LT1501IS8

LT1500 LINER | Alldatasheet

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Current Mode Switching Regulators FEATURES DESCRIPTIONU The LT 1500 is an adaptive-frequency current mode step- up switching regulator with an internal power switch that is rated up to 700mA. In contrast to pulse skipping switching regulators, the LT1500 uses a current mode topology that provides lower noise operation and im- proved efficiency. Only at very light loads is Burst Mode TM activated to give high efficiency and micropower opera- tion. High switching frequency (up to 500kHz) allows very small inductors to be used, along with ceramic capacitors if desired. The LT1500 operates with input voltages from 1.8V to 15V and has only 200µA operating current dropping to 8µA in shutdown. A low-battery comparator is included which stays alive in shutdown. A second output feedback pin with negative polarity allows negative output voltages to be regulated when the switcher is connected up as a Cuk or a flyback converter. Two package types are available. The LT1500 comes in a 14-pin SO package, with two options available for fixed output (3.3V or 5V) or adjustable operation. A reduced feature part, the LT1501, comes in the smaller 8-pin SO package with internal frequency compensation. It is also available in adjustable and fixed output voltage versions. n Low Noise Adaptive-Frequency Current Mode Operation Avoids Low Frequency Noise at Most Load Currents n Can Be Externally Synchronized (LT1500) n Micropower Quiescent Current: 200µA n Shutdown Current: 8µA Typ n Internal Loop Compensation n Low-Battery Comparator Active in Shutdown n Minimum Input Voltage: 1.8V Typ n Additional Negative Voltage Feedback Pin (LT1500) n Up to 500kHz Switching Frequency n Uses Low Profile, Low Cost Surface Mount Inductors , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. n Portable Instrumentation n Battery Operated Systems n PDA’s n Standby Power APPLICATIONSU TYPICAL APPLICATIONU 2-Cell to 5V Converter SHDN VIN LBO LBI SW ISENSE GND OUT LT1501-5 1nF 301k 301k LOW-BATTERY FLAG (USE EXTERNAL PULL-UP) 33µF* +220µF** 10V TANT

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22µH† 5V, 200mA LT1500/01 • TA01 AVX, TPSC107M006R0150 AVX, TPSD107M010 R0100 SUMIDA CD73-220, CD54-220 OR CD43-220. SELECT ACCORDING TO MAXIMUM LOAD CURRENT MBR0520L

ABSOLUTE MAXIMUM RATINGSW WW U Operating Ambient Temperature Range Operating Junction Temperature Range PACKAGE/ORDER INFORMATIONW UU TJMAX = 100°C, θJA = 100°C/ W ORDER PART NUMBER ORDER PART NUMBER ORDER PART NUMBER LT1500CS-3/5 LT1500IS-3/5 Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICSTJ = 25°C, VIN = 2.3V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Feedback/Output Pin Reference Voltage LT1500/LT1501, T J = 25°C 1.240 1.265 1.290 V All Conditions (Note 6) l 1.235 1.295 V LT1500-3/5, Select Pin Open 3.230 3.300 3.370 V All Conditions (Note 6) l 3.200 3.400 V LT1500-3/5, Select Pin Grounded 4.900 5.000 5.100 V All Conditions (Note 6) l 4.85 5.15 V Reference Voltage Line Regulation V IN = 2.3V to 15V l 0.02 0.06 %/V Feedback Pin Bias Current l 30 100 nA TJMAX = 100°C, θJA = 100°C/ W LT1500CS LT1500IS TJMAX = 100°C, θJA = 120°C/ W TOP VIEW FB/OUT LBI LBO SW SHDN V IN ISENSE GND S8 PACKAGE 8-LEAD PLASTIC SO LT1501CS8 LT1501CS8-3.3 LT1501CS8-5 LT1501IS8 LT1501IS8-3.3 LT1501IS8-5 TOP VIEW S PACKAGE 14-LEAD PLASTIC SO SHDN VC VIN ISENSE NC GND PGND FB NFB SS LBI LBO SYNC SW TOP VIEW S PACKAGE 14-LEAD PLASTIC SO SHDN VC VIN ISENSE NC GND PGND VOUT (3.3V/5V) SELECT SS LBI LBO SYNC SW

