LTC1433/LTC1434 450mA, Low Noise Current Mode Step-Down DC/DC Converters DESCRIPTION U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®1433/LTC1434 are monolithic pulse width modulated step-down DC/DC converters. By utilizing current mode switching techniques, they provide excellent AC and DC load and line regulation. Both devices operate at a fixed frequency with the LTC1434 phase-lockable to an external clock signal. High Efficiency: Up to 93% Constant Frequency Adaptive PowerTM Operation Input Voltage Range: 3V to 13.5V Internal 0.6Ω Power Switch (VIN = 10V) Low Dropout Operation: 100% Duty Cycle Low-Battery Detector Internal Power-On Reset Timer Current Mode Operation for Excellent Line and Load Transient Response Low Quiescent Current: 470µA Shutdown Mode Draws Only 15µA Supply Current ±1% Reference Accuracy Available in 16- and 20-Lead Narrow SSOP Both devices incorporate two internal P-channel power MOSFETs with a parallel combined resistance of 0.6Ω (at a supply of 10V). The Adaptive Power output stage selectively drives one or both of the switches at frequencies up to 700kHz to reduce switching losses and maintain high efficiencies at low output currents. The LTC1433/LTC1434 are capable of supplying up to 450mA of output current and boasts a ±2.4% output voltage accuracy. An internal low-battery detector has the same level of accuracy as the output voltage. A power-on reset timer (POR) is included which generates a signal delayed by 65536/fCLK (300ms typ) after the output is within 5% of the regulated output voltage. U APPLICATIONS ■ ■ ■ ■ ■ ■ ■ Cellular Telephones Portable Instruments Wireless Modems RF Communications Distributed Power Systems Scanners Battery-Powered Equipment Ideal for current sensitive applications, the devices draw only 470µA of quiescent current. In shutdown the devices draw a mere 15µA. To further maximize the life of the battery source, the internal P-channel MOSFET switch is turned on continuously in dropout. , LTC and LT are registered trademarks of Linear Technology Corporation. Adaptive Power is a trademark of Linear Technology Corporation. U TYPICAL APPLICATION LTC1433 Efficiency for VOUT = 3.3V 68µF** 20V 0.1µF + 100 D1 VOUT 3.3V + 1 L1 100µH 2 100µF* 10V 4 3 5 6 0.1µF 7 8 16 PWRVIN PGND 15 SSW NC BSW NC LTC1433 SGND RUN/SS LBO LBI SVIN COSC POR ITH VOSENSE VPROG 14 VIN 3.5V TO 12V 90 10k EFFICIENCY (%) ■ 13 12 11 10 POWER-ON RESET 5.1k VIN = 5V VIN = 12V 80 70 VIN = 9V 60 680pF 47pF 9 50 6800pF D1: MOTOROLA MBRS130LT3 *AVX TPSD107M010R0100 ** AVX TPSE686M020R0150 L1: COILCRAFT D03316-104 Figure 1. High Efficiency Step-Down Converter 1433/34 F01 40 0.001 0.01 0.1 LOAD CURRENT (A) 1 1433/34 TA01 1 LTC1433/LTC1434 W W W AXI U U ABSOLUTE RATI GS (Note 1) (Voltages Referred to PGND Pin) Input Supply Voltage (PWRVIN, SVIN) ... 13.5V to – 0.3V DC Small Switch Current (SSW) ......................... 100mA Peak Small Switch Current (SSW) ..................... 300mA Small Switch Voltage (SSW) ................................(VIN + 0.3V) to (VIN – 13.5V) DC Large Switch Current (BSW) ....................... 600mA Peak Large Switch Current (BSW) .......................... 1.2A Large Switch Voltage (BSW) ................................(VIN + 0.3V) to (VIN – 13.5V) PLLIN, PLL LPF, ITH, COSC ........................2.7V to – 0.3V POR, LBO .................................................. 12V to – 0.3V LBI, VOSENSE ..............................................10V to – 0.3V RUN/SS, VPROG Voltages VIN ≥ 11.7V ...........................................12V to – 0.3V VIN < 11.7V ............................... (VIN + 0.3V) to – 0.3V Commercial Temperature Range LTC1433C/LTC1434C .............................. 0°C to 70°C Extended Commercial Operating Temperature Range (Note 2) ....................................... – 40°C to 85°C Industrial Temperature Range (Note 3) LTC1433I/LTC1434I ........................... – 40°C to 85°C Junction Temperature (Note 4)............................. 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C U W U PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW SSW 1 16 PWRVIN NC 2 15 PGND BSW 3 14 SVIN NC 4 13 COSC SGND 5 12 POR RUN/SS 6 11 ITH LBO 7 10 VOSENSE LBI 8 9 LTC1433CGN LTC1433IGN VPROG TOP VIEW NC 1 20 PWRVIN SSW 2 19 PGND NC 3 18 SVIN BSW 4 17 PLLIN SGND 5 16 PLL LPF NC 6 15 COSC RUN/SS 7 14 POR NC 8 13 ITH LBO 9 12 VOSENSE LBI 10 GN PACKAGE 16-LEAD PLASTIC SSOP ORDER PART NUMBER LTC1434CGN LTC1434IGN 11 VPROG GN PACKAGE 20-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 150°C/ W TJMAX = 125°C, θJA = 150°C/ W Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 10V, VRUN/SS = 5V, unless otherwise noted. (Notes 2, 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 10 50 nA 1.178 3.220 4.880 1.190 3.300 5.000 1.202 3.380 5.120 V V V 1.24 1.28 1.32 V 0.002 0.01 %/V 0.5 – 0.5 0.8 – 0.8 % % Main Control Loop IIN VOSENSE Feedback Current VPROG Pin Open (Note 5) VOSENSE Regulated Output Voltage 1.19V (Adjustable) Selected 3.3V Selected 5V Selected (Note 5) VPROG Pin Open VPROG = 0V VPROG = VIN VOVL Output Overvoltage Lockout VPROG Pin Open ∆VOSENSE Reference Voltage Line Regulation VIN = 3.6V to 13V (Note 5), VPROG Pin Open VLOADREG Output Voltage Load Regulation ITH Sinking 5µA (Note 5) ITH Sourcing 5µA (Note 5) 2 ● ● ● ● ● LTC1433/LTC1434 ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 10V, VRUN/SS = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS IPROG VPROG