LT3008 3µA IQ, 20mA, 45V Low Dropout Linear Regulator FEATURES DESCRIPTION n The LT®3008 is a micropower, low dropout voltage (LDO) linear regulator. The device supplies 20mA output current with a dropout voltage of 300mV. No-load quiescent current is 3μA. Ground pin current remains at less than 5% of output current as load increases. In shutdown, quiescent current is less than 1μA. n n n n n n n n n n n Ultralow Quiescent Current: 3μA Input Voltage Range: 2.0V to 45V Output Current: 20mA Dropout Voltage: 300mV Adjustable Output (VADJ = VOUT(MIN) = 600mV) Output Tolerance: ±2% Over Load, Line and Temperature Stable with Low ESR, Ceramic Output Capacitors (2.2μF minimum) Shutdown Current: <1μA Current Limit Protection Reverse-Battery Protection Thermal Limit Protection TSOT-23 and 2mm × 2mm DFN Packages The LT3008 is ideal for applications that require moderate output drive capability coupled with ultralow standby power consumption. The device is available as an adjustable device with an output voltage range down to the 600mV reference. The LT3008 is available in the 6-lead DFN and 8-lead TSOT-23 packages. APPLICATIONS n n n n n n The LT3008 regulator optimizes stability and transient response with low ESR ceramic capacitors, requiring a minimum of only 2.2μF. The LT3008 does not require the addition of ESR as is common with other regulators. Internal protection circuitry includes current limiting, thermal limiting, reverse-battery protection and reversecurrent protection. Automotive Low Current Battery-Powered Systems Keep-Alive Power Supplies Remote Monitoring Utility Meters Low Power Industrial Applications , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION 3.3V, 20mA Supply with Shutdown Dropout Voltage/Quiescent Current 500 OUT 1μF 2.8M 1% LT3008 SHDN GND 2.2μF VOUT 3.3V 20mA ADJ 619k 1% 3008 TA01a DROPOUT VOLTAGE (mV) IN 6 ILOAD = 20mA DROPOUT VOLTAGE 400 350 5 4 300 250 IQ 3 200 2 150 100 QUIESCENT CURRENT (μA) VIN 3.8V TO 45V 450 1 50 0 –50 –25 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 3008 TA01b 3008f 1 LT3008 ABSOLUTE MAXIMUM RATINGS (Note 1) IN Pin Voltage .........................................................±50V OUT Pin Voltage ......................................................±50V Input-to-Output Differential Voltage ........................±50V ADJ Pin Voltage ......................................................±50V SHDN Pin Voltage (Note 8) .....................................±50V Output Short-Circuit Duration .......................... Indefinite Operating Junction Temperature Range (Notes 2, 3) LT3008E .............................................–40°C to 125°C LT3008I ..............................................–40°C to 125°C Storage Temperature Range...................–65°C to 150°C Lead Temperature: Soldering, 10 sec TS8 Package Only ............................................. 300°C PIN CONFIGURATION TOP VIEW TOP VIEW 6 GND ADJ 1 OUT 2 7 OUT 3 SHDN GND GND GND 5 SHDN 4 IN 1 2 3 4 8 7 6 5 NC ADJ OUT IN TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 DC PACKAGE 6-LEAD (2mm s 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 65°C/W TO 85°C/W* TJMAX = 125°C, θJA = 65°C/W TO 85°C/W* EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB * See Applications Information Section. ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3008EDC#PBF LT3008EDC#TRPBF LDPS 6-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C LT3008IDC#PBF LT3008IDC#TRPBF LDPS 6-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C LT3008ETS8#PBF LT3008ETS8#TRPBF LTDSX 8-Lead Plastic TSOT-23 –40°C to 125°C LT3008ITS8#PBF LT3008ITS8#TRPBF LTDSX 8-Lead Plastic TSOT-23 –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3008EDC LT3008EDC#TR LDPS 6-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C LT3008IDC LT3008IDC#TR LDPS 6-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C LT3008ETS8 LT3008ETS8#TR LTDSX 8-Lead Plastic TSOT-23 –40°C to 125°C LT3008ITS8 LT3008ITS8#TR LTDSX 8-Lead Plastic TSOT-23 –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3008f 2 LT3008 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 45 V 600 600 606 612 mV mV l 2 ADJ Pin Voltage (Notes 3, 4) VIN = 2V, ILOAD = 100μA 2V < VIN < 45V, 1μA < ILOAD < 20mA l 594 588 Line Regulation (Note 3) ΔVIN = 2V to 45V, ILOAD = 1mA l 0.6 3 mV Load Regulation (Note 3) VIN = 2V, ILOAD = 1μA to 10mA VIN = 2V, ILOAD = 1μA to 20mA l l 0.4 0.5 2 5 mV mV Dropout Voltage VIN = VOUT(NOMINAL) (Notes 5, 6) ILOAD = 100μA ILOAD = 100μA l 115 180 250 mV mV ILOAD = 1mA ILOAD = 1mA l 170 250 350 mV mV ILOAD = 10mA ILOAD = 10mA l 270 340 470 mV mV ILOAD = 20mA ILOAD = 20mA l 300 365 500 mV mV ILOAD = 0μA ILOAD = 0μA l 6 μA μA GND Pin Current VIN = VOUT(NOMINAL) + 0.5V (Notes 6, 7) ILOAD = 0μA ILOAD = 100μA ILOAD = 1mA ILOAD = 10mA ILOAD = 20mA l l l l l 6 12 50 500 1200 μA μA μA μA μA Output Voltage Noise (Note 9) COUT = 2.2μF, ILOAD = 20mA, BW = 10Hz to 100kHz Operating Voltage Quiescent Current (Notes 6, 7) 3 3 6 21 160 350 92 μVRMS l –10 0.4 10 nA VOUT = Off to On VOUT = On to Off l l 0.67 0.61 1.5 0.25 V V VSHDN = 0V, VIN = 45V VSHDN = 45V, VIN = 45V l l ±1 2 μA μA Quiescent Current in Shutdown VIN = 6V, VSHDN = 0V l <1 μA Ripple Rejection (Note 3) VIN – VOUT = 1.5V, VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 20mA Current Limit VIN = 45V, VOUT = 0 VIN = VOUT(NOMINAL) + 1V, ΔVOUT = – 5% l Input Reverse Leakage Current VIN = –45V, VOUT = 0 l Reverse Output Current VOUT = 1.2V, VIN = 0 ADJ Pin Bias Current Shutdown Threshold SHDN Pin Current 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: The LT3008 is tested and specified under pulse load conditions such that TJ ≅ TA. The LT3008E is 100% tested at TA=25°C. Performance at – 40°C and 125°C is assured by design, characterization and correlation with statistical process controls. The LT3008I is guaranteed over the full – 40°C to 125°C operating junction temperature range. Note 3: The LT3008 adjustable version is tested and specified for these conditions with the ADJ pin connected to the OUT pin. 0.65 58 70 dB 75 mA mA 22 1 30 μA 0.6 10 μA Note 4: Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at the maximum input voltage, the output current range must be limited. When operating at the maximum output current, the input voltage must be limited. Note 5: Dropout voltage is the minimum input to output voltage differential needed to maintain regulation at a specified output current. In dropout, the output voltage equals (VIN – VDROPOUT). 3008f 3 LT3008 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. (Note 2) Note 6: To satisfy minimum input voltage requirements, the LT3008 adjustable version is tested and specified for these conditions with an external resistor divider (61.9k bottom, 280k top) which sets VOUT to 3.3V. The external resistor divider adds 9.69μA of DC load on the output. This external current is not factored into GND pin current. Note 7: GND pin current is tested with VIN = VOUT(NOMINAL) + 0.5V and a current source load. GND pin current will increase in dropout. See the GND Pin Current curves in the Typical Performance Characteristics section. Note 8: The SHDN pin can be driven below GND only when tied to