LTC3458

LTC3458 1.4A, 1.5MHz Synchronous Step-Up DC/DC Converter with Output Disconnect DESCRIPTIO 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. 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 1µF per amp of peak input current is recommended. See Table 3 for a list of capacitor manufacturers for input and output capacitor selection. Table 3. Capacitor Vendor Information Supplier AVX Sanyo TDK Murata Taiyo Yuden Phone (803) 448 - 9411 (619) 661 - 6322 (847) 803 - 6100 USA: (814) 237-1431 (800) 831-9172 (408) 573 - 4150 Website www.avxcorp.com www.sanyovideo.com www.component.tdk.com 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. 12 U Compensating the Feedback Loop 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: W UU G DC = G CONTROL • G EA • G CONTROL = G EA ≈ 1000 , 2 • VIN , IOUT VREF • G CURRENT _ SENSE VOUT 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: fFILTER _ ZERO = where RESR resistance. , 2π • RESR • C OUT is the output capacitor equivalent series 1 A troublesome feature of the boost regulator topology is the right half plane zero (RHP), and is given by: fRHPZ VIN = 2π • IOUT • VOUT • L 2 At heavy loads this gain increase with phase lag can occur at a relatively low frequency. The loop gain is typically 3458f LTC3458 APPLICATIO S I FOR ATIO rolled off before the RHP zero frequency. The typical error amp compensation is shown in Figure 2. The equations for the loop dynamics are as follows: 2π • 10e 6 • CC1 1 fZERO1 = 2π • RZ • CC1 1 fPOLE2 ≈ 2π • RZ • CC 2 fPOLE1 ≈ 1 which is close to DC U 1.25V VOUT W UU + ERROR AMP R1 FB 7 R2 COMP 8 CC1 RZ CC2 – 3458 F01 Figure 2 3458f 13 LTC3458 TYPICAL APPLICATIO S Lithium-Ion to 5V, 500mA at 850kHz WURTH 12µH 774775112 Li-Ion 2.5V to 4.2V VIN 2.2µF LTC3458 GND/PGND SHDN SYNC RT ILIM 243k 124k EFFICIENCY ON OFF Two Cell to 5VOUT, 200mA at 850kHz WURTH 12µH 774775112 2 ALKALINE 1.8V to 3.3V VIN 2.2µF LTC3458 GND/PGND SHDN SYNC RT ILIM 243k 124k ON OFF FB COMP 0.01µF SS 0.01µF BURST 133k 560pF 33k 10pF EFFICIENCY Lithium-Ion Battery to 7VOUT, 250mA at 1MHz COEV 10µH DQ7545 Li-Ion 2.5V to 4.2V VIN 2.2µF LTC3458 GND/PGND SHDN SYNC RT ILIM 200k 124k ON OFF FB COMP 0.01µF SS 0.01µF BURST 133k 560pF 33k 10pF EFFICIENCY 14 U Li-Ion to 5VOUT 100 SW VOUT 10pF FB 1M VOUT 5V 450mA 95 90 85 80 75 70 22µF X5R 4.2VIN 3.6VIN 2.5VIN COMP 0.01µF SS 0.01µF BURST 133k 560pF 3458 TA03a 324k 33k 10pF 65 0.1 1 10 100 LOAD CURRENT (mA) 1000 3458 TA03b Two Alkaline to 5VOUT SW VOUT 10pF 1M VOUT 5V 200mA 100 95 3.3VIN 90 85 80 75 22µF X5R 1.8VIN 324k 70 65 0.1 1 10 100 LOAD CURRENT (mA) 1000 3458 TA04b 3458 TA04a Li-Ion to 7VOUT 100 SW 95 VOUT 10pF 1.5M VOUT 7V 250mA 4.2VIN 90 85 80 75 3.6VIN 2.5VIN 316k 22µF X5R 70 65 0.1 1 10 100 LOAD CURRENT (mA) 1000 3458 TA05b 3458 TA05a 3458f LTC3458 PACKAGE DESCRIPTIO 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) R = 0.20 TYP 3.00 ± 0.10 (2 SIDES) PIN 1 TOP MARK 6 0.25 ± 0.05 3.30 ± 0.10 (2 SIDES) 1 0.50 BSC 1.70 ± 0.10 (2 SIDES) PIN 1 NOTCH (UE12/DE12) DFN 0802 0.200 REF 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 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. U DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 0.58 ± 0.05 7 R = 0.115 TYP 0.38 ± 0.10 12 0.75 ± 0.05 0.00 – 0.05 3458f 15 LTC3458 