MCP1662 High-Voltage Step-Up LED Driver with UVLO and Open Load Protection Features General Description • • • • The MCP1662 device is a compact, space-efficient, fixed-frequency, non-synchronous step-up converter optimized to drive LED strings with constant current from a two- or three-cell alkaline or lithium Energizer®, or NiMH/NiCd, or one-cell Lithium-Ion or Li-Polymer batteries. • • • • • • • • • • 36V, 800 m Integrated Switch Up to 92% Efficiency Drive LED Strings in Constant Current 1.3A Peak Input Current Limit: - ILED up to 200 mA @ 5.0V VIN, 4 White LEDs - ILED up to 125 mA @ 3.3V VIN, 4 White LEDs - ILED up to 100 mA @ 4.2V VIN, 8 White LEDs Input Voltage Range: 2.4V to 5.5V Feedback Voltage Reference: VFB = 300 mV Undervoltage Lockout (UVLO): - UVLO @ VIN Rising: 2.3V, typical - UVLO @ VIN Falling: 1.85V, typical Sleep Mode with 20 nA Typical Quiescent Current 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, 800 m low-side switch, which is protected by the 1.3A cycle-by-cycle inductor peak current limit operation. 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 Undervoltage Lockout (UVLO) that avoids start-up with low inputs or discharged batteries for two-cell-powered applications. There is 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. For standby applications (EN = GND), the device stops switching, enters into Sleep mode and consumes 20 nA typical of input current. Package Types MCP1662 SOT-23 Applications • Two and Three-Cell Alkaline or NiMH/NiCd White LED Driver for Backlighting Products • Li-Ion Battery LED Lighting Application • Camera Flash • LED Flashlights and Backlight Current Source • Medical Equipment • Portable Devices: - Handheld Gaming Devices - GPS Navigation Systems - LCD Monitors - Portable DVD Players SW 1 5 VIN GND 2 VFB 3 4 EN MCP1662 2x3 TDFN* VFB 1 SGND 2 SW 3 NC 4 8 EN EP 9 7 PGND 6 NC 5 V IN * Includes Exposed Thermal Pad (EP); see Table 3-1. 2014-2015 Microchip Technology Inc. DS20005316E-page 1 MCP1662 Typical Application D MBR0540 L 4.7 – 10 µH VOUT LED1 CIN 4.7 – 30 µF VIN 2.4V – 3.0V SW LED2 VIN + ALKALINE ILED = LED6 EN VFB ON ALAKLINE COUT 10 µF MCP1662 - + 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 250 4 wLEDs, L = 4.7 µH IOUT LED (mA) 200 150 8 wLEDs, L = 10 µH 100 50 0 2 DS20005316E-page 2 2.5 3 3.5 4 VIN (V) 4.5 5 5.5 2014-2015 Microchip Technology Inc. MCP1662 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 ..................................................................300V 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 = 9V or 3 white LEDs (VF = 2.75V @ IF = 20 mA or VF = 3.1V @ 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 — 100 — mA 4.2V VIN, 8 LEDs 125 — mA 3.3V VIN, 4 LEDs 200 — mA 5.0V VIN, 4 LEDs Input Voltage Range Undervoltage Lockout (UVLO) Feedback Voltage Reference Conditions Note 1 VFB 275 300 325 mV VFB_OLP — 50 — mV Feedback Input Bias Current IVFB — 0.005 — µA Shutdown Quiescent Current IQSHDN — 0.02 — µA EN = GND IN(MAX) — 1.3 — A Note 2 INLK — 0.4 — µA VIN = VSW = 5V; VOUT = 5.5V VEN = VFB = GND RDS(ON) — 0.8 — VIN = 5V, ILED = 100 mA, 4 series white LEDs (Note 2) |(VFB/VFB)/VIN| — 0.25 — %/V Feedback Open Load Protection (OLP) Threshold NMOS Peak Switch Current Limit NMOS Switch Leakage NMOS Switch ON Resistance Feedback Voltage Line Regulation VFB falling (Note 2) VIN = 3.0V to 5V Maximum Duty Cycle DCMAX — 90 — % Note 2 Switching Frequency fSW 425 500 575 kHz ±15% EN Input Logic High VIH 85 — — % of VIN Note 1: 2: 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 (VOUT = VLED + V_RSET). Determined by characterization, not production tested. 2014-2015 Microchip Technology Inc. DS20005316E-page 3 MCP1662 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 = 9V or 3 white LEDs (VF = 2.75V @ IF = 20 mA or VF = 3.1V @ 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 VIL — — 7.5 % of VIN IENLK — 0.025 — µA VEN = 5V Start-up Time tSS — 100 — µs EN Low-to-High, 90% of ILED (Note 2, Figure 2-10) Thermal Shutdown Die Temperature TSD — 150 — °C TSDHYS — 15 — °C EN Input Logic Low EN Input Leakage Current Die Temperature Hysteresis Note 1: 2: Conditions 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 (VOUT = VLED + V_RSET). 