LTC3458 1.4A, 1.5MHz Synchronous Step-Up DC/DC Converter with Output Disconnect DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency: Up to 93% Inrush Current Limiting and Output Disconnect Programmable Output Voltages up to 7.5V 1.5V to 6V Input Range Programmable/Synchronizable Fixed Frequency Operation up to 1.5MHz Programmable Automatic Burst Mode® Operation Current Mode Control with Programmable Soft-Start Period and Peak Current Limit 700mA at 7V from 5V Input 0.3Ω N-Channel and 0.4Ω P-Channel 1.4A Switches at 5VOUT Ultralow Quiescent Currents: 15µA Sleep, <1µA in Shutdown 3mm × 4mm Thermally Enhanced DFN Package U APPLICATIO S ■ ■ ■ Point-of-Load Regulators USB VBUS Power LCD Bias OLED Displays Quiescent current is only 15µA during Burst Mode operation maximizing battery life in portable applications. The Burst Mode current threshold, peak current limit, and softstart are externally programmable. Other features include <1µA shutdown current, antiringing control, and thermal limit. The LTC3458 is available in a low profile (0.75mm), 3mm × 4mm 12-pin DFN package. , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. U ■ The LTC®3458 is a high efficiency, current mode, fixed frequency, step up DC/DC converter with true output disconnect and inrush current limiting. The LTC3458 is rated for a 7.5V output and includes a 0.3Ω N-channel MOSFET switch and a 0.4Ω P-channel MOSFET synchronous rectifier. The LTC3458 is well suited for battery powered applications and includes programmable output voltage, switching frequency and loop compensation. The oscillator frequency can be set up to 1.5MHz or synchronized to an external clock. TYPICAL APPLICATIO USB to 7V at 1MHz COEV 10µH DQ7545 USB to 7VOUT 1000 100 SW VIN 95 LTC3458 2.2µF VOUT 10pF ON OFF SHDN FB SYNC COMP 200k 124k 4.35VIN 10 85 POWER LOSS 80 33k SS 0.01µF ILIM 90 316k 0.01µF RT 1.5M 5.25VIN POWER LOSS (mW) GND/PGND VOUT 7V 500mA EFFICIENCY USB 4.35V to 5.25V 75 22µF X5R 10pF BURST 133k 560pF 70 0.1 1 10 100 LOAD CURRENT (mA) 0.1 1000 3458 TA01b 3458 TA01a 3458f 1 LTC3458 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART NUMBER TOP VIEW VIN, SS, SYNC Voltages ................................. –0.3 to 7V BURST, SHDN, VOUT Voltages ....................... –0.3 to 8V Operating Temperature Range (Notes 2, 3) .........................................–40°C to 85°C Storage Temperature Range ..................–65°C to 125°C SW Voltage DC ........................................................... –0.3V to 8V Pulsed <100ns ...................................... –0.3V to 10V SW 1 12 VOUT VIN 2 11 BURST SYNC 3 SHDN 4 ILIM RT LTC3458EDE 10 SS 13 9 GND 5 8 COMP 6 7 FB DE PART MARKING 3458 DE12 PACKAGE 12-LEAD (4mm × 3mm) PLASTIC DFN EXPOSED PAD IS PGND (PIN 13), MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 45°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V, VOUT = 5V, RT = 200k, unless otherwise noted. PARAMETER CONDITIONS Minimum VIN Operating Voltage TA = 0°C to 85°C TA = –40°C to 0°C MIN ● Output Voltage Adjust Range TYP MAX 1.4 1.4 1.5 1.7 V V 7.5 V 1.25 1.25 V V 2.0 1.21 1.20 1.23 UNITS Feedback Voltage 0°C to 85°C, VOUT = 3.3V –40°C to 0°C Undervoltage (Exit Burst Mode Operation) Below Feedback Voltage Feedback Input Current VFB = 1.23V 1 50 nA Quiescent Current - Burst Mode Operation VIN Current at 3.3V VOUT Current at 5V 15 5 30 10 µA µA Quiescent Current - Shutdown VIN Current at 3.3V VOUT Current at 0V 0.5 1 1 3 µA µA Quiescent Current - Active VIN Current Switching –4% V 1 3 mA NMOS Switch Leakage ● 0.05 5 µA PMOS Switch Leakage ● 0.05 5 µA NMOS Switch On Resistance VOUT = 5V 0.3 Ω PMOS Switch On Resistance VOUT = 5V 0.4 Ω Fixed NMOS Current Limit RILIM = 124k ● 1.4 1.6 A Maximum Duty Cycle VIN = 3.3V, fOSC = 1MHz ● 80 90 ● Minimum Duty Cycle Frequency Accuracy RT = 200k ● % 0 0.85 Error Amplifier Transconductance 1 1.15 100 % MHz µA/V Error Amplifier Source Current 7 µA Error Amplifier Sink Current 7 µA SYNC Input High ● SYNC Input Low ● 1.5 V 0.35 V 3458f 2 LTC3458 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V, VOUT = 5V, RT = 200k, unless otherwise noted. PARAMETER CONDITIONS MIN SHDN Input High ● SHDN Input Low ● BURST Mode Peak Current TYP 0.3 RILIM = 124k U W ILIMIT, IBURST, TZERO Currents Current Limit Accuracy 15 1000 800 600 IBURST PEAK 400 CURRENT (µA) 1200 CURRENT (A) CURRENT (mA) VIN = 3.3V VOUT = 5V 1,7 VOUT = 7V L = 10µH RILIM = 124k 1.6 10 IVOUT IZERO 0 –200 2.0 2.