LTC1174 LTC1174-3.3/LTC1174-5 High Efficiency Step-Down and Inverting DC/DC Converter U FEATURES DESCRIPTIO ■ The LTC®1174 is a simple current mode DC/DC converter ideally suited for 9V to 5V, 5V to 3.3V or 5V to – 5V operation. With an internal 0.9Ω switch (at a supply voltage of 9V), the LTC1174 requires only four external components to construct a complete high efficiency DC/DC converter. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency: Up to 94% Peak Inductor Current Independent of Inductor Value Short-Circuit Protection Optimized for 5V to – 5V Applications Wide VIN Range: 4V to 18.5V Low Dropout Operation Low-Battery Detector Pin Selectable Current Limit Internal 0.9Ω Power Switch: VIN = 9V Only Four External Components Required 130µA Standby Current Active Low Micropower Shutdown Under a no load condition the LTC1174 draws only 130µA. In shutdown, it draws a mere 1µA making this converter ideal for current sensitive 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 LTC1174 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. U APPLICATIO S ■ ■ ■ ■ ■ Distributed Power Systems Step-Down Converters Inverting Converters Memory Backup Supply Portable Instruments Battery-Powered Equipment For applications requiring higher output current or ultrahigh efficiency, see the LTC1148 data sheet. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. U ■ TYPICAL APPLICATIO High Efficiency Step-Down Converter LTC1174-5 Efficiency 100 3 2 7 + 6 VIN LBIN SHUTDOWN LBOUT VOUT IPGM SW LTC1174-5 GND 8 95 15µF* 25V ×3 VIN = 6V 1 5 5V 175mA 100µH† + 1N5818 100µF** 10V 4 EFFICIENCY (%) VIN 9V 90 VIN = 9V 85 80 L = 100µH VOUT = 5V IPGM = 0V 75 1174 TA01 * (3) AVX TPSD156K025 ** AVX TPSD107K010 † COILTRONICS CTX100-4 70 1 10 LOAD CURRENT (mA) 100 200 1174 TA02 1174fe 1 LTC1174 LTC1174-3.3/LTC1174-5 W W W AXI U U ABSOLUTE RATI GS (Note 1) (Voltage Referred to GND Pin) Input Supply Voltage (Pin 6) LTC1174 ........................................... – 0.3V to 13.5V LTC1174HV ...................................... – 0.3V to 18.5V Switch Current (Pin 5) .............................................. 1A Switch Voltage (Pin 5) LTC1174 ................................................. VIN – 13.5V LTC1174HV ............................................ VIN – 18.5V Operating Temperature Range LTC1174CX ............................................ 0°C to 70°C LTC1174IX ........................................ – 40°C to 85°C Junction Temperature (Note 2) ............................ 125°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C U U W PACKAGE/ORDER I FOR ATIO TOP VIEW TOP VIEW VOUT (VFB*) 1 8 SHUTDOWN LBOUT 2 7 IPGM VOUT (VFB*) 1 8 LBOUT 2 7 IPGM 6 VIN 5 SW LBIN 3 6 VIN LBIN 3 GND 4 5 SW GND 4 SHUTDOWN N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO * ADJUSTABLE OUTPUT VERSION * ADJUSTABLE OUTPUT VERSION TJMAX = 125°C, θJA = 150°C/W TJMAX = 125°C, θJA = 110°C/W ORDER PART NUMBER LTC1174CN8 LTC1174CN8-3.3 LTC1174CN8-5 LTC1174IN8 LTC1174HVCN8 LTC1174HVCN8-3.3 LTC1174HVCN8-5 ORDER PART NUMBER S8 PART MARKING LTC1174CS8 LTC1174CS8-3.3 LTC1174CS8-5 LTC1174IS8 LTC1174HVCS8 LTC1174HVCS8-3.3 LTC1174HVCS8-5 LTC1174HVIS8 1174 117433 117450 1174I 1174H 1174H3 1174H5 1174HI Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 9V, VSHUTDOWN = VIN, IPGM = 0V, unless otherwise noted. SYMBOL IFB VFB VOUT PARAMETER Feedback Current Feedback Voltage Regulated Output Voltage ∆VOUT Output Voltage Line Regulation CONDITIONS LTC1174/LTC1174HV LTC1174/LTC1174HV LTC1174-3.3/LTC1174HV-3.3 LTC1174-5/LTC1174V-5 VIN = 6V to 12V, ILOAD = 100mA, IPGM = VIN (Note 3) ● ● ● MIN TYP 1.20 3.14 4.75 1.25 3.30 5.00 10 MAX 1 1.30 3.46 5.25 70 UNITS µA V V V mV 1174fe 2 LTC1174 LTC1174-3.3/LTC1174-5 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 9V, VSHUTDOWN = VIN, IPGM = 0V, unless otherwise noted. SYMBOL PARAMETER Output Voltage Load Regulation IQ Input DC Supply Current (Note 4) VLBTRIP ILBIN