MCP1643 1 MHz Low Start-up Voltage Synchronous Boost LED Constant Current Regulator Features Description • 1.6A Typical Peak Input Current Limit • Up to 550 mA LED Load Current • Low Start-up Voltage: 0.65V (typical, 25 mA LED Current) • Low Operating Input Voltage: down to 0.5V • Maximum Input Voltage < VLED < 5.0V • Maximum Output Voltage: - 5.0V - Overvoltage Protection • Low Reference Voltage: - VFB = 120 mV - Minimal Power Loss on Sense Resistor • Pulse-Width Modulation Mode Operation (1 MHz) • Internal Synchronous Rectifier • Internal Compensation • Inrush Current Limiting • Internal Soft-Start (240 µs typical) • Shutdown (EN = GND): - True Load Disconnect - Dimming Control by Variable Duty Cycle • Shutdown Current: 1.2 µA (typical) • Overtemperature protection • Packages: - MSOP-8 - 2x3 DFN-8 MCP1643 is a compact, high-efficiency, fixed frequency, synchronous step-up converter optimized to drive one LED with constant current, that operates from one and two-cell alkaline and NiMH/NiCd batteries. The device can also drive two red/green/yellow series connection LEDs. Applications • One and Two Cell Alkaline and NiMH/NiCd Portable LED Lighting Products • LED Flashlight and Head Lamps • Rechargeable Flashlights • Wall LED Lamps with Motion Detectors • LED supply for backlights • General LED constant current applications Low-voltage technology allows the regulator to start up without high-output voltage and load-current overshoot from a low 0.65V input. High efficiency is accomplished by integrating the low resistance N-Channel Boost switch and synchronous P-Channel switch. All compensation and protection circuitry are integrated to minimize external components. The internal feedback (VFB) voltage is set to 120 mV for low power dissipation when sensing and regulating LED current. A single resistor sets the constant current output that drives the LED load. The device features an output overvoltage protection that limits the output voltage to 5.0V typical, in case the LED fails or output load is disconnected. The LED will either be turned OFF or turned ON using the enable input. A True Output Load Disconnect mode provides input-to-output isolation while Shutdown (EN = GND) by removing the normal boost regulator diode path from input to output. Shutdown state consumes 1.2 µA from input at room temperature. The LED can be turned on and off with a variable duty cycle pulse-width modulation (PWM) signal applied to the EN pin for dimming applications. The device also features a thermal shutdown at +150°C, with +25°C hysteresis. Two package options, MSOP-8 and 2x3 DFN-8, are available. Package Types MCP1643 MSOP-8 EN 1 VFB 2 NC 3 VOUT 4 MCP1643 2x3 DFN* 8 VIN EN 1 7 SGND VFB 2 NC 3 6 PGND VOUT 4 5 SW 8 VIN EP 9 7 SGND 6 PGND 5 SW * Includes Exposed Thermal Pad (EP), see Table 3-1. 2013 Microchip Technology Inc. DS20005208A-page 1 MCP1643 Typical Applications L1 4.7 µH I CIN 4.7...10 µF LED ILED = 25 mA SW VOUT VIN 0.12V = ----------------R SET LED COUT 4.7 µF MCP1643 ALKALINE + VFB EN - RSET 4.7 GND ON L1 4.7 µH OFF CIN 4.7...10 µF SW VOUT VIN REN 1 M NIMH 1.2V + WHITE LED ILED = 360 mA COUT 20 µF MCP1643 VFB EN - RSET 0.33 GND ON/OFF NIMH 1.2V + - RSET Minimum and Maximum Limits for ILED in Regulation, with ±6% Tolerance 10 1000 ILED MAX ILED MAX 1 100 RSET for ILED MAX ILED MIN ILED MIN WHITE LED TA = +25oC 0.1 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 LED Current (mA) RSET (Ω) RSET for ILED MIN 10 3 Input Voltage (V) DS20005208A-page 2 2013 Microchip Technology Inc. MCP1643 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 † EN, FB, VIN, VSW, VOUT - GND ........................... +6.5V EN, FB ......... < maximum VOUT or VIN > (GND – 0.3V) Output Short Circuit Current....................... Continuous Power Dissipation ............................ Internally Limited Storage Temperature ......................... -65°C to +150°C Ambient Temp. with Power Applied...... -40°C to +85°C Operating Junction Temperature........ -40°C to +125°C ESD Protection On All Pins: HBM .............................................................. 