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 1.4 –45 –30 –15 5.5 0 15 30 45 60 TEMPERATURE (°C) 3458 G01 60 85 Oscillator Programming Resistor 550 7.5VOUT 500 450 INTO BURST 150 RT (kΩ) CURRENT (mA) 100 5VOUT 3.3VOUT 200 OUT OF BURST 35 10 TEMPERATURE (°C) 600 RILIM = 124k 120 –15 3458 G03 Maximum Load Current in Burst 140 60 0 –40 90 250 160 80 75 3458 G02 Typical Burst Mode Threshold and Hysteresis vs RBURST CURRENT (mA) IVIN 5 1.5 200 V Burst Mode Quiescent Current RILIMIT = 124k 1400 A 20 ILIMIT 1600 0.4 1.10 (TA = 25°C unless otherwise specified) 1.8 1800 V Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 3: The LTC3458 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. TYPICAL PERFOR A CE CHARACTERISTICS 2000 UNITS V BURST Threshold Voltage Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. MAX 1.25 100 400 350 300 250 40 200 50 20 0 50 150 100 150 200 RBURST (kΩ) 250 300 0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) 3458 G04 3458 G05 100 400 600 1000 1200 1400 800 OSCILLATOR FREQUENCY (kHz) 3458 G06 3458f 3 LTC3458 U W TYPICAL PERFOR A CE CHARACTERISTICS Frequency Accuracy Efficiency vs Frequency 1.01 0.99 0.4 91 89 87 0.97 0.95 –45 –30 –15 0 15 30 45 60 TEMPERATURE (°C) 75 85 500 90 0.3 N-CHANNEL 0.2 700 1100 1300 900 FREQUENCY (kHz) 0 –40 1500 –15 35 10 TEMPERATURE (°C) 60 3458 G08 1200 85 3458 G09 SHDN Pin Threshold and Hysteresis Maximum Load Current 1.8 to 5.5VIN at 700kHz RILIM = 124k P-CHANNEL 0.1 3458 G07 SYNC Pin Threshold 1.5 1.0 5VOUT 1.4 0.9 1.3 3.3VOUT 600 7.5VOUT OPERATING 0.8 0.7 SHUTDOWN 400 1.2 1.1 1.0 0.6 200 0 1.5 2.0 VOLTAGE (V) 800 VOLTAGE (V) MAX LOAD CURRENT (mA) VIN = 3.3V VOUT = 5V 93 EFFICIENCY (%) FREQUENCY (MHz) 0.5 VIN = 3.3V VOUT = 5V at 100mA RT = 200k 1.03 1000 N-Channel and P-Channel RDS(ON) 95 RDS(ON) (Ω) 1.05 (TA = 25°C unless otherwise specified) 2.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 0.9 0.5 –45 –30 –15 5.5 0 15 30 45 60 TEMPERATURE (°C) 75 90 3458 G11 3458 G10 0.8 –45 –30 –15 0 15 30 45 60 TEMPERATURE (°C) 75 90 3458 G12 FB Voltage 1.25 VOLTAGE (V) 1.24 1.23 1.22 1.21 1.20 –45 –30 –15 0 15 30 45 60 TEMPERATURE (°C) 75 90 3458 G13 3458f 4 LTC3458 U W TYPICAL PERFOR A CE CHARACTERISTICS Fixed Frequency (FF) Discontinuous Current Fixed Frequency (FF) Continuous Current IL 200mA/DIV SW 2V/DIV SW 2V/DIV IL 100mA/DIV 0mA 0mA VIN = 3.3V VOUT = 7V L = 10µH VIN = 3.3V VOUT = 7V L = 10µH 200ns/DIV Over-Current with 1.5A ILIMIT 200ns/DIV Burst Mode Operation VOUT 100mV/DIV SW 2V/DIV SW 5V/DIV IL 0.5A/DIV IL 200mA/DIV 0mA VIN = 3.3V VOUT = 7V L = 10µH RILIM = 133k VIN = 3.3V VOUT = 7V L = 10µH COUT = 22µF CFF = 22pF 1µs/DIV Burst Mode Operation Close-Up 0mA 50µs/DIV Soft-Start into 50Ω Load VOUT 100mV/DIV VOUT 2V/DIV VIN 2V/DIV SW 5V/DIV SS 200mV/DIV IL 200mA/DIV IL 200mA/DIV 0mA VIN = 3.3V VOUT = 7V L = 10µH COUT = 22µF CFF = 22pF 2µs/DIV VIN = 3.3V VOUT = 7V L = 10µH 5ms/DIV 3458f 5 LTC3458 U W TYPICAL PERFOR A CE CHARACTERISTICS Sync Operation at 1.33MHz FF Mode 100-300mA Load Step SW 5V/DIV VOUT 200mV/DIV SYNC 2V/DIV COMP 500mV/DIV IL 200mA/DIV IL 0.5A/DIV 0mA 0mA VIN = 3.3V VOUT = 7V ROSC = 200k 500ns/DIV VIN = 3.3V VOUT = 5V RZ = 33K CC1 = 270pF CC2 = 10pF COUT = 22µF 200µs/DIV L = 10µH F = 1MHz Auto Mode 10mA to 100mA Load Step Burst Mode Operation 10mA to 50mA Load Step VOUT 200mV/DIV VOUT 200mV/DIV BURST 500mV/DIV 50mA LOAD 10mA BURST 1V/DIV 100mA LOAD 10mA IL 200mA/DIV IL 200mA/DIV VIN = 3.3V VOUT = 5V L = 10µH COUT = 22µF 500µs/DIV VIN = 3.3V VOUT = 5V L = 10µH CBURST = 0.015µF RBURST = 133k 200µs/DIV 10mA to 200mA Load Step