LT1761IS5-3-TR

LT1761 Series 100mA, Low Noise, LDO Micropower Regulators in TSOT-23 FEATURES n n n n n n n n n n n n n n n DESCRIPTION The LT®1761 series are micropower, low noise, low dropout regulators. With an external 0.01μF bypass capacitor, output noise drops to 20μVRMS over a 10Hz to 100kHz bandwidth. Designed for use in battery-powered systems, the low 20μA quiescent current makes them an ideal choice. In shutdown, quiescent current drops to less than 0.1μA. The devices are capable of operating over an input voltage from 1.8V to 20V, and can supply 100mA of output current with a dropout voltage of 300mV. Quiescent current is well controlled, not rising in dropout as it does with many other regulators. The LT1761 regulators are stable with output capacitors as low as 1μF Small ceramic capacitors can be used without . the series resistance required by other regulators. Internal protection circuitry includes reverse battery protection, current limiting, thermal limiting and reverse current protection. The device is available in fixed output voltages of 1.2V, 1.5V, 1.8V, 2V, 2.5V, 2.8V, 3V, 3.3V and 5V, and as an adjustable device with a 1.22V reference voltage. The LT1761 regulators are available in the 5-lead TSOT-23 package. L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Low Noise: 20μVRMS (10Hz to 100kHz) Low Quiescent Current: 20μA Wide Input Voltage Range: 1.8V to 20V Output Current: 100mA Very Low Shutdown Current: 3300pF CHANGE IN VALUE (%) 0 –20 –40 –60 –80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF 50 25 75 0 TEMPERATURE (°C) 100 125 1761 F04 and temperature coefficients as shown in Figures 3 and 4. When used with a 5V regulator, a 16V 10μF Y5V capacitor can exhibit an effective value as low as 1μF to 2μF for the DC bias voltage applied and over the operating temperature range. The X5R and X7R dielectrics result in more stable characteristics and are more suitable for use as the output capacitor. The X7R type has better stability across temperature, while the X5R is less expensive and is available in higher values. Care still must be exercised when using X5R and X7R capacitors; the X5R and X7R codes only specify operating temperature range and maximum capacitance change over temperature. Capacitance change due to DC bias with X5R and X7R capacitors is better than Y5V and Z5U capacitors, but can still be significant enough to drop capacitor values below appropriate levels. Capacitor DC bias characteristics tend to improve as component case size increases, but expected capacitance at operating voltage should be verified. 20 0 CHANGE IN VALUE (%) X5R –20 –40 –60 Y5V –80 –100 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF 0 2 4 8 6 10 12 DC BIAS VOLTAGE (V) 14 16 1761 F03 Figure 3. Ceramic Capacitor DC Bias Characteristics 40 X5R Y5V –100 –50 –25 Figure 2. Stability Figure 4. Ceramic Capacitor Temperature Characteristics 1761sff 16 LT1761 Series APPLICATIONS INFORMATION Voltage and temperature coefficients are not the only sources of problems. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress, similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. The resulting voltages produced can cause appreciable amounts of noise, especially when a ceramic capacitor is used for noise bypassing. A ceramic capacitor produced Figure 5’s trace in response to light tapping from a pencil. Similar vibration induced behavior can masquerade as increased output voltage noise. The ground pin current can be found by examining the GND Pin Current curves in the Typical Performance Characteristics section. Power dissipation will be equal to the sum of the two components listed above. The LT1761 series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal conditions, the maximum junction temperature rating of 125°C must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional heat sources mounted nearby must also be considered. For surface mount devices, heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Copper board stiffeners and plated through-holes can also be used to spread the heat generated by power devices. The following table lists thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 3/32" FR-4 board with one ounce copper. Table 1. Measured Thermal Resistance LT1761-5 COUT = 10μF CBYP = 0.01μF ILOAD = 100mA 100ms/DIV 1761 F05 VOUT 500μV/DIV COPPER AREA TOPSIDE* 2500mm2 1000mm2 225mm2 100mm2 50mm2 BACKSIDE 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 125°C/W 125°C/W 130°C/W 135°C/W 150°C/W Figure 5. Noise Resulting from Tapping on a Ceramic Capacitor Thermal Considerations The power handling capability of the device will be limited by the maximum rated junction temperature (125°C). The power dissipated by the device will be made up of two components: 1. Output current multiplied by the input/output voltage differential: (IOUT)(VIN – VOUT), and 2. GND pin current multiplied by the input voltage: (IGND)(VIN). *Device is mounted on topside. Calculating Junction Temperature Example: Given an output voltage of 3.3V, an input voltage range of 4V to 6V, an output current range of 0mA to 50mA 1761sff 17 LT1761 Series APPLICATIONS INFORMATION and a maximum ambient temperature of 50°C, what will the maximum junction temperature be? The power dissipated by the device will be equal to: IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX)) where, IOUT(MAX) = 50mA VIN(MAX) = 6V IGND at (IOUT = 50mA, VIN = 6V) = 1mA So, P = 50mA(6V – 3.3V) + 1mA(6V) = 0.14W The thermal resistance will be in the range of 125°C/W to 150°C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to: 0.14W(150°C/W) = 21.2°C The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50°C + 21.2°C = 71.2°C Protection Features