4 kV MM................................................................ 300V DC CHARACTERISTICS Electrical Characteristics: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. Parameters Sym Min Typ Max Units Conditions Minimum Input Voltage After Start-Up VIN — 0.5 — V Note 1, Note 3 Start-Up Voltage VIN — 0.65 0.8 V Note 2, Note 1 Output Overvoltage Protection VOUT_OVP — 5.0 — V Note 3 Shutdown Quiescent Current IQSHDN — 1.2 — µA EN = GND; includes N-Channel and P-Channel Switch Leakage Feedback Voltage VFB 105 120 135 mV Feedback Input Bias Current IVFB — 60 — pA NMOS Switch Leakage INLK — 0.4 — µA VIN = VSW = 4.0V VOUT = 4.5V VEN = VFB = GND PMOS Switch Leakage IPLK — 0.25 — µA VIN = VSW = GND; VOUT = 4.5V NMOS Switch ON Resistance RDS(ON)N — 0.2 — ILED = 250 mA, Note 3 PMOS Switch ON Resistance RDS(ON)P — 0.4 — ILED = 250 mA, Note 3 NMOS Peak Switch Current Limit IN(MAX) — 1.6 — A Note 3 Maximum Duty Cycle DCMAX — 90 — % Note 3 Minimum Duty Cycle DCMIN — 5 — % Note 3 Switching Frequency fSW 0.85 1.0 1.15 EN Input Logic High VIH 75 — — EN Input Logic Low VIL — — 20 Input Characteristics Note 1: 2: 3: MHz %of VIN ILED= 25 mA %of VIN ILED = 25 mA For VIN < VOUT, ILED remains in regulation up to VIN = VLED minus a headroom @ LED typical VF and IF. VOUT completely discharged. If the output capacitor remains partially charged, the device will start-up at the minimum possible voltage. Determined by characterization, not production tested. 2013 Microchip Technology Inc. DS20005208A-page 3 MCP1643 DC CHARACTERISTICS (CONTINUED) Electrical Characteristics: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. Parameters Sym Min Typ Max Units EN Input Leakage Current IENLK — 0.9 — µA VEN = 1.2V tSS — 240 — µs EN Low-to-High, 90% of VOUT; ILED = 25 mA, Note 3 — 270 — µs EN Low-to-High, 90% of VOUT; ILED = 300 mA, Note 3 TSD — 150 — C ILED= 25 mA TSDHYS — 25 — C Soft Start Time Thermal Shutdown Die Temperature Die Temperature Hysteresis Note 1: 2: 3: Conditions For VIN < VOUT, ILED remains in regulation up to VIN = VLED minus a headroom @ LED typical VF and IF. VOUT completely discharged. If the output capacitor remains partially charged, the device will start-up at the minimum possible voltage. Determined by characterization, not production tested. TEMPERATURE SPECIFICATIONS Electrical Characteristics: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. Parameters Sym Min Typ Max Units Conditions Temperature Ranges Operating Ambient Temperature Range TA -40 — +85 °C Storage Temperature Range TA -65 — +150 °C Maximum Junction Temperature TJ — — +150 °C Thermal Resistance, 8L-2x3 DFN JA — 68 — °C/W Thermal Resistance, 8L-MSOP JA — 211 — °C/W Steady State Transient Package Thermal Resistances DS20005208A-page 4 2013 Microchip Technology Inc. MCP1643 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 = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C, MSOP-8 package. LED Current (mA) 450 100 LED VF = 3.5V @ IF = 700 mA 95 RSET = 0.25ȍ 400 Efficiency (%) 500 350 RSET = 0.41ȍ 300 250 200 RSET = 0.82ȍ 150 100 50 0.9 FIGURE 2-1: RSET = 5ȍ 65 1.2 1.5 1.8 Input Voltage (V) 2.1 2.4 One White LED ILED vs. VIN. 10 FIGURE 2-4: vs. ILED. 100 ILED (mA) 1000 One White LED Efficiency 100 LED VF = 2.5V @ IF = 350 mA 95 200 175 Efficiency (%) LED Current (mA) VIN = 1.8V VIN = 1.2V 75 70 RSET = 0.82ȍ 150 125 RSET = 1.2ȍ 100 75 50 RSET = 5ȍ 25 90 VIN = 2.4V VIN = 1.8V 85 VIN = 1.2V 80 75 0 70 0.6 0.7 0.8 0.9 1 1.1 1.2 Input Voltage (V) 1.3 1.4 1.5 One Red LED ILED vs. VIN. FIGURE 2-2: 10 FIGURE 2-5: ILED. 350 100 ILED (mA) 1000 One Red LED Efficiency vs. 100 LED VF = 2.5V @ IF = 350 mA 300 95 RSET = 0.41ȍ 90 Efficiency (%) LEDs Current (mA) 80 60 0.6 225 VIN = 2.4V 85 RSET = 1.2ȍ 0 250 90 250 200 RSET = 0.82ȍ 150 RSET = 1.2ȍ 100 VIN = 3.6V 85 80 75 VIN = 2.4V VIN = 3.0V 70 65 60 50 RSET = 5ȍ 55 0 50 0.6 0.9 1.2 1.5 1.8 Input Voltage (V) 2.1 2.4 FIGURE 2-3: Two Series Connection Red LEDs ILED vs. VIN. 2013 Microchip Technology Inc. 10 100 ILED (mA) 1000 FIGURE 2-6: Two Red LEDs Efficiency (in Series Connection) vs. ILED. DS20005208A-page 5 MCP1643 Note: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C, MSOP-8 package. 