Showing UV Trip Forced BURST to FF Mode Switch with 50mA Load VOUT 200mV/DIV VOUT 200mV/DIV –4% FIXED FREQUENCY VIN = 3.3V VOUT = 5V L = 10µH RZ = 33k CC1 = 270pF CC2 = 10pF COUT = 22µF BURST VIN = 3.3V VOUT = 5V L = 10µH CBURST = 0.015µF RBURST = 133k IL 200mA/DIV 200µs/DIV IL 500mA/DIV 200µs/DIV 3458f 6 LTC3458 U U U PI FU CTIO S SW (Pin 1): Switch Pin for Inductor Connection. During discontinuous conduction mode an antiring resistor connects SW to VIN to reduce noise. VIN (Pin 2): Input Supply Pin. Connect this to the input supply and decouple with 1µF minimum. SYNC (Pin 3): Oscillator Synchronization Pin. A clock pulse width of 100ns to 2µs is required to synchronize the internal oscillator. This pin is disabled when grounded. SHDN (Pin 4): Shutdown Pin. Grounding this pin shuts down the IC. Connect to >1.25V to enable. ILIM (Pin 5): Adjustable Peak Current Limit. Connect a resistor from ILIM to GND to program the peak inductor current according to the following formula: 200 RILIM where ILIMIT is in amps and RT is in kΩ. ILIMIT = RT (Pin 6): Connect a resistor to ground to program the oscillator frequency, according to the formula: 1 0.2 + 0.004 • RT where fOSC is in MHz and RT is in kΩ. fOSC = FB (Pin 7): Connect Resistor Divider Tap Here. The output voltage can be adjusted from 2V to 7.5V. Feedback reference voltage is typically 1.23V. GND (Pin 9): Signal Ground Pin. SS (Pin 10): Connect a capacitor between this pin and ground to set soft-start period. 5µA of current is sourced from SS during soft-start. t(msec) = CSS (µF )• 200 BURST (Pin 11): Burst Mode Threshold Adjust Pin. A resistor/capacitor combination from this pin to ground programs the average load current at which automatic Burst Mode operation is entered, according to the formula: RBURST = 10 IBURST where RBURST is in kΩ and IBURST is in amps. C BURST = C OUT • VOUT 10, 000 where CBURST(MIN) and COUT are in µF. To force fixed frequency PWM mode, connect BURST to VOUT through a 50k resistor. VOUT (Pin 12): Output of the Synchronous Rectifier and Internal Gate Drive Source for the Power Switches. ⎛ R2⎞ VOUT = 1.23⎜ 1 + ⎟ ⎝ R1⎠ Exposed Pad (PGND) (Pin 13): Must be soldered to PCB ground, for electrical contact and optimum thermal performance. COMP (Pin 8): gm Error Amp Output. A frequency compensation network is connected from this pin to ground to compensate the loop. See the section “Compensating the Feedback Loop” for guidelines. 3458f 7 LTC3458 W BLOCK DIAGRA BURST SW VCC 11 1 2 VCC 3 OSC/SYNC RT 6 MAX DUTY CLOCK SYNC ANTIRING SLOPE UNDER BURST MODE CONTROL P-DRIVE N-DRIVE + MODE VBEST IZERO SW1 IZERO DETECT P-DRIVE PWM AND BURST MODE 12 VOUT N-DRIVE P-DRIVE DRIVE LOGIC 4% UNDERVOLTAGE UNDER SLEEP IPEAK – VSELECT MODE FIXED FREQUENCY BURST MODE MUX SLEEP CONTROL ICOMP/LIMIT_PEAK IBURST_PEAK SLOPE PGND SLEEP TO ALL BLOCKS BURST ACTIVE – 7 FB VCC + (DISABLED IN BURST MODE) PEAK CURRENT COMPARATOR ICOMP, ILIMIT, IBURST_PEAK, SLOPE COMP ERROR AMPLIFIER/ BURST COMPARATOR BIAS CURRENTS MODE I_SENSE UVLO REFERENCE/ BIAS TSD VBEST SOFT-START THERMAL SD N-DRIVE SD SDB TO ALL BLOCKS PGND 9 5 13 10 8 4 GND ILIM PGND SS COMP SHDN 3458 BD U W U U APPLICATIO S I FOR ATIO Detailed Description LTC3458 Programmable Functions The LTC3458 provides high efficiency, low noise power for boost applications with output voltages up to 7.5V. The true output disconnect feature eliminates inrush current, and allows VOUT to go to zero during shutdown. The current mode architecture with adaptive slope compensation provides ease of loop compensation with excellent transient load response. The low RDS(ON), low gate charge synchronous switches eliminate the need for an external Schottky rectifier, and provide efficient high frequency pulse width modulation (PWM) control. High efficiency is achieved at light loads when Burst Mode operation is entered, where the IC’s quiescent current is a low 15µA typical on VIN. The LTC3458 is designed to provide custom performance in a variety of applications with programmable