LTC1174CN8

LTC1174 LTC1174-3.3/LTC1174-5 High Efficiency Step-Down and Inverting DC/DC Converter FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 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 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. 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. 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. APPLICATIO S ■ ■ ■ ■ ■ ■ Distributed Power Systems Step-Down Converters Inverting Converters Memory Backup Supply Portable Instruments Battery-Powered Equipment TYPICAL APPLICATIO VIN 9V 3 2 7 High Efficiency Step-Down Converter 100 LTC1174-5 Efficiency 6 VIN LBIN LBOUT IPGM LTC1174-5 GND 4 SHUTDOWN VOUT SW + 8 1 5 100µH† EFFICIENCY (%) 15µF* 25V ×3 95 VIN = 6V 90 85 80 75 L = 100µH VOUT = 5V IPGM = 0V 1 10 LOAD CURRENT (mA) 100 200 1174 TA02 5V 175mA + 1N5818 100µF** 10V 1174 TA01 * (3) AVX TPSD156K025 ** AVX TPSD107K010 † COILTRONICS CTX100-4 70 U VIN = 9V 1174fe U U 1 LTC1174 LTC1174-3.3/LTC1174-5 ABSOLUTE AXI U RATI GS (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 PACKAGE/ORDER I FOR ATIO TOP VIEW VOUT (VFB*) 1 LBOUT 2 LBIN 3 GND 4 N8 PACKAGE 8-LEAD PDIP * ADJUSTABLE OUTPUT VERSION TJMAX = 125°C, θJA = 110°C/W 8 7 6 5 SHUTDOWN IPGM VIN SW ORDER PART NUMBER LTC1174CN8 LTC1174CN8-3.3 LTC1174CN8-5 LTC1174IN8 LTC1174HVCN8 LTC1174HVCN8-3.3 LTC1174HVCN8-5 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 SYMBOL IFB VFB VOUT ∆VOUT PARAMETER Feedback Current Feedback Voltage Regulated Output Voltage Output Voltage Line Regulation 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. 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 ● ● ● 2 U U W WW U W (Note 1) 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 TOP VIEW VOUT (VFB*) 1 LBOUT 2 LBIN 3 GND 4 8 7 6 5 SHUTDOWN IPGM VIN SW S8 PACKAGE 8-LEAD PLASTIC SO * ADJUSTABLE OUTPUT VERSION TJMAX = 125°C, θJA = 150°C/W ORDER PART NUMBER LTC1174CS8 LTC1174CS8-3.3 LTC1174CS8-5 LTC1174IS8 LTC1174HVCS8 LTC1174HVCS8-3.3 LTC1174HVCS8-5 LTC1174HVIS8 S8 PART MARKING 1174 117433 117450 1174I 1174H 1174H3 1174H5 1174HI TYP 1.25 3.30 5.00 10 1.20 3.14 4.75 MAX 1 1.30 3.46 5.25 70 UNITS µA V V V mV 1174fe LTC1174 LTC1174-3.3/LTC1174-5 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER Output Voltage Load Regulation 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. 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 TYP –5 –45 –5 –50 450 450 130 130 1 2 1.25 1.0 0.6 7.5 0.54 0.27 1.2 0.8 15 0.60 0.34 0.75 0.90 4 MAX –70 –70 –70 –70 600 600 180 180 10 25 1.4 0.5 1.5 1.5 30 0.83 0.53 1.30 1.55 5 0.75 0.5 2.0 0.5 UNITS mV mV mV mV µA µA µA µA µA µA V µA mA mA mV A A Ω Ω µs V V µA µA µA IQ Input DC Supply Current (Note 4) VLBTRIP ILBIN ILBOUT VHYST IPEAK RON tOFF VIH VIL IIH IIL Low-Battery Trip Point Current into Pin 3 Current Sunk by Pin 2 Comparator Hysteresis Current Limit