700 350 TA = +85oC VIN = 1.5V 250 200 RSET = 0.82ȍ 150 RSET = 1.2ȍ 100 50 400 TA = 0oC 300 200 0 -40 -25 -10 5 20 35 50 65 Ambient Temperature (°C) FIGURE 2-7: Temperature. 0.6 80 One White ILED vs. Ambient 150 0.9 1.2 1.5 1.8 2.1 Input Voltage (V) 2.4 2.7 3 Maximum ILED vs. VIN. FIGURE 2-10: 1010 VIN = 1.5V RSET = 0.82ȍ 125 Switching Frequency (kHz) LED Current (mA) 500 100 RSET = 5ȍ 0 1005 100 1000 75 50 fEN = 400 Hz fEN = 1 kHz 25 0 995 990 985 ILED = 100 mA 980 0 10 20 30 40 50 60 Duty Cycle (%) FIGURE 2-8: 70 80 90 100 ILED vs. VEN Duty Cycle. -40 -25 -10 5 20 35 50 65 Ambient Temperature (°C) FIGURE 2-11: Temperature. 40 80 fSW vs. Ambient 123 RSET = 1.2ȍ (ILED = 100 mA) 122 Feadback Voltage (mV) 39 Duty Cycle (%) TA = +25oC 600 RSET = 0.41ȍ LED Current (mA) LED Current (mA) 300 38 37 36 35 121 120 119 118 ILED = 100 mA 117 34 -40 -25 -10 5 20 35 50 65 Ambient Temperature (°C) FIGURE 2-9: Temperature. DS20005208A-page 6 80 Duty Cycle vs. Ambient -40 -25 FIGURE 2-12: Temperature. -10 5 20 35 50 65 Ambient Temperature (°C) 80 VFB vs. Ambient 2013 Microchip Technology Inc. MCP1643 Note: Unless otherwise indicated, VIN = EN = 1.2V, COUT = 20 µF, CIN = 10 µF, L = 4.7 µH, ILED = 25 mA, TA = +25°C, MSOP-8 package. ILED 20 mA/div ILED 20 mA/div VIN 1 V/div VIN 1 V/div VEN 80 us/div FIGURE 2-13: Start-up After Enable. IL 500 mA/div 80 us/div FIGURE 2-16: Start-up when VIN = VEN. VOUT 20 mV/div, AC Coupled ILED 50 mA/div VSW 1 V/div VSW 1 V/div ILED 100 mA/div VEN 1 V/div 400 us/div 1 us/div FIGURE 2-14: 100 mA PWM Operation. ILED 50 mA/div FIGURE 2-17: 15% Duty Cycle. 400 Hz PWM Dimming, VOUT 5V 2 V/div VSW 1 V/div 2V Step from ILED = 100 mA to Open Load ILED 100 mA/div VSW 2 V/div VEN 1 V/div FIGURE 2-15: 85% Duty Cycle. 10 ms/div 400 us/div 400 Hz PWM Dimming, 2013 Microchip Technology Inc. FIGURE 2-18: Open Load Response. DS20005208A-page 7 MCP1643 NOTES: DS20005208A-page 8 2013 Microchip Technology Inc. MCP1643 3.0 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 3-1. TABLE 3-1: PIN FUNCTION TABLE MCP1643 2 x 3 DFN MCP1643 MSOP Symbol 1 1 EN Enable pin. The logic high enables the operation. Do not allow this pin to float. 2 2 VFB Reference Voltage pin. Connect to the VFB pin, the RSET (LED current set resistor), and the cathode of the LED load. 3 3 NC Unconnected pin 4 4 VOUT 5 5 SW 6 6 PGND Power Ground Reference pin 7 7 SGND Signal Ground Reference pin 8 8 VIN Input Supply Voltage pin. A local bypass capacitor is required. 9 — EP Exposed Thermal Pad, must be connected to VSS 3.1 Description Boost Converter Output pin. Connect to this pin the anode of the LED load. An output filter capacitor is required. Boost and Rectifier Switch Input pin. Connect the boost inductor between SW and VIN. Enable Pin (EN) The EN pin is a logic-level input used to enable or disable device switching. Device has low quiescent current while disabled. A logic high (>75% of VIN) will enable the regulator output. A logic low (<20% of VIN) will ensure that the regulator is disabled. 3.2 Feedback Voltage Pin (VFB) The VFB pin is used to regulate the voltage across the RSET sense resistor to 120 mV, to keep the output LED current in regulation. 3.3 Output Voltage Power Pin (VOUT) High current flows through the integrated P-Channel and out of this pin to the output capacitor, LED load and RSET sense resistor. The output voltage must be filtered using a 4.7 to 20 µF X7R or X5R ceramic capacitor. The value of the output capacitor depends on the load current. 3.5 Power Ground (PGND) and Signal Ground Pins (SGND) The power ground pins are used as a return for the high-current N-Channel switch. The signal ground pin is used as a return for the integrated VFB and error amplifier. The length of the trace from input cap return, output cap return and PGND and SGND should be made as short as possible to minimize noise on the ground pins. The SGND and PGND pins are connected externally. 3.7 Unconnected Pin (NC) This pin is unconnected. 3.4 3.6 Power Supply Input Voltage Pin (VIN) Connect the input voltage source to VIN. The input source should be decoupled to GND with a 4.7 µF minimum capacitor. 