TYPICAL APPLICATIO L1 Dual Lumiled Application with BURST Pin Current Regulation 2-Lumileds in Series Li-Ion 2.7V to 4.2V VIN CIN 2.2µF LTC3458 GND/PGND SHDN SYNC RT ILIM 243k 124k VOUT Z1 EFFICIENCY (%) ON OFF COMP 0.01µF SS 0.01µF BURST RBURST 33k CIN, COUT: TAIYO YUDEN JMK107BJ225MA D1, D2: LUXEON EMITTER LUMILED WHITE LXHLMW1D (2.9V AT 350mA) L1: Wurth 12µH 774775112 RELATED PARTS PART NUMBER LT1310 LT1613 LT1615/ LT1615-1 LT1618 LT1944 (Dual) LT1945 (Dual) DESCRIPTION 1.5A ISW, 4.5MHz, High Efficiency Step-Up DC/DC Converter 550mA ISW, 1.4MHz, High Efficiency Step-Up DC/DC Converter 300mA/80mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter 1.5A ISW, 1.4MHz, High Efficiency Step-Up DC/DC Converter Dual Output 350mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter Dual Output Pos/Neg 350mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter COMMENTS VIN: 2.75V to 18V, VOUT(MAX) = 35V, IQ = 12mA, ISD < 1µA, MS10E VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1µA, ThinSOT VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD < 1µA, ThinSOT VIN: 1.6V to 18V, VOUT(MAX) = 35V, IQ = 1.8mA, ISD < 1µA, MS10 VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD < 1µA, MS10 VIN: 1.2V to 15V, VOUT(MAX) = ±34V, IQ = 20µA, ISD < 1µA, MS10 VIN: 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD < 1µA, MS8 VIN: 1.5V to 12V, VOUT(MAX) = 28V, IQ = 4.5mA, ISD < 25µA, SO-8, MS8 VIN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD < 6µA, MS8E VIN: 0.5V to 5V, VOUT(MAX) = 5V, IQ = 19µA/300µA ISD < 1µA, ThinSOT VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA ISD < 1µA, MS10 VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA ISD < 1µA, MS10 VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12µA, ISD < 1µA, VIN: 0.5V to 5V, VOUT(MAX) = 5V, IQ = 20µA/300µA ISD < 1µA, ThinSOT VIN: 2.5V to 16V, VOUT(MAX) = 36V, IQ = 2mA, ISD < 1µA, SC70, ThinSOT VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25µA, ISD < 1µA, ThinSOT 3458f LT/TP 0904 1K • PRINTED IN USA LT1946/LT1946A 1.5A ISW, 1.2MHz/2.7MHZ, High Efficiency Step-Up DC/DC Converter LT1949/ LT1949-1 LT1961 LTC3400/ LTC3400B LTC3401 LTC3402 LTC3425 LTC3429 LTC3459 LT3460 LT3464 550mA ISW, 600kHz/1.1MHz, High Efficiency Step-Up DC/DC Converter 1.5A ISW, 1.25MHz, High Efficiency Step-Up DC/DC Converter 600mA ISW, 1.2MHz, Synchronous Step-Up DC/DC Converter 1A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 5A ISW, 8MHz, 4-Phase Synchronous Step-Up DC/DC Converter QFN32 600mA, 500kHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Soft-Start 320mA ISW, 1.3MHz, High Efficiency Step-Up DC/DC Converter 85mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter with Integrated Schottky/Output Disconnect 70mA ISW, 10V Micropower Synchronous Boost/Output Disconnect VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10µA, ThinSOT 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● U SW fOSC = 850kHz VOUT 6.4V TO 6.8V 100 90 150mA, 6.4V 250mA, 6.6V FB 80 350mA, 6.8V 70 D1 COUT 2.2µF D2 0.01µF 60 NOTE: LUMILED CURRENT REGULATION ~10% OVER VIN RANGE 50 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 5.0 5.5 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 3458 TA06b www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004