ILBOUT Low-Battery Trip Point Current into Pin 3 Current Sunk by Pin 2 VHYST IPEAK Comparator Hysteresis Current Limit RON ON Resistance of Switch tOFF VIH VIL IIH Switch Off-Time (Note 6) SHUTDOWN Pin High SHUTDOWN Pin Low SHUTDOWN Pin Input Current IIL SHUTDOWN Pin Input Current CONDITIONS LTC1174-3.3 (Note 3) 20mA < ILOAD < 175mA, IPGM = 0V 20mA < ILOAD < 400mA, IPGM = VIN LTC1174-5 (Note 3) 20mA < ILOAD < 175mA, IPGM = 0V 20mA < ILOAD < 400mA, IPGM = VIN Active Mode LTC1174: 4V < VIN < 12V, IPGM = 0V LTC1174HV: 4V < VIN < 16V, IPGM = 0V Sleep Mode LTC1174: 4V < VIN < 12V LTC1174HV: 4V < VIN < 16V SHUTDOWN (Note 4) LTC1174: VSHUTDOWN = 0V, 4V < VIN < 12V LTC1174HV: VSHUTDOWN = 0V, 4V < VIN < 16V MIN LTC1174: VLBOUT = 0.4V LTC1174HV: VLBOUT = 0.4V LTC1174/LTC1174HV IPGM = VIN, VOUT = 0V IPGM = 0V, VOUT = 0V LTC1174 LTC1174HV VOUT at Regulated Value Minimum Voltage at Pin 8 for Device to Be Active Maximum Voltage at Pin 8 for Device to Be in Shutdown LTC1174: VSHUTDOWN = 12V LTC1174HV: VSHUTDOWN = 16V 0 ≤ VSHUTDOWN ≤ 0.8V 1.0 0.6 7.5 0.54 0.27 ● ● ● ● 3 1.2 TYP MAX UNITS –5 –45 –70 –70 mV mV –5 –50 –70 –70 mV mV 450 450 600 600 µA µA 130 130 180 180 µA µA 1 2 1.25 10 25 1.4 0.5 1.5 1.5 30 0.83 0.53 1.30 1.55 5 µA µA V µA mA mA mV A A Ω Ω µs V V µA µA µA 1.2 0.8 15 0.60 0.34 0.75 0.90 4 0.75 0.5 2.0 0.5 The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at – 40°C ≤ TA ≤ 85°C. LTC1174I and LTC1174HVI Only. SYMBOL PARAMETER VFB Feedback Voltage ILBOUT Current Sunk by Pin 2 IPEAK Current Limit tOFF Switch Off-Time (Note 6) RON Switch On Resistance CONDITIONS LTC1174I/LTC1174HVI VLBOUT = 0.4V (LTC1174I) VLBOUT = 0.4V (LTC1174HVI) IPGM = VIN, VOUT = 0V (LTC1174I) IPGM = 0V, VOUT = 0V (LTC1174I) IPGM = VIN, VOUT = 0V (LTC1174HVI) IPGM = 0V, VOUT = 0V (LTC1174HVI) VOUT at Regulated Value (LTC1174I) VOUT at Regulated Value (LTC1174HVI) LTC1174I/LTC1174HVI Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. ● MIN 1.18 0.75 0.50 0.54 ● 0.5 ● ● 2.0 1.8 ● ● ● ● TYP 1.25 1.2 0.8 0.60 0.34 0.60 0.34 4 4 0.9 MAX 1.31 2.0 1.6 0.84 0.86 6.0 6.2 1.7 UNITS V mA mA A A A A µs µs Ω Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formulas: LTC1174CN8, LTC1174CN8-3.3, LTC1174CN8-5: TJ = TA + (PD × 110°C/W) LTC1174CS8, LTC1174CS8-3.3, LTC1174CS8-5: TJ = TA + (PD × 150°C/W) 1174fe 3 LTC1174 LTC1174-3.3/LTC1174-5 ELECTRICAL CHARACTERISTICS Note 3: Guaranteed by design. Note 4: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 5: Current into Pin 6 only, measured without electrolytic input capacitor. Note 6: The off-time is wafer-sort trimmed. U W TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Load Current Efficiency vs Load Current VIN = 9V 85 80 L = 50µH VOUT = 5V IPGM = 0V COIL = CTX50-4 75 10 LOAD CURRENT (mA) VIN = 6V VIN = 6V 90 EFFICIENCY (%) 90 1 95 95 VIN = 6V EFFICIENCY (%) EFFICIENCY (%) 95 70 VIN = 9V 85 80 L = 50µH VOUT = 5V IPGM = VIN COIL = CTX50-4 75 10 100 LOAD CURRENT (mA) Efficiency vs Load Current VIN = 5V 90 EFFICIENCY (%) L = 50µH VOUT = 3.3V IPGM = 0V COIL = CTX50-4 70 L = 50µH VOUT = 3.3V IPGM = VIN COIL = CTX50-4 10 100 LOAD CURRENT (mA) 300 1174 G04 VIN = 9V 80 70 L = 100µH VOUT = 3.3V IPGM = VIN COIL = CTX100-4 60 50 1 VIN = 5V 90 VIN = 9V 80 60 50 500 100 EFFICIENCY (%) VIN = 5V 70 10 100 LOAD CURRENT (mA) 1174 G03 Efficiency vs Load Current VIN = 9V L = 100µH VOUT = 5V IPGM = VIN COIL = CTX100-4 1 400 100 60 80 1174 G02 Efficiency vs Load Current 80 VIN = 9V 85 70 1 100 90 90 75 70 100 200 1174 G01 EFFICIENCY (%) Efficiency vs Load Current 100 100 100 50 1 10 100 LOAD CURRENT (mA) 500 1174 G05 1 10 100 LOAD CURRENT (mA) 500 1174 G06 1174fe 4 LTC1174 LTC1174-3.3/LTC1174-5 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Leakage Current vs Temperature Line Regulation 6 ILOAD = 100mA IPGM = 0V 95 VIN = 13.5V 160 LEAKAGE CURRENT (nA) 2 0 –2 –4 –6 –8 94 140 93 120 EFFICIENCY (%) 4 ∆VOUT (mV) Efficiency vs Input Voltage 180 100 80 60 89 –12 20 88 –14 