LTC1574-3.3

LTC1574 LTC1574-3.3/LTC1574-5 High Efficiency Step-Down DC/DC Converters with Internal Schottky Diode FEATURES s s s s s s s s s s s s s DESCRIPTION The LTC®1574 is a family of easy-to-use current mode DC/DC converters ideally suited for 9V to 5V, 5V to 3.3V and inverting operation. With an internal 0.9Ω switch (at a supply voltage of 12V) and a low forward drop Schottky diode (0.450V typ at 200mA, TA = 25°C), the LTC1574 requires only three external components to construct a complete high efficiency DC/DC converter. Under no load condition, the LTC1574 draws only 130µA. In shutdown, it draws a mere 2µA making this converter ideal for battery-powered applications. In dropout, the internal P-channel MOSFET switch is turned on continuously allowing the user to maximize the life of the battery source. The maximum inductor current of the LTC1574 family is pin selectable to either 340mA or 600mA, optimizing efficiency for a wide range of applications. Operation up to 200kHz permits the use of small surface mount inductors and capacitors. For applications requiring higher output current or ultrahigh efficiency, see the LTC1148 and LTC1265 data sheets. For detailed applications information, see the LTC1174 data sheet. High Efficiency: Up to 94% Usable in Noise-Sensitive Products Peak Inductor Current Independent of Inductor Value Short-Circuit Protection Internal Low Forward Drop Schottky Diode Only Three External Components Required Wide VIN Range: 4V to 18.5V (Absolute Maximum) Low Dropout Operation Low-Battery Detector Pin Selectable Current Limit Internal 0.9Ω Power Switch: VIN = 12V Standby Current: 130µA Active Low Micropower Shutdown APPLICATIONS s s s s s s Inverting Converters Step-Down Converters Memory Backup Supply Portable Instruments Battery-Powered Equipment Distributed Power Systems and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation. TYPICAL APPLICATION High Efficiency Step-Down Converter VIN 5.5V to 16V 12 11 6 100 LTC1574-5 Efficiency L = 100µH VOUT = 5V IPGM = 0V 5 VIN LBIN SHDN 7 10 3, 14 100µH† + 22µF* 35V 95 EFFICIENCY (%) 90 VIN = 9V 85 80 75 70 LBOUT LTC1574-5 VOUT IPGM GND 2, 4, 13, 15 SW + 5V 175mA 100µF* 10V * AVX TPSD226K035 ** AVX TPSD107K010 † COILTRONICS CTX100-4 1574 TA01 1 U U U VIN = 6V 10 LOAD CURRENT (mA) 100 200 1574 TA02 1 LTC1574 LTC1574-3.3/LTC1574-5 ABSOLUTE MAXIMUM RATINGS (Voltage Referred to GND Pin) Input Supply Voltage (Pin 5).................. – 0.3V to 18.5V Switch Current (Pin 3, 14) ........................................ 1A Switch Voltage (Pin 3, 14) .......................... VIN – 18.5V Operating Temperature Range .................... 0°C to 70°C Junction Temperature (Note 1) ............................ 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C PACKAGE/ORDER INFORMATION TOP VIEW NC 1 GND 2 SW 3 GND 4 VIN 5 IPGM 6 SHDN 7 NC 8 16 NC 15 GND 14 SW 13 GND 12 LBIN 11 LBOUT 10 VOUT (VFB*) 9 NC ORDER PART NUMBER LTC1574CS LTC1574CS-3.3 LTC1574CS-5 S PACKAGE 16-LEAD PLASTIC SO *ADJUSTABLE OUTPUT VERSION TJMAX = 125°C, θJA = 110°C/W Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER IFB VFB VOUT ∆VOUT Feedback Current into Pin 10 Feedback Voltage Regulated Output Voltage