LT3495/LT3495B/ LT3495-1/LT3495B-1 650mA/350mA Micropower Low Noise Boost Converter with Output Disconnect DESCRIPTION FEATURES n n n n n n n n n Low Quiescent Current 60μA in Active Mode 0.1μA in Shutdown Mode Low Noise Control Scheme (Switching Frequency Always Stays Above Audible Range for LT3495/-1) Integrated Power NPN: 650mA Current Limit (LT3495/B) 350mA Current Limit (LT3495-1/B-1) Integrated Output Disconnect Integrated Output Dimming Wide input range: 2.3V to 16V Wide output range : Up to 40V Integrated feedback resistor Tiny 10-Lead 3mm × 2mm DFN Package The LT®3495/LT3495B/LT3495-1/LT3495B-1 are low noise boost converters with integrated power switch, feedback resistor and output disconnect circuitry. The parts control power delivery by varying both the peak inductor current and switch off-time. This novel* control scheme results in low output voltage ripple as well as high efficiency over a wide load range. For the LT3495/LT3495-1, the off-time of the switch is not allowed to exceed a fixed level, guaranteeing the switching frequency stays above the audio band for the entire load range. The parts feature a high performance NPN power switch with a 650mA and 350mA current limit for the LT3495/LT3495B and LT3495-1/LT3495B-1 respectively. The quiescent current is a low 60μA, which is further reduced to 0.1μA in shutdown. The internal disconnect circuitry allows the output voltage to be isolated from the input during shutdown. An auxiliary reference input (CTRL pin) overrides the internal 1.235V feedback reference with any lower value allowing full control of the output voltage during operation. The LT3495 series are available in a tiny 10-lead 3mm × 2mm DFN package. APPLICATIONS n n n OLED Power Low Noise Power MP3 Player L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. *Patent pending. TYPICAL APPLICATION Output Voltage Ripple vs Load Current OLED Power Supply from One Li-Ion Cell 4.7μF 2.2μF CAP VCC VOUT 909k LT3495 SHDN FB CTRL GND VOUT 16V 70mA 1μF 3495 TA01a 1.0μF 0603 CAPACITOR AT VOUT 40 80 30 20 10 0 2.2μF 1206 CAPACITOR AT VOUT 0 1 10 LOAD CURRENT (mA) VIN = 3.6V 100 3495 TA01b 400 LOAD FROM CAP 320 LOAD FROM VOUT 70 240 60 160 50 80 40 0.1 1 10 LOAD CURRENT (mA) POWER LOSS (mW) SW EFFICIENCY (%) 10μH VOUT PEAK-TO-PEAK RIPPLE (mV) ONE Li-Ion CELL Efficiency vs Load Current 90 50 0 100 3495 TA01c 3495b1b1f 1 LT3495/LT3495B/ LT3495-1/LT3495B-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VCC Voltage ...............................................................16V SW Voltage ...............................................................40V CAP Voltage ..............................................................40V VOUT Voltage .............................................................40V SHDN Voltage ...........................................................10V CTRL Voltage ............................................................10V FB Voltage ................................................................2.5V Maximum Junction Temperature........................... 125°C Operating Temperature Range (Note 2).. –40°C to 125°C Storage Temperature Range................... –65°C to 150°C TOP VIEW GND 1 10 SW GND 2 VCC 3 11 9 CAP 8 CAP CTRL 4 7 VOUT SHDN 5 6 FB DDB PACKAGE 10-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 76°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3495EDDB#PBF LT3495EDDB#TRPBF LDSS 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C LT3495EDDB-1#PBF LT3495EDDB-1#TRPBF LDSV 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C LT3495BEDDB#PBF LT3495BEDDB#TRPBF LDST 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C LT3495BEDDB-1#PBF LT3495BEDDB-1#TRPBF LDSW 10-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN Minimum Operating Voltage TYP MAX 2.2 2.5 V 16 V 1.255 V Maximum Operating Voltage UNITS VCTRL = 3V, (Note 3) l FB Resistor FB Voltage = 1.235V l 76 77 kΩ Quiescent Current Not Switching 60 70 μA Quiescent Current in Shutdown VSHDN = 0V, VCC = 3V 0 1 μA Minimum Switch-Off