ON Resistance of Switch Switch Off-Time (Note 6) SHUTDOWN Pin High SHUTDOWN Pin Low SHUTDOWN Pin Input Current SHUTDOWN Pin Input Current 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 ● ● ● ● 3 1.2 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 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 ● ● ● ● ● ● ● ● MIN 1.18 0.75 0.50 0.54 0.5 2.0 1.8 tOFF RON Switch Off-Time (Note 6) Switch On Resistance 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 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. 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. TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Load Current 100 95 100 95 VIN = 6V EFFICIENCY (%) EFFICIENCY (%) VIN = 9V 85 80 75 70 EFFICIENCY (%) 90 L = 50µH VOUT = 5V IPGM = 0V COIL = CTX50-4 1 10 LOAD CURRENT (mA) 100 200 1174 G01 Efficiency vs Load Current 100 VIN = 5V 100 90 EFFICIENCY (%) EFFICIENCY (%) 80 80 VIN = 9V EFFICIENCY (%) VIN = 9V 70 L = 50µH VOUT = 3.3V IPGM = 0V COIL = CTX50-4 1 10 100 LOAD CURRENT (mA) 300 1174 G04 60 50 4 UW Efficiency vs Load Current 100 95 VIN = 6V VIN = 9V 85 80 75 70 1 10 100 LOAD CURRENT (mA) 400 1174 G02 Efficiency vs Load Current VIN = 6V 90 VIN = 9V 85 80 75 70 1 10 100 LOAD CURRENT (mA) 500 1174 G03 90 L = 50µH VOUT = 5V IPGM = VIN COIL = CTX50-4 L = 100µH VOUT = 5V IPGM = VIN COIL = CTX100-4 Efficiency vs Load Current 100 VIN = 5V Efficiency vs Load Current 90 90 VIN = 5V 80 VIN = 9V 70 L = 50µH VOUT = 3.3V IPGM = VIN COIL = CTX50-4 1 10 100 LOAD CURRENT (mA) 500 1174 G05 70 L = 100µH VOUT = 3.3V IPGM = VIN COIL = CTX100-4 1 10 100 LOAD CURRENT (mA) 500 1174 G06 60 60 50 50 1174fe LTC1174 LTC1174-3.3/LTC1174-5 TYPICAL PERFOR A CE CHARACTERISTICS Line Regulation 6 4 2 ILOAD = 100mA IPGM = 0V LEAKAGE CURRENT (nA) EFFICIENCY (%) 0 ∆VOUT (mV) –2 –4 –6 –8 –10 –12 –14 0 2 8 6 4 10 INPUT VOLTAGE (V) 12 14 Efficiency vs Input Voltage 95 94 93 92 91 90 0.2 89 5 6 7 8 9 10 11 12 INPUT VOLTAGE (V) 13 14 0 ILOAD = 100mA IPGM = 0V VOUT = 5V L = 100µH COIL = CTX100-4 1.8 1.6 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) EFFICIENCY (%) ILOAD = 300mA IPGM = VIN Operating Frequency vs VIN – VOUT 2.0 VOUT = 5V NORMALIZED FREQUENCY 1.7 1.6 1.5 1.5 RDS(ON) (Ω) OFF-TIME (µs) TA = 25°C 1.0 TA = 70°C 0.5 0 0 1 5 7 3 6 2 4 (VIN – VOUT) VOLTAGE (V) 8 9 UW 1174 G07 1174 G10 Switch Leakage Current vs Temperature 180 160 140 120 100 80 60 40 20 0 0 20 60 40 TEMPERATURE (°C) 80 100 1174 G08 Efficiency vs Input Voltage 95 94 93 92 91 90 89 88 87 5 6 7 9 10 11 12 8 INPUT VOLTAGE (V) 13 14 VOUT = 5V IPGM = 0V ILOAD = 75mA CORE = CTX (Kool Mµ®) L = 50µH L = 100µH VIN = 13.5V 1174 G09 Supply Current in Shutdown 500 SHUTDOWN = 0V TA = 25°C CURRENT INTO PIN 6 ONLY 450 400 350 300 250 200 150 100 50 0 0 2 4 6 8 10 INPUT VOLTAGE (V) 12 14 DC Supply Current ACTIVE MODE IPGM = 0V IPGM = VIN 1.4 1.2 