the IN pin directly or through a pull-up resistor. If the SHDN pin is driven below GND by more than –0.3V while IN is powered, the output will turn on. Note 9: Output noise is listed for the adjustable version with the ADJ pin connected to the OUT pin. See the RMS Output Noise vs Load Current curve in the Typical Performance Characteristics Section. TYPICAL PERFORMANCE CHARACTERISTICS Dropout Voltage Minimum Input Voltage 450 2 400 400 1.8 TJ = 125°C 350 300 TJ = 25°C 250 200 150 100 350 20mA 300 10mA 250 200 1mA 100 50 0 0 2 4 100μA 150 50 0 6 8 10 12 14 16 18 20 OUTPUT CURRENT (mA) 1.4 –50 –25 0 25 50 75 1 0.8 0.6 0.4 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3008 G02 3008 G03 ADJ Pin Bias Current IL = 100μA Quiescent Current 6 8 0.604 0.602 0.600 0.598 0.596 0.594 0.592 5 6 QUIESCENT CURRENT (μA) ADJ PIN BIAS CURRENT (nA) 0.606 4 2 0 –2 –4 –6 4 3 2 1 –8 0.590 0.588 –50 –25 1.2 0 100 125 150 10 0.608 ADJ PIN VOLTAGE (mV) 1.6 TEMPERATURE (°C) ADJ Pin Voltage 0.610 ILOAD = 20mA 0.2 3008 G01 0.612 MINIMUM INPUT VOLTAGE (V) 450 DROPOUT VOLTAGE (mV) DROPOUT VOLTAGE (mV) Dropout Voltage TJ = 25°C, unless otherwise noted. –10 0 25 50 75 100 125 150 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) TEMPERATURE (°C) 3008 G04 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 3008 G05 3008 G06 3008f 4 LT3008 TYPICAL PERFORMANCE CHARACTERISTICS Quiescent Current GND Pin Current VOUT = 3.3V VOUT = 3.3V ILOAD = 1μA 20mA (RLOAD = 165Ω) 350 24 18 15 12 9 250 200 10mA (RLOAD = 330Ω) 150 100 6 3 0 0 2 4 6 8 10 12 0 1 2 3 4 5 6 7 8 1 0.001 10 2 1.8 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 1.4 1.2 1 5 10 15 20 25 30 35 SHDN PIN VOLTAGE (V) 3008 G10 0.6 0.4 0 –50 –25 45 VIN = 2V 30 20 0 Input Ripple Rejection OUT = ADJ = 1.2V IN = SHDN = GND 35 30 25 20 15 ADJ 10 25 50 75 100 125 150 TEMPERATURE (°C) 3008 G13 0 –50 –25 OUT 0 VIN = 2.1V + 50mVRMS VOUT = 600mV ILOAD = 20mA 80 40 5 10 25 50 75 100 125 150 TEMPERATURE (°C) 90 INPUT RIPPLE REJECTION (dB) REVERSE OUTPUT CURRENT (μA) 90 50 0 3008 G12 Reverse Output Current 50 40 40 45 3008 G11 Current Limit 60 VSHDN = 45V 0.8 0.2 0 100 100 1.6 0 25 50 75 100 125 150 TEMPERATURE (°C) VIN = 45V 10 SHDN Pin Input Current 2 0.2 70 1 3008 G09 SHDN PIN INPUT CURRENT (μA) SHDN PIN INPUT CURRENT (μA) ON TO OFF 80 0.1 LOAD (mA) SHDN Pin Input Current OFF TO ON 0 0.01 3008 G08 SHDN Pin Thresholds SHDN PIN THRESHOLD (V) 9 INPUT VOLTAGE (V) 3008 G07 0 –50 –25 10 1mA (RLOAD = 3.3k) INPUT VOLTAGE (V) 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 –50 –25 100 100μA (RLOAD = 33k) 50 0 VIN = 3.8V VOUT = 3.3V 300 GND PIN CURRENT (μA) 21 GND CURRENT (μA) 27 QUIESCENT CURRENT (μA) GND Pin Current vs ILOAD 1000 400 30 CURRENT LIMIT (mA) TJ = 25°C, unless otherwise noted. 25 50 75 100 125 150 TEMPERATURE (°C) 3008 G14 70 60 50 40 10μF 30 20 2.2μF 10 0 10 100 1000 10000 100000 1000000 FREQUENCY (Hz) 3008 G15 3008f 5 LT3008 TYPICAL PERFORMANCE CHARACTERISTICS 5 70 4.5 50 40 30 20 10 $IL = 1μA to 20mA VOUT = 600mV VIN = 2V 4 60 0 3.5 3 2.5 2 1.5 1 VIN = VOUT (NOMINAL) + 2V + 0.5VP-P RIPPLE AT f = 120Hz ILOAD = 20mA 0 –50 –25 Output Noise Spectral Density OUTPUT NOISE SPECTRAL DENSITY (μV Hz) Load Regulation 80 LOAD REGULATION (mV) INPUT RIPPLE REJECTION (dB) Input Ripple Rejection 0.5 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 25 50 75 100 125 150 TEMPERATURE (°C) RMS Output Noise vs Load Current 450 COUT = 2.2μF ILOAD = 20mA 5V 3.3V 2.5V 1.8V 1.5V 1V 0.6V 10 1 0.1 10 100 1k 10k FREQUENCY (Hz) 100k 3008 G18 Transient Response COUT = 10μF 5V IOUT = 1mA TO 20mA VIN = 5.5V VOUT = 5V COUT = 2.2μF 400 OUTPUT NOISE (μVRMS) 100 3008 G17 3008 G16 500 TJ = 25°C, unless otherwise noted. 