Time After Start-Up (Note 4) During Start-Up (Note 4) Maximum Switch-Off Time LT3495/LT3495-1, VFB = 1.5V FB Voltage 1.220 FB Voltage Line Regulation 0.03 74.7 %/V 200 500 l 17 Maximum Switch-On Time Switch Current Limit 1.235 26 ns ns 35 10 LT3495/LT3495B l 550 650 μs μs 780 mA 3495b1b1f 2 LT3495/LT3495B/ LT3495-1/LT3495B-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN l Switch Current Limit LT3495-1/LT3495B-1 Switch VCESAT LT3495/LT3495B, ISW = 400mA LT3495-1/LT3495B-1, ISW = 200mA Switch Leakage Current VSW = 5V PMOS Disconnect Current Limit After Start-Up During Start-Up PMOS Disconnect VCAP – VOUT IOUT = 50mA, VCAP = 15V 275 TYP MAX 350 450 250 110 SHDN Input Voltage High 1 μA 370 150 450 190 mA mA 150 mV 8.7 V 1.5 SHDN Pin Bias Current VSHDN = 3V VSHDN = 0V CTRL Pin Bias Current VCTRL = 0.5V, Current Flows Out of Pin CTRL to FB Offset VCTRL = 0.5V Maximum Shunt Current LT3495/LT3495-1, VFB = 1.5V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3495/LT3495B/LT3495-1/LT3495B-1 are guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. V Switching Frequency vs Load Current 400 200 VCC = 3.6V VOUT = 16V 1.0 FIGURE 7 CIRCUIT 0.5 0.0 –0.5 –1.5 20 40 80 60 LOAD CURRENT (mA) 100 120 3495 G01 μA μA 20 100 nA 6 14 mV μA FIGURE 7 CIRCUIT 15 –1.0 0 8 VOUT vs CTRL Voltage 18 VOUT VOLTAGE (V) 600 5.3 0 TA = 25°C unless otherwise noted. Load Regulation VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT V Note 3: Internal reference voltage is determined by finding VFB voltage level which causes quiescent current to increase 150μA above “Not Switching” level. Note 4: If CTRL is overriding the internal reference, Start-Up mode occurs when VFB is less then half the voltage on CTRL. If CTRL is not overriding the internal reference, Start-Up mode occurs when VFB is less then half the voltage of the internal reference. 1.5 VOUT VOLTAGE CHANGE (%) SWITCHING FREQUENCY (kHz) l 0.3 230 TYPICAL PERFORMANCE CHARACTERISTICS 0 mV mV 0.01 SHDN Input Voltage Low 800 mA 200 125 VCAP – VOUT Clamp Voltage 1000 UNITS 12 9 6 3 0 20 40 80 60 LOAD CURRENT (mA) 100 120 3495 G02 0 0 0.3 0.6 0.9 CTRL VOLTAGE (V) 1.2 1.5 3495 G03 3495b1b1f 3 LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL PERFORMANCE CHARACTERISTICS Output Voltage vs Temperature Minimum Switching Frequency 50 0.25 0.00 –0.25 –0.50 –0.75 0 40 80 TEMPERATURE (°C) FIGURE 7 CIRCUIT 45 40 35 30 –40 125 0 40 80 TEMPERATURE (°C) 3495 G04 150 100 0 100 200 300 400 500 SWITCH CURRENT (mA) SHDN PIN CURRENT (μA) INDUCTOR PEAK CURRENT (mA) 0 2 4 6 8 SHDN PIN VOLTAGE (V) 600 0 700 10 3495 G10 0 100 200 300 SWITCH CURRENT (mA) Peak Inductor Current vs Temperature (LT3495-1) 600 VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT 900 800 700 600 –40 0 40 80 TEMPERATURE (°C) 400 3495 G09 INDUCTOR PEAK CURRENT (mA) 1000 16 80 Peak Inductor Current vs Temperature (LT3495) 5 14 120 3495 G08 SHDN Current vs SHDN Voltage 10 12 40 3495 G07 15 8 10 VCC (V) 160 200 0 125 20 6 4 200 50 40 80 TEMPERATURE (°C) 2 SW Saturation Voltage vs Switch Current (LT3495-1) SWITCH VCESAT (mV) SWITCH VCESAT (mV) QUIESCENT CURRENT (μA) 60 0 60 3495 G06 250 90 50 –40 70 50 125 300 70 80 SW Saturation Voltage vs Switch Current (LT3495) 100 80 90 3495 G05 Quiescent Current vs Temperature 0 Quiescent Current - Not Switching 100 QUIESCENT CURRENT (μA) VCC = 3.6V 0.75 VOUT = 16V LOAD = 5mA 0.50 FIGURE 7 CIRCUIT MINIMUM SWITCHING FREQUENCY (kHz) OUTPUT VOLTAGE CHANGE (%) 1.00 –1.00 –40 TA = 25°C unless otherwise noted. 125 3495 G11 FIGURE 9 CIRCUIT 550 500 450 400 350 300 –40 0 40 80 TEMPERATURE (°C) 125 3495 G12 3495b1b1f 4 LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL PERFORMANCE CHARACTERISTICS LT3495 Switching Waveform at 10mA LT3495 Switching Waveform at No Load VOUT VOLTAGE 10mV/DIV AC COUPLED VOUT VOLTAGE 50mV/DIV AC COUPLED SW VOLTAGE 10V/DIV SW VOLTAGE 10V/DIV INDUCTOR CURRENT 100mA/DIV INDUCTOR CURRENT 500mA/DIV VCC = 3.6V VOUT = 16V 10μs/DIV VCC = 3.6V VOUT = 16V 3495 G13 VOUT VOLTAGE 50mV/DIV AC COUPLED VOUT VOLTAGE 20mV/DIV AC COUPLED SW VOLTAGE 10V/DIV SW VOLTAGE 10V/DIV INDUCTOR CURRENT 500mA/DIV INDUCTOR CURRENT 100mA/DIV 500ns/DIV VCC = 5V VOUT = 16V 3495 G15 LT3495B-1 Switching Waveform at 10mA 3495 G14 VOUT VOLTAGE 50mV/DIV AC COUPLED SW VOLTAGE 10V/DIV SW VOLTAGE 10V/DIV INDUCTOR CURRENT 200mA/DIV INDUCTOR CURRENT 200mA/DIV 2μs/DIV 3495 G17 20μs/DIV 3495 G16 LT3495B-1 Switching Waveform at 60mA VOUT VOLTAGE 50mV/DIV AC COUPLED VCC = 5V VOUT = 16V 2μs/DIV LT3495B-1 Switching Waveform at No Load LT3495 Switching Waveform at 80mA VCC = 3.6V VOUT = 16V TA = 25°C unless otherwise noted. VCC = 5V VOUT = 16V 500ns/DIV 3495 G18 3495b1b1f 5 LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL PERFORMANCE CHARACTERISTICS Output Disconnect PMOS Current vs CAP to VOUT Voltage Difference 0.30 600 0.25 500 PMOS CURRENT (mA) OUTPUT VOLTAGE CHANGE (%) Line Regulation 0.20 0.15 0.10 400 AFTER START-UP 300 200 IN START-UP 100 0.05 0 TA = 25°C unless otherwise noted. IN SHUTDOWN 0 0 4 –100 16 8 12 VCC VOLTAGE (V) 3495 G19 0 2 4 6 8 10 12 CAP TO VOUT VOLTAGE DIFFERENCE (V) 3495 G20 LT3495 Start-Up Waveforms SHDN VOLTAGE 5V/DIV INDUCTOR CURRENT 500mA/DIV CAP VOLTAGE 5V/DIV VOUT VOLTAGE 5V/DIV VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT 50μs/DIV 3495 G21 LT3495 Transient Response LT3495-1 Transient Response 20mA → 60mA → 20mA LOAD PULSE 10mA → 30mA → 10mA LOAD PULSE VOUT VOLTAGE 200mV/DIV AC COUPLED VOUT VOLTAGE 200mV/DIV AC COUPLED INDUCTOR CURRENT 500mA/DIV INDUCTOR CURRENT 200mA/DIV LOAD CURRENT 20mA/DIV LOAD CURRENT 20mA/DIV VCC = 3.6V VOUT = 16V FIGURE 7 CIRCUIT 20μs/DIV 3495 G22 VCC = 3.6V VOUT = 16V FIGURE 9 CIRCUIT 20μs/DIV 3495 G23 3495b1b1f 6 LT3495/LT3495B/ LT3495-1/LT3495B-1 PIN FUNCTIONS GND (Pins 1, 2): Ground. Tie directly to local ground plane. achieve the desired output voltage, choose R1 according to the following formula: VCC (Pin 3): Input Supply Pin. Must be locally bypassed. R1 = 76 • (VOUT/1.235 – 1)kΩ VOUT (Pin 7): Drain of Output Disconnect PMOS. Place a bypass capacitor from this pin to GND. See Applications information. CTRL (Pin 4): Dimming Pin. If not used, tie CTRL to 1.5V or higher. If in use, drive CTRL below 1.235V to override the internal reference. See Applications section for more information. CAP (Pins 8, 9): Source of Output Disconnect PMOS. Place a bypass capacitor from this pin to GND. SHDN (Pin 5): Shutdown Pin. Tie to 1.5V or more to enable chip. Ground to shut down. SW (Pin 10): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. FB (Pin 6): Feedback Pin. Minimize the metal trace area to this pin to minimize noise. Reference voltage is 1.235V. There is an internal 76k resistor from the FB pin to GND. To Exposed Pad (Pin 11): Ground. This pin must be soldered to PCB. BLOCK DIAGRAM INPUT R1 6 3 10 VCC FB 76k 9 8 CAP SW 4 5 SHDN + VOUT START-UP CONTROL – CTRL 7 CAP + + DISCONNECT CONTROL SWITCH CONTROL VREF SHUNT CONTROL GND 2 GND 1 11 3495 BD 3495b1b1f 7 LT3495/LT3495B/ LT3495-1/LT3495B-1 OPERATION The LT3495 series utilizes a variable peak current, variable off-time control scheme to provide high efficiency over a wide range of output current. The operation of the part can be better understood by referring to the Block Diagram. The part senses the output voltage by monitoring the voltage on the FB pin. The user sets the desired output voltage by choosing the value of the external top feedback resistor. The parts incorporate a precision 76k bottom feedback resistor. Assuming that output voltage adjustment is not used (CTRL pin is tied to 1.5V or greater), the internal reference (VREF = 1.235V) sets the voltage at which FB will servo to during regulation. The Switch Control block senses the output of the amplifier and adjusts the switching frequency as well as other parameters to achieve regulation. During the start-up of the circuit, special precautions are taken to ensure that the inductor current remains under control. For the LT3495/LT3495-1, the switching frequency is never allowed to fall below approximately 45kHz. Because of