0 8 6 4 10 INPUT VOLTAGE (V) 12 14 60 40 TEMPERATURE (°C) 5 SUPPLY CURRENT (µA) ILOAD = 100mA IPGM = 0V ILOAD = 300mA IPGM = VIN SHUTDOWN = 0V TA = 25°C CURRENT INTO PIN 6 ONLY 1.6 91 1.4 5 6 7 8 9 10 11 12 INPUT VOLTAGE (V) 13 1.0 0.8 0.6 300 250 200 100 50 0 0 4 6 8 10 INPUT VOLTAGE (V) 1174 G10 TA = 25°C 0 14 12 SLEEP MODE 150 0.2 2 IPGM = 0V 350 0.4 0 8 6 4 10 INPUT VOLTAGE (V) 2 Switch Resistance vs Input Voltage VOUT = 5V 50 TA = 25°C 1.6 1.5 1.5 14 Off-Time vs Output Voltage 1.7 2.0 12 1174 G12 1174 G11 Operating Frequency vs VIN – VOUT 14 IPGM = VIN 400 1.2 14 ACTIVE MODE 450 90 89 13 DC Supply Current SUPPLY CURRENT (µA) VOUT = 5V L = 100µH COIL = CTX100-4 92 9 10 11 12 8 INPUT VOLTAGE (V) 500 1.8 93 7 6 1174 G09 Supply Current in Shutdown Efficiency vs Input Voltage EFFICIENCY (%) 100 80 1174 G08 95 94 VOUT = 5V IPGM = 0V ILOAD = 75mA CORE = CTX (Kool Mµ®) 87 20 0 1174 G07 40 TA = 25°C 1.0 TA = 70°C OFF-TIME (µs) 1.4 RDS(ON) (Ω) NORMALIZED FREQUENCY 90 40 2 L = 50µH 91 –10 0 L = 100µH 92 1.3 1.2 1.1 LTC1174HV 30 20 LTC1174-5 LTC1174HV-5 1.0 0.5 0.9 10 LTC1174 0.8 0 0.7 0 1 5 7 3 6 2 4 (VIN – VOUT) VOLTAGE (V) 8 9 1174 G13 LTC1174-3.3 LTC1174HV-3.3 0 4 6 8 10 12 14 16 INPUT VOLTAGE (V) 18 20 1174 G14 0 1 3 4 2 OUTPUT VOLTAGE (V) 5 1174 G15 1174fe 5 LTC1174 LTC1174-3.3/LTC1174-5 U U U PI FU CTIO S SW(Pin5): Drain of the P-Channel MOSFET Switch. Cathode of Schottky diode must be closely connected to this pin. VOUT (VFB) (Pin 1): For the LTC1174, this pin connects to the main voltage comparator’s input. On the LTC1174-3.3 and LTC1174-5 this pin goes to an internal resistive divider which sets the output voltage. VIN (Pin 6): Input Supply Voltage. It must be decoupled close to ground Pin 4. LBOUT (Pin 2): Open Drain of an N-Channel Pull-Down. This pin will sink current when Pin 3 (LBIN) goes below 1.25V. During shutdown the state of this pin is indeterminate. IPGM (Pin 7): 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 value is reduced to 340mA. LBIN (Pin 3): The “–” Input of the Low-Battery Voltage Comparator. The “+” input is connected to a reference voltage of 1.25V. SHUTDOWN (Pin 8): Pulling this pin to ground keeps the internal switch off and puts the LTC1174 in micropower shutdown. GND (Pin 4): Ground Pin. W FU CTIO AL DIAGRA U U (Pin 1 connection shown for LTC1174-3.3 and LTC1174-5, changes create LTC1174) VIN 6 VLIM1 VLIM2 + IPGM SLEEP A5 VTH2 + – RSENSE 0.1Ω 7 A2 – – RESET A4 gmVFB Q + CT VOUT (VFB) SET VTH1 1 LBIN LBOUT 2 R1* 3 – – A1 A3 + 5 SW × 1.25V REFERENCE SHUTDOWN VFB 31.5k + 8 GND 4 * R1 = 51k FOR LTC1174-3.3 R1 = 93.5k FOR LTC1174-5 1174 BD 1174fe 6 LTC1174 LTC1174-3.3/LTC1174-5 U OPERATIO (Refer to Functional Diagram) The LTC1174 uses a constant off-time architecture to switch its internal P-channel power MOSFET. The off-time is set by an internal timing capacitor and the operating frequency is a function of VIN. The output voltage is set by an internal resistive divider (LTC1174-3.3 and LTC1174-5) or an external divider returned to VFB Pin 1 (LTC1174). A voltage comparator A1 compares the divided output voltage to a reference voltage of 1.25V. To optimize efficiency, the LTC1174 automatically switches between continuous and Burst Mode® operation. The voltage comparator is the primary control element when the device is in Burst Mode operation, while the current comparator controls the output voltage in continuous mode. During the switch“ON” time, switch current flows through the 0.1Ω sense resistor. When this current reaches the threshold of the current comparator A2, its output signal will change state, setting the flip-flop and turning the switch off. The timing capacitor, CT, begins to discharge until its voltage goes below VTH1. Comparator A4 will then trip, which resets the flip-flop and causes the switch to turn on again. Also, the timing capacitor is recharged. The inductor current will again ramp up until the current comparator