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 Transient Package Thermal Resistances DS20005316E-page 4 2014-2015 Microchip Technology Inc. MCP1662 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 = 12V or 4 white LEDs (VF = 2.75V @ IF = 20 mA or VF = 3.1V @ IF = 100 mA), CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. 150 100 4 x wLED, L = 4.7 µH RSET = 2.2ȍ 80 Efficiency (%) LED Current (mA) VIN = 5.5V 90 125 RSET = 3.2ȍ 100 75 RSET = 6.2ȍ 50 VIN = 4.0V 70 60 VIN = 3.0V 50 40 30 25 L = 4.7 µH, 4 wLEDs 20 RSET = 15ȍ 10 0 0 2.3 2.7 FIGURE 2-1: 3.1 3.5 3.9 4.3 Input Voltage (V) 4.7 5.1 5.5 4 White LEDs, ILED vs. VIN. 0 50 75 100 125 150 175 200 225 250 ILED (mA) FIGURE 2-4: ILED. 4 White LEDs, Efficiency vs. 100 120 4 x wLED, L = 4.7 µH, VIN = 3.3V 90 RSET = 3.2ȍ 80 60 RSET = 6.2ȍ 40 80 Efficiency (%) 100 LED Current (mA) 25 VIN = 5.5V 70 VIN = 3.0V VIN = 4.0V 60 50 40 30 RSET = 15ȍ 20 L = 10 µH, 8 wLEDs 20 10 0 0 -40 -25 -10 FIGURE 2-2: 4 White LEDs, ILED vs. Ambient Temperature. 40 60 80 100 ILED (mA) 120 140 160 8 White LEDs, Efficiency vs. 300 8 x wLED, L = 10 µH, VIN = 4.2V 250 RSET = 3.2ȍ 100 LED Current (mA) 20 FIGURE 2-5: ILED. 80 60 RSET = 6.2ȍ 40 RSET = 15ȍ 20 LED Current (mA) 120 0 5 20 35 50 65 80 95 110 125 Ambient Temperature (oC) 200 2 wLEDs, L = 4.7 µH 150 5 wLEDs, L = 10 µH 4 wLEDs, L = 4.7 µH 100 8 wLEDs, L = 10 µH 50 0 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 Ambient Temperature (oC) FIGURE 2-3: 8 White LEDs, ILED vs. Ambient Temperature. 2014-2015 Microchip Technology Inc. 2.3 2.7 FIGURE 2-6: 3.1 3.5 3.9 4.3 Input Voltage (V) 4.7 5.1 5.5 Maximum ILED vs. VIN. DS20005316E-page 5 MCP1662 Note: Unless otherwise indicated: VIN = 3.3V, ILED = 20 mA, VOUT = 12V or 4 white LEDs (VF = 2.75V @ IF = 20 mA or VF = 3.1V @ IF = 100 mA), CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. 2.5 250 UVLO Start 2.3 Blue Bars - ILED = 20 mA Red Bars - ILED = 40 mA 200 2.2 2.1 2 UVLO Stop 1.9 1.8 1.7 Start-up Time (µs) UVLO Thresholds (V) 2.4 150 100 50 1.6 0 1.5 -40 -25 -10 5 3 20 35 50 65 80 95 110 125 Ambient Temperature 4 5 6 Number of LEDs 7 8 (oC) FIGURE 2-7: Undervoltage Lockout (UVLO) vs. Ambient Temperature. FIGURE 2-10: of LEDs. Soft Start Time vs. Number 50 3 LEDs, ILED = 20 mA Shutdown Iq (nA) 40 ILED 10 mA/div 30 20 VEN 2V/div 10 VIN 2V/div 0 2.2 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). 40 µs/div FIGURE 2-11: VIN = VENABLE. Start-Up When Switching Frequency (kHz) 550 3 LED, ILED = 20 mA 525 ILED 10 mA/div 500 VEN 2V/div 475 VIN 2V/div 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. DS20005316E-page 6 40 µs/div FIGURE 2-12: Start-Up After Enable. 2014-2015 Microchip Technology Inc. MCP1662 Note: Unless otherwise indicated: VIN = 3.3V, ILED = 20 mA, VOUT = 12V or 4 white LEDs (VF = 2.75V @ IF = 20 mA or VF = 3.1V @ IF = 100 mA), CIN = COUT = 10 µF, X7R ceramic, L = 4.7 µH. 3 LEDs 3 LEDs VOUT 3V/div ILED 10 mA/div VSW 4V/div VSW 4V/div ILED 20 mA/div VEN 3V/div 1 µs/div 2 ms/div FIGURE 2-13: Duty Cycle. 100 Hz PWM Dimming, 15% FIGURE 2-16: 3.3V Input, 20 mA 3 White LEDs PWM Discontinuous Mode Waveforms. 3 LEDs 3 LEDs ILED 100 mA/div VOUT 3V/div VSW 4V/div ILED 50 mA/div VSW 4V/div VEN 3V/div 1 µs/div 2 ms/div FIGURE 2-14: Duty Cycle. 100 Hz PWM Dimming, 85% FIGURE 2-17: 3.3V Input, 100 mA 3 White LEDs PWM Continuous Mode Waveforms. 3 LEDs VFB 300 mV/div ILED 10 mA/div VSW 4V/div 50 ms/div FIGURE 2-15: Open Load (LED Fail or FB to GND) Response. 