feedback, current limit, oscillator frequency, softstart, and Burst Mode threshold. Current Limit/Peak Burst Current. The programmable current limit circuit sets the maximum peak current in the internal N-channel MOSFET switch. This clamp level is programmed using a resistor to ground on ILIM. In Burst Mode operation, the current limit is automatically set to ~1/4 of the programmed current limit for optimal efficiency. A 124k RILIM resistor is recommended in most applications unless a lower limit is needed to prevent the external inductor from saturating. ILIM = 200 R I is in amps and R is in kΩ. IBURSTPEAK ≈ 1 • ILIM 4 3458f 8 LTC3458 U W U U APPLICATIO S I FOR ATIO Error Amp. The error amplifier is a transconductance type, with its positive input internally connected to the 1.23V reference, and its negative input connected to FB. A simple compensation network is placed from COMP to ground. Internal clamps limit the minimum and maximum error amp output voltage for improved large signal transient response. During sleep (in Burst Mode), the compensation pin is high impedance, however clamps limit the voltage on the external compensation network, preventing the compensation capacitor from discharging to zero during the sleep time. Oscillator. The frequency of operation is set through a resistor from RT to ground. An internally trimmed timing capacitor resides inside the IC. The oscillator frequency is calculated using the following formula: fOSC = 1 0.2 + 0.004 • RT where fOSC is in MHz and RT is in kΩ The oscillator can be synchronized with an external clock applied to the SYNC pin. When synchronizing the oscillator, the free running frequency must be set to approximately 30% lower than the desired synchronized frequency. Soft-Start. The soft-start time is programmed with an external capacitor to ground on SS. An internal current source charges it with a nominal 5µA. The voltage on the SS pin (in conjunction with the external resistor on ILIM) is used to control the peak current limit until the voltage on the capacitor exceeds ~1V, at which point the external resistor sets the peak current. In the event of a commanded shutdown, severe short-circuit, or a thermal shutdown, the capacitor is discharged automatically. t(msec) = CSS (µF) • 200 Current Sensing. Lossless current sensing converts the peak current signal to a voltage to sum in with the internal slope compensation. This summed signal is compared to the error amplifier output to provide a peak current control command for the PWM. The slope compensation in the IC is adaptive to the input and output voltage, therefore the converter provides the proper amount of slope compensation to ensure stability, but not an excess to cause a loss of phase margin in the converter. Output Disconnect and Inrush Limiting. The LTC3458 is designed to allow true output disconnect by eliminating body diode conduction of the internal P-channel MOSFET rectifier. This allows V0UT to go to zero volts during shutdown, drawing no current from the input source. It also allows for inrush current limiting at turn-on, minimizing surge currents seen by the input supply. Note that to obtain the advantages of output disconnect, there must be no external Schottky diodes connected between SW and VOUT. Shutdown. The part is shut down by pulling SHDN below 0.3V, and made active by pulling the pin above 1.25V. Note that SHDN can be driven above VIN or VOUT, as long as it is limited to less than 8V. Synchronous Rectifier. To prevent the inductor current from running away, the P-channel MOSFET synchronous rectifier is only enabled when VOUT > (VIN + 0.25V). Thermal Shutdown. If the die temperature reaches approximately 150°C, the part will go into thermal shutdown and all switches will be turned off and the soft-start capacitor will be reset. The part will be enabled again when the die temperature has dropped by 10°C (nominal). Zero Current Amplifier. The zero current amplifier monitors the inductor current to the output and shuts