Input Current MIN TYP MAX UNITS 0.5V > VPROG VIN – 0.5V < VPROG < VIN –4 4 – 10 10 µA µA (Note 6) 3.6V < VIN < 13V VRUN/SS = 0V, 3.6V < VIN < 13V, LBI > 0.9V VRUN/SS = 0V, 3.6V < VIN < 13V, LBI ≤ 0.48V 470 35 15 70 30 µA µA µA 0.8 1.3 2 V VRUN/SS = 0V 1.2 3 4.5 µA COSC = 100pF (Note 7) VPLL LPF = 2.4V 112 200 125 240 142 kHz kHz Main Control Loop IQ Input DC Supply Current Normal Mode Shutdown, Reference Alive Complete Shutdown VRUN/SS RUN/SS Threshold IRUN/SS Soft Start Current Source ● Oscillator and Phase-Locked Loop fOSC Oscillator Frequency VCO High RPLLIN PLL Input Resistance IPLL LPF Phase Detector Output Current Sinking Capability Sourcing Capability 50 fPLLIN < fOSC fPLLIN > fOSC 10 10 kΩ 15 15 20 20 µA µA 0.6 1.0 V 0.2 1.0 µA – 7.5 –4 % Power-On Reset VSATPOR POR Saturation Voltage IPOR = 1.6mA, VOSENSE = 1V, VPROG Open ILPOR POR Leakage VPOR = 10V, VOSENSE = 1.2V, VPROG Open VTRPOR POR Trip Voltage from Regulated Output VPROG Pin Open, VOSENSE Ramping Negative tDPOR POR Delay VPROG Pin Open – 11 65536 Cycles Low-Battery Comparator VSATLBO LBO Saturation Voltage ILBO = 1.6mA, VLBI = 1.1V 0.6 ILLBO LBO Leakage VLBO = 10V, VLBI = 1.4V VTRLBI LBI Trip Voltage High to Low Transition on LBO VHYSTLB Low-Battery Comparator Hysteresis VSDLB Low-Battery Shutdown Trip Point IINLBI LBI Input Current 1.16 1.0 V 0.01 1.0 µA 1.19 1.22 V 40 mV 0.74 V VLBI = 1.19V 1 50 nA P-Channel Power FETs Characteristics RSMFET RDS(ON) of Small FET ISSW = 15mA 3.3 4.1 Ω RBIGFET RDS(ON) of Big FET IBSW = 150mA 0.8 1.2 Ω ILSSW Small FET Leakage VRUN/SS = 0V ● 7 1000 nA ILBSW Big FET Leakage VRUN/SS = 0V ● 5 1000 nA The ● denotes specifications which apply over the specified temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: C-grade device specifications are guaranteed over the 0°C to 70°C temperature range. In addition, C-grade device specifications are assured over the – 40°C to 85°C temperature range by design or correlation, but are not production tested. Note 3: I-grade device specifications are guaranteed over the – 40°C to 85°C temperature range by design, testing or correlation. Note 4: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: LTC1433/LTC1434: TJ = TA + (PD)(150°C/W) Note 5: The LTC1433/LTC1434 are tested in a feedback loop which servos VOSENSE to the feedback point for the error amplifier (VITH = 1.19V). Note 6: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 7: Oscillator frequency is tested by measuring the COSC charge and discharge currents and applying the formula: ( )( ) 8.4(10 8) 1 + 1 –1 fOSC (kHz) = C OSC (pF) + 11 ICHG IDIS 3 LTC1433/LTC1434 U W TYPICAL PERFORMANCE CHARACTERISTICS Efficiency of Figure 1 for L = 22µH Dropout Characteristics at Different Load Currents (VOUT = 3.3V) Supply Current vs Supply Voltage 100 3.4 480 VIN = 3.6V 3.3 IOUT 3.2 300mA VIN = 5V 80 70 VIN = 12V 60 VOUT = 3.3V L = 22µH CSOC = 47pF 50 40 0.001 0.01 0.1 LOAD CURRENT (A) OUTPUT VOLTAGE (V) 460 SUPPLY CURRENT (µA) EFFICIENCY (%) 90 440 420 400 360 1 3 8 9 6 5 7 SUPPLY VOLTAGE (V) 4 4.7 IOUT 300mA 4.5 VPROG = VIN L = 20µH COSC = 50pF 4.8 5.0 5.2 5.4 5.6 5.8 SUPPLY VOLTAGE (V) 6.0 1.202 700 1.198 VOUT 3.3V 600 500 VOUT 5V 400 300 200 6.2 7 1.8 5 3 9 11 7 SUPPLY VOLTAGE (V) RDS(ON) OF BIG FET (Ω) TA = 70°C 4 3 TA = 0°C 2 4 5 6 7 8 9 10 11 12 13 SUPPLY VOLTAGE (V) 1433/34 G07 –5 15 35 55 75 TEMPERATURE (°C) 115 1433/34 G06 280 VIN = 13.5V 1.4 TA = 25°C 1.2 TA = 70°C 1.0 0.8 0.6 0 95 Switch Leakage Current vs Temperature TA = 0°C 0.2 3 1.178 70 0.4 1 1.182 1.170 – 45 – 25 13 1.6 TA = 25°C 1.186 60 240 50 200 40 160 30 120 20 80 SSW PIN 10 40 BSW PIN 0 3 4 5 6 7 8 9 10 11 12 13 SUPPLY VOLTAGE (V) 1433/34 G08 0 20 80 60 100 40 TEMPERATURE (°C) 120 0 140 1433/34 G09 SWITCH LEAKAGE AT BSW PIN (nA) 2.0 5 1.190 1.174 Switch Resistance of Big FET 8 6 1.194 1433/34 G05 Switch Resistance of Small FET RDS(ON) OF SMALL FET (Ω) Reference Voltage vs Temperature L = 22µH COSC = 50pF 1433/34 G04 4 1433/34 G03 REFERENCE VOLTAGE (V) IOUT 400mA 4.2 4.6 VPROG = 0V L = 20µH COSC = 50pF 2.4 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 SUPPLY VOLTAGE (V) 11 SWITCH LEAKAGE AT SSW PIN (nA) OUTPUT VOLTAGE (V) MAXIMUM OUTPUT CURRENT (mA) IOUT 200mA 4.3 2.7 Maximum Output Current vs Input Supply 5.0 0 10 800 4.4 IOUT 500mA 2.8 1433/34 G02 5.1 4.6 IOUT 400mA 2.9 2.5 Dropout Characteristics at Different Load Currents (VOUT = 5V) 4.8 3.0 2.6 380 1433/34 G01 4.9 3.1 LTC1433/LTC1434 U U U PIN FUNCTIONS (LTC1433/LTC1434) SSW (Pin 1/Pin 2): Drain of the Small P-Channel MOSFET Switch. BSW (Pin 3/Pin 4): Drain of the Large P-Channel MOSFET Switch. SGND (Pin 5): Small-Signal Ground. Must be routed separately from other grounds to the (–) terminal of COUT. RUN/SS (Pin 6/Pin 7): Combination of Soft Start and Run Control Inputs. A capacitor to ground at this pin sets the ramp time to full current output. The time is approximately 0.5s/µF. Forcing this pin below 1.3V causes all circuitry to be shut down except the low-battery comparator. For input voltages above 6V this pin is clamped by a 6V Zener (see Functional Diagram). Applying voltages greater than 6V to this pin will cause additional current to flow into this pin. LBO (Pin 7/Pin 9): Open-Drain Output of an N-Channel Pull-Down. This pin will sink current when LBI goes below 1.19V. LBI (Pin 8/Pin 10): The (+) Input of the Low-Battery Voltage Comparator. The (–) input is connected to the 1.19V reference. When LBI is grounded along with