2014-2015 Microchip Technology Inc. DS20005316E-page 7 MCP1662 3.0 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 3-1. TABLE 3-1: 3.1 PIN FUNCTION TABLE MCP1662 SOT-23 MCP1662 2x3 TDFN 3 1 VFB — 2 SGND Symbol Description Feedback Voltage Pin Signal Ground Pin 1 3 SW Switch Node, Boost Inductor Input Pin — 4, 6 NC Not Connected Input Voltage Pin 5 5 VIN — 7 PGND Power Ground Pin 4 8 EN Enable Control Input Pin — 9 EP Exposed Thermal Pad (EP); must be connected to Ground 2 — GND Ground Pin 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. The signal ground and power ground must be connected externally in one point. 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 1.3A peak. The integrated N-Channel switch drain is internally connected to the SW node. 3.4 Not Connected (NC) 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 5-lead SOT-23 package uses a single ground pin. This is an unconnected pin. 3.5 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. DS20005316E-page 8 2014-2015 Microchip Technology Inc. MCP1662 4.0 DETAILED DESCRIPTION 4.1 Device Overview The MCP1662 device 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 MCP1662 integrates a peak current mode architecture. It delivers high-efficiency conversion for an LED lighting application when it is powered by twoor three-cell alkaline, lithium, NiMH, NiCd, or single-cell Lithium-Ion batteries. The maximum input voltage is 5.5V. A high level of integration lowers total system cost, eases implementation and reduces board area. 4.2 Functional Description The MCP1662 is a compact, high-efficiency, fixed 500 kHz frequency, step-up DC-DC converter. It operates as a constant current generator for applications powered by two- or three-cell alkaline or lithium Energizer® batteries, or three-cell NiCd or NiMH batteries, or one-cell Lithium-Ion or Li-Polymer batteries. Figure 4-1 depicts the functional block diagram of the MCP1662. It incorporates a Current mode control scheme, in which the PWM ramp signal is derived from the NMOS power switch current (VSENSE). This ramp signal adds a slope ramp compensation signal (VRAMP) and is compared to the output of the error amplifier (VERROR) to control the “on” time of the power switch. 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) that is used to regulate the LED current must be low. In the case of MCP1662, the VFB value is 300 mV. The device features controlled start-up voltage (UVLOSTART = 2.3V) and open load protection, in case the LED fails or a short circuit of the VFB pin to GND occurs. If the VFB voltage drops to 50 mV typical, 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 when there is an accidental drop in voltage. The 800 m, 36V integrated switch is protected by the 1.3A cycle-by-cycle inductor peak current limit operation. When the Enable pin is pulled to ground (EN = GND), the device stops switching, enters into Shutdown mode and consumes less than 50 nA of input current (Figure 2-8). 2014-2015 Microchip Technology Inc. DS20005316E-page 9 MCP1662 SW VIN Internal Bias UVLO_COMP VBIAS VUVLO_REF VIN_OK Gate Drive and Shutdown VEXT Control Logic EN Overcurrent Comparator OC REF VLIMIT + + - + VRAMP S + Slope Compensation Oscillator VSENSE 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: DS20005316E-page 10 Rc 300 mV Cc VOLP_REF VUVLO_REF VFB VIN_OK Bandgap EN MCP1662 Simplified Block Diagram. 2014-2015 Microchip Technology Inc. MCP1662 4.2.1 INTERNAL BIAS The MCP1662 gets its bias from VIN. The VIN bias is used to power the device and drive circuits over the entire operating range. 4.2.2 START-UP 4.2.4.1 Shutdown Mode. Input to Output Path (EN = GND) In Shutdown mode, the MCP1662 device 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. The MCP1662 is capable of starting from two alkaline cells. MCP1662 starts switching at approximately 2.3V typical for a light load current. Once started, the device will continue to operate down to 1.85V, typical. 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 are turned off. The start-up time is dependent on the LED’s current, on the number of LEDs connected at output, and on the output capacitor value (see Figure 2-10). In Shutdown mode, the current consumed by the MCP1662 device from batteries is very low (below 50 nA over VIN range; see Figure 2-8). Due to the direct path from input to output, in the case of pulsing enable 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. The internal oscillator has a delayed start to let the output capacitor completely charge to the input voltage value. 