A2 trips. The cycle then repeats. When the load is relatively light, the LTC1174 automatically goes into Burst Mode operation. The current mode loop is interrupted when the output voltage reaches the desired regulated value. The hysteretic voltage comparator A1 trips when VOUT is above the desired output voltage, shutting off the switch and causing the timing capacitor to discharge. This capacitor discharges past VTH1 until its voltage drops below VTH2. Comparator A5 then trips and a sleep signal is generated. In sleep mode, the LTC1174 is in standby and the load current is supplied by the output capacitor. All unused circuitry is shut off, reducing quiescent current from 0.45mA to 0.13mA. When the output capacitor discharges by the amount of the hysteresis of the comparator A1, the P-channel switch turns on again and the process repeats itself. Operating Frequency and Inductor Since the LTC1174 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) where tOFF = 4µs and VD is the voltage drop across the diode. Note that the operating frequency is a function of the input and ouput voltage. Although the size of the inductor does not affect the frequency, it does affect the ripple current. The peak-to-peak ripple current is given by: + VD ⎞ ⎛V IRIPPLE = 4 • 10 −6 ⎜ OUT ⎟ ⎝ ⎠ L ( A P− P) By choosing a smaller inductor, a low ESR output filter capacitor has to be used (see CIN and COUT). Moreover, core loss will also increase (see Inductor Core Selection section) due to higher ripple current. Burst Mode is a registered trademark of Linear Technology Corporation. 1174fe 7 LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO Inductor Core Selection With the value of L selected, the type of inductor must be chosen. Basically there are two kinds of losses in an inductor, core and copper Core losses are dependent on the peak-to-peak ripple current and the core material. However it is independent of the physical size of the core. By increasing the inductance the inductor’s peak-to-peak ripple current will decrease, therefore reducing core loss. Utilizing low core loss material, such as molypermalloy or Kool Mµ will allow users to concentrate on reducing copper loss and preventing saturation. Figure 1 shows the effect of different core material on the efficiency of the LTC1174. The CTX core is Kool Mµ and the CTXP core is powdered iron (material 52). EFFICIENCY (%) 50 10 100 LOAD CURRENT (mA) 500 100 EFFICIENCY (%) VIN To avoid overheating, the output capacitor must be sized to handle the ripple current generated by the inductor. The worst case RMS ripple current in the output capacitor is given by: VIN = 5V VOUT = 3.3V IPGM = VIN 60 CTX50-4 CTX50-4P 80 70 VIN = 5V VOUT = 3.3V IPGM = VIN 50 1 ]1/2 (A ) RMS COUT 70 60 IRMS ≈ [ IOUT VOUT ( VIN − VOUT ) CTX100-4P 80 90 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 CIN RMS current is given by: CTX100-4 100 1 CIN This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst case is commonly used for design because even significant deviations do not offer much relief. Note that ripple current directly affects capacitor’s lifetime. DO NOT UNDERSPECIFY THIS COMPONENT. An additional 0.1µF ceramic capacitor is also required on VIN for high frequency decoupling. Although higher inductance reduces core loss, it increases copper loss as it requires more windings. When space is not 90 a premium larger gauge wire can be used to reduce the wire resistance. This also prevents excessive heat dissipation. 10 100 LOAD CURRENT (mA) 500 1174 F01 Figure 1. Efficiency Using Different Types of Inductor Core Material IPEAK ( A RMS) 2 = 170 mA or 300mA IRMS ≈ Although the output voltage ripple is determined by the hysteresis of the voltage comparator, ESR of the output capacitor is also a concern. Too high of an ESR will create a higher ripple output voltage and at the same time cause the LTC1174 to sleep less often. This will affect the efficiency of the LTC1174. For a given technology, ESR is a direct function of the volume of the capacitor. Several small-sized capacitors can also be paralleled to obtain the same ESR as one large can. Manufacturers such as Nichicon, Chemicon and Sprague should be considered for high performance capacitors. The OS-CON semiconductor dielectric capacitor available from Sanyo has the lowest ESR for its size, at a higher price. 