ELECTRICAL CHARACTERISTICSTJ = 25°C, VIN = 2.3V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Internal Divider Current LT1500-3.3/LT1501-3.3 l 22 30 µA LT1500-5/LT1501-5 l 33 45 µA Operating Quiescent Current V IN ≤ 5V, VSHDN = 2.3V (Note 1) l 200 280 µA VIN = 15V l 320 µA Supply Current in Shutdown V SHDN ≤ 0.2V, Fixed Voltages (Note 7) TJ ≥ 0°C l 81 5 µA TJ < 0°C2 0 µA Shutdown Pin Threshold l 0.4 1.1 V Shutdown Pin Input Current V SHDN = 2.3V l 31 0 µA Input Start-Up Voltage V SHDN = VIN TJ ≥ 0°C l 2.0 2.1 V TJ < 0°C 2.2 V Undervoltage Lockout Light Load 1.8 V Full Load 2.0 2.1 V Power Switch Switch On Resistance I SW = 0.7A (Note 2) l 0.50 0.72 Ω Peak Switch Current (Note 3) l 0.7 0.85 1.3 A Switch Breakdown Voltage I SW = 100µA l 30 45 V Switch Leakage Current V SW = 5V l 0.2 5 µA VSW = 20V l 0.3 10 µA Switch Turn-On Delay (Note 5) 800 ns Switch Turn-Off Delay (Note 5) 400 ns Current Sense Resistor l 0.28 0.42 Ω Low-Battery Comparator Low-Battery Threshold Falling Edge l 1.20 1.24 1.28 V Threshold Hysteresis 20 mV LBI Input Bias Current l 20 50 nA LBO Output Low State V LBI = 1.2V, ISINK = 100µA l 0.1 0.25 V ISINK = 2mA l 0.3 0.5 V LBO Leakage Current V LBI = 1.3V, VLBO ≤ 15V l 2 µA LT1500 Functions SYNC Pin Bias Current V SYNC = 3.3V l 15 35 µA SYNC Pin Threshold l 0.4 1.3 V Error Amplifier Transconductance 600 µmho VC Pin Source Current 20 µA VC Pin High Clamp Voltage 1.20 1.26 1.32 V NFB Reference Voltage FB Pin Open l 1.230 1.265 1.300 V NFB Pin Bias Current l 12 20 µA NFB to FB Transconductance Note 4 10,000 µmho Soft Start Bias Current Current Flows Out of Pin l 247 µA

ELECTRICAL CHARACTERISTICS

The l denotes specifications which apply over the full operating temperature range. Note 1: Feedback pin or output is held sightly above the regulated value to force the VC node low and switching to stop. Note 2: See Typical Performance Characteristics for graph of Guaranteed Switch Voltage vs Saturation Voltage. Note 3: Peak switch current is the guaranteed minimum value of switch current available in normal operation. Highest calculated switch current at full load should not exceed the minimum value shown. Note 4: Loading on FB pin will affect NFB reference voltage. ΔV NFB = IFB/gm. Do not exceed 10µA loading on FB when NFB is being used. Note 5: This is the delay between sense pin current reaching its upper or lower threshold and switch transition. Switch delay times cause peak-to- peak inductor current to increase and therefore switching frequency to be low. This effect will be significant for frequencies above 100kHz. See Application Information and Typical Performance Characteristics. Note 6: Reference voltage under all conditions includes V IN = 2.1V to 15V, all loads and full temperature range. Note 7: As with all boost regulators the output voltage of the LT1500 cannot fall to less than input voltage because of the path through the catch diode. This means that the output voltage divider on adjustable parts will still be generating feedback voltage at the FB pin (fixed voltage parts have an internal switch to disconnect the divider in shutdown). If the voltage on FB is greater than 0.6V in shutdown, the internal error amplifier will draw current that adds to shutdown current. See graph of Shutdown Current vs FB voltage in Typical Performance Characteristics. TYPICAL PERFORMANCE CHARACTERISTICS UW Switching Frequency (3.3V Output) LOAD CURRENT (mA) 0 50 100 FREQUENCY (kHz) 100 1000 150 200 250 300 LTC1500/01 • TPC20 10µH 20µH 50µH 100µH BURST REGION VIN = 2.3V Switching Frequency (5V Output) LOAD CURRENT (mA) 0 50 100 FREQUENCY (kHz) 100 1000 150 200 250 300 LTC1500/01 • TPC21 10µH 20µH 50µH 100µH BURST REGION VIN = 3V Switching Frequency (12V Output) LOAD CURRENT (mA) 02 55 0 7 5 FREQUENCY (kHz) 1000 100 100 125 150 175 200 LTC1500/01 • TPC22 10µH 50µH 20µH 100µH BURST REGION VIN = 5V Efficiency (3.3V Output) LOAD CURRENT (mA) EFFICIENCY (%) 100 10 100 1000 LTC1500/01 • TPC17 TJ = 25°C VIN = 2.3V LOW LOSS INDUCTOR L = 100µH L = 10µH L = 33µH Efficiency (5V Output) LOAD CURRENT (mA) EFFICIENCY (%) 100 10 100 1000 LTC1500/01 • TPC18 VIN = 3V LOW LOSS INDUCTOR L = 100µH L = 10µH L = 33µH Efficiency (12V Output) LOAD CURRENT (mA) EFFICIENCY (%) 100 10 100 1000 LTC1500/01 • TPC19 VIN = 5V LOW LOSS INDUCTOR L = 100µH L = 10µH L = 33µH