3.8 Exposed Thermal Pad (EP) There is no internal electrical connection between the Exposed Thermal Pad (EP) and the PGND and SGND pins. They must be connected to the same potential on the Printed Circuit Board (PCB). Switch Node Pin (SW) Connect the inductor from the input voltage to the SW pin. The SW pin carries inductor current and can be as high as 1.6 A typical peak value. The integrated N-Channel switch drain and integrated P-Channel switch source are internally connected at the SW node. 2013 Microchip Technology Inc. DS20005208A-page 9 MCP1643 NOTES: DS20005208A-page 10 2013 Microchip Technology Inc. MCP1643 4.0 DETAILED DESCRIPTION 4.1 Device Overview that protects the device if the output voltage (VOUT) is higher than 5.0V. This usually happens if the LED is disconnected. While VIN < VOUT, the load current (ILED) remains in regulation until VIN is close to VLED (see Typical Applications and Figures 2-1 to 2-3). A True Output Load Disconnect mode provides inputto-output isolation while in Shutdown (EN = GND). In this state, the MCP1643 LED driver drains 1.2 µA current from the battery at room temperature. A high level of integration lowers the total system cost, eases the implementation and reduces board area. The device also features internal compensation, low noise, soft start and thermal shutdown. The MCP1643 is capable of starting up with a low voltage, while achieving high efficiency to drive one or more LEDs with constant current. The MCP1643 is a fixed frequency, synchronous step-up converter, with a low voltage reference of 120 mV, optimized to keep the output current constant by regulating the voltage across the feedback resistor (RSET). The normal boost converter with a high voltage reference has a high voltage drop across the current sense resistor. The power dissipated in the sense resistor reduces the efficiency of a LED driver solution. Therefore, the voltage drop on the sense resistor used to regulate the LED current must be low, in this case by a low VFB value of 120 mV. The device can operate from one or two-cell alkaline and NiMH/NiCd batteries. The maximum input voltage is 5.0V. The device features an Overvoltage Protection 4.2 Functional Description The MCP1643 is a compact, high-efficiency, fixed frequency, step-up DC-DC converter that operates as a constant current generator for applications powered by either one or two-cell, alkaline, NiCd, or NiMH batteries. Figure 4-1 depicts the functional block diagram of the MCP1643 device. VOUT Internal BIAS VIN IZERO Direction Control SOFT-START SW Gate Drive and Shutdown Control Logic EN PGND Oscillator ILIMIT ISENSE Slope Compensation S SGND PWM/PFM Logic 120 mV VFB EA FIGURE 4-1: MCP1643 Block Diagram. 2013 Microchip Technology Inc. DS20005208A-page 11 MCP1643 4.2.1 LOW-VOLTAGE START-UP The MCP1643 LED Constant Current Driver is capable of starting from a low-input voltage. Start-up voltage is typically 0.65V for a 25 mA LED load. For applications in which the device turns on and off fast, the start-up voltage is lower than 0.65V, because the output capacitor remains partially charged. After start-up, the device operates down to 0.5V input. There is no Undervoltage-Lockout feature for the MCP1643 LED Constant Current Driver. The device will start up at the lowest possible voltage and run down to the lowest possible voltage. When enabled, the internal start-up logic turns the rectifying P-Channel switch on until the output capacitor is charged to a value close to the input voltage. The rectifying switch is current limited during this time. After charging the output capacitor to the input voltage, the device starts switching in open loop, because the LED is turned off and the feedback input voltage is zero. Once VOUT is equal to the minimum forward voltage (VF) of the LED, the device enters in close loop and regulates the voltage across the RSET resistor, which is connected between VFB pin and GND. 4.2.2 PWM MODE OPERATION The MCP1643 LED Constant Current Driver operates as a fixed frequency, synchronous boost converter. The switching frequency is internally maintained with a precision oscillator typically set to 