1174fe 8 LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO 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 LTC1174 circuits will be well served by either a 1N5818, a MBRS140T3 or a MBR0520L Schottky diode. compared with a 1.25V reference voltage. With the current going into Pin 3 being negligible, the following expression is used for setting the trip limit: ⎛ R4 ⎞ VLBTRIP = 1.25⎜1 + ⎟ ⎝ R3 ⎠ When the LTC1174 is shut down, the low-battery detector is inactive. VIN LTC1174 R4 3 R3 – + 1.25V REFERENCE Short-Circuit Protection 1174 F03 The LTC1174 is protected from output short by its internal current limit. Depending on the condition of IPGM pin, the limit is either set to 340mA or 600mA. In addition, the offtime of the switch is increased to allow the inductor’s current to decay far enough to prevent any current build-up (see Figure 2). IPGM = VIN Figure 3. Low-Battery Comparator LTC1174 Adjustable/Low Noise Applications The LTC1174 develops a 1.25V reference voltage between the feedback (Pin 1) terminal and ground (see Figure 4). 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⎠ IPGM = 0 GND L = 100µH VIN = 13.5V 20µs/DIV 1174 F02 Figure 2. Inductor's 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 3) which is 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 LTC1174. Alternatively, a capacitor across R2 can be used to increase the switching frequency for low noise operation. Inverting Applications The LTC1174 can easily be set up for a negative output voltage. If – 5V is desired, the LTC1174-5 is ideal for this application as it requires the least components. Figure 5 shows the schematic for this application. Note that the 1174fe 9 LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO VOUT LTC1174 VFB 6.8nF** R2 100pF* R1 1 * ADJUSTABLE APPLICATIONS ** LOW NOISE APPLICATIONS 1174 F04 Figure 4. LTC1174 Adjustable Configuration INPUT VOLTAGE 4V TO 12V 3 2 7 + 6 VIN LBIN 0.1µF SHUTDOWN LBOUT VOUT IPGM SW LTC1174HV-5 GND 4 8 47µF* 16V ×2 1 5 50µH** MBRS140T3 + 47µF* 16V ×2 * AVX TPSD476K016 ** COILTRONICS CTX50-4 VOUT –5V 45mA 1174 F05 Figure 5. Positive-to-Negative 5V Converter output voltage is now taken off the GND pin. Therefore, the maximum input voltage is now determined by the difference between the absolute maximum voltage rating and the output voltage. A maximum of 12V is specified in Figure 5, giving the circuit a 1.5V of headroom for VIN. Note that the circuit can operate from a minimum of 4V, making it ideal for a 4 NiCad cell application. For a higher output current circuit, please refer to the Typical Applications section. LTC1174-5 regulator and also to one or more loads in parallel with the the regulator’s VIN. If the battery is disconnected while the LTC1174/LTC1174-3.3/LTC1174-5 regulator is supplying a light load and one of the parallel circuits is a heavy load, the input capacitor of the LTC1174/ LTC1174-3.3/LTC1174-5 regulator could be pulled down faster than the output capacitor, causing the absolute maximum ratings to be exceeded. The result is often a latchup which can be destructive if VIN is reapplied. Battery disconnect is possible as a result of mechanical stress, bad battery contacts or use of a lithium-ion battery with a built-in internal disconnect. The user needs to assess his/her application to determine whether this situation could occur. If so, additional protection is necessary. Prevention against latchup can be accomplished by simply connecting a Schottky diode across the SW and VIN pins as shown