TYPICAL PERFORMANCE CHARACTERISTICS UW Efficiency (3.3V Output) ILOAD = 100mA ILOAD = 10mA INPUT VOLTAGE (V) 1.75 EFFICIENCY (%) 100 2.00 2.25 2.50 2.75 LT1500/01 • TPC11 3.00 3.25 TJ = 25°C L = 33µH LOW LOSS INDUCTOR Efficiency (5V Output) ILOAD = 100mA ILOAD = 10mA INPUT VOLTAGE (V) 2.0 EFFICIENCY (%) 100 2.5 3.0 3.5 4.0 LT1500/01 • TPC12 4.5 5.0 TJ = 25°C L = 33µH LOW LOSS INDUCTOR Efficiency (12V Output) ILOAD = 50mA ILOAD = 10mA INPUT VOLTAGE (V) EFFICIENCY (%) 100 2 468 LT1500/01 • TPC13 10 12 TJ = 25°C L = 33µH LOW LOSS INDUCTOR Inductor Copper Loss (5V Output) Inductor Copper Loss (3.3V Output) LOAD CURRENT (mA) 0 50 100 0.1 EFFICIENCY LOSS (%) 150 200 250 300 LT1500/01 • TPC14 R = 1Ω R = 0.5Ω R = 0.2Ω R = 0.1Ω VIN = 2.3V LOAD CURRENT (mA) 0 50 100 0.1 EFFICIENCY LOSS (%) 150 200 250 300 LT1500/01 • TPC15 R = 0.5Ω R = 0.2Ω R = 1ΩVIN = 3V R = 0.1Ω Inductor Copper Loss (12V Output) LOAD CURRENT (mA) 02 55 0 7 5 EFFICIENCY LOSS (%) 0.1 100 125 150 175 200 LTC1500/01 • TPC16 R = 0.2Ω R = 0.5Ω R = 1Ω VIN = 5V Maximum Load Current (3.3V Output) INPUT VOLTAGE (V) 1.50 OUTPUT CURRENT (mA) 600 500 400 300 200 100 1.75 2.00 2.25 2.50 LT1500/01 • TPC08 2.75 3.00 L ‡ 33µH L = 10µH Maximum Load Current (5V Output) INPUT VOLTAGE (V) 2.0 OUTPUT CURRENT (mA) 600 500 400 300 200 100 2.5 3.0 3.5 4.0 LT1500/01 • TPC09 4.5 5.0 L ‡ 33µH L = 10µH Maximum Load Current (12V Output) L = 100µH INPUT VOLTAGE (V) OUTPUT CURRENT (mA) 600 500 400 300 200 100 2 468 LT1500/01 • TPC10 10 12 L = 33µH L = 10µH