1 MHz. Because the LEDs require high currents, the device will work in PWM Continuous mode. At very low LED currents, the MCP1643 might run in PWM Discontinuous mode. As it features an anti-ringing control, the switching noise is low. The P-Channel switch acts as a synchronous rectifier, by turning off to prevent reverse current flow from the output cap back to the input in order to keep efficiency high. Lossless current sensing converts the peak current signal to a voltage to sum with the internal slope compensation. This summed signal is compared to the voltage error amplifier output to provide a peak current control command for the PWM signal. The slope compensation is adaptive to the input and output voltage. Therefore, the converter provides the proper amount of slope compensation to ensure stability, but is not excessive, which causes a loss of phase margin. The peak current limit is set to 1.6 A typical. DS20005208A-page 12 4.2.3 ADJUSTABLE OUTPUT LED CURRENT The MCP1643 LED’s current is adjustable with an external resistor, called RSET, connected to VFB pin and GND. The device regulates the voltage on the RSET and provides a constant current trough LED while VIN VOUT (minus a 300 – 400 mV headroom in case of low LED currents) (see Figures 2-1 and 2-2). The internal VREF voltage is 120 mV. There are limits applied when the RSET value is calculated over the input voltages (see Typical Applications). 4.2.4 ENABLE The enable pin is used to turn the boost converter on and off. The enable threshold voltage varies with input voltage. To enable the boost converter, the EN voltage level must be greater than 75% of the VIN voltage. To disable the boost converter, the EN voltage must be less than 20% of the VIN voltage. 4.2.4.1 True Output Disconnect The MCP1643 device incorporates a true output disconnect feature. With the EN pin pulled low, the output of the MCP1643 is isolated or disconnected from the input by turning off the integrated P-Channel switch and removing the switch bulk diode connection. This removes the DC path, typical in boost converters, which allows the output to be disconnected from the input. During this mode, 1.2 µA (typical) of current is consumed from the input (battery). True output disconnect does not discharge the output; this allows a faster start-up in dimming or load step applications. 4.2.4.2 PWM Dimming The MCP1643 allows dimming by turning the LED on and off with a variable duty cycle PWM signal applied to the EN pin. The maximum frequency for dimming is limited by the internal soft-start of 240 µs (typical). By varying the duty cycle of the PWM signal applied on EN input, the LED current is changing linearly (see Figure 2-8). 4.2.5 INTERNAL BIAS The MCP1643 LED Constant Current Driver gets its start-up bias from VIN. Once the output exceeds the input, bias comes from the output. Therefore, once started, the operation is completely independent of VIN. The operation is only limited by the output power level and the input source series resistance. Once started, the output will remain in regulation, down to 0.5V typical with 25 mA LED current for low-source impedance inputs. 2013 Microchip Technology Inc. MCP1643 4.2.6 INTERNAL COMPENSATION The error amplifier, with its associated compensation network, completes the closed loop system by comparing the voltage from the sense resistor to a 120 mV reference at the input of the error amplifier and 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 components and slope compensation are integrated. 4.2.7 SHORT CIRCUIT PROTECTION Unlike most boost converters, the MCP1643 LED Constant Current Driver allows its output to be shorted during normal operation. The internal current limit and overtemperature protection limit excessive stress and protect the device during periods of short circuit, overcurrent and overtemperature. 