RUN/ SS, this comparator will shut down along with the rest of the control circuitry. LBO will go to high impedance. ITH (Pin 11/Pin 13): Error Amplifier Compensation Point. The current comparator threshold increases with this control voltage. Nominal voltage range for this pin is 0V to 2.4V. POR (Pin 12/Pin 14): Open-Drain Output of an N-Channel Pull-Down. This pin sinks current when the output voltage is 7.5% out of regulation. When the output rises to – 5% of its regulated value, the pin goes into high impedance after 216 (65536) oscillator cycles. The POR output is asserted when the device is in shutdown, independent of VOUT. COSC (Pin 13/Pin 15): External capacitor connects between this pin and ground to set the operating frequency. PLL LPF (Pin 16 LTC1434): Output of the Phase Detector and Control Input of the Oscillator. Normally a series RC lowpass network is connected from this pin to ground. Tie this pin to SGND in applications which do not use the phase-locked loop. Can be driven by a 0V to 2.4V logic signal for a frequency shifting option. PLLIN (Pin 17 LTC1434): External Synchronizing Input to the Phase Detector. This pin is internally terminated to SGND with 50kΩ. Tie this pin to SGND in applications which do not use the phase-locked loop. SVIN (Pin 14/Pin 18): Main Supply for All the Control Circuitry. VPROG (Pin 9/Pin 11): The voltage at this pin selects the output voltage. When VPROG = 0V or VPROG = VIN, the output is set to 3.3V and 5V respectively, with VOSENSE connected to the output. Leaving VPROG open (DC) allows the output voltage to be set by an external resistive divider. VOSENSE is then connected to the common node of the resistive divider. PGND (Pin 15/Pin 19): Switch Driver Ground. Connects to the (–) terminal of CIN. Anode of the Schottky diode must be connected close to this pin. VOSENSE (Pin 10/Pin 12): This pin receives the feedback voltage either from the output or from an external resistive divider across the output. The VPROG pin determines at which point VOSENSE must be connected. NC (Pins 2, 4,/Pins 1, 3, 6, 8): No Connection. VPROG = 0V VOUT = 3.3V VPROG = VIN VOUT = 5V VPROG = Open (DC) VOUT = Adjustable PWRVIN (Pin 16/Pin 20): Supply for the Internal Power MOSFETs and Switch Drivers. Must decouple this pin properly to ground. 5 LTC1433/LTC1434 W FUNCTIONAL DIAGRA U PWRVIN PLLIN U PLL POR 50k SLOPE COMP VCO OSC PLL LPF COSC LBO FREQ SHIFT + LOBAT RSENSE 0.143Ω CK Q FF1 D Q LBI BSW VREF SSW + – LIDET – SB Q FF2 RB Q SVIN VREF IPEAK DET GM SHDN POR + 30k OVDET 6V SB Q FF3 RB Q 12mV – RUN/SS + + – 180k – VOLTAGE SELECT ICOMP – SHDN + + ITH – 0.6V VREF + 89mV VSET VPROG 120k PGND SHDN SVIN REF AND VCC VREF (1.19V) 240k 60k VOSENSE 1433/34 FD SGND VCC U OPERATION (Refer to Functional Diagram) Main Control Loop The LTC1433/LTC1434 is a constant frequency, pulsewidth modulated current mode switching regulator. During normal operation, the internal P-channel power MOSFET is turned on each cycle when the oscillator sets the RS latch FF3, and turned off when the main current comparator ICOMP resets the latch. The peak inductor current at which the ICOMP resets the RS latch is controlled by the voltage on the ITH pin , which is the output of error amplifier GM. Pins VPROG and VOSENSE, described in the Pin Functions section, allow GM to receive an output feedback voltage VFB from either the internal or external resistive dividers. When the load current increases, it causes a slight decrease in VFB relative to the 1.19V reference, which in turn causes the ITH voltage to increase until the average inductor current matches the new load current. 6 60k The main control loop is shut down by pulling the RUN/SS pin low. Releasing RUN/SS allows an internal 3µA current source to charge up the soft start capacitor CSS. When CSS reaches 1.3V, the main control loop is enabled with the ITH voltage clamped at approximately 30% of its maximum value. As CSS continues to charge, ITH is gradually released allowing normal operation to resume. Comparator OVDET guards against transient overshoots > 7.5% by turning off the P-channel power MOSFETs and keeping them off until the fault is removed. Low Current Operation The LTC1433/LTC1434 have two internal P-channel MOSFETs sized for low and high load current conditions. At low load current, only the small MOSFET will be turned on while at high load current both MOSFETs will be on. LTC1433/LTC1434 U OPERATION (Refer to Functional Diagram) Having only the small MOSFET on with low load current reduces switching and gate charge losses, hence boosting efficiency. For the device to go into low current mode, two conditions must be satisfied: the peak current of the inductor should not exceed 260mA and the voltage at the ITH pin should not exceed 0.6V. When either one of the conditions is exceeded, the big MOSFET will be turned on at the next clock cycle. source connected to the PLLIN pin. The output of the phase detector at the PLL LPF pin is also the control input of the oscillator, which operates over a 0V to 2.4V range corresponding to – 30% to + 30% in the oscillator’s center frequency. When locked, the PLL aligns the turn-on of the MOSFETs to the rising edge of the synchronizing signal. When the PLLIN is left open, PLL LPF goes low, forcing the oscillator to minimum frequency. Dropout Operation When the input supply voltage decreases toward the output voltage, the rate of change of inductor current during