TYPICAL PERFORMANCE CHARACTERISTICS UW Peak-to-Peak Inductor Ripple Current AVERAGE SWITCH CURRENT 220 200 180 160 140 120 100 0.3 0.5 LT1500/01 • TPC07 PEAK-TO-PEAK INDUCTOR CURRENT VIN = 3.3V VOUT = 5V L = 50µH NOTE THAT RIPPLE CURRENT INCREASES WITH SMALLER INDUCTORS DUE TO PROPAGATION DELAY IN THE CURRENT COMPARATOR Switch Saturation Voltage SWITCH CURRENT (A) SWITCH VOLTAGE (V) 1.0 0.8 0.6 0.4 0.2 0.8 LT1500/01 • TPC06 0.2 0.4 0.6 1.0 TJ = 25°C INPUT VOLTAGE (V) LOAD CURRENT (mA) 120 100 2 468 LT1500/01 • TPC01 10 12 TJ = 25°C LOAD CURRENT IS REDUCED UNTIL Burst Mode OPERATION STARTS VOUT = 3.3V VOUT = 5V VOUT = 12V Burst Mode Threshold SINK CURRENT (mA) VOLTAGE (V) 0.6 0.5 0.4 0.3 0.2 0.1 1 234 LT1500/01 • TPC02 TJ = 25°C VLBI ≤ 1.2V Low-Battery Output Saturation VoltageQuiescent Input Supply Current INPUT VOLTAGE (V) SUPPLY CURRENT (µA) 15 25 LT1500/01 • TPC04 51 0 2 0 400 350 300 250 200 150 100 TJ = 25°C VFB OR VOUT HELD 5% HIGH, SO THAT Burst Mode OPERATION IS ACTIVATED. DOES NOT INCLUDE OUTPUT DIVIDER CURRENT INPUT VOLTAGE (V) CURRENT (µA) LT1500/01 • TPC03 5 10 15 25 TJ = 25°C VSHDN = 0V Input Current in Shutdown Shutdown Input Current vs Feedback Pin Voltage FEEDBACK PIN VOLTAGE (V) 140 120 100 0.6 1.0 LT1500/01 • TPC05 CURRENT (µA) TJ = 25°C VIN = 5V ADJUSTABLE PARTS ONLY. FIXED VOLTAGE PARTS DO NOT SHOW SHUTDOWN CURRENT INCREASE WITH FEEDBACK VOLTAGE

NFB/SELECT (LT1500 Only): NFB is a second feedback node used to regulate a negative output voltage. Negative output voltages can be generated by using a transformer flyback circuit, a Cuk converter or a capacitor charge pump added to a boost converter. The regulating point for NFB is 1.265V and the internal resistance to ground is 100kΩ . External divider current should be 300 µA or greater to avoid negative output voltage variations due to production variations in the internal resistor value. FB should be left open when using NFB. On fixed voltage parts, NFB is replaced with Select. The Select pin is used to set output voltage at either 3.3V or 5V. V C (LT1500 Only): This is the output of the error amplifier and the input to the current comparator. The VC pin voltage is about 700mV at very light loads and about 1.2V at full load. An internal comparator detects when the VC voltage drops below about 750mV and shuts down the current comparator and the power switch biasing to reduce quies- cent current. This forces the regulator to operate in Burst Mode operation. SYNC (LT1500 Only): This is a logic level input used to synchronize switching frequency to an external clock. The sync signal overrides the internal current comparator and turns the switch on. Minimum sync pulse width should be 50ns and maximum width should be 300ns. A continuous high sync signal will force the power switch to stay on indefinitely and current will increase without limit. Don’t do this! SS (LT1500 Only): This is the soft start function using the base of a PNP transistor whose emitter is tied to the V C pin. Grounding SS will turn off switching by pulling VC low. A capacitor tied from SS to ground will force VC to ramp up slowly during start-up at a rate set by the capacitor value and the internal 4µA pull-up current. An external resistor must be used to reset the capacitor voltage completely to 0V at power down. SHDN: Logic Level Shutdown Pin. This pin must be held high (> 1.1V) for the regulator to run . SHDN can be tied directly to V IN, even with V IN = 18V. The low-battery detector remains active in shutdown, but all other circuitry is turned off. V IN: This pin supplies power to the regulator and is connected to one side of the inductor sense resistor. It should be bypassed close to the chip with a low ESR capacitor. I SENSE: This is one end of the internal inductor-current sense resistor. With most applications, only the external inductor is tied to this pin. GND: This pin carries only low level current in the LT1500, but it carries full switch current in the LT1501. The negative end of the input bypass capacitor should be connected close to this pin and the pin should go directly to the ground plane with the LT1501. PGND (LT1500 Only): This pin is the emitter of the internal NPN power switch. Connect it directly to the ground plane. SW: This is the collector of the internal NPN power switch. To avoid EMI and overvoltage spikes, keep connections to this pin very short. LBI: This is the input to the low-battery detector with a threshold of 1.24V. Maximum pin voltage is 5V. Bypass LBI with a small filter capacitor when used. If unused, tie LBI to ground. The low-battery detector remains active in shutdown. LBO : This is the open collector output of the low-battery detector. It will sink up to 2mA. Leave open if not used. FB/V OUT: FB is the inverting input to the error amplifier with a regulating point of 1.265V and a typical bias current of 30nA. Bias current is reduced with a canceling circuit, so bias current could flow in either direction. FB is replaced with V OUT on fixed voltage parts. V OUT is the top of an internal divider that is connected to the internal FB node. A switch disconnects the divider in shutdown so that the divider current does not load VIN through the inductor and catch diode.