1.0 0.8 0.6 0.4 SLEEP MODE TA = 25°C 0 2 8 6 4 10 INPUT VOLTAGE (V) 12 14 1174 G11 1174 G12 Switch Resistance vs Input Voltage 50 TA = 25°C Off-Time vs Output Voltage 40 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 4 6 8 10 12 14 16 INPUT VOLTAGE (V) 18 20 LTC1174 LTC1174HV 30 20 LTC1174-5 LTC1174HV-5 10 LTC1174-3.3 LTC1174HV-3.3 0 1 3 4 2 OUTPUT VOLTAGE (V) 5 1174 G15 0 1174 G13 1174 G14 1174fe 5 LTC1174 LTC1174-3.3/LTC1174-5 PI FU CTIO S 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. 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. LBIN (Pin 3): The “–” Input of the Low-Battery Voltage Comparator. The “+” input is connected to a reference voltage of 1.25V. GND (Pin 4): Ground Pin. SW(Pin5): Drain of the P-Channel MOSFET Switch. Cathode of Schottky diode must be closely connected to this pin. VIN (Pin 6): Input Supply Voltage. It must be decoupled close to ground Pin 4. 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. SHUTDOWN (Pin 8): Pulling this pin to ground keeps the internal switch off and puts the LTC1174 in micropower shutdown. FU CTIO AL DIAGRA + VTH2 A5 SLEEP A2 – – A4 gmVFB CT RESET Q VOUT (VFB) + SET VTH1 LBIN LBOUT 2 – A3 + GND 4 6 W U U U U U (Pin 1 connection shown for LTC1174-3.3 and LTC1174-5, changes create LTC1174) VIN 6 VLIM1 VLIM2 IPGM RSENSE 0.1Ω + – 7 × R1* 3 1 5 SW – A1 1.25V REFERENCE SHUTDOWN 8 VFB 31.5k + * R1 = 51k FOR LTC1174-3.3 R1 = 93.5k FOR LTC1174-5 1174 BD 1174fe LTC1174 LTC1174-3.3/LTC1174-5 OPERATIO 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. U (Refer to Functional Diagram) 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 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). Although higher inductance reduces core loss, it increases copper loss as it requires more windings. When space is not 100 CTX100-4 CTX100-4P 80 90 EFFICIENCY (%) 70 60 VIN = 5V VOUT = 3.3V IPGM = VIN 1 10 100 LOAD CURRENT (mA) 500 50 100 CTX50-4 CTX50-4P 80 90 EFFICIENCY (%) 70 60 VIN = 5V VOUT = 3.3V IPGM = VIN 1 10 100 LOAD CURRENT (mA) 500 1174 F01 50 Figure 1. Efficiency Using Different Types of Inductor Core Material 8 U a premium larger gauge wire can be used to reduce the wire resistance. This also prevents excessive heat dissipation. CIN 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: IRMS ≈ IOUT VOUT ( VIN − VOUT ) VIN W UU [ ]1/2 (A ) RMS 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. COUT 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: IRMS ≈ IPEAK ( A RMS) 2 = 170 mA or 300mA 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 LTC1174 LTC1174-3.3/LTC1174-5 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. Short-Circuit Protection 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 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 U 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 R4 3 R3 LTC1174 