4.2.3 UNDERVOLTAGE LOCKOUT (UVLO) MCP1662 features an UVLO which prevents fault operation below 1.85V typical, which corresponds to the value of two discharged alkaline batteries. Essentially, there is a hysteresis comparator which monitors VIN at the reference voltage derived from the bandgap. The device starts its normal operation at 2.3V typical input, which corresponds to the voltage value of two rechargeable Ni-MH or Ni-Cd cells. A hysteresis is set 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 4.2.5 PWM MODE OPERATION The MCP1662 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 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 1.3A. 4.2.6 INTERNAL COMPENSATION 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 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 components and slope compensation are integrated. ENABLE PIN The MCP1662 device 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. 2014-2015 Microchip Technology Inc. DS20005316E-page 11 MCP1662 4.2.7 OPEN LOAD PROTECTION (OLP) An internal VFB fault signal turns off the PWM signal (VEXT) when output goes out of regulation and one of the following occurs: • open load (LED string fails) • 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, MCP1662 has implemented 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. 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. 4.2.9 OUTPUT SHORT CIRCUIT CONDITION Like all non-synchronous boost converters, the MCP1662 inductor current will increase excessively during a short circuit on the converter’s output. A short circuit on the output will cause the diode rectifier to fail, the inductor’s temperature to rise, and the saturation current to decrease, further increasing the peak current. When the diode fails, the SW pin becomes a high-impedance node: it remains connected only to the inductor and the resulting excessive ringing may cause damage to the MCP1662 device. 4.2.10 OVERTEMPERATURE PROTECTION Overtemperature protection circuitry is integrated into the MCP1662 device. 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 15°C. The OLP is disabled during an overtemperature condition. The OLP comparator is disabled during start-up sequences and thermal shutdown. Because the OLP comparator is turned off during start-up, care must be taken when using PWM dimming on the EN pin, as this might damage the device if a fault event occurs. 4.2.8 OVERCURRENT LIMIT The MCP1662 device uses a 1.3A 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. DS20005316E-page 12 2014-2015 Microchip Technology Inc. MCP1662 5.0 APPLICATION INFORMATION 5.1 Typical Applications The MCP1662 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 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 1.3A 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 ADJUSTABLE CONSTANT CURRENT CALCULATIONS To calculate the resistor value to set 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 R SET = ----------I LED EXAMPLE 1: 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 it in small steps with a variable duty cycle PWM signal applied to the EN pin. The maximum frequency for dimming is limited by the 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 on the input and output voltage. As there is a 1.3A 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 voltage at the output of the MCP1662, plus a margin, should be below 36V. 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: V Fmax nLED + V FB 36V VFB = 300 mV ILED = 25 mA RSET = 12 EXAMPLE 2: VFB = 300 mV ILED = 100 mA RSET = 3 The power dissipated on the RSET resistor is very 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. 