Output Voltage Line Regulation Output Voltage Load Regulation CONDITIONS LTC1574 LTC1574 LTC1574-3.3 LTC1574-5 TA = 25°C, VIN = 9V, VSHUTDOWN = VIN, IPGM = 0V, unless otherwise specified. MIN TYP MAX 1 q q q UNITS µA V V V mV mV mV mV mV µA µA µA V µA mA µA mV A A Ω µs V 1.20 3.14 4.75 1.25 3.30 5.00 10 –5 – 45 –5 – 50 450 130 2 1.25 1.30 3.46 5.25 70 – 70 – 70 – 70 – 70 600 180 25 1.4 0.5 VIN = 6V to 12V, ILOAD = 100mA, IPGM = VIN (Note 2) LTC1574-3.3 (Note 2) LTC1574-5 (Note 2) 20mA < ILOAD < 175mA, IPGM = 0V 20mA < ILOAD < 400mA, IPGM = VIN 20mA < ILOAD < 175mA, IPGM = 0V 20mA < ILOAD < 400mA, IPGM = VIN IQ Input DC Supply Current (Note 3) Active Mode Sleep Mode Shutdown (Note 4) Low-Battery Trip Point Current into Pin 12 Current Sunk by Pin 11 Comparator Hysteresis Current Limit ON Resistance of Switch Switch Off Time Shutdown Pin High Shutdown Pin Low Shutdown Pin Input Current 4V < VIN < 16V, IPGM = 0V 4V < VIN < 16V VSHUTDOWN = 0V, 4V < VIN < 16V VLBTRIP ILBIN ILBOUT VHYST IPEAK RON tOFF VIH VIL IIH VLBOUT = 0.4V, VLBIN = 0V VLBOUT = 5V, VLBIN = 10V IPGM = VIN, VOUT = 0V IPGM = 0V, VOUT = 0V VOUT at Regulated Value Minimum Voltage at Pin 7 for Device to Be Active Maximum Voltage at Pin 7 for Device to Be in Shutdown VSHUTDOWN = 16V q q q 0.5 7.5 0.54 0.27 1.0 15 0.60 0.34 0.9 1.5 1.0 30 0.78 0.50 1.55 5 3 1.2 4 0.75 2 2 U W U U WW W V µA LTC1574 LTC1574-3.3/LTC1574-5 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER IIL VF IR Shutdown Pin Input Current Schottky Diode Forward Voltage Schottky Reverse Current CONDITIONS 0 ≤ VSHUTDOWN ≤ 0.8V Forward Current = 200mA Reverse Voltage = 5V Reverse Voltage = 18.5V 0.450 10 100 TA = 25°C, VIN = 9V, VSHUTDOWN = VIN, IPGM = 0V, unless otherwise specified. MIN TYP MAX 0.5 0.570 25 250 UNITS µA V µA µA The q denotes specifications which apply over the full operating temperature range. Note 1: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formulas: TJ = TA + (PD × 110°C/W) Note 2: Guaranteed by Design. Note 3: Does not include Schottky reverse current. Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 4: Current into Pin 5 only, measured without electrolytic input capacitor. TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current 100 VIN = 5V 100 95 90 EFFICIENCY (%) EFFICIENCY (%) 80 VIN = 9V VIN = 9V 85 80 75 70 L = 50µH VOUT = 5V IPGM = VIN COIL = CTX50-4 1 10 100 LOAD CURRENT (mA) 400 1574 • TPC02 EFFICIENCY (%) 70 L = 50µH VOUT = 3.3V IPGM = VIN COIL = CTX50-4 1 10 100 LOAD CURRENT (mA) 500 1574 • TPC01 60 50 Efficiency Using Different Types of Inductor Core Material 100 CTX50-4 90 EFFICIENCY (%) LEAKAGE CURRENT (nA) RDS(ON) (Ω) CTX50-4P 80 70 60 VIN = 5V VOUT = 3.3V IPGM = VIN 1 10 100 LOAD CURRENT (mA) 500 1574 • TPC04 50 UW Efficiency vs Load Current 95 94 Efficiency vs Input Voltage VOUT = 5V L = 100µH COIL = CTX100-4 90 VIN = 6V 93 92 91 90 89 5 6 7 8 9 10 11 12 INPUT VOLTAGE (V) 13 14 ILOAD = 100mA IPGM = 0V ILOAD = 300mA IPGM = VIN 1574 • TPC03 Switch Leakage Current vs Temperature 180 160 140 120 100 80 60 40 20 0 0 20 60 40 TEMPERATURE (°C) 80 100 1574 • TPC05 Switch Resistance vs Input Voltage 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 4 6 8 10 12 14 16 INPUT VOLTAGE (V) 18 20 TA = 25°C VIN = 13.5V 1574 • TPC06 3 LTC1574 LTC1574-3.3/LTC1574-5 PIN FUNCTIONS NC (Pins 1, 8, 9, 16): No Connection. GND (Pins 2, 4, 13, 15): Ground. SW (Pins 3, 14): Drain of P-Channel MOSFET Switch and Cathode of Schottky Diode. VIN (Pin 5): Input Supply Voltage. It must be decoupled close to ground (Pin 4). IPGM (Pin 6): This pin selects the current limit of the P-channel switch. With IPGM = VIN, the current trip point is 600mA and with IPGM = 0V, the current trip point is reduced to 340mA. SHDN (Pin 7): Pulling this pin to ground keeps the internal switch off and puts the LTC1574 in micropower shutdown. VOUT or VFB (Pin 10): For the LTC1574, this pin connects to the main voltage comparator input. On the LTC1574-5 and LTC1574-3.3, this pin goes to an internal resistive divider which sets the output voltage. LBOUT (Pin 11): Open drain of an N-Channel Pull-Down. This pin will sink current when (Pin 12) LBIN goes below 1.25V. LBIN (Pin 12): The (–) Input of the Low-Battery Voltage Comparator. The (+) input is connected to a reference voltage of 1.25V. APPLICATIONS INFORMATION Operating Frequency and Inductor Since the LTC1574 utilizes a constant off-time architecture, its operating frequency is dependent on the value of VIN. The frequency of operation can be expressed as: f= 1  VIN − VOUT  t OFF  VIN + VD    (Hz) IPGM = VIN 100mA/DIV where tOFF = 4µs and VD is the voltage drop across the internal Schottky diode. Note that the operating frequency is a function of the input and output voltage. Although the size of the inductor does not affect the frequency or inductor peak current, it does affect the ripple current. The peak-to-peak ripple current is given by: V + VD  IRIPPLE = 4 × 10 −6  OUT  L   (AP-P ) By choosing a smaller inductor, a low ESR (Effective Series Resistance) output filter capacitor has to be used. Core loss will increase due to higher ripple current. Short-Circuit Protection The LTC1574 is protected from output short circuits by its internal current limit. Depending on the condition of the 4 U W U U U U U IPGM pin, the limit is either set to 340mA or 600mA. In addition, the off-time of the switch is increased to allow the inductor current to decay far enough to prevent any current build-up (see Figure 1). IPGM = 0 GND L = 100µH VIN = 13.5V 20µs/DIV 1574 • F01 Figure 1. Inductor Current with Output Shorted Low-Battery Detector The low-battery indicator senses the input voltage through an external resistive divider. This divided voltage connects to the “–” input of a voltage comparator (Pin 12) which is compared with a 1.25V reference voltage. With the current LTC1574 LTC1574-3.3/LTC1574-5 APPLICATIONS INFORMATION going into Pin 12 being negligible, the following expression is used for setting the trip limit:  R4  VLBTRIP = 1.25 1 +   R3  VIN R4 12 R3 LTC1574 – + 1.25V REFERENCE 1574 • F02 Figure 2. Low-Battery Comparator LTC1574 Adjustable Applications The LTC1574 develops a 1.25V reference voltage between the feedback terminal (Pin 10) and ground (see Figure 3). By selecting resistor R1, a constant current is caused to flow through R1 and R2 to set the overall output voltage. The regulated output voltage is determined by:  