the on cycle decreases. This reduction means that the P-channel MOSFETs will remain on for more than one oscillator cycle since the ICOMP is not tripped. Further reduction in input supply voltage will eventually cause the P-channel MOSFET to be turned on 100%, i.e., DC. The output voltage will then be determined by the input voltage minus the voltage drop across the MOSFETs. Typically under dropout, both the power MOSFETs are on since the voltage on the ITH pin is greater than 0.6V. Power-On Reset Frequency Synchronization The POR pin is an open-drain output which pulls low when the regulator is out of regulation. When the output voltage rises to within 5% of regulation, a timer is started which releases POR after 216 (65536) oscillator cycles. In shutdown the POR output is pulled low. Short-Circuit Protection When the output is shorted to ground, the frequency of the oscillator will be reduced to about 1/4.5 of its designed rate. This low frequency allows the inductor current to discharge, thereby preventing runaway. The oscillator’s frequency will gradually increase to its designed rate when the output voltage increases above 0.65V. A phase-locked loop (PLL) is available on the LTC1434 to allow the oscillator to be synchronized to an external U W U U APPLICATIONS INFORMATION The basic LTC1434 application circuit is shown in Figure 1. External component selection is driven by the load requirement and begins with the selection of COSC and L. Next, the Schottky diode D1 is selected followed by CIN and COUT. COSC Selection for Operating Frequency The LTC1433/LTC1434 use a constant frequency architecture with the frequency determined by an external oscillator capacitor COSC. During the on-time, COSC is charged by a fixed current plus an additional current which is proportional to the output voltage of the phase detector (VPLL LPF on LTC1434). When the voltage on the COSC capacitor reaches 1.19V, it is reset to ground. The process then repeats. The value of COSC is calculated from the desired operating frequency. Assume the phase-locked loop has no external oscillator input, i.e. VPLL LPF = 0V. 4 1.37 10 COSC pF = Frequency kHz ( ) ( ) – 11 A graph for selecting COSC vs Frequency is given in Figure 2. For the LTC1433, the expression above is also applicable since its oscillator is internally set up to run at a condition equal to VPLL LPF = 0V. Therefore when using the graph for determining the capacitance value for the oscillator frequency, the VPLL LPF = 0V curve should be used for LTC1433. 7 LTC1433/LTC1434 U W U U APPLICATIONS INFORMATION 700 LTC1433/LTC1434 are used at 100% duty cycle with low input voltages. 600 FREQUENCY (kHz) VPLLLPF = 2.5V 500 Inductor Value Calculation 400 The operating frequency and inductor selection are interrelated in that higher operating frequencies permit the use of a smaller inductor for the same amount of inductor ripple current. However, this is at the expense of efficiency due to an increase in MOSFET gate charge losses. 300 VPLLLPF = 1.19V 200 VPLLLPF = 0V 100 0 0 50 100 150 CAPACITANCE ON COSC PIN (pF) 200 1433/34 F02 Figure 2. Selecting COSC for Oscillator Frequency As the operating frequency is increased the gate charge losses will be higher, reducing efficiency. The maximum recommended switching frequency is 700kHz. When using Figure 2 for synchronizable applications, the value of COSC is selected corresponding to a frequency 30% below your center frequency (see Phase-Locked Loop and Frequency Synchronization). Low Supply Operation The LTC1433/LTC1434 can function down to 3V and the maximum allowable output current is also reduced at low input voltages. Figure 3 shows the amount of change as the supply is reduced down to 2.5V. The minimum guaranteed input supply is 3V. 90 NOT RECOMMENDED MAXIMUM OUTPUT CURRENT (%) 100 80 70 60 50 4.0 3.0 3.5 SUPPLY VOLTAGE (V) ∆IL = V 1 VOUT 1– OUT VIN ( f)(L) Core losses are dependent on the peak-to-peak ripple current and core material. Hence, by choosing a larger inductance the peak-to-peak inductor ripple current will decrease, therefore decreasing core loss. To further reduce losses, low core loss material such as molypermalloy or Kool Mµ® can be chosen as the inductor core material. An indirect way that the inductor affects efficiency is through the usage of the big P-channel at low load currents. Lower inductance values will result in high peak inductor current. Because one of the conditions that determines the turning on of the large P-channel is peak current, this will result in the usage of the large P-channel even though the load current is low. Hence, efficiency at low load current will be affected. See Efficiency Considerations. Inductor Core Selection 2.5 1433/34 F03 Figure 3. Maximum Allowable Output Current vs Supply Voltage Another important point to note is that at a low supply voltages, the RDS(ON) of the P-channel switch increases (see Typical Performance Characteristics). Therefore, the user should calculate the power dissipation when the 8 The inductor value has a direct effect on ripple current. The ripple current ∆IL decreases with higher inductance or frequency and increases with higher VIN or VOUT: Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite, molypermalloy or Kool Mµ cores. Actual core loss is independent of core size for a fixed inductor value, but it is very dependent on inductance selected. As inductance increases, core losses go down. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Kool Mµ is a registered trademark of Magnetics, Inc. LTC1433/LTC1434 U W U U APPLICATIONS INFORMATION Ferrite designs have very low core loss and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “hard,” which means that inductance collapses abruptly when the peak design current is exceeded. This results in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate! Molypermalloy (from Magnetics, Inc.) is a very good, low loss core material for toroids, but it is more expensive than ferrite. A reasonable compromise from the same manufacturer is Kool Mµ. Toroids are very space efficient, especially when you can use several layers of wire. Because they generally lack a bobbin, mounting is more difficult. However, designs for surface mount are available which do not increase the height significantly. Catch Diode Selection The catch diode carries load current during the off-time. The average diode current is therefore dependent on the P-channel switch duty cycle. At high input voltages the diode conducts most of the time. As VIN approaches VOUT the diode conducts only a small fraction of the time. The most stressful condition for the diode is when the output is short circuited. Under this condition the diode must safely handle IPEAK at close to 100% duty cycle. A fast switching diode must also be used to optimize efficiency. Schottky diodes are a good choice for low forward drop and fast switching times. Most LTC1433/LTC1434 circuits will be well served by either a 1N5818, an MBRS130LT3 or an MBRM5819 Schottky diode. CIN and COUT Selection In continuous mode, the source current of the P-channel MOSFET is a square wave of duty cycle VOUT/VIN. To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by: CIN required IRMS ≈ IMAX [V (V OUT IN − VOUT )] 1/ 2 VIN This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that capacitor manufacturer’s ripple current ratings are often based on 2000 hours of life. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. Always consult the manufacturer if there is any question. The selection of COUT is driven by the required effective series resistance (ESR). Typically once the ESR requirement is satisfied the capacitance is adequate for filtering. The output ripple (∆VOUT) is determined by: 1 ∆VOUT ≈ ∆IL ESR + 4fCOUT where f = operating frequency, COUT = output capacitance and ∆IL = ripple current in the inductor. The output ripple is highest at maximum input voltage since ∆IL increases with input voltage. For the LTC1433/LTC1434, the general rule for proper operation is: COUT required ESR < 0.25Ω Manufacturers such as Nichicon, United Chemicon and Sanyo should be considered for high performance through-hole capacitors. The OS-CON semiconductor dielectric capacitor available from Sanyo has the lowest ESR/size ratio of any aluminum electrolytic at a somewhat higher price. Once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. In surface mount applications multiple capacitors may have to be paralleled to meet the ESR or RMS current handling requirements of the application. Aluminum electrolytic and dry tantalum capacitors are both available in surface mount configurations. In the case of tantalum, it is critical that the capacitors are surge tested for use in switching power supplies. An excellent choice is the AVX TPS series of surface mount tantalums, available in case heights ranging from 2mm to 4mm. Other capacitor types include Sanyo OS-CON, Nichicon PL series and Panasonic SP series. Consult the manufacturer for other specific recommendations. 9 LTC1433/LTC1434 U U W U APPLICATIONS INFORMATION Efficiency Considerations Since there are two separate pins for the drain of the small and large P-channel switch, we could utilize two inductors to further enhance the efficiency of the regulator over the low load current range. Figure 4 shows the circuit connection.(Also refer to the Typical Applications section.) L1 BSW LTC1433/ LTC1434 D1 L2 Hence, the dual inductor configuration is good for the user who requires as high an efficiency as possible at low load while retaining constant frequency operation. Output Voltage Programming The LTC1433/LTC1434 family all have pin selectable output voltage programming. The output voltage is selected by the VPROG pin as follows: VPROG = 0V VOUT = 3.3V VPROG = VIN VOUT = 5V VPROG = Open (DC) VOUT = Adjustable SSW D2 1433/34 F04 Figure 4. Using Two Inductors for Higher Low Current Efficiency To reduce core losses, the user can use a higher value inductor on the small P-channel switch. Since this switch only carries a small part of the overall current, the user can still use a small physical size inductor without sacrificing on copper losses. The Schottky diode can also be chosen with a lower current rating. For the graph in Figure 5, a Coilcraft DT1608C series inductor is used along with a MBRS0520LT3 Schottky diode on the SSW pin. As can be seen from Figure 5, the average efficiency gain over the region where the small P-channel is on is about 3%. 