– + BIAS 1.265V REFERENCE BURST COMPARATOR NEGATIVE ERROR AMP ERROR AMP CURRENT COMPARATOR FIXED HYSTERESIS 100k 150pF V CFBNFB GND 100k VARIABLE HYSTERESIS ISENSE SW PGND 18mV RSENSE 0.28ΩRh INSYNCLBO 1.24V 0.75V SHDN LBI OUTPUT LTC1500/01 • BD APPLICATIONS INFORMATIONWU UU OPERATION (SEE BLOCK DIAGRAM) The LT1500 uses a current mode architecture without the need for an internal oscillator. Switching frequency is determined by the value of the external inductor used. This technique allows the selection of an operating frequency best suited to each application and considerably simplifies the internal circuitry needed. It also eliminates a subharmonic oscillation problem common to all fixed frequency (clocked) current mode switchers. In addition, it allows for high efficiency micropower operation while maintaining higher operating frequencies. Because the power switch (Q1) is grounded, the basic topology used will normally be a boost converter with output voltage always higher than the input voltage. Special topologies such as the SEPIC, flyback and Cuk converter can also be used when the output voltage may not always be higher than the input or when full shutdown of the output voltage is needed. Operation as a boost converter is as follows. Assume that inductor current is continuous, meaning that it never drops to zero. When the switch is on, inductor current will increase with voltage across the inductor equal to V IN. When the switch is off inductor current will decrease with inductor voltage equal to V OUT – V IN. Switching frequency will be determined by the inductor