350 VOUT 50mV/DIV 3.3V 300 2.5V 250 1.8V 200 1.5V 150 100 1.2V 50 0.6V 0 0.001 0.01 0.1 1 10 IOUT 20mA/DIV 500μs/DIV 3008 G21 100 ILOAD (mA) 3008 G19 Transient Response (Load Dump) Transient Response IOUT = 1mA TO 20mA VIN = 5.5V VOUT = 5V COUT = 10μF VOUT 50mV/DIV VOUT 50mV/DIV 45V VOUT = 5V IOUT = 20mA COUT = 4.7μF VIN 10V/DIV IOUT 20mA/DIV 500μs/DIV 3008 G22 1ms/DIV 12V 3008 G23 3008f 6 LT3008 PIN FUNCTIONS (TSOT-23/DFN) SHDN (Pin 1/Pin 5): Shutdown. Pulling the SHDN pin low puts the LT3008 into a low power state and turns the output off. If unused, tie the SHDN pin to VIN. The LT3008 does not function if the SHDN pin is not connected. The SHDN pin cannot be driven below GND unless tied to the IN pin. If the SHDN pin is driven below GND while IN is powered, the output will turn on. SHDN pin logic cannot be referenced to a negative rail. GND (Pins 2, 3, 4/Pin 6): Ground. Connect the bottom of the resistor divider that sets output voltage directly to GND for the best regulation. IN (Pin 5/Pin 4): Input. The IN pin supplies power to the device. The LT3008 requires a bypass capacitor at IN if the device is more than six inches away from the main input filter capacitor. In general, the output impedance of a battery rises with frequency, so it is advisable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 0.1μF to 10μF will suffice. The LT3008 withstands reverse voltages on the IN pin with respect to ground and the OUT pin. In the case of a reversed input, which occurs with a battery plugged in backwards, the LT3008 acts as if a blocking diode is in series with its input. No reverse current flows into the LT3008 and no reverse voltage appears at the load. The device protects both itself and the load. OUT (Pin 6/Pins 2, 3): Output. This pin supplies power to the load. Use a minimum output capacitor of 2.2μF to prevent oscillations. Large load transient applications require larger output capacitors to limit peak voltage transients. See the Applications Information section for more information on output capacitance and reverse output characteristics. ADJ (Pin 7/Pin 1): Adjust. This pin is the error amplifier’s inverting terminal. Its 400pA typical input bias current flows out of the pin (see curve of ADJ Pin Bias Current vs Temperature in the Typical Performance Characteristics section). The ADJ pin voltage is 600mV referenced to GND and the output voltage range is 600mV to 44.5V. NC (Pin 8, TSOT-23 Package Only): No Connect. Pin 8 is an NC pin in the TSOT-23 package. This pin is not tied to any internal circuitry. It may be floated, tied to VIN or tied to GND. Exposed Pad (Pin 7, DFN Package Only): Ground. The Exposed Pad (backside) of the DFN package is an electrical connection to GND. To ensure optimum performance, solder Pin 7 to the PCB and tie directly to Pin 6. 3008f 7 LT3008 APPLICATIONS INFORMATION The LT3008 is a low dropout linear regulator with ultralow quiescent current and shutdown. Quiescent current is extremely low at 3μA and drops well below 1μA in shutdown. The device supplies up to 20mA of output current. Dropout voltage at 20mA is typically 300mV. The LT3008 incorporates several protection features, making it ideal for use in battery-powered systems. The device protects itself against both reverse-input and reverse-output voltages. In battery backup applications, where a backup battery holds up the output when the input is pulled to ground, the LT3008 acts as if a blocking diode is in series with its output and prevents reverse current flow. In applications where the regulator load returns to a negative supply, the output can be pulled below ground by as much as 50V without affecting startup or normal operation. Typical Performance Characteristics. Specifications for output voltages greater than 0.6V are proportional to the ratio of the desired output voltage to 0.6V: VOUT/0.6V. For example, load regulation for an output current change of 100μA to 20mA is –0.5mV typical at VOUT = 0.6V. At VOUT = 5V, load regulation is: 5V • (− 0 . 