off the synchronous rectifier once the current is below 50mA typical, preventing negative inductor current. Other LTC3458 Features and Functions Antiringing Control. The antiringing control places a resistor across the inductor to damp the ringing on SW pin discontinuous conduction mode. The LC ringing (L = inductor, CSW = Capacitance on SW pin) is low energy, but can cause EMI radiation. Burst Mode Operation Burst Mode operation can be automatic or user controlled. In automatic operation, the IC will automatically enter Burst Mode operation at light load and return to fixed frequency PWM mode for heavier loads. The user can program the average load current at which the mode 3458f 9 LTC3458 U W U U APPLICATIO S I FOR ATIO transition occurs using a single resistor. During Burst Mode operation, the oscillator is shut down, since the on time is determined by the time it takes the inductor current to reach a fixed peak current, and the off time is determined by the time it takes for the inductor current to return to zero. In Burst Mode operation, the IC delivers energy to the output until it is regulated and then goes into a sleep mode where the outputs are off and the IC is consuming only 15µA of quiescent current. In this mode the output ripple voltage has a variable frequency component with load current and will be typically 2% peak-to-peak. This maximizes efficiency at very light loads by minimizing switching and quiescent losses. Burst Mode ripple can be reduced slightly by using more output capacitance (22µF or greater). This capacitor does not need to be a low ESR type if low ESR ceramics are also used. Another method of reducing Burst Mode ripple is to place a small feedforward capacitor across the upper resistor in the VOUT feedback divider network. During Burst Mode operation, COMP is disconnected from the error amplifier in an effort to hold the voltage on the external compensation network where it was before entering Burst Mode operation. To minimize the effects of leakage current and stray resistance, voltage clamps limit the minimum and maximum voltage on COMP during Burst Mode operation. This minimizes the transient experienced when a heavy load is suddenly applied to the converter after being in Burst Mode operation for an extended period of time. For automatic operation, an RC network should be connected from BURST to ground. The value of the resistor will control the average load current (IBURST) at which Burst Mode operation will be entered and exited (there is hysteresis to prevent oscillation between modes). The equation given for the capacitor on BURST is for the minimum value, to prevent ripple on the BURST pin from causing the part to oscillate in and out of Burst Mode operation at the current where the mode transition occurs. RBURST = 10 C BURST = C OUT • VOUT 10, 000 where CBURST(MIN) and COUT are in µF. Note: the BURST pin only sources current based on current delivered to VOUT through the P-channel MOSFET. If current in the inductor is allowed to go negative (this can occur at very light loads and high step-up ratios), the burst threshold may become inaccurate, preventing the IC from entering Burst Mode operation. For RBURST values greater than 200k, a larger than recommended inductor value may be needed to ensure positive inductor current and automatic Burst Mode operation. In the event that a sudden load transient causes the voltage level on FB to drop by more than 4% from the regulation value, an internal pull-up is applied to BURST, forcing the part quickly out of Burst Mode operation. For optimum transient response when going between Burst Mode operation and PWM mode, Burst can be controlled manually by the host. This way PWM mode can be commanded before the load step occurs, minimizing output voltage drop. Note that Burst Mode operation is inhibited during start-up and soft-start. Manual Control For applications requiring fixed frequency operation at all load currents, connect the BURST pin to VOUT through a 50kΩ resistor. To force Burst Mode operation, ground the BURST pin. For applications where a large load step can be anticipated, the circuit below can be used to reduce the voltage transient on VOUT. Automatic operation is achieved when the external PMOS is off and fixed frequency operation is commanded when the external PMOS is on. In shutdown, the PMOS should be off. VIN HIGH: AUTO MODE LOW: FIXED FREQUENCY PMOS BURST 133k 0.01µF IBURST 3458 FO2 where RBURST is in kΩ and IBURST is in amps. Figure 1 3458f 10 LTC3458 U W U U APPLICATIO S I FOR ATIO COMPONENT SELECTION Some example inductor part types are: Inductor Selection The high frequency operation of the LTC3458 allows for the use of small surface mount inductors. Since the internal slope compensation circuit relies on the inductor’s current slope and frequency, Table 1 should be used to select an inductor value for a given frequency of operation (± 25%). The recommended value will yield optimal transient performance while maintaining stable operation. Inductor values larger than listed in Table 1 are permissible to reduce the current ripple. Table 1. Recommended Inductor Values Frequency Inductor Value(µH) 1.5MHz 3.3 to 4.7 1.25MHz 4.7 to 6.8 1MHz 6.8 to 10 750Hz 10 to 15 500kHz 15 to 22 For high efficiency, choose an inductor with high frequency core material, such as ferrite, to reduce core losses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses, and must be able to handle the peak inductor current without saturating. Molded chokes or chip inductors usually do not have enough core to support peak inductor currents in the 1A to 3A region. To minimize radiated noise, use a toroidal or shielded inductor. (Note that the inductance of shielded types will drop more as current increases, and will saturate more easily). See Table 2 for a list of inductor manufacturers. Table 2. Inductor Vendor Information Supplier Phone Website Coilcraft (847) 639-6400 www.coilcraft.com TDK (847) 803-6100 www.component.tdk.com Murata Sumida USA: (814) 237-1431 (800) 831-9172 USA: (847) 956-0666 Japan: 81-3-3607-5111 www.murata.com www.japanlink.com/sumida COEV (800) 227-7040 www.coev.net Toko .. Wurth (847) 297-0070 www.tokoam.com (202) 785-8800 www.we-online.com Coilcraft: DO1608 and MSS5131 Series TDK: RLF5018T and SLF7045 Series Murata: LQH4C and LQN6C Series Sumida: CDRH4D28 and CDRH6D28 Series COEV: DQ7545 Series TOKO: D62CB and D63LCB Series .. WURTH: WE-PD2 Series Output Capacitor Selection The output voltage ripple has three components to it. The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The max ripple due to charge is given by: VRBULK = IP • VIN C OUT • VOUT • f where IP = peak inductor current and f = switching frequency. The ESR (equivalent series resistance) is usually the most dominant factor for ripple in most power converters. The ripple due to capacitor ESR is given by: VRCESR = IP • CESR where CESR = Capacitor Series Resistance. The ESL (equivalent series inductance) is also an important factor for high frequency converters. Using small, surface mount ceramic capacitors, placed as close as possible to the VOUT pins, will minimize ESL. Low ESR/ESL capacitors should be used to minimize output voltage ripple. For surface mount applications, AVX TPS Series tantalum capacitors, Sanyo POSCAP, or Taiyo Yuden X5R type ceramic capacitors are recommended. For through-hole applications, Sanyo OS-CON capacitors offer low ESR in a small package size. In all applications, a minimum of 4.7µF (generally 22µF is recommended), low ESR ceramic capacitor should be placed as close to the VOUT pin as possible, and grounded to a local ground plane. 