this, a minimum load must be present to prevent the output voltage from drifting too high. For most applications, this minimum load is automatically generated within the part via the Shunt Control block. The level of this current is adaptable, removing itself when not needed to improve efficiency at higher load levels. However when the input voltage and output voltage are close, the internal shunt current may not be large enough. Under this condition, a minimum output load is required to prevent the output voltage from drifting too high. For the LT3495B/B-1, the minimum switching frequency feature is disabled and the switching frequency can be as low as zero. As a result, the output voltage will never drift high and no minimum output load is required. The LT3495 series also has a PMOS output disconnect switch. The PMOS switch is turned on when the part is enabled via the SHDN pin. When the parts are in shutdown, the PMOS switch turns off, allowing the VOUT node to go to ground. This type of disconnect function is often required in power supplies. The LT3495 series also sets a maximum switch on time of 10μs. This feature guarantees that the parts can continue to deliver energy to the output even if the input supply impedance becomes so large that the commanded peak switch current is never reached. The difference between the LT3495/LT3495B and LT3495-1/ LT3495B-1 is the level of the current limit. LT3495/LT3495B have a typical peak current limit of 650mA while the LT3495-1/LT3495B-1 have a typical peak current limit of 350mA. The differences between the LT3495 and LT3495B/ LT3495-1/LT3495B-1 are listed in Table 1. Table 1. Difference Between LT3495 and LT3495B/LT3495-1/LT3495B-1 PART SWITCH CURRENT LIMIT (mA) LT3495 650 LT3495B LT3495-1 LT3495B-1 MINIMUM SWITCHING FREQUENCY (kHz) MINIMUM OUTPUT LOAD REQUIREMENT 45 Required under certain conditions 650 0 Not Required 350 45 Required under certain conditions 350 0 Not Required 3495b1b1f 8 LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION Inductor Selection Several inductors that work well with the LT3495/LT3495B are listed in Table 2 and those for the LT3495-1/LT3495B-1 are listed in Table 3. These tables are not complete, and there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts, as many different sizes and shapes are available. Inductors with a value of 3.3μH or higher are recommended for most LT3495 series designs. Inductors with low core losses and small DCR (copper wire resistance) are good choices for LT3495 series applications. For full output power, the inductor should have a saturation current rating higher than the peak inductor current. The peak inductor current can be calculated as: input capacitor and a 1μF to 10μF output capacitor are sufficient for most applications. Always use a capacitor with a sufficient voltage rating. Many capacitors rated at 1μF to 10μF, particularly 0603 case sizes, have greatly reduced capacitance when bias voltages are applied. Be sure to check actual capacitance at the desired output voltage. Generally a 0805 or 1206 size capacitor will be adequate. A 2.2μF capacitor placed on the CAP node is recommended to filter the inductor current while a 1μF to 10μF capacitor placed on the VOUT node will give excellent transient response and stability. Table 4 shows a list of several capacitor manufacturers. Consult the manufacturers for more detailed information and for their entire selection of related parts. Table 3. Recommended Inductors for LT3495-1/LT3495B-1 PART L DCR (μH) (mΩ) where ILIMIT is 0.65A and 0.35A for LT3495/LT3495B and LT3495-1/LT3495B-1 respectively. L is the inductance value in Henrys and VIN is the input voltage to the boost circuit. LPO4815-472MLC LPO4815-682MLC LPO4815-103MLC LPS3008-472MLC LPS3008-682MLC LPS3008-103MLC 4.7 6.8 10 4.7 6.8 10 150 180 230 350 500 650 4.8 × 4.8 × 1.5 Coilcraft 4.8 × 4.8 × 1.5 www.coilcraft.com 4.8 × 4.8 × 1.5 3.0 × 3.0 × 0.8 3.0 × 3.0 × 0.8 3.0 × 3.0 × 0.8 LQH32CN4R7M53 LQH32CN100K33 4.7 10 150 300 3.2 × 2.5 × 1.6 