APPLICATIONS INFORMATIONWU UU value, the peak-to-peak inductor current (set internally) and the values for V IN and V OUT. The LT1500 controls output voltage in continuous mode by adjusting the aver- age value of inductor current while maintaining the peak- to-peak value of the current relatively constant, hence, the name “current mode architecture.” The LT1500 sets the peak-to-peak value of switch current internally to establish operating frequency. This peak-to- peak value is scaled down somewhat at light load currents to avoid as long as possible the characteristic of other micropower converters wherein their switching frequency drops very low (into the audio range) at less than full load currents. At extremely light loads, even the LT1500 can no longer maintain higher frequency operation, and utilizes a Burst Mode operation to control output voltage. Details of Continuous Mode Operation At the start of a switch cycle, inductor current has de- creased to the point where the voltage across R SENSE is less than the internally generated voltage across Rh. This causes the current comparator output to go high and turn on the switch. At the same time, extra current is added to Rh via S1 to create hysteresis in the trip point of the comparator. This extra current is composed of a fixed amount (I1), and an amount proportional to average inductor current (I2). The presence of a variable I2 in- creases switching frequency at lighter loads to extend the load current range where high frequency operation is maintained and no Burst Mode operation exists. With the switch turned on, inductor current will increase until the voltage drop across R SENSE is equal to the higher voltage across Rh. Then the comparator output will go low, the switch will turn off and the current through Rh will be switched back to its lower value. Inductor current will decrease until the original condition is reached, complet- ing one switch cycle. Control of output voltage is maintained by adjusting the continuous current flowing through Rh. This affects both upper and lower inductor current trip levels at the same time. Continuous Rh current is controlled by the error amplifier which is comparing the voltage on the Feedback pin to the internal 1.265V reference. An internal frequency compensation capacitor filters out most the ripple voltage at the amplifier output. Operation at Light Loads At light load currents the lower trip level (switch turn-on) for inductor current drops below zero. At first glance, this would seem to initiate a permanent switch off-state be- cause the inductor current cannot reverse in a boost topology. In fact, what happens is that output voltage drops slightly between switch cycles, causing the error amplifier output to increase and bring the current trip level back up to zero. The switch then turns back on and inductor current increases to a value set by I1 (I2 is near zero at this point). The switch then turns off, and the inductor energy is delivered to the output, causing it to rise back up slightly. One or more switch cycles may be needed to raise the output voltage high enough that the amplifier output drops enough to force a sustained switch off period. The output voltage then slowly drops back low enough to cause the amplifier output to rise high enough to initiate a switch turn-on. Switching operation now consists of a series of bursts where the switch runs at normal frequency for one or more cycles, then turns off for a number of cycles. This Burst Mode operation is what allows the LT1500 to have micropower operation and high efficiency at very light loads. Saving Current in Burst Mode Operation Internal current drain for the LT1500 control circuitry is about 400µA when everything is operating. To achieve higher efficiency at extremely light loads, a special oper- ating mode is initiated when the error amplifier output is toward the low end of its range. The adaptive bias circuit comparator detects that the error amplifier output is below a predetermined level and turns off the current comparator and switch driver biasing. This reduces current drain to about 200µA, and forces a switch off state. Hysteresis in the comparator forces the device to remain in this micropower mode until the error amplifier output rises up beyond the original trip point. The regulated output volt- age will fall slightly over a relatively long period of time (remember that load current is very low) until the error amplifier output rises enough to turn off the adaptive bias

APPLICATIONS INFORMATIONWU UU mode. Normal operation resumes for one or more switch cycles and the output voltage increases until the error amplifier output falls below threshold, initiating a new adaptive bias shutdown. DESIGN GUIDE Selecting Inductor Value Inductor value is chosen as a compromise between size, switching frequency, efficiency and maximum output cur- rent. Larger inductor values become physically larger but provide higher output current and give better efficiency (because of the lower switching frequency). Low induc- tance minimizes size but may limit output current and the higher switching frequency reduces efficiency. The simplest way to handle these trade-offs is to study the graphs in the Typical Performance Characteristics sec- tion. A few minutes with these graphs will clearly show the trade-offs and a value can be quickly chosen that meets the requirements of frequency, efficiency and output current. This leaves only physical size as the final consideration. The concern here is that for a given inductor value, smaller size usually means higher series resistance. The graphs showing efficiency loss vs inductor series resistance will allow a quick estimate of the additional losses associated with very small inductors. One final consideration is inductor construction. Many small inductors are “open frame ferrites” such as rods or barrels. These geometries do not have a closed magnetic path, so they radiate significant B fields in the vicinity of the inductor. This can affect surrounding circuitry that is sensitive to magnetic fields. Closed geometries such as toroids or E-cores have very low stray B fields, but they are larger and more expensive (naturally). Catch Diode The catch diode in a boost converter has an average current equal to output current, but the peak current can be significantly higher. Maximum reverse voltage is equal to output voltage. A 0.5A Schottky diode like MBR0520L works well in nearly all applications. Input Capacitor Input capacitors for boost regulators are less critical than the output capacitor because the input capacitor ripple current is a simple triwave without the higher frequency harmonics found in the output capacitor current. Peak-to- peak current is less than 200mA and worst-case RMS ripple current in the input capacitor is less than 70mA. Input capacitor series resistance (ESR) should be low enough to keep input ripple voltage to less than 100mV P-P. This assumes that the capacitor is an aluminum or tanta- lum type where the capacitor reactance at the switching frequency is small compared to the ESR. C f ESR≥ () ( ) π A typical input capacitor is a 33µF, 6V surface mount solid tantalum type TPS from AVX. It is a “C” case size, with 0.15Ω maximum ESR. Some caution must be used with solid tantalum input capacitors because they can be dam- aged with turn-on surge currents that occur when a low impedance power source is hot-switched to the input of the regulator. This problem is mitigated by using a capaci- tor with a voltage rating at least twice the highest expected input voltage. Consult with the manufacturer for additional guidelines. If a ceramic input capacitor is used, different design criteria are used because these capacitors have extremely low ESR and are chosen for a minimum number of microfarads. C Ceramic f() = 1 f = switching frequency A typical unit is an AVX or Tokin 3.3µF or 4.7µF. Output Capacitor Output ripple voltage is determined by the impedance of the output capacitor at the switching frequency. Solid tantalum capacitors rated for switching applications are recommended. These capacitors are essentially resistive at frequencies above 50kHz, so ESR is the important factor in determining ripple voltage. A typical unit is a 220µF, 10V