R2  VOUT = 1.25 1 +   R1 For most applications, a 30k resistor is suggested for R1. To prevent stray pickup, a 100pF capacitor is suggested across R1 located close to the LTC1574. VOUT R2 LTC1574 VFB 10 100pF R1 1574 • F03 Figure 3. LTC1574 Adjustable Configuration Inverting Applications The LTC1574 can easily be set up for a negative output voltage. If – 5V is desired, the LTC1574-5 is ideal for this application as it requires the least components. Figure 4 shows the schematic for this application. Note that the output voltage is now taken off the GND pins. Therefore, the maximum input voltage is now determined by the U W U U difference between the absolute maximum voltage rating and the output voltage. A maximum of 12V is specified in Figure 4, giving the circuit 1.5V of headroom for VIN. Note that the circuit can operate from a minimum of 4V, making it ideal for a four NiCd cell application. For a higher output current circuit, please refer to the Typical Applications section. INPUT VOLTAGE 4V TO 12V 12 11 6 5 VIN LBIN LBOUT IPGM LTC1574-5 GND 2, 4, 13, 15 SHDN VOUT SW + 7 10 3, 14 0.1µF + 2 × 47µF* 16V 50µH** + * AVX TPSD476K016 ** COILTRONICS CTX50-4 2 × 47µF* 16V VOUT –5V 45mA 1574 • F04 Figure 4. Positive-to-Negative 5V Converter Low Noise Regulators In some applications it is important not to introduce any switching noise within the audio frequency range. Due to the nature of the LTC1574 during Burst ModeTM operation, there is a possibility that the regulator will introduce audio noise at some load currents. To circumvent this problem, a feed-forward capacitor can be used to shift the noise spectrum up and out of the audio band. Figure 5 shows the low noise connection with C2 being the feed-forward capacitor. The peak-to-peak output ripple is reduced to 30mV over the entire load range. A toroidal surface mount Burst Mode is a trademark of Linear Technology Corporation 5 VIN 12 11 6 LTC1574 LBIN LBOUT IPGM GND 2, 4, 13, 15 SHDN SW VFB 7 3, 14 10 L1** 100µH + 100µF* 10V VIN 5V 56k C2 6.8nF VOUT 3.3V 425mA 100µF* 10V + 33k * AVX TPSD107K010 ** COILTRONICS CTX100-4 1574 • F05 Figure 5. Low Noise 5V to 3.3V Regulator 5 LTC1574 LTC1574-3.3/LTC1574-5 APPLICATIONS INFORMATION inductor L1 is chosen for its excellent self-shielding properties. Open magnetic structures such as drum and rod cores are to be avoided since they inject high flux levels into their surroundings. This can become a major source of noise in any converter circuit. Design Example As a design example, assume VIN = 9V (nominal), VOUT = 5V and IOUT = 350mA maximum. The LTC1574-5 is used for this application with IPGM (Pin 6) connected to VIN. The minimum value of L is determined by assuming the LTC1574-5 is operating in continuous mode. INDUCTOR CURRENT IPEAK AVG CURRENT = IOUT +I I = PEAK V IV 2 = 350mA TIME Figure 6. Continuous Inductor Current With IOUT = 350mA and IPEAK = 0.6A (IPGM = VIN), IV = 0.1A. The peak-to-peak ripple inductor current, IRIPPLE, is 0.5A and is also equal to: TYPICAL APPLICATIONS Low Noise, High Efficiency 3.3V Regulator VIN 4V TO 12.5V VIN 6 12 11 IPGM LBIN LBOUT GND 2, 4, 13, 15 * AVX TPSD226K025 ** AVX TPSD107K010 † COILTRONICS CTX50-4 100pF LTC1574 SHDN