5mV) = − 4 . 17mV 0 . 6V Table 1 shows resistor divider values for some common output voltages with a resistor divider current of about 1μA. Table 1. Output Voltage Resistor Divider Values Adjustable Operation The LT3008 has an output voltage range of 0.6V to 44.5V. Figure 1 shows that output voltage is set by the ratio of two external resistors. The IC regulates the output to maintain the ADJ pin voltage at 600mV referenced to ground. The current in R1 equals 600mV/R1 and the current in R2 is the current in R1 minus the ADJ pin bias current. The ADJ pin bias current, typically 400pA at 25°C, flows out of the pin. Calculate the output voltage using the formula in Figure 1. An R1 value of 619k sets the divider current to 0.97μA. Do not make R1’s value any greater than 619k to minimize output voltage errors due to the ADJ pin bias current and to insure stability under minimum load conditions. In shutdown, the output turns off and the divider current is zero. Curves of ADJ Pin Voltage vs Temperature and ADJ Pin Bias Current vs Temperature appear in the VOUT = 600mV • (1 + R2/R1) – (IADJ • R2) VADJ = 600mV IADJ = 0.4nA at 25°C OUTPUT RANGE = 0.6V to 44.5V VOUT R1 R2 1V 604k 402k 1.2V 590k 590k 1.5V 590k 887k 1.8V 590k 1.18M 2.5V 590k 1.87M 3V 590k 2.37M 3.3V 619k 2.8M 5V 590k 4.32M Because the ADJ pin is relatively high impedance (depending on the resistor divider used), stray capacitances at this pin should be minimized. Special attention should be given to any stray capacitances that can couple external signals onto the ADJ pin producing undesirable output transients or ripple. IN VIN VOUT OUT LT3008 SHDN GND R2 ADJ R1 3008 F01 Figure 1. Adjustable Operation 3008f 8 LT3008 APPLICATIONS INFORMATION Extra care should be taken in assembly when using high valued resistors. Small amounts of board contamination can lead to significant shifts in output voltage. Appropriate post-assembly board cleaning measures should be implemented to prevent board contamination. If the board is to be subjected to humidity cycling or if board cleaning measures cannot be guaranteed, consideration should be given to using resistors an order of magnitude smaller than in Table 1 to prevent contamination from causing unwanted shifts in the output voltage. Output Capacitance and Transient Response The LT3008 is stable with a wide range of output capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. Use a minimum output capacitor of 2.2μF with an ESR of 3Ω or less to prevent oscillations. The LT3008 is a micropower device and output load transient response is a function of output capacitance. Larger values of output capacitance decrease the peak deviations and provide improved transient response for larger load current changes. Give extra consideration to the use of ceramic capacitors. Manufacturers make ceramic capacitors with a variety of 20 dielectrics, each with different behavior across temperature and applied voltage. The most common dielectrics are specified with EIA temperature characteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics provide high C-V products in a small package at low cost, but exhibit strong voltage and temperature coefficients as shown in Figures 2 and 3. 