The LT1761 regulators incorporate several protection features which make them ideal for use in battery-powered circuits. In addition to the normal protection features associated with monolithic regulators, such as current limiting and thermal limiting, the devices are protected against reverse input voltages, reverse output voltages and reverse voltages from output to input. Current limit protection and thermal overload protection are intended to protect the device against current overload conditions at the output of the device. For normal operation, the junction temperature should not exceed 125°C. The input of the device will withstand reverse voltages of 20V. Current flow into the device will be limited to less than 1mA (typically less than 100μA) and no negative voltage will appear at the output. The device will protect both itself and the load. This provides protection against batteries which can be plugged in backward. The output of the LT1761-X can be pulled below ground without damaging the device. If the input is left open circuit or grounded, the output can be pulled below ground by 20V. For fixed voltage versions, the output will act like a large resistor, typically 500k or higher, limiting current flow to typically less than 100μA. For adjustable versions, the output will act like an open circuit; no current will flow out of the pin. If the input is powered by a voltage source, the output will source the short-circuit current of the device and will protect itself by thermal limiting. In this case, grounding the SHDN pin will turn off the device and stop the output from sourcing the short-circuit current. The ADJ pin of the adjustable device can be pulled above or below ground by as much as 7V without damaging the device. If the input is left open circuit or grounded, the ADJ pin will act like an open circuit when pulled below ground and like a large resistor (typically 100k) in series with a diode when pulled above ground. 1761sff 18 LT1761 Series APPLICATIONS INFORMATION In situations where the ADJ pin is connected to a resistor divider that would pull the ADJ pin above its 7V clamp voltage if the output is pulled high, the ADJ pin input current must be limited to less than 5mA. For example, a resistor divider is used to provide a regulated 1.5V output from the 1.22V reference when the output is forced to 20V. The top resistor of the resistor divider must be chosen to limit the current into the ADJ pin to less than 5mA when the ADJ pin is at 7V. The 13V difference between output and ADJ pin divided by the 5mA maximum current into the ADJ pin yields a minimum top resistor value of 2.6k. In circuits where a backup battery is required, several different input/output conditions can occur. The output voltage may be held up while the input is either pulled to ground, pulled to some intermediate voltage or is left open circuit. Current flow back into the output will follow the curve shown in Figure 6. When the IN pin of the LT1761-X is forced below the OUT pin or the OUT pin is pulled above the IN pin, input current will typically drop to less than 2μA. This can happen if the input of the device is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or a second regulator circuit. The state of the SHDN pin will have no effect on the reverse output current when the output is pulled above the input. 100 REVERSE OUTPUT CURRENT (μA) TJ = 25°C LT1761-BYP LT1761-SD 90 VIN = 0V CURRENT FLOWS 80 INTO OUTPUT PIN LT1761-1.2 70 VOUT = VADJ (LT1761-BYP, -SD) 60 LT1761-1.5 LT1761-1.8 50 LT1761-2 LT1761-2.5 40 LT1761-2.8 30 LT1761-3 20 10 0 0 1 2 LT1761-5 345678 OUTPUT VOLTAGE (V) 9 10 LT1761-3.3 1761 F06 Figure 6. Reverse Output Current 1761sff 19 LT1761 Series PACKAGE DESCRIPTION S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 1.00 MAX DATUM ‘A’ 0.01 – 0.10 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 1.90 BSC S5 TSOT-23 0302 REV B 1761sff 20 LT1761 Series REVISION HISTORY REV F DATE 5/10 DESCRIPTION Added MP-grade Added Typical Application (Revision history begins at Rev F) PAGE NUMBER 2, 3 22 1761sff 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. 21 LT1761 Series TYPICAL APPLICATION Noise Bypassing Provides Soft-Start 100 VIN 5.4V TO 20V IN 1μF LT1761-5 BYP OFF ON SHDN GND 1761 TA02a Startup Time 5V AT 100mA OUT CBYP 10μF STARTUP TIME (ms) 10 1 0.1 10 100 CBYP (pF) 1761 TA02b 1000 10000 RELATED PARTS PART NUMBER LT1120 LT1121 LT1129 LT1175 LT1521 LT1529 LT1762 Series LT1763 Series LTC1928 LT1962 Series LT1963 LT1764 LTC3404 DESCRIPTION 125mA Low Dropout Regulator with 20μA IQ 150mA Micropower Low Dropout Regulator 700mA Micropower Low Dropout Regulator 500mA Negative Low Dropout Micropower Regulator 300mA Low Dropout Micropower Regulator with Shutdown 3A Low Dropout Regulator with 50μA IQ 150mA, Low Noise, LDO Micropower Regulator 500mA, Low Noise, LDO Micropower Regulator Doubler Charge Pump with Low Noise Linear Regulator 300mA, Low Noise, LDO Micropower Regulator 1.5A, Low Noise, Fast Transient Response LDO 3A, Low Noise, Fast Transient Response LDO High Efficiency Synchronous Step-Down Switching Regulator COMMENTS Includes 2.5V Reference and Comparator 30μA IQ, SOT-223 Package 50μA Quiescent Current 45μA IQ, 0.26V Dropout Voltage, SOT-223 Package 15μA IQ, Reverse-Battery Protection 500mV Dropout Voltage 25μA Quiescent Current, 20μVRMS Noise 30μA Quiescent Current, 20μVRMS Noise Low Output Noise: 60μVRMS (100kHz BW) 30μA Quiescent Current, 20μVRMS Noise 40μVRMS, SOT-223 Package 40μVRMS, 340mV Dropout Voltage Burst Mode® Operation, Monolithic, 100% Duty Cycle 1761sff 22 Linear Technology Corporation (408) 432-1900 ● FAX: (408) 434-0507 ● LT 0510 REV F • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005