Murata 3.2 × 2.5 × 2.0 www.murata.com Table 2. Recommended Inductors for LT3495/LT3495B CDH28D09/S-6R2 6.2 369 3.3 × 3.0 × 1.0 Sumida www.sumida.com 744030004 4.7 290 3.5 × 3.3 × 1.0 Wurth Elektronik www.weonline.com IPK =ILIMIT + VIN • 200 • 10 L –9 amps SIZE (mm) VENDOR PART L DCR (μH) (mΩ) LPS4018-103ML MSS5131-103MLC LPS3015-472MLC LPS3015-682MLC 10 10 4.7 6.8 200 83 200 300 4.4 × 4.4 × 1.7 Coilcraft 5.1 × 5.1 × 3.1 www.coilcraft.com 3.0 × 3.0 × 1.5 3.0 × 3.0 × 1.5 LQH43CN4R7M03 4.7 150 4.5 × 3.2 × 2.8 Murata www.murata.com MANUFACTURER PHONE WEBSITE Taiyo Yuden (408) 573-4150 www.t-yuden.com CR32-6R8 6.8 202 4.1 × 3.7 × 3.0 Sumida www.sumida.com AVX (843) 448-9411 www.avxcorp.com 3.8 × 3.8 × 1.7 Wurth Elektronik www.weonline.com Murata (814) 237-1431 www.murata.com Kemet (408) 986-0424 www.kemet.com TDK (847) 803-6100 www.tdk.com 744031004 4.7 105 SIZE (mm) VENDOR Table 4. Recommended Ceramic Capacitor Manufacturers Capacitor Selection Diode Selection The small size and low ESR of ceramic capacitors makes them suitable for most LT3495 series applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 4.7μF Schottky diodes, with their low forward voltage drops and fast switching speeds, are recommended for use with the LT3495 series. The Diodes Inc. B0540WS-7 is a very good choice. This diode is rated to handle an average forward current of 0.5A with 40V reverse breakdown. 3495b1b1f 9 LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION Setting Output Voltage and the Auxiliary Reference Input The LT3495 series is equipped with both an internal 1.235V reference and an auxiliary reference input. This allows the user to select between using the built-in reference and supplying an external reference voltage. The voltage at the CTRL pin can be adjusted while the chip is operating to alter the output voltage for purposes such as display dimming or contrast adjustment. To use the internal 1.235V reference, the CTRL pin must be held higher than 1.5V. When the CTRL pin is held between 0V and 1.235V, the parts will regulate the output such that the FB pin voltage is nearly equal to the CTRL pin voltage. At CTRL voltages close to 1.235V, a soft transition occurs between the CTRL pin and the internal reference. Figure 1 shows this behavior. To set the maximum output voltage, select the values of R1 according to the following equation: V R1= 76 • OUT – 1 k 1.235 When CTRL is used to override the internal reference, the output voltage can be lowered from the maximum value down to nearly the input voltage level. If the voltage source driving the CTRL pin is located at a distance to the LT3495, a small 0.1μF capacitor may be needed to bypass the pin locally. Choosing a Feedback Node The single feedback resistor may be connected to the VOUT pin or to the CAP pin (see Figure 2). Regulating the VOUT pin eliminates the output offset resulting from the voltage drop across the output disconnect PMOS. Regulating the CAP pin does not compensate for the voltage drop across the output disconnect, resulting in an output voltage VOUT that is slightly lower than the voltage set by the resistor divider. Under most conditions, it is advised that the feedback resistor be tied to the VOUT pin. Connecting the Load to the CAP Node The efficiency of the converter can be improved by connecting the load to the CAP pin instead of the VOUT pin. The power loss in the PMOS disconnect circuit is then made negligible. By connecting the feedback resistor to the VOUT pin, no quiescent current will be consumed in the feedback resistor string during shutdown since the PMOS transistor will be open (see Figure 3). The disadvantage of this method is that the CAP node cannot go to ground during shutdown, but will be limited to around a diode drop below VCC. Loads connected to the part should only sink current. Never force external power supplies onto the CAP or VOUT pins. C1 SW CAP VCC VOUT VOUT R1 LT3495 1.5 C1 C3 SW CAP VCC VOUT R1 LT3495 SHDN FB SHDN FB CTRL GND CTRL GND 3495 F02 FB VOLTAGE (V) 1.2 Figure 