W UU – + 1.25V REFERENCE 1174 F03 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⎠ 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 APPLICATIO S I FOR ATIO 6.8nF** LTC1174 VFB 1 100pF* R1 R2 * ADJUSTABLE APPLICATIONS ** LOW NOISE APPLICATIONS 1174 F04 Figure 4. LTC1174 Adjustable Configuration INPUT VOLTAGE 4V TO 12V 3 2 7 6 VIN LBIN LBOUT IPGM LTC1174HV-5 GND 4 SHUTDOWN VOUT SW 0.1µF 8 1 5 50µH** MBRS140T3 + 47µF* 16V ×2 + 47µF* 16V ×2 * AVX TPSD476K016 ** COILTRONICS CTX50-4 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. 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/ 10 U VOUT W UU 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 VOUT –5V 45mA 1174 F05 VIN SW VOUT LTC1174 LTC1174-3.3 LTC1174-5 + 1174 F06 Figure 6. Preventing Absolute Maximum Ratings from Being Exceeded 1174fe LTC1174 LTC1174-3.3/LTC1174-5 APPLICATIO S I FOR ATIO Board Layout Checklist 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: 1. Is the Schottky catch diode closely connected between ground (Pin 4) and switch (Pin 5)? 2. Is the “+” plate of CIN closely connected to VIN (Pin 6)? This capacitor provides the AC current to the internal P-channel MOSFET. 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. INDUCTOR CURRENT OUTPUT DIVIDER REQUIRED WITH ADJUSTABLE VERSION ONLY R2 Figure 7. LTC1174 Layout Diagram (See Board Layout Checklist) + U DESIGN EXAMPLE 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. IPEAK AVG CURRENT = IOUT I +I = PEAK V IV 2 = 350mA TIME 1174 F08 W UU 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 ( A P− P) R1 1 VOUT (VFB) 2 LBOUT 3 LBIN 4 SHUTDOWN IPGM LTC1174 VIN 8 7 6 0.1µF 5 D VIN CIN + GND SW BOLD LINES INDICATE HIGH CURRENT PATH COUT L VOUT 1174 F07 1174fe 11 LTC1174 LTC1174-3.3/LTC1174-5 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: IRMS ≈ IPEAK ( A RMS) 2 = 300mA 12 U 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 W UU 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 LTC1174 LTC1174-3.3/LTC1174-5 TYPICAL APPLICATIO S 6V to 5V Step-Down Regulator with Low-Battery Detection * 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 INPUT VOLTAGE 4V TO 12.5V 7 3 * AVX TPSD226K025 ** AVX TPSD476K016 † COILTRONICS CTX50-4 U INPUT VOLTAGE 6V 6 VIN 7 2 IPGM SHUTDOWN 4.7k *LOWBATTERY INDICATOR 162k 0.1µF 8 + 47µF** 16V ×2 1 LBOUT VOUT LTC1174-5 3 5 SW LBIN GND 4 D1 47.5k L1 100µH † + 1174 TA03 VOUT 5V 47µF** 365mA 16V ×2 High Efficiency 3.3V Regulator 6 VIN IPGM LBIN SHUTDOWN + 8 22µF* 25V ×3 0.1µF 1 VOUT LTC1174-3.3 2 5 LBOUT SW GND 4 50µH† 1N5818 + 1174 TA04 VOUT 3.3V 47µF** 425mA 16V ×2 1174fe 13 LTC1174 LTC1174-3.3/LTC1174-5 TYPICAL APPLICATIO S Low Noise 3V Regulator INPUT VOLTAGE 4V TO 12.5V 7 3 2 * AVX TPSD226K025 ** AVX TPSD105K010 † COILTRONICS CTX50-4 * 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 14 U 6 VIN IPGM LBIN