APPLICATIONS INFORMATIONWU UU and it should be no more than 300k to keep bias current errors under 1%, giving: R RV V R R V DIV BAT BAT 3 12 4 4 312 4 12 4 = () = () VBAT = low battery voltage RDIV = Thevenin divider resistance = R3 in parallel with R4 There is about 20mV of hysteresis at the LBI pin. Hyster- esis can be increased by adding a resistor (R5) from the output (LBO) back to LBI. This resistor can be calculated from the following equation, but note that the equation for R4 will have to be changed when R5 is added. R RV Vm V V CC HYST BAT 5 3 17= () () ( ) ± VCC = supply voltage for LBO pull-up resistor VHYST = desired hysteresis at the battery R4 (When R5 is Used)= R3 R5() ( ) −() +− () 12 4 5 1 24 3 1 24 ..RV RVBAT CC The LBO pin is open collector. The external pull-up resistor value is determined by user needs. Generally the resistor is 100k to 1M to keep current drain low, but the LBO pin can sink several milliamperes if needed. Example: low battery voltage = 2.5V, desired hysteresis = 200mV, V CC = 5V. Use RDIV = 150k R k R kV 3 150 2 5 12 4 302 5 301 5 02 00 1 725 9 = () = = () () () .± . . k (use 301k, 1%) .56M (Use 10M) R kM Mk4 301 10 1 24 10 2 5 1 24 301 5 1 24= () ( ) () −() +− () .. . 272k (Use 274k 1%) The total divider resistance will be 274k + 301k = 575k, and this will draw about 7µA from a fully charged battery. Synchronizing The SYNC pin on the LT1500 can be used to synchronize switching frequency to an external clock. The pin should be driven with a 50ns to 300ns pulse which will trigger the switch to an on state. There is a fairly restricted range over which synchronizing will work, because the period between sync pulses must be greater than the natural on-time of the regulator when it is running unsynchronized, and the sync frequency must be greater than the unsynchronized switching frequency. This puts the following restrictions on synchronized operation: ff f fV VV SYNC NATURAL SYNC NATURAL OUT OUT IN < () ± (Use Minimum V )IN fNATURAL is the natural unsynchronized switching fre- quency of the regulator. It is a function of load current, so a careful check must be done to ensure that the above conditions are met under all load and input voltage condi- tions. Soft Start (SS) The LT1500 can be soft started by connecting a capacitor to the SS pin. This pin is the base of a PNP transistor whose emitter is tied to the V C pin. Soft start action will occur over the range of 0V to 0.8V on the SS pin and the pin is clamped at 1.2V with an internal clamp. An internal 4µA pull-up current and the external capacitor value determine soft start time. In a typical application a 0.22µF capacitor is sufficient to limit input surges and prevent output overshoot, even with overcompensation on the V C pin. Output voltages greater than 6V with very large output