VFB SW 7 10 3, 14 6 U 5 W U U U V + VD  IRIPPLE = 4 × 10 −6  OUT  L   (AP-P ) Solving for L in the above equation and with VD = 0.5V, L = 44µH. The next higher standard value of L is 50µH (example: Coiltronics CTX50-4). The operating frequency, ignoring voltage across diode VD is: V  f ≈ 2.5 × 105 1 − OUT  VIN   = 111kHz With the value of L determined, the requirements for CIN and COUT are calculated. For CIN, its RMS current rating should be at least: IRMS = IOUT VOUT VIN − VOUT VIN [ ( )] 1/ 2 (ARMS) 1574 • F06 = 174mA For COUT, the RMS current rating should be at least: IRMS ≈ IPEAK A RMS 2 = 300mA ( ) + 22µF* 25V ×2 0.1µF 50µH† 100µF** 10V ×2 6.8nF 56k VOUT 3.3V 450mA + 33k 1574 TA03 LTC1574 LTC1574-3.3/LTC1574-5 TYPICAL APPLICATIONS Low Dropout 5V Step-Down Regulator with Low-Battery Detection VIN 5.5V to 12.5V * LOW-BATTERY INDICATOR IS SET UP TO TRIP AT V IN = 5.5V ** AVX TPSD476K016 † SELECTION MANUFACTURER COILTRONICS SUMIDA GOWANDA PART NO. CTX100-4 CD75-101 GA10-103K TYPE SURFACE MOUNT SURFACE MOUNT THROUGH HOLE VIN 4V TO 12.5V * AVX TPSD226K025 ** AVX TPSD476K016 † COILTRONICS CTX50-4 * LOW-BATTERY INDICATOR IS SET TO TRIP AT V IN = 4.4V ** AVX TPSD106K035 *** AVX TPSD107K010 † SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA PART NO. CTX50-3 DT3316-473 CD54-470 GA10-472K TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE 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 4.7k *LOWBATTERY INDICATOR 162k 6 11 12 47.5k IPGM 5 VIN SHDN 7 10 3, 14 0.1µF + 47µF** 16V ×2 LBOUT LTC1574-5 VOUT LBIN GND 2, 4, 13, 15 SW L1 100µH† + VOUT 5V 47µF** 365mA 16V ×2 1574 TA04 High Efficiency 3.3V Regulator 5 VIN 6 12 11 IPGM LBIN LBOUT GND 2, 4, 13, 15 SHDN LTC1574-3.3 VOUT SW 7 10 3, 14 + 22µF* 25V ×2 0.1µF 50µH† + 47µF* 16V ×2 VOUT 3.3V 425mA 1574 TA05 Positive to –5V Converter VIN 4V TO 12.5V 4.7k *LOWBATTERY INDICATOR 280k 6 11 12 43k IPGM LBOUT 5 VIN SHDN VOUT LTC1574-5 LBIN GND 2, 4, 13, 15 SW 7 10 3, 14 0.1µF + 10µF** 35V ×2 V IN (V) I OUT (mA) 4 110 6 140 8 170 10 200 12.5 235 L1† 50µH + 100µF*** 10V VOUT –5V 1574 TA06 7 LTC1574 LTC1574-3.3/LTC1574-5 PACKAGE DESCRIPTION 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0° – 8° TYP 0.016 – 0.050 0.406 – 1.270 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE RELATED PARTS PART NUMBER LT ® 1076 LTC1174 LTC1265 LT1375/LT1376 DESCRIPTION Step-Down Switching Regulator High Efficiency Step-Down/Inverting DC/DC Converter 1.2A, High Efficiency Step-Down DC/DC Converter 1.5A, 500kHz Step-Down Switching Regulator COMMENTS 2A Monolithic Bipolar Switcher for VIN to 60V Same as LTC1574 Without Schottky Diode in SO-8 Package Current Mode with 0.3Ω Switch for Higher Current High Frequency, Synchronizable in SO-8 Package 8 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977 U Dimension in inches (millimeters) unless otherwise noted. S Package 16-Lead Plastic SOIC 0.386 – 0.394* (9.804 – 10.008) 16 15 14 13 12 11 10 9 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157** (3.810 – 3.988) 1 0.053 – 0.069 (1.346 – 1.752) 2 3 4 5 6 7 8 0.004 – 0.010 (0.101 – 0.254) 0.014 – 0.019 (0.355 – 0.483) 0.050 (1.270) TYP SO16 0695 LT/GP 0795 6K • PRINTED IN USA © LINEAR TECHNOLOGY CORPORATION 1995