3458f 11 LTC3458 U W U U APPLICATIO S I FOR ATIO Input Capacitor Selection Compensating the Feedback Loop The input filter capacitor reduces peak currents drawn from the input source and reduces input switching noise. In most applications >1µF per amp of peak input current is recommended. See Table 3 for a list of capacitor manufacturers for input and output capacitor selection. The LTC3458 uses current mode control, with internal adaptive slope compensation. Current mode control eliminates the 2nd order filter due to the inductor and output capacitor exhibited in voltage mode controllers, and simplifies the power loop to a single pole filter response. The product of the modulator control to output DC gain, and the error amp open-loop gain gives the DC gain of the system: Table 3. Capacitor Vendor Information Supplier Phone Website AVX (803) 448 - 9411 www.avxcorp.com Sanyo (619) 661 - 6322 www.sanyovideo.com TDK (847) 803 - 6100 www.component.tdk.com Murata Taiyo Yuden USA: (814) 237-1431 (800) 831-9172 (408) 573 - 4150 G DC = G CONTROL • G EA • www.murata.com www.t-yuden.com Operating Frequency Selection There are several considerations in selecting the operating frequency of the converter. The first is staying clear of sensitive frequency bands, which cannot tolerate any spectral noise. For example in products incorporating RF communications the 455kHz IF frequency is sensitive to any noise, therefore switching above 600kHz is desired. Some communications have sensitivity to 1.1MHz and in that case a 1.5MHz switching converter frequency may be employed. The second consideration is the physical size of the converter. As the operating frequency goes up, the inductor and filter capacitors go down in value and size. The trade off is in efficiency, since the switching losses due to gate charge increase proportional with frequency. Thermal Considerations For the LTC3458 to deliver its full output power, it is imperative that a good thermal path be provided to dissipate the heat generated within the package. This can be accomplished by taking advantage of the large thermal pad on the underside of the IC. It is recommended that multiple vias in the printed circuit board be used to conduct heat away from the IC and into a copper plane with as much area as possible. If the junction temperature rises above ~150°C, the part will go into thermal shutdown, and all switching will stop until the temperature drops. G CONTROL = VREF • G CURRENT _ SENSE VOUT 2 • VIN , IOUT G EA ≈ 1000 , G CURRENT _ SENSE = 1 RDS(ON) The output filter pole is given by: IOUT , π • VOUT • C OUT where COUT is the output filter capacitor. fFILTER _ POLE = The output filter zero is given by: 1 , 2π • RESR • C OUT is the output capacitor equivalent series fFILTER _ ZERO = where RESR resistance. A troublesome feature of the boost regulator topology is the right half plane zero (RHP), and is given by: 2 fRHPZ VIN = 2π • IOUT • VOUT • L At heavy loads this gain increase with phase lag can occur at a relatively low frequency. The loop gain is typically 3458f 12 LTC3458 U W U U APPLICATIO S I FOR ATIO The typical error amp compensation is shown in Figure 2. The equations for the loop dynamics are as follows: fPOLE1 ≈ 1 2π • 10e 6 • CC1 1 fZERO1 = 2π • RZ • CC1 1 fPOLE2 ≈ 2π • RZ • CC 2 VOUT 1.25V rolled off before the RHP zero frequency. + ERROR AMP – R1 FB 7 R2 which is close to DC COMP 8 CC1 RZ CC2 3458 F01 Figure 2 3458f 13 LTC3458 U TYPICAL APPLICATIO S Lithium-Ion to 5V, 500mA at 850kHz WURTH 12µH 774775112 Li-Ion to 5VOUT 100 LTC3458 10pF FB SHDN ON OFF 1M 33k SS RT 0.01µF 124k 80 70 22µF X5R 10pF 65 0.1 BURST ILIM 2.5VIN 85 75 324k 0.01µF 3.6VIN 90 COMP SYNC 243k VOUT 5V 450mA VOUT GND/PGND 4.2VIN 95 SW VIN 2.2µF EFFICIENCY Li-Ion 2.5V to 4.2V 1 560pF 133k 10 100 LOAD CURRENT (mA) 1000 3458 TA03b 3458 TA03a Two Cell to 5VOUT, 200mA at 850kHz WURTH 12µH 774775112 Two Alkaline to 5VOUT SW VIN LTC3458 2.2µF 10pF ON OFF SHDN FB SYNC COMP 0.01µF 22µF X5R 10pF 80 65 0.1 560pF 133k 1.8VIN 70 BURST 124k 85 75 33k SS ILIM 243k 1M 3.3VIN 90 324k 0.01µF RT 95 VOUT 5V 200mA VOUT GND/PGND EFFICIENCY 2 ALKALINE 1.8V to 3.3V 100 1 10 100 LOAD CURRENT (mA) 3458 TA04a 1000 3458 TA04b Lithium-Ion Battery to 7VOUT, 250mA at 1MHz COEV 10µH DQ7545 Li-Ion to 7VOUT 100 SW VIN 95 LTC3458 2.2µF GND/PGND 10pF ON OFF SHDN FB SYNC COMP ILIM 124k 22µF X5R 10pF BURST 133k 