in Figure 6. The diode will normally be reverse biased unless VIN is pulled below VOUT at which time the diode will clamp the (VOUT – VIN) potential to less than the 0.6V required for latchup. Note that a low leakage Schottky should be used to minimize the effect on no-load supply current. Schottky diodes such as MBR0530, BAS85 and BAT84 work well. Another more serious effect of the protection diode leakage is that at no load with nothing to provide a sink for this leakage current, the output voltage can potentially float above the maximum allowable tolerance. To prevent this from occuring, a resistor must be connected between VOUT and ground with a value low enough to sink the maximum possible leakage current. LATCHUP PROTECTION SCHOTTKY Absolute Maximum Ratings and Latchup Prevention The absolute maximum ratings specify that SW (Pin 5) can never exceed VIN (Pin 6) by more than 0.3V. Normally this situation should never occur. It could, however, if the output is held up while the supply is pulled down. A condition where this could potentially occur is when a battery is supplying power to an LTC1174/LTC1174-3.3/ VIN VOUT SW LTC1174 LTC1174-3.3 LTC1174-5 + 1174 F06 Figure 6. Preventing Absolute Maximum Ratings from Being Exceeded 1174fe 10 LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO Board Layout Checklist DESIGN EXAMPLE When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC1174. These items are also illustrated graphically in the layout diagram in Figure 7. Check the following in your layout: As a design example, assume VIN = 9V (nominal), VOUT = 5V, and IOUT = 350mA maximum. The LTC1174-5 is used for this application, with IPGM (Pin 7) connected to VIN. The minmum value of L is determined by assuming the LTC1174-5 is operating in continuous mode. 2. Is the “+” plate of CIN closely connected to VIN (Pin 6)? This capacitor provides the AC current to the internal P-channel MOSFET. IPEAK INDUCTOR CURRENT 1. Is the Schottky catch diode closely connected between ground (Pin 4) and switch (Pin 5)? AVG CURRENT = IOUT I +I = PEAK V IV 2 = 350mA 3. Is the 0.1µF VIN decoupling capacitor closely conected between VIN (Pin 6) and ground (Pin 4)? This capacitor carries the high frequency peak currents. 4. Is the SHUTDOWN (Pin 8) actively pulled to VIN during normal operation? The SHUTDOWN pin is high impedance and must not be allowed to float. 5. Is the IPGM (Pin 7) pulled either to VIN or ground? The IPGM pin is high impedance and must not be allowed to float. OUTPUT DIVIDER REQUIRED WITH ADJUSTABLE VERSION ONLY R2 R1 1 VOUT (VFB) 2 LBOUT 3 LBIN 4 GND TIME 1174 F08 Figure 8. 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: + VD ⎞ ⎛V IRIPPLE = 4 • 10 −6 ⎜ OUT ⎟ ⎝ ⎠ L SHUTDOWN IPGM LTC1174 VIN SW ( A P− P) 8 7 6 0.1µF VIN + CIN 5 D COUT + BOLD LINES INDICATE HIGH CURRENT PATH L VOUT 1174 F07 Figure 7. LTC1174 Layout Diagram (See Board Layout Checklist) 1174fe 11 LTC1174 LTC1174-3.3/LTC1174-5 U W U U APPLICATIO S I FOR ATIO Solving for L in the above equation and with VD = 0.6V, L = 44.8µH. The next higher standard value of L is 50µH (example: Coiltronics CTX50-4). The operating frequency, neglecting 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 ( A RMS) = 174mA For COUT, the RMS current rating should be at least: IPEAK ( A RMS) 2 = 300mA IRMS ≈ Now allow VIN to drop to 6V. At this minimum input voltage the operating frequency will decrease. The new frequency is 42kHz. Table 1. Inductor Manufacturers MANUFACTURER Coilcraft 1102 Silver Lake Road Cary, IL 60013 (708) 639-2361 Coiltronics Inc. 6000 Park of Commerce Blvd. Boca Raton, FL 33487 (407) 241-7876 Gowanda Electronics Corporation 1 Industrial Place Gowanda, NY 14070 (716) 532-2234 Sumida Electric Co. Ltd. 637 E. Golf Road, Suite 209 Arlington Heights, IL 60005 (708) 956-0666/7 PART NUMBER DT3316 Series Econo-Pac Octa-Pac GA10 Series CD 54 Series CD 75 Series Table 2. Capacitor Manufacturers MANUFACTURER