100 90 The LTC1433/LTC1434 family also has remote output voltage sense capability. The top of the internal resistive divider is internally connected to VOSENSE. For fixed output voltage applications, the VOSENSE pin is connected to the output voltage as shown in Figure 6. When using an external resistive divider, the VPROG pin is left open DC and the VOSENSE pin is connected to the feedback resistors as shown in Figure 7. To prevent stray pickup, a 100pF capacitor is suggested across R1 located close to the LTC1433/LTC1434. VPROG LTC1433/ VOSENSE LTC1434 GND: VOUT = 3.3V VIN: VOUT = 5V VOUT + COUT SGND VOUT = 3.3V COSC = 47pF 1433/34 F06 VIN = 5V EFFICIENCY (%) Figure 6. LTC1433/LTC1434 Fixed Output Applications 80 VIN = 9V 70 VOUT VPROG 60 50 40 0.001 LTC1433/ VOSENSE LTC1434 ONE 22µH INDUCTOR ON SSW AND BSW 100µH ON SSW 22µH ON BSW 0.01 0.1 LOAD CURRENT (A) 100pF R2 R1 SGND 1 ( ) VOUT = 1.19V 1 + 1433/34 • F05 Figure 5. Efficiency Comparison Between Single Inductor and Dual Inductor 10 OPEN (DC) R2 R1 1433/34 F07 Figure 7. LTC1433/LTC1434 Adjustable Applications LTC1433/LTC1434 U W U U APPLICATIONS INFORMATION Power-On Reset Function (POR) The power-on reset function monitors the output voltage and turns on an open-drain device when it is out of regulation. An external pull-up resistor is required on the POR pin. When power is first applied or when coming out of shutdown, the POR output is pulled to ground. When the output voltage rises above a level which is 5% below the regulated output value, an internal counter starts. After counting 216 (65536) clock cycles the POR pull-down device turns off. The POR output will go low whenever the output voltage drops below 7.5% of its regulated value for longer than approximately 30µs, signaling an out-of-regulation condition. In shutdown the POR output is pulled low even if the regulator’s output is held up by an external source. Run/Soft Start Function The RUN/SS pin is a dual purpose pin which provides the soft start function and a means to shut down the LTC1433/ LTC1434. Soft start reduces input surge currents by providing a gradual ramp-up of the internal current limit. Power supply sequencing can also be accomplished using this pin. An internal 3µA current source charges up an external capacitor CSS. When the voltage on RUN/SS reaches 1.3V the LTC1433/LTC1434 begins operating. As the voltage on RUN/SS continues to ramp from 1.3V to 2.4V the internal current limit is also ramped at a proportional linear rate. The current limit begins at approximately 350mA (at VRUN/SS = 1.3V) and ends at 1.2A (VRUN/SS = 2.4V). The output voltage thus ramps up slowly, charging the output capacitor while input surge currents are reduced. If RUN/SS has been pulled all the way to ground there is a delay of approximately 0.5s/µF before starting, followed by a like time to reach full current. tDELAY = 5(105)CSS seconds By pulling the RUN/SS pin below 1.3V, the LTC1433/ LTC1434 are put in low current shutdown. This pin can be driven directly from logic as shown in Figure 8. Diode D1 in Figure 8 reduces the start delay but allows CSS to ramp up slowly providing the soft start function. This diode can be deleted if soft start is not needed. The RUN/SS pin has an internal 6V Zener clamping the voltage on this pin (see Functional Diagram). RUN/SS RUN/SS D1 CSS CSS 1433/34 F08 Figure 8. RUN/SS Pin Interfacing Phase-Locked Loop and Frequency Synchronization The LTC1434 has an internal voltage-controlled oscillator and phase detector comprising a phase-locked loop. This allows the MOSFET turn-on to be locked to the rising edge of an external source. The frequency range of the voltage-controlled oscillator is ±30% around the center frequency fO. The value of COSC is calculated from the desired operating frequency (fO) with the following expression (assuming the phase-locked loop is locked, i.e VPLL LPF = 1.19V): 4 2.06 10 COSC pF = Frequency kHz ( ) ( ) – 11 Instead of using the above expression, Figure 2 graphically shows the relationship between the oscillator frequency and the value of COSC under various voltage conditions at the PLL LPF pin. The phase detector used is an edge sensitive digital type which provides zero degrees phase shift between the external and internal oscillators. This type of phase detector will not lock up on input frequencies close to the harmonics of the VCO center frequency. The PLL hold-in range ∆fH is equal to the capture range, ∆fH = ∆fC = ±0.3fO. The output of the phase detector is a pair of complementary current sources charging or discharging the external filter network on the PLL LPF pin. The relationship between the voltage on the PLL LPF pin and operating frequency is shown in Figure 9. A simplified block diagram is shown in Figure 10. 11 LTC1433/LTC1434 U W U U APPLICATIONS INFORMATION stable input to the voltage controlled oscillator. The filter components CLP and RLP determine how fast the loop acquires lock. Typically RLP = 10k and CLP is 0.01µF to 0.1µF. Be sure to connect the low side of the filter to SGND. FREQUENCY (kHz) 1.3fO The PLL LPF pin can be driven with external logic to obtain a 1:1.9 frequency shift. The circuit shown in Figure 11 will provide a frequency shift from fO to 1.9fO as the voltage VPLL LPF increases from 0V to 2.4V. Do not exceed 2.4V on VPLL LPF. fO 0.7fO 0 0.5 1.0 1.5 VPLLLPF (V) 2.5 2.0 3.3V OR 5V PLL LPF 1433/34 F09 2.4V MAX Figure 9. Relationship Between Oscillator Frequency and Voltage at PLL LPF Pin 1433/34 F11 EXTERNAL FREQUENCY RLP Figure 11. Directly Driving PLL LPF Pin 2.4V Low-Battery Comparator PLL LPF PLLIN DIGITAL PHASE/ FREQUENCY DETECTOR COSC CLP PHASE DETECTOR 50k 18k COSC OSC The LTC1433/LTC1434 have an on-chip, low-battery comparator which can be used to sense a low-battery condition when implemented as shown in Figure 12. The resistor divider