2014-2015 Microchip Technology Inc. Characterization graphs show the maximum current the device can supply according to the number of LEDs at the output. For example, to ensure a 100 mA load current for 4 LEDs (output equal to approximately 12V), a minimum of 3.1V input voltage is necessary. If an application requires driving 8 LEDs and is powered by one Li-Ion battery (VIN from 3.3V to 4.2V), the LED current the MCP1662 device can regulate is close to 75 mA (Figure 2-6). DS20005316E-page 13 MCP1662 5.2.4 OPEN LOAD PROTECTION The MCP1662 device 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, and excessive current into LEDs. OLP is not enabled during start-up and thermal shutdown events. Since OLP is not enabled during these events, a PWM dimming application on the EN pin needs extra overvoltage circuits such as a Zenner diode connected in parallel with the LED string. 5.3 Input Capacitor Selection The boost input current is smoothed 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 MCP1662 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, an 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 10–20 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. 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 static applications, and up to 20 µF for hundreds of mA LED current applications. 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 Equation 5-3 or 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 Table 5-1 contains the recommended range for the input capacitor value. DS20005316E-page 14 2014-2015 Microchip Technology Inc. MCP1662 5.5 Inductor Selection 5.6 The MCP1662 device 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 a maximum of 10 LEDs), an inductance value of 10 µH is optimum. TABLE 5-2: MCP1662 RECOMMENDED INDUCTORS FOR BOOST CONVERTER Rectifier Diode Selection Schottky diodes are used to reduce losses. The diode’s average current must be higher than the maximum output current. The diode’s reverse breakdown voltage must be higher than the internal switch 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. Value (µH) DCR (typ) ISAT (A) Size WxLxH (mm) MSS5131-472 4.7 0.038 1.42 5.1x5.1x3.1 XFL4020-472 4.7 0.057 2.7 4.2x4.2x2.1 Type VOUTmax TA LPS5015-562 5.6 0.175 1.6 5.0x5.0x1.5 PMEG2005 18V < 85°C LPS6235-103 10 0.065 1.5 6.2x6.2x3.5 XAL4040-103 10 0.084 1.9 4.3x4.3x4.1 PMEG4005 36V < 85°C MBR0520 18V < 125°C MBR0540 36V < 125°C Part Number TABLE 5-3: Coilcraft Würth Elektronik 744025004 WE-TPC 4.7 0.1 1.7 2.8x2.8x2.8 744043004 WE-TPC 744773112 WE-PD2 4.7 0.05 1.7 4.8x4.8x2.8 10 0.156 1.6 4.0x4.5x3.2 74408943100 WE-SPC 10 0.082 2.1 4.8x4.8x3.8 6.3x6.3x3.0 TDK Corporation B82462G4472 4.7 0.04 1.8 B82462G4103 10 0.062 1.3 6.3x6.3x3.0 VLCF4024T-4R7 4.7 0.087 1.43 4.0x4.0x2.4 Several parameters are used to select the correct inductor: maximum rated current, saturation current, and direct 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 30-40% higher than the average. The lower the inductor DCR, the higher the efficiency of the converter: a common trade-off in size versus efficiency. The 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. 2014-2015 Microchip Technology Inc. 5.7 RECOMMENDED SCHOTTKY DIODES Thermal Calculations The MCP1662 device 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 continuous junction temperature rating for the MCP1662 device 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 I OUT OUT ------------------------------------ Efficiency – VOUT I OUT = P Dis The difference between the first term, input power, and the second term, power delivered, is the power dissipated when using the MCP1662 device. This is an estimate, assuming that most of the power lost is internal to the MCP1662 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 estimate 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 loss for the LED driver that is external to the MCP1662 is the sense resistor. The losses for the sense resistor can be approximated by VFB x ILED. DS20005316E-page 15 MCP1662 5.8 PCB Layout Information 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. 