4.2.8 OUTPUT OVERVOLTAGE PROTECTION Overvoltage Protection is designed to protect the MCP1643 if the output voltage (VOUT) becomes higher than 5.0V. Because the device is a step-up converter that runs as a constant current generator, if the load is disconnected, the output increases up to dangerous voltages. This happens when the LED fails. The device stops switching and the VOUT value is verified periodically if it is higher than 5.0V (see Figure 2-18). This feature does not protect the LED. An optional Zener diode is added between VOUT and VFB pins to clamp the output voltage and protects the LED against excessive voltage and current. 4.2.9 OVERTEMPERATURE PROTECTION Overtemperature protection circuitry is integrated in the MCP1643 LED Constant Current Driver. This circuitry monitors the device junction temperature and shuts the device off if the junction temperature exceeds the typical +150°C threshold. If this threshold is exceeded, the device will automatically restart once the junction temperature drops by 25°C. 2013 Microchip Technology Inc. DS20005208A-page 13 MCP1643 NOTES: DS20005208A-page 14 2013 Microchip Technology Inc. MCP1643 5.0 APPLICATION INFORMATION 5.1 Typical Applications The MCP1643 synchronous boost regulator operates at 0.5V input. The maximum output voltage range is limited by overvoltage protection at 5.0V. LED current stays in regulation while VIN VOUT minus a 300 – 400 mV headroom. The power efficiency conversion is high when driving LED currents up to hundreds of mA. Output current capability is limited by the 1.6A 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 values for the MCP1643’s LED current, use Equation 5-1, where RSET is connected to VFB and GND. The reference voltage (VFB) is 120 mV. EQUATION 5-1: I LED VFB = -----------R SET EXAMPLE 1: VFB = 120 mV ILED = 25 mA RSET = 4.8with a standard value of 4.7 ILED is 25.53 mA) 5.2.2 LED’s brightness can also be controlled by setting a maximum current allowed for LED (using Equation 5-1) and 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 soft start, 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 (see Figure 2-8). 5.3 VFB = 120 mV ILED = 100 mA RSET = 1.2 Power dissipated on the RSET resistor is very low and equal with VFB*ILED. For 100 mA LED current, the power dissipated on sense resistor is only 12 mW, and the efficiency of the conversion is high. Equation 5-1 applies for one or even two LEDs in series connection. The Typical Applications graphic shows the maximum and minimum limits for RSET over the input voltage range that ensures current regulation for a white LED. 2013 Microchip Technology Inc. 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. Low ESR X5R or X7R are well suited, since they have a low temperature coefficient and small size. For most applications, 4.7 µF of capacitance is sufficient at the input. For highpower applications that have high-source impedance or long leads, connecting the battery to 10 µF capacitance is recommended. Additional input capacitance can be added to provide a stable input voltage. 5.4 Output Capacitor Selection The output capacitor helps provide a stable output voltage and smooth load current during sudden load transients, as is the PWM dimming. Ceramic capacitors are well suited for this application (X5R and X7R). The range of the output capacitor vary from 4.7 µF (in case of light loads and static applications) up to 20 µF (for hundreds of milliamp LED currents and PWM dimming applications). 5.5 EXAMPLE 2: PWM DIMMING Connecting More LEDs to Output White LEDs have a typical 2.7 to 3.2V forward voltage (VF), which depends on the power dissipated according to its VF/IF characteristic. Because MCP1643 allows up to 5.0V maximum to output, two white LEDs in series connection are not possible. Two or more white LEDs can be connected in parallel to output, as shown in Figure 6-1. Current sensing is necessary only for one LED. Each LED of the string is passed by the calculated current according to Equation 5-1. A protection circuit formed by a Zener and general purpose diodes will protect the rest of LEDs, if the LED in the sense loop fails. Two red, green or yellow LEDs can be connected in series to the output of MCP1643 (see application example on Figure 6-2). Red LEDs have a typical VF between 1.8V and 2.2V (it depends on the real color), yellow LEDs have the VF between 2.1V and 2.2V, while for green