APPLICATIONS INFORMATIONWU UU capacitors may require the capacitor to be larger. To ensure proper reset of the soft start capacitor, an external resistor must be connected in parallel with the capacitor. The resistor value should be 470k or more. Calculating Temperature Rise For most applications, temperature rise in the IC will be fairly low and will not be a problem. However, if load currents are near the maximum allowed and ambient temperatures are also high, a calculation should be done to ensure that the maximum junction temperature of 100°C is not exceeded. The calculations must account for power dissipation in the switch, the drive circuitry and the sense resistor. P IR V V V V IV V R I V V TOTAL OUT SW OUT OUT IN IN OUT OUT IN SENSE OUT OUT IN = () () ( ) −() + −() + () 230 PTOTAL = total device power dissipation RSW = switch resistance (0.72Ω max) RSENSE = sense resistance (0.42Ω max) With VIN = –2.2V, VOUT = 5V, IOUT = 150mA, an 8-pin SO package and maximum ambient temperature of 85 °C (industrial range), P W + −() + () =+ + = 01 5 07 2 5 5 22 01 55 22 0 42 0 15 5 0 47 0 014 0 049 0 11 .. . .. · .. . . The SO package has a thermal resistance of 120°C/W, so maximum device temperature will be: TJMAX = 85°C + 0.11W(120°C/W) = 98°C PACKAGE DESCRIPTIONU Dimensions in inches (millimeters) unless otherwise noted. 1 2 3 4 0.150 – 0.157** (3.810 – 3.988) 8 7 6 5 0.189 – 0.197* (4.801 – 5.004) 0.228 – 0.244 (5.791 – 6.197) 0.016 – 0.050 0.406 – 1.270 0.010 – 0.020 0°– 8° TYP 0.008 – 0.010 (0.203 – 0.254) SO8 0695 0.053 – 0.069 (1.346 – 1.752) 0.014 – 0.019 (0.355 – 0.483) 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSCDIMENSION 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 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610)

14-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) Dimensions in inches (millimeters) unless otherwise noted.PACKAGE DESCRIPTIONU 1 2 3 4 0.150 – 0.157** (3.810 – 3.988) 14 13 0.337 – 0.344* (8.560 – 8.738) 0.228 – 0.244 (5.791 – 6.197) 12 11 10 9 5 6 7 0.016 – 0.050 0.406 – 1.270 0.010 – 0.020 0° – 8° TYP 0.008 – 0.010 (0.203 – 0.254) S14 0695 0.053 – 0.069 (1.346 – 1.752) 0.014 – 0.019 (0.355 – 0.483) 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) TYP 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 l FAX: (408) 434-0507 l TELEX: 499-3977 LT/GP 0896 7K • PRINTED IN USA  LINEAR TECHNOLOGY CORPORATION 1 996 TYPICAL APPLICATIONU SHDN IN SS LBI LBO SYNC SW ISENSE COMP OUT SELECT LT1500-3.3/LT1501-5 GND PGND 1nF402k 1M 249k 33µH LT1500/01 • TA02 ON(HI) OFF (LO) 470k TO SYSTEM 1000pF + 220µF 10V MBR0520L 0.22µF 100k Typical LT1500 (14-Pin) Application, 2-Cell to 5V Converter PART NUMBER DESCRIPTION COMMENTS LTC 1163 Triple High Side Driver for 2-Cell Inputs 1.8V Minimum Input, Drives N-Channel MOSFETs LTC1174 Micropower Step-Down DC/DC Converter 94% Efficiency, 130 µA IQ, 9V to 5V at 300mA LT1302 High Output Current Micropower DC/DC Converter 5V/600mA from 2V, 2A Internal Switch, 200 µA IQ LT1304 2-Cell Micropower DC/DC Converter Low-Battery Detector Active in Shutdown LTC1440/1/2 Ultralow Power Single/Dual Comparator with Reference 2.8 µA IQ, Adjustable Hysteresis LTC1516 2-Cell to 5V Regulated Charge Pump 12 µA IQ, No Inductors, 5V at 50mA from 3V Input LT1521 Micropower Low Dropout Linear Regulator 500mV Dropout, 300mA Current, 12 µA IQ RELATED PARTS