AVX Corporation P.O. Box 887 Myrtle Beach, SC 29578 (803) 448-9411 Nichicon America Corporation 927 East State Parkway Schaberg, IL 60173 (708) 843-7500 Sanyo Video Components 2001 Sanyo Avenue San Diego, CA 92173 (619) 661-6385 Attn: Sales Dept. PART NUMBER TPS Series TAJ Series PL Series OS-CON Series 1174fe 12 LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S 6V to 5V Step-Down Regulator with Low-Battery Detection INPUT VOLTAGE 6V * LOW-BATTERY INDICATOR IS SET TO TRIP AT VIN = 5.5V ** AVX TPSD476K016 D1 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER PART NO. TYPE COILTRONICS CTX100-4 SURFACE MOUNT SUMIDA CD75-101 SURFACE MOUNT GOWANDA GA10-103K THROUGH HOLE 6 VIN 4.7k *LOWBATTERY INDICATOR 162k 7 IPGM 0.1µF SHUTDOWN + 8 47µF** 16V ×2 2 1 LBOUT VOUT LTC1174-5 3 5 SW LBIN GND 47.5k † D1 L1 100µH + 4 VOUT 5V 47µF** 365mA 16V ×2 1174 TA03 High Efficiency 3.3V Regulator INPUT VOLTAGE 4V TO 12.5V 6 VIN 7 IPGM SHUTDOWN + 8 1 VOUT LTC1174-3.3 2 5 LBOUT SW 3 * AVX TPSD226K025 ** AVX TPSD476K016 † COILTRONICS CTX50-4 22µF* 25V ×3 0.1µF LBIN GND 50µH† 1N5818 + 4 VOUT 3.3V 47µF** 425mA 16V ×2 1174 TA04 1174fe 13 LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S Low Noise 3V Regulator INPUT VOLTAGE 4V TO 12.5V + 6 VIN 7 3 2 IPGM SHUTDOWN LBIN VFB LTC1174 LBOUT SW 22µF* 25V ×3 8 0.1µF 1 6.8nF 50µH† 5 GND + 4 42k 100µF** 10V ×2 1N5818 * AVX TPSD226K025 ** AVX TPSD105K010 † COILTRONICS CTX50-4 VOUT 3V 450mA 30k 1174 TA05 Positive-to-Negative (– 5V) Converter INPUT VOLTAGE 4V TO 12.5V * LOW-BATTERY INDICATOR VIN(V) IOUT MAX(mA) IS SET TO TRIP AT VIN = 4.4V 4 110 ** AVX TPSD106K035 6 140 *** AVX TPSD105K010 170 D1 = MBRS130LT3 (SURFACE MOUNT) 8 10 200 1N5818 † 12.5 235 L1 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 6 VIN 4.7K *LOWBATTERY INDICATOR 280k 43k 7 IPGM SHUTDOWN + 0.1µF 8 10µF** 35V ×2 2 1 LBOUT VOUT LTC1174HV-5 3 5 SW LBIN GND 4 D1 L1† 50µH + 100µF*** 10V 1174 TA06 VOUT –5V 1174fe 14 LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S Positive-to-Negative (– 3.3V) Converter INPUT VOLTAGE 4V TO 13.5V * LOW-BATTERY INDICATOR IS SET TO TRIP AT VIN = 4.4V VIN(V) IOUT MAX(mA) ** AVX TPSD336K020 175 4 *** AVX TPSD105K010 205 D1 = MBRS140T3 (SURFACE MOUNT) 5 230 6 1N5818 † 255 7 L1 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 6 VIN 4.7K *LOWBATTERY INDICATOR 220k 7 IPGM + 33µF** 20V ×2 + 100µF*** 10V ×2 0.1µF SHUTDOWN 8 2 1 LBOUT VOUT LTC1174HV-3.3 3 5 SW LBIN GND 43k D1 L1† 50µH 4 VOUT –3.3V 210mA 1174 TA07 Negative Boost Converter * AVX TPSD336K020 D1 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA PART NO. CTX50-3 DT3316-473 CD54-470 GA10-472K 6 VIN 7 TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE IPGM SHUTDOWN 310k 8 2 + 33µF* 16V ×2 1 LBOUT VOUT LTC1174-3.3 3 5 SW LBIN GND 4 0.1µF D1 L1† 50µH 50k + 33µF* 20V ×2 0.1µF 1174 TA08 VOUT –9V 175mA INPUT VOLTAGE –5V 1174fe 15 LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S 9V to 5V Pre-Post Regulator INPUT VOLTAGE 6V TO 12.5V 3 * SANYO OS-CON ** AVX TPSD476K016 D1 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA †† PART NO. CTX50-3 DT3316-473 CD54-470 GA10-472K 2 7 TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE + 6 VIN LBIN SHUTDOWN LBOUT VFB LTC1174 IPGM SW 100µF* 16V 0.1µF 8 1 8 5 L1† 50µH GND 4 + D1 110k†† 47µF** 16V, ×2 100pF 0.1µF VOUT 5V 150mA 1 VIN OUT LT®1121-5 5 SHUTDOWN + GND 3 30.1k†† USE 1% METAL FILM RESISTORS 1µF SOLID TANTALUM 1174 TA09 LCD Display Power Supply INPUT VOLTAGE 4V TO 12.5V 3 7 2 * AVX TAJE106K050 ** AVX TPSD476K016 D1 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA PART NO. CTX100-3 DT3316-104 CD75-101 GA10-103K 56.2k†† 6 TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE VIN LBIN SHUTDOWN IPGM VFB LTC1174 LBOUT SW 8 2N2222 1 50k†† 5 2N5210 1N914 GND 4 + 47µF** 16V ×2 998k†† 0.1µF Si9435 D1 0.1µF L1† 100µH + VIN(V) IOUT MAX(mA) 4 20 5 25 6 30 7 35 8 43 9 50 10 55 11 60 12 65 VOUT –24V 50mA AT 10µF* VIN = 9V 