options, consider values from 2.0V to 2.4V. DS20005208A-page 15 MCP1643 5.6 Inductor Selection 5.7 The MCP1643 device is designed to be used with small surface mount inductors. An inductance value of 4.7 µH is recommended to achieve a good balance between the inductor size, converter load transient response and minimized noise. TABLE 5-1: Part Number MCP1643 RECOMMENDED INDUCTORS Value DCR (µH) (– typ) ISAT (A) Size WxLxH (mm) Thermal Calculations The MCP1643 is available in two different packages: MSOP-8 and 2 x 3 DFN-8. By calculating the power dissipation and applying the package thermal resistance (JA), the junction temperature is estimated. The maximum continuous ambient temperature rating for the MCP1643 family of devices is +85°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 5-2: Wurth® Group 744025004 4.7 0.100 1.7 2.8x2.8x2.8 744042004 4.7 0.082 1.65 4.8x4.8x1.8 ME3220 4.7 0.190 1.5 2.5x3.2x2.0 LPS4018 4.7 0.125 1.8 4x4x1.8 XFL4020 4.7 0.052 2.0 4x4x2.1 B82462 G4472M 4.7 0.04 1.8 6x6x3 B82462 A4472M 4.7 0.08 2.8 6x6x3 SLF60284R7M1R6 4.7 0.028 1.6 6x6x2.8 EQUATION 5-2: V I OUT OUT ------------------------------------– V I = P Dis Efficiency OUT OUT Coilcraft TDK Corporation Several parameters are used to select the correct inductor: • maximum-rated current • saturation current • copper resistance (ESR) For boost converters, the inductor current can be much higher than the output current. The lower the inductor ESR, 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 the 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. DS20005208A-page 16 The difference between the first term, input power, and the second term, power delivered, is the internal MCP1643’s power dissipation. This is an estimate assuming that most of the power lost is internal to the MCP1643 device and not CIN, COUT and the inductor. There is some percentage of power lost in the boost inductor, with very little loss in the input and output capacitors. For a more accurate estimation of the internal power dissipation, subtract the IINRMS2 x LDCR power dissipation. 5.8 PCB Layout Information 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. For the MCP1643, these paths are from VIN pin to the VOUT, output capacitor, LED load, RSET sense resistor, and SGND and PGND pins to the input capacitor. Therefore, it is important that the input and output capacitors be placed as close as possible to the MCP1643, to minimize the loop area. The feedback track should be routed away from the switching node and close to the VFB pin. RSET must be connected as close as possible to the VFB pin, unless regulation issues appears. When possible, ground planes and traces should be used to help shield the feedback signal and minimize noise and magnetic interference. 2013 Microchip Technology Inc. MCP1643 L +VIN SW CIN GND GND MCP1643 COUT Enable 1 RSET Wired on Bottom Plane +VOUT LED K A FIGURE 5-1: MCP1643 LED Constant Current Driver MSOP8 Recommended Layout. Apply the same guidance for 8-DFN package. 2013 Microchip Technology Inc. DS20005208A-page 17 MCP1643 NOTES: DS20005208A-page 18 2013 Microchip Technology Inc. MCP1643 6.0 TYPICAL APPLICATION CIRCUITS L1 4.7 µH ILED1 = 50 mA CIN Battery input 4.7...10 µF (One or Two Cells) VZ = 2.4V SW EN VOUT MCP1643 VIN WLED1 DZ ILED2 = 50 mA ILED3 = 50 mA WLED2 WLED3 COUT 10...20 µF D VFB RSET 2.4 R2 2.4 R3 2.4 GND ON OFF Note: 0.12V I LED = -------------R SET DZ and D group protects WLED2 and WLED3 from excessive voltage and current, if WLED1 fails. The MCP1643 input quiescent current in Shutdown (EN = GND) is typically 1.2 µA. Highload currents require additional output capacitance. FIGURE 6-1: Three White LEDs Application Powered from One or Two Cells. L1 4.7 µH SW CIN 4.7 – 10 µF VIN EN PWM signal, f = 400 Hz, Duty Cycle variable From PIC® MCU I/O FIGURE 6-2: Microcontroller. VOUT LED1 - RED MCP1643 Battery input (One or Two Cells) 0.12V I LED = -------------RSET GND COUT 20 µF LED2 - RED VFB RSET 0.82 ILED = 150 mA 150 mA Two Power Red LEDs Driver with PWM Dimming Control from PIC® 2013 Microchip Technology Inc. DS20005208A-page 19 MCP1643 NOTES: DS20005208A-page 20 2013 Microchip Technology Inc. MCP1643 7.0 PACKAGING INFORMATION 7.1 Package Marking Information 8-Lead DFN (2 x 3 x 0.9 mm) Part Number Example Code MCP1643-I/MC AKF MCP1643T-I/MC AKF 8-Lead MSOP Example Part Number Legend: XX...X Y YY WW NNN e3 * Note: AKF 312 25 Code MCP1643-I/MS 1643I MCP1643T-I/MS 1643I 1643I 312256 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 RoHS Compliant JEDEC designator for Matte Tin (Sn) This package is RoHS Compliant. The RoHS Compliant 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. 