2. Feedback Connection Using the CAP Pin or the VOUT Pin 0.9 0.6 0.3 SW CAP VCC VOUT C1 ILOAD LT3495 0 0 0.3 0.6 0.9 CTRL VOLTAGE (V) 1.2 1.5 3495 F01 Figure 1. CTRL to FB Transfer Curve SHDN FB CTRL GND 3495 F03 Figure 3. Improved Efficiency Connection 3495b1b1f 10 LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION Maximum Output Load Current Inrush Current The maximum output current of a particular LT3495 series circuit is a function of several circuit variables. The following method can be helpful in predicting the maximum load current for a given circuit: When VCC is stepped from ground to the operating voltage while the output capacitor is discharged, a higher level of inrush current may flow through the inductor and Schottky diode into the output capacitor. Conditions that increase inrush current include a larger more abrupt voltage step at VIN, a larger output capacitor tied to the CAP pin and an inductor with a low saturation current. While the chip is designed to handle such events, the inrush current should not be allowed to exceed 1.5A. For circuits that use output capacitor values within the recommended range and have input voltages of less than 5V, inrush current remains low, posing no hazard to the device. In cases where there are large steps at VCC (more than 5V) and/or a large capacitor is used at the CAP pin, inrush current should be measured to ensure safe operation. Step 1: Calculate the peak inductor current: IPK =ILIMIT + VIN • 200 • 10 –9 amps L where ILIMIT is 0.65A and 0.35A for LT3495/LT3495B and LT3495-1/LT3495B-1 respectively. L is the inductance value in Henrys and VIN is the input voltage to the boost circuit. Step 2: Calculate the inductor ripple current: IRIPPLE VOUT + 1– VIN ) • 200 • 10 –9 ( = amps L where VOUT is the desired output voltage. If the inductor ripple current is greater than the peak current, then the circuit will only operate in discontinuous conduction mode. The inductor value should be increased so that IRIPPLE < IPK. An application circuit can be designed to operate only in discontinuous mode, but the output current capability will be reduced. Soft-Start By connecting the SHDN and CTRL pins as shown in Figure 4, using an RC filter at the CTRL pin to limit the start-up current, the LT3495 is able to achieve soft-start. The small bias current of the CTRL pin allows using a small capacitor for a large RC time constant. The softstart waveform is shown in Figure 5. The soft-start time Step 3: Calculate the average input current: IIN(AVG) =IPK – SW CAP VCC VOUT LT3495 IRIPPLE amps 2 CHIP ENABLE RCTRL SHDN FB CTRL GND 3495 F04 Step 4: Calculate the nominal output current: IOUT(NOM) = IIN(AVG) • VIN • 0.8 VOUT CCTRL amps Step 5: Derate output current: IOUT = IOUT(NOM) • 0.8 amps For low output voltages the output current capability will be increased. When using output disconnect (load current taken from VOUT), these higher currents will cause the drop in the PMOS switch to be higher resulting in reduced output current capability than those predicted by the preceding equations. Figure 4. Soft-Start Circuitry SHDN VOLTAGE 5V/DIV INDUCTOR CURRENT 500mA/DIV CTRL VOLTAGE 2V/DIV VOUT VOLTAGE 5V/DIV VCC = 3.6V VOUT = 16V 500μs/DIV 3495 F05 Figure 5. Soft-Start Waveform 3495b1b1f 11 LT3495/LT3495B/ LT3495-1/LT3495B-1 APPLICATIONS INFORMATION can be set by the value of RCTRL and CCTRL. The following expression can be used to design the soft-start time: Also be aware of the thermal dissipation in the PMOS at all times. In addition, if the input voltage is more than 8V, the PMOS will turn on during shutdown, resulting in the output voltage no longer being blocked from the input. Under this condition, the output voltage will be about 8V lower than the input voltage. VSHDN TSTARTUP = RCTRL • CCTRL •In VSHDN – 1.235 where VSHDN is the voltage at SHDN pin when the part is enabled. To ensure soft-start will work, the initial voltage at CTRL pin when the part is enabled should be close to 0V. The soft-start may not work if this initial condition is not satisfied. Board Layout Considerations As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signal of the SW pin has sharp rising and falling edges. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the FB pin feeds into the internal error amplifier and is sensitive to noise. Minimizing the length and area of all traces to this pin is recommended. Connect the feedback resistor R1 directly from the VOUT pin to the FB pin and keep the trace as short as possible. Recommended component placement is shown in Figure 6. Output Disconnect The LT3495 series has an output disconnect PMOS that blocks the load from the input during shutdown. During normal operation, the maximum current through the PMOS is limited by circuitry inside the chip. When the CAP and VOUT voltage difference is more than 8.7V (typ), the current through the PMOS is no longer limited, and can be much higher. As a result, forcing 8.7V or higher voltage from the CAP to the VOUT pins can damage the PMOS. In cases when the CAP voltage is high and/or a large capacitor is used at the CAP pin, shorting VOUT to GND can cause large PMOS currents to flow. Under this condition, the PMOS peak current should be kept at less than 1A. GND SW GND CAP VCC GND CAP CTRL VOUT SHDN FB GND 3495 F06 CTRL SHDN VIAS TO GROUND PLANE REQUIRED TO IMPROVE THERMAL PERFORMANCE VIAS FOR CAP GROUND RETURN THROUGH SECOND METAL LAYER, CAPACITOR GROUNDS MUST BE RETURNED DIRECTLY TO IC GROUND Figure 6. Recommended Board Layout 3495b1b1f 12 LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATIONS L1 10μH C1 4.7μF 90 CAP VOUT OUTPUT 16V 70mA R1 909k LT3495 TURN ON/OFF SHDN FB VOUT DIMMING CTRL GND C3 1μF 400 VIN = 3.6V LOAD FROM CAP 80 3495 F07a C1: 4.7μF, 6.3V, X5R, 0603 C2: 2.2μF, 25V, X5R, 0805 C3: 1μF, 25V, X5R, 0603 D1: DIODES INC. B0540WS-7 L1: COILCRAFT LPS4018-103MLB 320 LOAD FROM VOUT 70 240 60 160 50 80 40 0.1 POWER LOSS (mW) SW VCC C2 2.2μF EFFICIENCY (%) ONE Li-Ion CELL Efficiency vs Load Current D1 0 100 1 10 LOAD CURRENT (mA) 3495 F07b Figure 7. One Li-Ion Cell Input Boost Converter with the LT3495 Efficiency vs Load Current L1 6.8μH C1 4.7μF 90 CAP VCC VOUT OUTPUT 16V 70mA R1 909k LT3495B TURN ON/OFF SHDN FB VOUT DIMMING CTRL GND C3 1μF 3495 F08a C1: 4.7μF, 6.3V, X5R, 0603 C2: 2.2μF, 25V, X5R, 0805 C3: 1μF, 25V, X5R, 0603 D1: DIODES INC. B0540WS-7 L1: SUMIDA CR32-6R8 400 VIN = 3.6V LOAD FROM CAP 320 80 LOAD FROM VOUT 70 240 60 160 50 80 40 0.1 1 10 LOAD CURRENT (mA) POWER LOSS (mW) SW C2 2.2μF EFFICIENCY (%) ONE Li-Ion CELL D1 0 100 3495 F08b Figure 8. One Li-Ion Cell Input Boost Converter with the LT3495B LT3495/LT3495B Maximum Output Current vs Output Voltage VOUT R1 VALUE REQUIRED (MΩ) MAXIMUM OUTPUT CURRENT AT 3V INPUT (mA) 40 2.37 26 35 2.05 31 30 1.78 37 25 1.47 43 20 1.15 57 15 0.845 74 10 0.536 120 5 0.232 250 3495b1b1f 13 LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATIONS Efficiency vs Load Current L1 10μH C1 2.2μF 90 CAP VCC VOUT OUTPUT 16V 30mA LT3495B-1/ LT3495-1 TURN ON/OFF SHDN FB VOUT DIMMING CTRL GND 909k C3 1μF 250 VIN = 3.6V LOAD FROM CAP 80 3495 F09a C1: 2.2μF, 6.3V, X5R, 0603 C2: 1μF, 25V, X5R, 0603 C3: 1μF, 25V, X5R, 0603 D1: DIODES INC. B0540WS-7 L1: MURATA LQH32CN100K33 200 70 150 LOAD FROM VOUT 60 100 50 50 40 0.1 POWER LOSS (mW) SW C2 1μF EFFICIENCY (%) ONE LI-ION CELL D1 0 100 1 10 LOAD CURRENT (mA) 3495 F09b Figure 9. One Li-Ion Cell Input Boost Converter with the LT3495-1/LT3495B-1 LT3495-1/LT3495B-1 Maximum Output Current vs Output Voltage VOUT R1 VALUE REQUIRED (MΩ) MAXIMUM OUTPUT CURRENT AT 3V INPUT (mA) 40 2.37 12 35 2.05 15 30 1.78 18 25 1.47 21 20 1.15 28 15 0.845 36 10 0.536 63 5 0.232 120 5V to 12V, 130mA Boost Converter Efficiency vs Load Current 100 L1 10μH SW CAP VCC VOUT LT3495B VOUT = 12V 130mA 665k TURN ON/OFF SHDN FB VOUT DIMMING CTRL GND 3495 TA02a C1: 4.7μF, 6.3V, X5R, 0603 C2: 2.2μF, 25V, X5R, 0805 C3: 10μF, 25V, X5R, 1206 D1: DIODES INC. B0540WS-7 L1: COILCRAFT LPS4018-103MLB LOAD FROM CAP 90 C2 2.2μF C3 10μF 750 LOAD FROM VOUT 80 