50V ×4 1174 TA10 †† USE 1% METAL FILM RESISTORS 1174fe 16 LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S 9V to 5V, – 5V Outputs INPUT VOLTAGE 4V TO 12.5V * SANYO OS-CON ** WIMA MKS2 † COILTRONICS CTX100-4 VIN(V) IOUT MAX(mA) 4 75 6 100 8 125 10 145 12 160 13 180 L1B 3 2 CTX100-4 4 + 6 VIN 7 IPGM 0.1µF SHUTDOWN 100µF* 20V 0.1µF 8 1 VOUT LBIN LTC1174HV-5 2 5 LBOUT SW 3 VOUT 5V 135mA AT VIN = 9V 3.3µF** GND L1A† 100µH † 4 MBRS140T3 L1B 100µH + MBRS140T3 100µF* 16V L1A + 1 100µF* 16V 1174 TA11 –VOUT –5V 135mA AT VIN = 9V 9V to 12V, – 12V Outputs INPUT VOLTAGE 4V TO 12.5V * AVX TAJD226K035 ** WIMA MKS2 † COILTRONICS CTX100-4 †† USE 1% METAL FILM RESISTORS VIN(V) IOUT MAX(mA) 4 20 5 25 6 35 7 45 8 50 9 55 10 62 11 67 12 73 6 0.1µF VIN 7 3 2 IPGM SHUTDOWN LBIN VFB LTC1174 LBOUT SW 8 22µF* 35V ×3 L1B 3 2 CTX100-4 4 L1A 1 1 5 3.3µF** Si9430DY 1 L1A† 2 100µH + 4 GND 4 + † L1B 100µH 1N914 MBRS140T3 3 + MBRS140T3 22µF* 35V ×2 301k†† VOUT 12V 55mA AT VIN = 9V 34k†† 22µF* 35V ×2 1174 TA12 –VOUT –12V 55mA AT VIN = 9V 1174fe 17 LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO S Automatic Current Selection INPUT VOLTAGE 6V TO 12.5V 6 VIN 100k 100µF* 20V 2 TPO610L + 7 0.1µF 3 LBOUT SHUTDOWN IPGM VOUT LTC1174-5 LBIN SW 8 1 5 50µH† + GND 100k 1N5818 4 100k 100µF* 16V VOUT 5V 0mA TO 320mA 36.5k * SANYO OS-CON CAPACITOR † COILTRONICS CTX50-4 1174 TA13 Buck-Boost Converter INPUT VOLTAGE 4V TO 12V 6 VIN 7 * SANYO OS-CON ** WIMA MKS2 † COILTRONICS CTX100-4 L1B 3 2 CTX100-4 4 1 IPGM SHUTDOWN + 100µF* 20V 8 1 VOUT LBIN LTC1174HV-5 2 5 LBOUT SW 3 GND L1A 0.1µF 3.3µF** VOUT 5V 160mA † 4 L2A† 100µH 4 1 L1A 2 100µH + 1N5818 3 100µF* 16V 1174 TA14 1174fe 18 LTC1174 LTC1174-3.3/LTC1174-5 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .300 – .325 (7.620 – 8.255) ( 8.255 +0.889 –0.381 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .008 – .015 (0.203 – 0.381) +.035 .325 –.015 .400* (10.160) MAX ) 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 .100 (2.54) BSC N8 1002 (0.457 ± 0.076) NOTE: 1. DIMENSIONS ARE INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .053 – .069 (1.346 – 1.752) .014 – .019 (0.355 – 0.483) TYP INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) 2 3 4 .004 – .010 (0.101 – 0.254) .050 (1.270) BSC SO8 0303 1174fe 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. 19 LTC1174 LTC1174-3.3/LTC1174-5 U TYPICAL APPLICATIO Battery Charger INPUT VOLTAGE 8V TO 12.5V * AVX TAJD226K020 ** AVX TAJD107K010 D1,D2 = MBRS140T3 (SURFACE MOUNT) 1N5818 † L1 SELECTION MANUFACTURER COILTRONICS COILCRAFT SUMIDA GOWANDA PART NO. CTX50-2P DT3316-473 CD54-470 GA10-472K VIN(V) IOUT MAX(mA) 8 320 9 325 10 330 11 335 12 335 TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE + 6 VIN 7 3 2 0.1µF IPGM SHUTDOWN LBIN VFB LTC1174 LBOUT SW 8 1 D2 5 L1† 50µH GND 4 22µF* 20V ×2 150k + D1 VOUT TO 4 NiCAD BATTERY 100µF** 10V 33k 1174 TA15 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1074/LT1076 Step-Down Switching Regulator 100kHz, 5A (LT1074) or 2A (LT1076) Monolithic LTC1147 High Efficiency Step-Down DC/DC Controller 8-Pin Controller LTC1265 1.2A High Efficiency Step-Down DC/DC Regulator Burst Mode Operation, Monolithic LT1375/LT1376 1.5A 500kHz Step-Down Switching Regulator High Frequency Small Inductor LTC1574 High Efficiency Step-Down DC/DC Regulator LTC1174 with Internal Schottky Diode LT1611 Inverting 1.4MHz Switching Regulator in SOT-23 – 5V at 150mA from 5V Input, 1mVP-P Output Ripple, SOT-23 Package LTC1701 1MHz Step-Down DC/DC Converter in SOT-23 VIN = 2.5V to 5.5V, IQ = 135µA, VOUT = 5V to 1.25V LTC1707 High Efficiency Synchronous Step-Down Regulator VIN = 2.85 to 8.5V, Selectable Burst Mode Operation, 600mA Output Current, SO-8 Package LTC1877 High Efficiency Synchronous Step-Down Regulator 600mA at VIN = 5V, 2.65V to 10V = VIN, IQ = 10µA ® 1174fe 20 Linear Technology Corporation LT 1006 REV E • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 1994