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 should be used. Therefore it is important that the input and output capacitors be placed as close as possible to the MCP1662 to minimize the loop area. EN +VIN CIN MCP1662 Vias to GND Bottom Plane 1 L RSET A LED1 K LEDs A GND D COUT K LEDN +VOUT GND Vias to GND Bottom Plane FIGURE 5-1: GND Bottom Plane MCP1662 5-Lead SOT-23 Recommended Layout. A L +VIN K +VOUT D A COUT LED1 LED2 CIN MCP1662 LEDs Via to GND EN 1 LEDN K RSET GND GND Bottom Plane FIGURE 5-2: DS20005316E-page 16 Vias to GND Bottom Plane MCP1662 TDFN Recommended Layout. 2014-2015 Microchip Technology Inc. MCP1662 6.0 PACKAGING INFORMATION 6.1 Package Marking Information 5-Lead SOT-23 Example AAAMY XXXXY AAAM5 25256 8-Lead TDFN (2x3x0.75 mm) Example ACA 543 25 Legend: XX...X Y YY WW NNN e3 * 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. Note: 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. 2014-2015 Microchip Technology Inc. DS20005316E-page 17 MCP1662 .# #$# /!- 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 : ( !"!#$!!% #$ !% #$ #&! ! !# "'( )*+ ) #&#,$ --#$## - *) DS20005316E-page 18 2014-2015 Microchip Technology Inc. MCP1662 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging 2014-2015 Microchip Technology Inc. DS20005316E-page 19 MCP1662 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging DS20005316E-page 20 2014-2015 Microchip Technology Inc. MCP1662 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging 2014-2015 Microchip Technology Inc. DS20005316E-page 21 MCP1662 ! "#$%&''()*+, ! .# #$# /!- 0 # 1/ %##!# ## +22--- 2 / DS20005316E-page 22 2014-2015 Microchip Technology Inc. MCP1662 APPENDIX A: REVISION HISTORY Revision E (September 2015) • The following is the list of modifications: • Updated Features and General Description sections. • Updated parameters in the DC and AC Characteristics table. • Updated Figures 2-10, 2-11 and 2-12. • Corrected Section 4.2.2 “Start-up”. • Minor updates in Section 4.2.6 “Internal Compensation” and Section 4.2.9 “Output Short Circuit Condition”. • Corrected Figure 5-1. Revision D (March 2015) The following is the list of modifications Updated the example packages in Section 6.0 “Packaging Information”. Revision C (December 2014) The following is the list of modifications: Updated the example packages in Section 6.0 “Packaging Information”. Revision B (November 2014) The following is the list of modifications: • Updated the example packages in Section 6.0 “Packaging Information” • Minor typographical corrections. Revision A (June 2014) • Original Release of this Document. 2014-2015 Microchip Technology Inc. DS20005316E-page 23 MCP1662 NOTES: DS20005316E-page 24 2014-2015 Microchip Technology Inc. MCP1662 PRODUCT IDENTIFICATION SYSTEM To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office. PART NO. [X](1) X /XX Device Tape and Reel Option Temperature Range Package Examples: a) b) Device: MCP1662: High-Voltage Step-Up LED Driver with UVLO and OLP Tape and Reel Option: T = Tape and Reel(1) Temperature Range: E = -40C to +125C (Extended) Package: MN* MCP1662T-E/MNY: Tape and Reel, Extended temperature, 8LD TFDN package MCP1662T-E/OT: Tape and Reel, Extended temperature, 5LD SOT-23 package Note 1: OT *Y = Plastic Dual Flat, No Lead – 2x3x0.75 mm Body (TDFN) = Plastic Small Outline Transistor (SOT-23) = Nickel palladium gold manufacturing designator. Only available on the TDFN package. 2014-2015 Microchip Technology Inc. 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. DS20005316E-page 25 MCP1662 NOTES: DS20005316E-page 26 2014-2015 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, motorBench, 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. © 2014-2015, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. ISBN: 978-1-63277-776-8 QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV == ISO/TS 16949 == 2014-2015 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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