664 to minimize the loop area. Good printed circuit board layout techniques are important to any switching circuitry and switching power supplies are no different. When wiring the switching high-current paths, short and wide traces The RSET resistor and feedback signal should be routed away from the switching node and the switching current loop. When possible, ground planes and traces should be used to help shield the feedback signal and minimize noise and magnetic interferences. EN +VIN CIN Vias to GND Bottom Plane MCP1664 1 L RSET A GND D K LED1 K LEDs A COUT LEDN +VOUT GND FIGURE 5-1: DS20005408A-page 18 Vias to GND Bottom Plane GND Bottom Plane MCP1664 5-Lead SOT-23 Recommended Layout. 2015 Microchip Technology Inc. MCP1664 A L +VIN K +VOUT D COUT CIN LED1 LED2 MCP1664 LEDs Via to GND EN A 1 LEDN K RSET GND GND Bottom Plane EN routed to the Bottom Plane FIGURE 5-2: Vias to GND Bottom Plane MCP1664 TDFN Recommended Layout. 2015 Microchip Technology Inc. DS20005408A-page 19 MCP1664 NOTES: DS20005408A-page 20 2015 Microchip Technology Inc. MCP1664 6.0 PACKAGING INFORMATION 6.1 Package Marking Information 5-Lead SOT-23 Example AABR5 10256 8-Lead TDFN (2x3x0.75 mm) Example ACH 510 25 Legend: XX...X Y YY WW NNN e3 * Note: Customer-specific information Year code (last digit of calendar year) Year code (last 2 digits of calendar year) Week code (week of January 1 is week ‘01’) Alphanumeric traceability code Pb-free JEDEC designator for Matte Tin (Sn) This package is Pb-free. The Pb-free JEDEC designator ( e3 ) can be found on the outer packaging for this package. In the event the full Microchip part number cannot be marked on one line, it will be carried over to the next line, thus limiting the number of available characters for customer-specific information. 2015 Microchip Technology Inc. DS20005408A-page 21 MCP1664 .# #$# /!- 0 # 1/ %##!# ## +22--- 2 / b N E E1 3 2 1 e e1 D A2 A c φ A1 L L1 3# 4# 5$8%1 44"" 5 56 7 5 ( 4!1# ()* 6$# !4!1# 6,9# : !!1// ; : #!%% : ( 6,<!# " : !!1/<!# " : ; 6,4# : )* ( .#4# 4 : = .# # 4 ( : ; .# > : > 4!/ ; : = 4!<!# 8 : ( !"!#$!!% #$ !% #$ #&! ! !# "'( )*+ ) #&#,$ --#$## - *) DS20005408A-page 22 2015 Microchip Technology Inc. MCP1664 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging 2015 Microchip Technology Inc. DS20005408A-page 23 MCP1664 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging DS20005408A-page 24 2015 Microchip Technology Inc. MCP1664 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging 2015 Microchip Technology Inc. DS20005408A-page 25 MCP1664 ! " #$%&'**+/;<>!" .# #$# /!- 0 # 1/ %##!# ## +22--- 2 / DS20005408A-page 26 2015 Microchip Technology Inc. MCP1664 APPENDIX A: REVISION HISTORY Revision A (June 2015) • Original Release of this Document. 2015 Microchip Technology Inc. DS20005408A-page 27 MCP1664 NOTES: DS20005408A-page 28 2015 Microchip Technology Inc. MCP1664 PRODUCT IDENTIFICATION SYSTEM To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office. [X](1) X /XX XXX Tape and Reel Option Temperature Range Package Pattern PART NO. Device Device: MCP1664: Tape and Reel Option: T = Tape and Reel(1) Temperature Range: E = -40C to +125C Package: MN = OT = Examples: a) MCP1664T-E/OT: b) MCP1664T-E/MNY: High-Voltage Step-Up LED Driver with UVLO and OLP (Extended) Note 1: Plastic Dual Flat, No Lead Package 2x3x0.75mm Body, 8-Lead (TDFN) Plastic Small Outline Transistor, 5-Lead (SOT-23) *Y = Nickel palladium gold manufacturing designator. Only available on the TDFN package. 2015 Microchip Technology Inc. Tape and Reel, Extended temperature, 5LD SOT-23 package Tape and Reel, Extended temperature, 8LD 2x3 TDFN package Tape and Reel identifier only appears in the catalog part number description. This identifier is used for ordering purposes and is not printed on the device package. Check with your Microchip Sales Office for package availability with the Tape and Reel option. DS20005408A-page 29 MCP1664 NOTES: DS20005408A-page 30 2015 Microchip Technology Inc. Note the following details of the code protection feature on Microchip devices: • Microchip products meet the specification contained in their particular Microchip Data Sheet. • Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions. • There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property. • Microchip is willing to work with the customer who is concerned about the integrity of their code. • Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable.” Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act. Information contained in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer’s risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights unless otherwise stated. Trademarks The Microchip name and logo, the Microchip logo, dsPIC, FlashFlex, flexPWR, JukeBlox, KEELOQ, KEELOQ logo, Kleer, LANCheck, MediaLB, MOST, MOST logo, MPLAB, OptoLyzer, PIC, PICSTART, PIC32 logo, RightTouch, SpyNIC, SST, SST Logo, SuperFlash and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. The Embedded Control Solutions Company and mTouch are registered trademarks of Microchip Technology Incorporated in the U.S.A. Analog-for-the-Digital Age, BodyCom, chipKIT, chipKIT logo, CodeGuard, dsPICDEM, dsPICDEM.net, ECAN, In-Circuit Serial Programming, ICSP, Inter-Chip Connectivity, KleerNet, KleerNet logo, MiWi, MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, MultiTRAK, NetDetach, Omniscient Code Generation, PICDEM, PICDEM.net, PICkit, PICtail, RightTouch logo, REAL ICE, SQI, Serial Quad I/O, Total Endurance, TSHARC, USBCheck, VariSense, ViewSpan, WiperLock, Wireless DNA, and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. SQTP is a service mark of Microchip Technology Incorporated in the U.S.A. Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries. GestIC is a registered trademark of Microchip Technology Germany II GmbH & Co. KG, a subsidiary of Microchip Technology Inc., in other countries. All other trademarks mentioned herein are property of their respective companies. © 2015, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. ISBN: 978-1-63277-526-9 QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV == ISO/TS 16949 == 2015 Microchip Technology Inc. Microchip received ISO/TS-16949:2009 certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona; Gresham, Oregon and design centers in California and India. The Company’s quality system processes and procedures are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001:2000 certified. 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