2013 Microchip Technology Inc. DS20005208A-page 21 MCP1643 !"##$%&' ( )RUWKHPRVWFXUUHQWSDFNDJHGUDZLQJVSOHDVHVHHWKH0LFURFKLS3DFNDJLQJ6SHFLILFDWLRQORFDWHGDW KWWSZZZPLFURFKLSFRPSDFNDJLQJ e D b N N L K E2 E EXPOSED PAD NOTE 1 NOTE 1 2 1 1 2 D2 BOTTOM VIEW TOP VIEW A A3 A1 NOTE 2 8QLWV 'LPHQVLRQ/LPLWV 1XPEHURI3LQV 0,//,0(7(56 0,1 1 120 0$; 3LWFK H 2YHUDOO+HLJKW $ 6WDQGRII $ &RQWDFW7KLFNQHVV $ 5() 2YHUDOO/HQJWK ' %6& 2YHUDOO:LGWK ( ([SRVHG3DG/HQJWK ' ± ([SRVHG3DG:LGWK ( ± E &RQWDFW/HQJWK / &RQWDFWWR([SRVHG3DG . ± ± &RQWDFW:LGWK %6& %6& ( 3LQYLVXDOLQGH[IHDWXUHPD\YDU\EXWPXVWEHORFDWHGZLWKLQWKHKDWFKHGDUHD 3DFNDJHPD\KDYHRQHRUPRUHH[SRVHGWLHEDUVDWHQGV 3DFNDJHLVVDZVLQJXODWHG 'LPHQVLRQLQJDQGWROHUDQFLQJSHU$60(<0 %6& %DVLF'LPHQVLRQ7KHRUHWLFDOO\H[DFWYDOXHVKRZQZLWKRXWWROHUDQFHV 5() 5HIHUHQFH'LPHQVLRQXVXDOO\ZLWKRXWWROHUDQFHIRULQIRUPDWLRQSXUSRVHVRQO\ 0LFURFKLS 7HFKQRORJ\ 'UDZLQJ && DS20005208A-page 22 2013 Microchip Technology Inc. MCP1643 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging 2013 Microchip Technology Inc. DS20005208A-page 23 MCP1643 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging DS20005208A-page 24 2013 Microchip Technology Inc. MCP1643 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging 2013 Microchip Technology Inc. DS20005208A-page 25 MCP1643 Note: For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging DS20005208A-page 26 2013 Microchip Technology Inc. MCP1643 APPENDIX A: REVISION HISTORY Revision A (August 2013) • Original Release of this Document. 2013 Microchip Technology Inc. DS20005208A-page 27 MCP1643 NOTES: DS20005208A-page 28 2013 Microchip Technology Inc. MCP1643 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 /XX Device Temperature Range Package Device: MCP1643: MCP1643T: LED Constant Current Regulator LED Constant Current Regulator (Tape and Reel) Temperature Range: I = -40C to Package: MC = MS = 2013 Microchip Technology Inc. Examples: +85C (Industrial) a) MCP1643-I/MC: b) MCP1643T-I/MC: c) MCP1643-I/MS: d) MCP1643T-I/MS: Industrial Temperature, 8LD 2x3 DFN package Tape and Reel, Industrial Temperature, 8LD 2x3 DFN package Industrial Temperature, 8LD MSOP package Tape and Reel, Industrial Temperature, 8LD MSOP package Plastic Dual Flat, No Lead Package 2x3x0.9 mm Body (DFN) Plastic Micro Small Outline Package (MSOP) DS20005208A-page 29 MCP1643 NOTES: DS20005208A-page 30 2013 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. Trademarks The Microchip name and logo, the Microchip logo, dsPIC, FlashFlex, KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro, PICSTART, PIC32 logo, rfPIC, SST, SST Logo, SuperFlash and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor, MTP, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries. Analog-for-the-Digital Age, Application Maestro, BodyCom, chipKIT, chipKIT logo, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN, ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP, Mindi, MiWi, MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, mTouch, Omniscient Code Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit, PICtail, REAL ICE, rfLAB, Select Mode, SQI, Serial Quad I/O, Total Endurance, TSHARC, UniWinDriver, WiperLock, ZENA and Z-Scale 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. GestIC and ULPP are registered trademarks 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. © 2013, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. ISBN: 978-1-62077-402-1 QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV == ISO/TS 16949 == 2013 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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