R3/R4 sets the comparator trip point as follows: R4 VLBTRIP = 1.19 + 1 R3 1433/34 F10 Figure 10. Phase-Locked Loop Block Diagram VIN R4 If the external frequency (VPLLIN) is greater than the center frequency f0, current is sourced continuously, pulling up the PLL LPF pin. When the external frequency is less than f0, current is sunk continuously, pulling down the PLL LPF pin. If the external and internal frequencies are the same but exhibit a phase difference, the current sources turn on for an amount of time corresponding to the phase difference. Thus the voltage on the PLL LPF pin is adjusted until the phase and frequency of the external and internal oscillators are identical. At this stable operating point the phase comparator output is open and the filter capacitor CLP holds the voltage. The loop filter components CLP and RLP smooth out the current pulses from the phase detector and provide a 12 LTC1433/LTC1434 – R3 + 1.19V REFERENCE 1433/34 F12 Figure 12. Low-Battery Comparator The divided down voltage at the negative (–) input to the comparator is compared to an internal 1.19V reference. A 40mV hysteresis is built in to assure rapid switching. The output is an open-drain MOSFET and requires a pull-up resistor to operate. This comparator is active in shutdown. To save more shutdown quiescent current, this comparator can be shut down by taking the LBI pin below 0.74V, LTC1433/LTC1434 U U W U APPLICATIONS INFORMATION 4. Is the Schottky diode closely connected between the power ground and switch pin? further reducing the current to 15µA. The low side of the resistive divider should connect to SGND. 5. Keep the switching nodes, SSW and BSW away from sensitive small-signal nodes VOSENSE, PLLIN, PLL LPF, COSC, ITH and LBI. PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC1433/LTC1434. These items are also illustrated graphically in the layout diagram of Figure 13. Check the following in your layout: Design Example As a design example, assume VIN = 6V, VOUT = 5V, IMAX = 400mA and fOSC = 200kHz. With these requirements we can start choosing all of the important components. 1. Are the signal and power grounds segregated? The LTC1433/LTC1434 signal ground pin must return to the (–) plate of COUT. The power ground returns to the anode of the Schottky diode and the (–) plate of CIN, which should have as short lead lengths as possible. With no frequency synchronization required, the LTC1433 can be used for this circuit. From Figure 2, the VPLL LPF = 0V curve is used to determine the value of the oscillator capacitor. From the graph a value of 50pF will provide the desired frequency. 2. Does the LTC1433/LTC1434 VOSENSE pin connect to the (+) plate of COUT? In adjustable applications, the resistive divider R1/R2 must be connected between the (+) plate of COUT and signal ground. Next the inductor value is selected. From the Maximum Output Current vs Input Supply graph in the Typical Performance Characteristics section, a value of L = 22µH would be able to meet the requirement for the output load current. 3. Does the (+) plate of CIN connect to the power VIN as close as possible? This capacitor provides the AC current to the internal P-channel MOSFETs and their drivers. For the catch diode, a MBRS130LT3 is selected. 0.1µF CIN D1 + OUTPUT DIVIDER REQUIRED WITH ADJUSTABLE VERSION ONLY. CONNECT VOSENSE TO VOUT FOR FIXED OUTPUT VOLTAGE L1 1 2 VOUT COUT 3 + 4 5 6 CSS 7 8 9 10 20 PWRVIN PGND 19 NC SSW NC LTC1434 BSW SGND SVIN PLLIN PLL LPF NC COSC RUN/SS POR NC LBO LBI ITH VOSENSE VPROG 18 17 16 15 14 13 COSC 12 11 1433/34 F13 BOLD LINES INDICATE HIGH CURRENT PATHS Figure 13. LTC1434 Layout Diagram (See Board Layout Check List) 13 LTC1433/LTC1434 U U W U APPLICATIONS INFORMATION CIN will require an RMS current rating of at least 0.2A at temperature and COUT will require an ESR of less than 0.25Ω. In most of the applications, the requirements for these capacitors are fairly similar. Latchup Prevention (Figure 15) In applications where the input supply can momentarily dip below the output voltage, it is recommended that a Schottky diode (D2) be connected from VOUT to VIN. This diode will prevent the output capacitor from forward biasing the parasitic diode of the internal monolithic power MOSFET, preventing a large amount of current from flowing into the substrate to create a potential latchup condition. Figure 14 shows the complete circuit along with its efficiency curve. 100 D1: MBRS130LT3 L1: SUMIDA CD54-220 *AVX TPSD107M010R0100 + L1 22µH 2 100µF* 10V 4 3 5 6 0.1µF 7 8 16 PWRVIN PGND 15 SSW NC BSW NC LTC1433 SGND RUN/SS LBO LBI SVIN COSC POR ITH VOSENSE VPROG EFFICIENCY (%) VOUT 5V 400mA 1 90 + D1 100µF* 10V 0.1µF VIN 6V 10k 14 13 12 POWER-ON RESET 11 10 5.1k VIN = 6V VOUT = 5V COSC = 50pF L = 22µH 80 70 60 50 680pF 40 0.001 50pF 9 6800pF 0.01 0.1 LOAD CURRENT (A) 1 1433/34 F14 Figure 14. Design Example Circuit and its Efficiency Curve VIN D2 SW L + LTC1434 D1 VOUT COUT 1433/34 F15 Figure 15 14 LTC1433/LTC1434 U TYPICAL APPLICATIONS N Highest Efficiency 3.3V/5V Converter L1 100µH D1 D2 2 L2 22µH VOUT + 1 3 4 100µF* 10V 5 6 0.1µF 7 8 BSW LTC1433 NC SGND 14 SVIN POWER-ON RESET 11 10 VOSENSE LBI 0.1µF 100k 12 ITH LBO 100pF 68µF** 20V 13 COSC POR RUN/SS + 15 PGND NC VIN 3.5V TO 12.5V FOR VOUT = 3.3V 6V TO 12.5V FOR VOUT = 5V 16 PWRVIN SSW 5.1k 9 VPROG VPROG = 0V, VOUT = 3.3V VPROG = VIN, VOUT = 5V 680pF 6800pF 1433/34 TA02 *AVX TPSD107M010R0100 D1: MOTOROLA MBRS0520LT3 ** AVX TPSE686M020R0150 D2: MOTOROLA MBRS130LT3 L1: COILCRAFT DT1608C SERIES L2: SUMIDA CD54 SERIES Positive-to-Negative – 5V Converter L1 68µH + 1 2 100µF* 10V 3 4 D1 5 VOUT –5V 6 0.01µF 7 8 D1: MOTOROLA MBRS130LT3 L1: COILCRAFT DO3316 SERIES PWRVIN SSW NC PGND BSW NC LTC1433 SGND RUN/SS LBO LBI SVIN COSC POR ITH VOSENSE VPROG *AVX TPSD107M010R0100 ** AVX TPSE107M016R0100 16 + 15 14 100µF** 16V VIN 3.5V TO 7.5V 0.1µF 100pF 13 12 6800pF VIN (V) IOUT(MAX) (mA) 11 10 9 680pF 5.1k 1433/34 TA03 3.0 4.0 5.0 6.0 7.0 7.5 180 240 290 340 410 420 15 LTC1433/LTC1434 U TYPICAL APPLICATIONS N Negative Boost Converter + + 100µF* 16V VOUT –9V + VIN – 3V TO – 7V 68µF** 20V 100µF* L1 100µH 16V 1 VIN (V) IOUT(MAX) (mA) NC NC 5 LTC1433 SGND 6 SVIN COSC POR RUN/SS 7 LBO 8 D1: MOTOROLA MBRS130LT3 L1: COILCRAFT DO3316 SERIES PGND BSW 4 0.1µF PWRVIN SSW 3 180 300 400 540 680 310k 1% D1 2 –3 –4 –5 –6 –7 0.1µF ITH VOSENSE LBI VPROG 16 50k 1% 100pF 15 14 100pF 13 12 6800pF 5.1k 680pF 11 10 1433/34 TA05 9 *AVX TPSE107M016R0100 ** AVX TPSE686M020R0150 Ultralow Output Ripple 5V to – 1.25V MR Head Amplifier Supply 0.1µF + D1: MOTOROLA MBRM5819 L1: SUMIDA CD54 SERIES L2: J.W. MILLER PM20-R33M *AVX TPSD107M010R0100 1 2 L1 22µH + VOUT –1.25V 280mA 100µF* L2 0.33µH 10V + 100µF* 10V 3 D1 6 0.1µF 1.2k 1% 4 5 23.8k 1% 100pF 100µF* 10V 7 8 PWRVIN SSW NC PGND BSW NC LTC1433 SGND RUN/SS LBO LBI SVIN COSC POR ITH VOSENSE VPROG 16 15 14 VIN 5V 10k 13 12 11 10 POWER-ON RESET 5.1k 680pF 100pF 9 6800pF 1433/34 TA04 16 LTC1433/LTC1434 U TYPICAL APPLICATIONS N 9V to 12V, – 12V Outputs D1 L1B 100µH 47µF** • 1N914 L1A 100µH 2 • VOUT 12V + 3 34k 1% 4 Si6447DQ D2 301k 1% 68µF* 20V 1 5 VOUT –12V 100pF 6 + 68µF* 20V 0.1µF 7 8 NC LOW-BATTERY TRIP AT VIN = 5V PGND BSW NC LTC1433 SGND SVIN COSC POR RUN/SS LBO LBI 30k *AVX TPSE686M020R0150 ** WIMA MKS2 PWRVIN SSW ITH VOSENSE VPROG 16 + 15 14 50pF 68µF* 20V VIN 4.5V TO 12.5V 0.1µF 100k 13 12 POWER-ON RESET 11 10 680pF 1k 9 6800pF 100k 96k 1433/34 TA07 L1A L1B 3 2 TOP VIEW 4 1• L1B L1A D1, D2: MOTOROLA MBRS130LT3 L1A, L1B: MANUFACTURER PART NO. COILTRONICS DALE CTX100-4 LPT4545-101LA EACH OUTPUT VIN (V) IOUT(MAX) (mA) 4.5 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 12.5 50 60 70 100 110 130 145 160 200 205 17 LTC1433/LTC1434 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. GN Package 16-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 0.189 – 0.196* (4.801 – 4.978) 16 15 14 13 12 11 10 9 0.229 – 0.244 (5.817 – 6.198) 0.150 – 0.157** (3.810 – 3.988) 1 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.007 – 0.0098 (0.178 – 0.249) 0.053 – 0.068 (1.351 – 1.727) 2 3 4 5 6 7 8 0.004 – 0.0098 (0.102 – 0.249) 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 18 0.009 (0.229) REF 0.008 – 0.012 (0.203 – 0.305) 0.025 (0.635) BSC GN16 (SSOP) 0398 LTC1433/LTC1434 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. GN Package 20-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 0.337 – 0.344* (8.560 – 8.737) 20 19 18 17 16 15 14 13 12 11 0.229 – 0.244 (5.817 – 6.198) 0.150 – 0.157** (3.810 – 3.988) 1 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.007 – 0.0098 (0.178 – 0.249) 0.058 (1.473) REF 2 3 4 5 6 7 8 0.053 – 0.068 (1.351 – 1.727) 9 10 0.004 – 0.0098 (0.102 – 0.249) 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.008 – 0.012 (0.203 – 0.305) 0.025 (0.635) BSC * 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 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. GN20 (SSOP) 0398 19 LTC1433/LTC1434 U TYPICAL APPLICATIO 5V to ±5V Outputs IOUT(MAX) = 130mA IOUT(MIN) = 10mA VOUT = 5V 2 100µF* 10V + L1B 20µH 3 100µF* + 10V D1 4.7µF** • • L1A 20µH 1 1 2 3 4 4 D2 IOUT(MAX) = 130mA IOUT(MIN) = 5mA VOUT = – 5V 5 6 0.01µF 7 8 PWRVIN SSW NC PGND BSW NC LTC1433 SVIN COSC SGND POR RUN/SS LBO LBI ITH VOSENSE VPROG 16 + 15 14 100µF* 10V VIN 5V 0.1µF 100k 50pF 13 12 POWER-ON RESET 11 10 5.1k 680pF 9 6800pF 1433/34 TA06 D1: MOTOROLA MBRS130LT3 *AVX TPSD107M010R0100 ** WIMA MKS2 L1A, L1B: MANUFACTURER PART NO. COILTRONICS DALE CTX20-4 LPT4545-200LA L1A L1B 3 2 TOP VIEW 4 1• L1A L1B RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT®1074/LT1076 Step-Down Switching Regulators 100kHz, 5A (LT1074) or 2A (LT1076) Internal Switch LTC1174/LTC1174-3.3/ LTC1174-5 High Efficiency Step-Down and Inverting DC/DC Converters Burst ModeTM Operation LTC1265 1.2A High Efficiency Step-Down DC/DC Converter Burst Mode Operation LT1375/LT1376 1.5A, 500kHz Step-Down Switching Regulators High Frequency, Small Inductor, High Efficiency Switchers, 1.5A Switch LTC1474 High Efficiency Step-Down Converter Low IQ = 10µA, 8-Pin MSOP LTC1435 High Efficiency Synchronous Step-Down Controller 16-Pin Narrow SO and SSOP LTC1436/LTC1436-PLL High Efficiency Low Noise Synchronous Step-Down Controllers 24-Pin Narrow and 28-Pin SSOP LTC1438/LTC1439 Dual High Efficiency Low Noise Synchronous Step-Down Controllers Up to Four Outputs Capability LTC1538-AUX Dual High Efficiency Synchronous Step-Down Controller Auxiliary Linear Regulator 5V Standby in Shutdown LTC1539 Dual High Efficiency Low Noise Synchronous Step-Down Controller Auxiliary Linear Regulator 5V Standby in Shutdown LTC1627 High Efficiency Monolithic Synchronous DC/DC Converter Low Supply Voltage: 2.65V to 10V, 0.5A Burst Mode is a trademark of Linear Technology Corporation. 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com 14334fa LT/TP 1298 2K REV A • PRINTED IN THE USA LINEAR TECHNOLOGY CORPORATION 1996