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 yield 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. One must still exercise care 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. 40 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF 20 X5R CHANGE IN VALUE (%) CHANGE IN VALUE (%) 0 –20 –40 –60 Y5V –80 –100 –20 –40 2 4 8 6 10 12 DC BIAS VOLTAGE (V) 14 16 3008 F02 Figure 2. Ceramic Capacitor DC Bias Characteristics 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 3008 F03 Figure 3. Ceramic Capacitor Temperature Characteristics 3008f 9 LT3008 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 4’s trace in response to light tapping from a pencil. Similar vibration induced behavior can masquerade as increased output voltage noise. VOUT = 0.6V COUT = 22μF ILOAD = 10μA VOUT 500μV/DIV 100ms/DIV 3008 F04 Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor Thermal Considerations The LT3008’s maximum rated junction temperature of 125°C limits its power-handling capability. Two components comprise the power dissipated by the device: 1. Output current multiplied by the input/output voltage differential: IOUT • (VIN – VOUT) 2. GND pin current multiplied by the input voltage: IGND • VIN GND pin current is found by examining the GND Pin Current curves in the Typical Performance Characteristics section. Power dissipation is equal to the sum of the two components listed prior. The LT3008 regulator has internal thermal limiting designed to protect the device during overload conditions. For continuous normal conditions, do not exceed the maximum junction temperature rating of 125°C. Carefully consider all sources of thermal resistance from junction to ambient including other heat sources mounted in proximity to the LT3008. 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. 3008f 10 LT3008 APPLICATIONS INFORMATION The following tables list thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 3/32" FR-4 two-layer boards with one ounce copper. PCB layers, copper weight, board layout and thermal vias affect the resultant thermal resistance. Although Tables 2 and 3 provide thermal resistance numbers for 2-layer boards with 1 ounce copper, modern multi-layer PCBs provide better performance than found in these tables. For example, a 4-layer, 1 ounce copper PCB board with 3 thermal vias from the DFN exposed backside or the 3 fused TSOT-23 GND pins to inner layer GND planes achieves 45°C/W thermal resistance. Demo circuit DC 1388A’s board layout achieves this 45°C/W performance. This is approximately a 30% improvement over the lowest numbers shown in Tables 2 and 3. Table 2: Measured Thermal Resistance for DC Package COPPER AREA TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 65°C/W 1000mm2 2500mm2 2500mm2 70°C/W 225mm2 2500mm2 2500mm2 75°C/W 100mm2 2500mm2 2500mm2 80°C/W 50mm2 2500mm2 2500mm2 85°C/W *Device is mounted on the topside. Calculating Junction Temperature Example: Given an output voltage of 3.3V, an input voltage range of 12V ±5%, an output current range of 0mA to 20mA and a maximum ambient temperature of 85°C, what will the maximum junction temperature be for an application using the DC package? The power dissipated by the device is equal to: IOUT(MAX) (VIN(MAX) – VOUT) + IGND (VIN(MAX)) where, IOUT(MAX) = 20mA VIN(MAX) = 12.6V IGND at (IOUT = 20mA, VIN = 12.6V) = 0.3mA So, P = 20mA(12.6V – 3.3V) + 0.3mA(12.6V) = 189.8mW The thermal resistance ranges from 65°C/W to 85°C/W depending on the copper area. So the junction temperature rise above ambient approximately equals: 0.1898W(75°C/W) = 14.2°C The maximum junction temperature equals the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJ(MAX) = 85°C + 14.2°C = 99.2°C Table 3: Measured Thermal Resistance for TSOT-23 Package COPPER AREA TOPSIDE* BACKSIDE BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 65°C/W 1000mm2 2500mm2 2500mm2 67°C/W 225mm2 2500mm2 2500mm2 70°C/W 100mm2 2500mm2 2500mm2 75°C/W 50mm2 2500mm2 2500mm2 85°C/W *Device is mounted on the topside. 