LT1761MPS5-5#TRMPBF

LT1761 Series 100mA, Low Noise, LDO Micropower Regulators in TSOT-23 FEATURES DESCRIPTION n 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. n n n n n n n n n n n n n n 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 1.5 1.0 0.5 CHANGE IN VALUE (%) 3.0 –20 –40 1 3 2 4 5 6 7 8 9 10 OUTPUT CAPACITANCE (μF) 1761 F02 Figure 2. Stability Y5V –60 –80 0 X5R 0 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF –100 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 1761 F04 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. VOUT 500μV/DIV Table 1. Measured Thermal Resistance LT1761-5 COUT = 10μF CBYP = 0.01μF ILOAD = 100mA 100ms/DIV 1761 F05 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 COPPER AREA THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) TOPSIDE* BACKSIDE 2500mm2 2500mm2 2500mm2 125°C/W 1000mm2 2500mm2 2500mm2 125°C/W 225mm2 2500mm2 2500mm2 130°C/W 100mm2 2500mm2 2500mm2 135°C/W 50mm2 2500mm2 2500mm2 150°C/W *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 2. GND pin current multiplied by the input voltage: (IGND)(VIN). 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. REVERSE OUTPUT CURRENT (μA) 100 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 LT1761-3.3 10 LT1761-5 0 0 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) 9 10 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 1.4 MIN 3.85 MAX 2.62 REF 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 0.01 – 0.10 1.00 MAX DATUM ‘A’ 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 (Revision history begins at Rev F) REV DATE DESCRIPTION PAGE NUMBER F 5/10 Added MP-grade 2, 3 Added Typical Application 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 Startup Time 100 IN VIN 5.4V TO 20V 5V AT 100mA OUT LT1761-5 1μF CBYP 10μF OFF ON STARTUP TIME (ms) BYP SHDN GND 1761 TA02a 10 1 0.1 10 100 1000 10000 CBYP (pF) 1761 TA02b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1120 125mA Low Dropout Regulator with 20μA IQ Includes 2.5V Reference and Comparator LT1121 150mA Micropower Low Dropout Regulator 30μA IQ, SOT-223 Package LT1129 700mA Micropower Low Dropout Regulator 50μA Quiescent Current LT1175 500mA Negative Low Dropout Micropower Regulator 45μA IQ, 0.26V Dropout Voltage, SOT-223 Package LT1521 300mA Low Dropout Micropower Regulator with Shutdown 15μA IQ, Reverse-Battery Protection LT1529 3A Low Dropout Regulator with 50μA IQ 500mV Dropout Voltage LT1762 Series 150mA, Low Noise, LDO Micropower Regulator 25μA Quiescent Current, 20μVRMS Noise LT1763 Series 500mA, Low Noise, LDO Micropower Regulator 30μA Quiescent Current, 20μVRMS Noise LTC1928 Doubler Charge Pump with Low Noise Linear Regulator Low Output Noise: 60μVRMS (100kHz BW) LT1962 Series 300mA, Low Noise, LDO Micropower Regulator 30μA Quiescent Current, 20μVRMS Noise LT1963 1.5A, Low Noise, Fast Transient Response LDO 40μVRMS, SOT-223 Package LT1764 3A, Low Noise, Fast Transient Response LDO 40μVRMS, 340mV Dropout Voltage LTC3404 High Efficiency Synchronous Step-Down Switching Regulator Burst Mode® Operation, Monolithic, 100% Duty Cycle 1761sff 22 Linear Technology Corporation LT 0510 REV F • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005