600 70 450 60 300 50 150 40 0.1 1 10 100 LOAD CURRENT (mA) POWER LOSS (mW) C1 4.7μF D1 EFFICIENCY (%) VIN = 5V 900 0 1000 3495 TA02b 3495b1b1f 14 LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATIONS Wide Input Range SEPIC Converter with 5V Output C2 1μF L1 10μH 1000 80 SW CAP VCC VOUT L2 10μH LT3495B 232k TURN ON/OFF SHDN FB VOUT DIMMING CTRL GND C3 10μF VOUT = 5V 200mA, VIN = 3.3V, 300mA, VIN = 5V, 500mA, VIN = 8V 800 70 600 60 400 50 3495 TA03a 200 40 0.1 C1: 2.2μF, 16V, X5R, 0805 C2: 1μF, 16V, X5R, 0805 C3: 10μF, 16V, X5R, 1206 D1: FAIRCHILD SEMI MBR0540 L1, L2: COILCRAFT LPS4018-103MLB POWER LOSS (mW) C1 2.2μF 1200 VCC = 3.3V D1 EFFICIENCY (%) INPUT 2.6V TO 12V Efficiency vs Load Current 90 1 0 1000 10 100 LOAD CURRENT (mA) 3495 TA03b PACKAGE DESCRIPTION DDB Package 10-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1722 Rev Ø) 0.64 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 6 0.40 ± 0.10 10 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.39 ±0.05 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 2.00 ±0.10 (2 SIDES) 0.75 ±0.05 0.64 ± 0.05 (2 SIDES) 5 0.25 ± 0.05 0 – 0.05 PIN 1 R = 0.20 OR 0.25 × 45° CHAMFER 1 (DDB10) DFN 0905 REV Ø 0.50 BSC 2.39 ±0.05 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3495b1b1f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LT3495/LT3495B/ LT3495-1/LT3495B-1 TYPICAL APPLICATION Adjustable High Voltage Power Supply Doesn’t Need a Transformer Output vs CTRL 150 DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY 3.3V TO 8V INPUT L1 22μH C6 1μF D5 C1 4.7μF D1 SW CAP VCC VOUT SHDN VOUT DIMMING CTRL D2 D3 C5 1μF 909k FB GND C1: 4.7μF, 16V, X5R, 0805 C2-C7: 1μF, 50V, X5R, 0805 D1-D5: DIODE INC. B0540WS-7 L1: COILCRAFT LPS4018-223MLB D4 C7 1μF C3 1μF LT3495B TURN ON/OFF C2 1μF 120 VOUT VOLTAGE (V) C4 1μF 10.7k 0 0.3 0.6 0.9 1.2 1.5 CTRL VOLTAGE (V) 1.8 2.1 3495 TA04b Output Voltage Ripple vs Load Current 700 VOUT PEAK-TO-PEAK RIPPLE (mV) 600 VIN = 5V VOUT = 120V 500 70 400 60 300 50 200 40 100 30 0.1 0 3495 TA04a POWER LOSS (mW) EFFICIENCY (%) 80 60 30 VOUT 15V TO 120V 10mA (VIN = 3.3V) 18mA (VIN = 5V) 35mA (VIN = 8V) Efficiency vs Load Current 90 90 1 10 LOAD CURRENT (mA) 500 400 300 200 100 0 0 100 VIN = 5V VOUT = 120V 600 0 4 8 16 12 LOAD CURRENT (mA) 20 3495 TA04d 3495 TA04c RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1930/LT1930A 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Step-Up DC/DC Converters VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.5mA, ISD <1μA, ThinSOT Package LT1945 (Dual) Dual Output, Boost/Inverter, 350mA (ISW), Constant OffTime, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = ±34V, IQ = 40μA, ISD <1μA, 10-Lead MS Package LT1946/LT1946A 1.5A (ISW), 1.2MHz/2.7MHz, High Efficiency Step-Up DC/DC Converters VIN: 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD <1μA, 8-Lead MS Package LT3463/LT3463A Dual Output, Boost/Inverter, 250mA (ISW), Constant VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40μA, ISD <1μA, Off-Time, High Efficiency Step-Up DC/DC Converters with DFN Package Integrated Schottkys LT3467/LT3467A 1.1A (ISW), 1.3MHz/2.1MHz, High Efficiency Step-Up DC/DC Converters with Soft-Start VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD <1μA, ThinSOT Package LT3471 Dual Output, Boost/Inverter, 1.3A (ISW), High Efficiency Boost-Inverting DC/DC Converter VIN: 2.4V to 16V, VOUT(MAX) = ±40V, IQ = 2.5mA, ISD <1μA, DFN Package LT3473/LT3473A 1A (ISW), 1.2MHz, High Efficiency Step-Up DC/DC Converters with Integrated Schottky Diode and Output Disconnect VIN: 2.2V to 16V, VOUT(MAX) = 36V, IQ = 100μA, ISD <1μA, DFN Package LT3494/LT3494A 180mA/350mA (ISW), High Efficiency Step-Up DC/DC Converters with Output Disconnect VIN: 2.1V to 16V, VOUT(MAX) = 40V, IQ = 65μA, ISD <1μA, DFN Package LT3580 2A, 40V, 2.5MHz Boost DC/DC Converter VIN: 2.5V to 32V, VOUT(MAX) = 40V, IQ = 1mA, ISD <1μA, MS8E 3mm × 3mm DFN-8 Package 3495b1b1f 16 Linear Technology Corporation LT 0708 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008