3008f 11 LT3008 APPLICATIONS INFORMATION Protection Features The LT3008 incorporates several protection features that make it 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 device also protects against reverse-input voltages, reverseoutput voltages and reverse output-to-input voltages. Current limit protection and thermal overload protection protect the device against current overload conditions at the output of the device. For normal operation, do not exceed a junction temperature of 125°C. The IN pin withstands reverse voltages of 50V. The device limits current flow to less than 20μA (typically less than 1μA) and no negative voltage appears at OUT. The device protects both itself and the load against batteries that are plugged in backwards. The SHDN pin cannot be driven below GND unless tied to the IN pin. If the SHDN pin is driven below GND while IN is powered, the output will turn on. SHDN pin logic cannot be referenced to a negative rail. The LT3008 incurs no damage if OUT is pulled below ground. If IN is left open circuit or grounded, OUT can be pulled below ground by 50V. No current flows from the pass transistor connected to OUT. However, current flows in (but is limited by) the resistor divider that sets output voltage. Current flows from the bottom resistor in the divider and from the ADJ pin’s internal clamp through the top resistor in the divider to the external circuitry pulling OUT below ground. If IN is powered by a voltage source, OUT sources current equal to its current limit capability and the LT3008 protects itself by thermal limiting if necessary. In this case, grounding the SHDN pin turns off the LT3008 and stops OUT from sourcing current. The LT3008 incurs no damage if the ADJ pin is pulled above or below ground by 50V. If IN is left open circuit or grounded, ADJ acts like a 100k resistor in series with a diode when pulled above or below ground. 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 follows the curve shown in Figure 5. If the LT3008 IN pin is forced below the OUT pin or the OUT pin is pulled above the IN pin, input current typically drops to less than 1μA. This occurs if the LT3008 input is connected to a discharged (low voltage) battery and either a backup battery or a second regulator circuit holds up the output. The state of the SHDN pin has no effect in the reverse current if OUT is pulled above IN. 100 REVERSE CURRENT (μA) 90 80 70 ADJ CURRENT 60 50 40 30 20 OUT CURRENT 10 0 0 1 2 3 4 5 6 7 8 9 OUTPUT AND ADJ VOLTAGE (V) 10 3008 F05 Figure 5. Reverse Output Current 3008f 12 LT3008 TYPICAL APPLICATIONS Keep-Alive Power Supply NO PROTECTION DIODES NEEDED! VIN 12V IN 1μF 3.3V OUT 2.8M 1% LT3008 SHDN ADJ 619k 1% GND 2.2μF LOAD: SYSTEM MONITOR, VOLATILE MEMORY, ETC. 3009 TA02 Last-Gasp Circuit LINE POWER VLINE 12V TO 15V SENSE DCHARGE LINE INTERRUPT DETECT RLIMIT IN SUPERCAP 1μF OUT 4.32M 1% LT3008 SHDN GND 5V PWR 2.2μF FAULT GND TO MONITORING CENTER 3008 TA03 ADJ 590k 1% 3008f 13 LT3008 PACKAGE DESCRIPTION DC Package 6-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1703) R = 