LTC1174 LBOUT GND 4 SW SHUTDOWN VFB + 8 1 5 22µF* 25V ×3 0.1µF 50µH† 6.8nF 42k VOUT 3V 450mA + 1N5818 100µF** 10V ×2 1174 TA05 30k Positive-to-Negative (– 5V) Converter INPUT VOLTAGE 4V TO 12.5V 6 VIN 7 2 IPGM SHUTDOWN 4.7K *LOWBATTERY INDICATOR 280k 0.1µF 8 + 10µF** 35V ×2 1 LBOUT VOUT LTC1174HV-5 3 5 SW LBIN GND 4 D1 43k L1† 50µH + 100µF*** 10V 1174 TA06 VOUT –5V 1174fe LTC1174 LTC1174-3.3/LTC1174-5 TYPICAL APPLICATIO S Positive-to-Negative (– 3.3V) Converter * 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 * AVX TPSD336K020 D1 = MBRS140T3 (SURFACE MOUNT) 1N5818 † 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 U INPUT VOLTAGE 4V TO 13.5V 6 VIN 7 2 IPGM SHUTDOWN 4.7K *LOWBATTERY INDICATOR 220k 0.1µF 8 + 33µF** 20V ×2 1 LBOUT VOUT LTC1174HV-3.3 3 5 SW LBIN GND 4 D1 43k L1† 50µH + 100µF*** 10V ×2 1174 TA07 VOUT –3.3V 210mA Negative Boost Converter 6 VIN 7 2 IPGM SHUTDOWN 8 310k 0.1µF + 33µF* 16V ×2 1 LBOUT VOUT LTC1174-3.3 3 5 SW LBIN GND 4 D1 L1† 50µH 50k + 33µF* 20V ×2 0.1µF VOUT –9V 175mA 1174 TA08 INPUT VOLTAGE –5V 1174fe 15 LTC1174 LTC1174-3.3/LTC1174-5 TYPICAL APPLICATIO S 9V to 5V Pre-Post Regulator INPUT VOLTAGE 6V TO 12.5V * 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 TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE USE 1% METAL FILM RESISTORS VIN(V) IOUT MAX(mA) 4 20 5 25 6 30 7 35 8 43 9 50 10 55 11 60 12 65 * 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 INPUT VOLTAGE 4V TO 12.5V 6 3 7 2 VIN LBIN IPGM LTC1174 LBOUT GND 4 0.1µF SW SHUTDOWN VFB 8 1 5 1N914 2N5210 1174 TA10 †† USE 1% METAL FILM RESISTORS 16 + TYPE SURFACE MOUNT SURFACE MOUNT SURFACE MOUNT THROUGH HOLE U 3 2 7 6 VIN LBIN LBOUT LTC1174 IPGM GND 4 SW SHUTDOWN VFB + 8 1 5 L1† 50µH D1 100µF* 16V 0.1µF 8 + 110k†† 47µF** 16V, × 2 100pF 0.1µF 30.1k†† VIN OUT LT®1121-5 5 SHUTDOWN GND 3 1 VOUT 5V 150mA + 1µ F SOLID TANTALUM 1174 TA09 LCD Display Power Supply 56.2k†† 2N2222 50k†† 998k†† Si9435 D1 VOUT –24V 50mA AT 10µF* VIN = 9V 50V ×4 + 47µF** 16V ×2 0.1µF L1† 100µH 1174fe LTC1174 LTC1174-3.3/LTC1174-5 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 3 2 CTX100-4 4 1 L1B L1A * 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 7 3 2 U 6 VIN 7 3 IPGM SHUTDOWN 0.1µF 8 0.1µF + 100µF* 20V 1 VOUT LBIN LTC1174HV-5 2 5 LBOUT SW GND 4 MBRS140T3 L1B 100µH † 3.3µF** L1A† 100µH MBRS140T3 VOUT 5V 135mA AT VIN = 9V + 100µF* 16V –VOUT –5V 135mA AT VIN = 9V + 100µF* 16V 1174 TA11 9V to 12V, – 12V Outputs INPUT VOLTAGE 4V TO 12.5V 6 VIN IPGM LBIN LTC1174 LBOUT GND 4 1N914 SW SHUTDOWN VFB 8 1 5 0.1µF + 22µF* 35V ×3 L1B 3 2 CTX100-4 4 1 L1A Si9430DY 4 3.3µF** 1 L1A† 2 100µH + MBRS140T3 301k†† 34k†† L1B 100µH 3 † 22µF* 35V ×2 VOUT 12V 55mA AT VIN = 9V + MBRS140T3 22µF* 35V ×2 1174 TA12 –VOUT –12V 55mA AT VIN = 9V 1174fe 17 LTC1174 LTC1174-3.3/LTC1174-5 TYPICAL APPLICATIO S Automatic Current Selection INPUT VOLTAGE 