4.2VIN 90 3458 TA05a 2.5VIN 80 70 65 0.1 560pF 3.6VIN 85 75 33k SS 0.01µF 200k 1.5M 316k 0.01µF RT VOUT 7V 250mA VOUT EFFICIENCY Li-Ion 2.5V to 4.2V 1 10 100 LOAD CURRENT (mA) 1000 3458 TA05b 3458f 14 LTC3458 U PACKAGE DESCRIPTIO DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 0.58 ±0.05 3.40 ±0.05 1.70 ±0.05 2.24 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 3.30 ±0.05 (2 SIDES) 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.38 ± 0.10 12 R = 0.20 TYP 3.00 ±0.10 (2 SIDES) 1.70 ± 0.10 (2 SIDES) PIN 1 TOP MARK PIN 1 NOTCH (UE12/DE12) DFN 0802 0.200 REF 0.75 ±0.05 0.00 – 0.05 6 0.25 ± 0.05 3.30 ±0.10 (2 SIDES) 1 0.50 BSC BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. 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 4. EXPOSED PAD SHALL BE SOLDER PLATED 3458f 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 LTC3458 U TYPICAL APPLICATIO Dual Lumiled Application with BURST Pin Current Regulation L1 2-Lumileds in Series SW VIN Li-Ion 2.7V to 4.2V CIN 2.2µF fOSC = 850kHz LTC3458 GND/PGND 100 VOUT 6.4V TO 6.8V VOUT 90 Z1 SHDN SYNC COMP D1 0.01µF RT 33k SS COUT 2.2µF 0.01µF ILIM 243k 150mA, 6.4V FB EFFICIENCY (%) ON OFF 124k RBURST 350mA, 6.8V 70 60 D2 BURST 250mA, 6.6V 80 NOTE: LUMILED CURRENT REGULATION ~10% OVER VIN RANGE 0.01µF 50 2.0 CIN, COUT: TAIYO YUDEN JMK107BJ225MA D1, D2: LUXEON EMITTER LUMILED WHITE LXHLMW1D (2.9V AT 350mA) L1: Wurth 12µH 774775112 RBURST: 35.7k FOR 350mA, 3458 TA06a 47.5k FOR 250mA, 82.5k FOR 150mA Z1: CENTRAL SEMI 6.8V ZENER DIODE SOT-23 CMPZ5235B 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 5.0 5.5 3458 TA06b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1310 1.5A ISW, 4.5MHz, High Efficiency Step-Up DC/DC Converter VIN: 2.75V to 18V, VOUT(MAX) = 35V, IQ = 12mA, ISD < 1µA, MS10E LT1613 550mA ISW, 1.4MHz, High Efficiency Step-Up DC/DC Converter VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1µA, ThinSOT LT1615/ LT1615-1 300mA/80mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD < 1µA, ThinSOT LT1618 1.5A ISW, 1.4MHz, High Efficiency Step-Up DC/DC Converter VIN: 1.6V to 18V, VOUT(MAX) = 35V, IQ = 1.8mA, ISD < 1µA, MS10 LT1944 (Dual) Dual Output 350mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD < 1µA, MS10 LT1945 (Dual) Dual Output Pos/Neg 350mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = ±34V, IQ = 20µA, ISD < 1µA, MS10 LT1946/LT1946A 1.5A ISW, 1.2MHz/2.7MHZ, High Efficiency Step-Up DC/DC Converter VIN: 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD < 1µA, MS8 LT1949/ LT1949-1 VIN: 1.5V to 12V, VOUT(MAX) = 28V, IQ = 4.5mA, ISD < 25µA, SO-8, MS8 550mA ISW, 600kHz/1.1MHz, High Efficiency Step-Up DC/DC Converter LT1961 1.5A ISW, 1.25MHz, High Efficiency Step-Up DC/DC Converter VIN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD < 6µA, MS8E LTC3400/ LTC3400B 600mA ISW, 1.2MHz, Synchronous Step-Up DC/DC Converter VIN: 0.5V to 5V, VOUT(MAX) = 5V, IQ = 19µA/300µA ISD < 1µA, ThinSOT LTC3401 1A ISW, 3MHz, Synchronous Step-Up DC/DC Converter VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA ISD < 1µA, MS10 LTC3402 2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA ISD < 1µA, MS10 LTC3425 5A ISW, 8MHz, 4-Phase Synchronous Step-Up DC/DC Converter QFN32 VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12µA, ISD < 1µA, LTC3429 600mA, 500kHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Soft-Start VIN: 0.5V to 5V, VOUT(MAX) = 5V, IQ = 20µA/300µA ISD < 1µA, ThinSOT LTC3459 70mA ISW, 10V Micropower Synchronous Boost/Output Disconnect VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10µA, ThinSOT LT3460 320mA ISW, 1.3MHz, High Efficiency Step-Up DC/DC Converter VIN: 2.5V to 16V, VOUT(MAX) = 36V, IQ = 2mA, ISD < 1µA, SC70, ThinSOT LT3464 85mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter with Integrated Schottky/Output Disconnect VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25µA, ISD < 1µA, ThinSOT 3458f 16 Linear Technology Corporation LT/TP 0904 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004