0.115 TYP 0.56 p 0.05 (2 SIDES) 0.675 p0.05 2.50 p0.05 0.61 p0.05 1.15 p0.05 (2 SIDES) PIN 1 BAR PACKAGE TOP MARK OUTLINE (SEE NOTE 6) 0.38 p 0.05 4 2.00 p0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.25 p 0.05 0.50 BSC 1.42 p0.05 (2 SIDES) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 6 0.75 p0.05 1 (DC6) DFN 1103 0.25 p 0.05 0.50 BSC 1.37 p0.05 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3008f 14 LT3008 PACKAGE DESCRIPTION TS8 Package 8-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1639 Rev Ø) 0.52 MAX 2.90 BSC (NOTE 4) 0.65 REF 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.22 – 0.36 8 PLCS (NOTE 3) 0.65 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) 1.95 BSC TS8 TSOT-23 0802 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 3008f 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. 15 LT3008 TYPICAL APPLICATION Low Duty Cycle Applications IN 1μF OUT 90 2.8M 1% LT3008 SHDN 100 3.3V 2.2μF LOW DUTY CYCLE PULSED LOAD 0 TO 10mA ADJ GND 619k 1% 3008 TA04a 80 POWER SAVINGS (%) VIN 12V Average Power Savings for Low Duty Cycle Applications 0mA to 10mA Pulsed Load, IN = 12V 70 60 100μA IQ 50 40 30μA IQ 30 20 10 0 0.1 10μA IQ 1 10 DUTY CYCLE (%) 3008 TA04b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1761 100mA, Low Noise Micropower LDO VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 20μA, ISD < 1μA, Low Noise < 20μVRMS , Stable with 1μF Ceramic Capacitors, ThinSOTTM Package LT1762 150mA, Low Noise Micropower LDO VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 25μA, ISD < 1μA, Low Noise < 20μVRMS , MS8 Package LT1763 500mA, Low Noise Micropower LDO VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 30μA, ISD < 1μA, Low Noise < 20μVRMS , S8 Package LT1764/LT1764A 3A, Low Noise, Fast Transient Response LDOs VIN : 2.7V to 20V, VOUT = 1.21V, VDO = 0.34V, IQ = 1mA, ISD < 1μA, Low Noise < 40μVRMS , “A” Version Stable with Ceramic Capacitors, DD and TO220-5 Packages LT1962 300mA, Low Noise Micropower LDO VIN : 1.8V to 20V, VOUT(MIN) = 1.22V, VDO = 0.27V, IQ = 30μA, ISD < 1μA, Low Noise: < 20μVRMS , MS8 Package LT1963/LT1963A 1.5A, Low Noise, Fast Transient Response LDOs VIN : 2.1V to 20V, VOUT(MIN) = 1.21V, VDO = 0.34V, IQ = 1mA, ISD < 1μA, Low Noise: < 40μVRMS , “A” Version Stable with Ceramic Capacitors, DD, TO220-5, SOT223 and S8 Packages LT3009 20mA, 3μA IQ Micropower LDO VIN : 1.6V to 20V, Low IQ: 3μA, VDO = 0.28V, 2mm × 2mm DFN and SC-70-8 Packages LT3020 100mA, Low Voltage VLDO VIN : 0.9V to 10V, VOUT(MIN) = 0.20V, VDO = 0.15V, IQ = 120μA, ISD < 1μA, 3mm × 3mm DFN and MS8 Packages LT3021 500mA, Low Voltage VLDO VIN : 0.9V to 10V, VOUT(MIN) = 0.20V, VDO = 0.16V, IQ = 120μA, ISD < 3μA, 5mm × 5mm DFN and SO8 Packages LT3080/ LT3080-1 1.1A, Parallelable, Low Noise, Low Dropout Linear Regulator 300mV Dropout Voltage (2-supply operation), Low Noise: 40μVRMS, VIN: 1.2V to 36V, VOUT: 0V to 35.7V, current-based reference with 1-resistor VOUT set; directly parallelable (no op amp required), stable with ceramic caps, TO-220, SOT-223, MSOP and 3 × 3 DFN Packages; “-1” version has integrated internal ballast resistor LT3085 500mA, Parallelable, Low Noise, Low Dropout Linear Regulator 275mV Dropout Voltage (2-supply operation), Low Noise: 40μVRMS, VIN: 1.2V to 36V, VOUT: 0V to 35.7V, current-based reference with 1-resistor VOUT set; directly parallelable (no op amp required), stable with ceramic caps, MSOP-8 and 2 × 3 DFN packages ThinSOT is a trademark of Linear Technology Corporation. 3008f 16 Linear Technology Corporation LT 1108 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007