6V TO 12.5V 100k 2 7 3 100k 100µF* 20V + * SANYO OS-CON CAPACITOR † COILTRONICS CTX50-4 * SANYO OS-CON ** WIMA MKS2 † COILTRONICS CTX100-4 L1B 3 2 CTX100-4 4 1 18 U 6 VIN LBOUT IPGM LTC1174-5 LBIN GND 4 SW SHUTDOWN VOUT TPO610L 0.1µF 8 1 5 50µH† VOUT 5V 0mA TO 320mA + 1N5818 100µF* 16V 100k 36.5k 1174 TA13 Buck-Boost Converter INPUT VOLTAGE 4V TO 12V 6 VIN 7 3 IPGM SHUTDOWN 0.1µF 8 + 100µF* 20V 1 VOUT LBIN LTC1174HV-5 2 5 LBOUT SW GND 4 L2A† 100µH 3 4 3.3µF** 1 L1A 2 100µH 1N5818 1174 TA14 † VOUT 5V 160mA L1A + 100µF* 16V 1174fe LTC1174 LTC1174-3.3/LTC1174-5 PACKAGE DESCRIPTIO U N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .400* (10.160) MAX 8 7 6 5 .045 – .065 (1.143 – 1.651) .130 ± .005 (3.302 ± 0.127) .255 ± .015* (6.477 ± 0.381) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 (0.457 ± 0.076) 1 2 3 4 N8 1002 .300 – .325 (7.620 – 8.255) .008 – .015 (0.203 – 0.381) .065 (1.651) TYP ( +.035 .325 –.015 8.255 +0.889 –0.381 ) .100 (2.54) BSC INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) NOTE: 1. DIMENSIONS ARE S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 8 7 6 5 .045 ±.005 .050 BSC .245 MIN .160 ±.005 .228 – .244 (5.791 – 6.197) .150 – .157 (3.810 – 3.988) NOTE 3 .030 ±.005 TYP RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP 1 2 3 4 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN 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) .014 – .019 (0.355 – 0.483) TYP .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 TYPICAL APPLICATIO * 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 RELATED PARTS PART NUMBER LT 1074/LT1076 LTC1147 LTC1265 LT1375/LT1376 LTC1574 LT1611 LTC1701 LTC1707 LTC1877 ® DESCRIPTION Step-Down Switching Regulator High Efficiency Step-Down DC/DC Controller 1.2A High Efficiency Step-Down DC/DC Regulator 1.5A 500kHz Step-Down Switching Regulator High Efficiency Step-Down DC/DC Regulator Inverting 1.4MHz Switching Regulator in SOT-23 1MHz Step-Down DC/DC Converter in SOT-23 High Efficiency Synchronous Step-Down Regulator High Efficiency Synchronous Step-Down Regulator 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● U Battery Charger INPUT VOLTAGE 8V TO 12.5V 6 VIN 7 3 2 IPGM LBIN LTC1174 LBOUT GND 4 D1 33k 1174 TA15 0.1µF 8 1 5 L1† 50µH + 22µF* 20V ×2 SHUTDOWN VFB SW D2 150k VOUT TO 4 NiCAD BATTERY + 100µF** 10V COMMENTS 100kHz, 5A (LT1074) or 2A (LT1076) Monolithic 8-Pin Controller Burst Mode Operation, Monolithic High Frequency Small Inductor LTC1174 with Internal Schottky Diode – 5V at 150mA from 5V Input, 1mVP-P Output Ripple, SOT-23 Package VIN = 2.5V to 5.5V, IQ = 135µA, VOUT = 5V to 1.25V VIN = 2.85 to 8.5V, Selectable Burst Mode Operation, 600mA Output Current, SO-8 Package 600mA at VIN = 5V, 2.65V to 10V = VIN, IQ = 10µA 1174fe LT 1006 REV E • PRINTED IN USA www.linear.com © LINEAR TECHNOLOGY CORPORATION 1994