LT3027EDD

LT3027 Dual 100mA, Low Dropout, Low Noise, Micropower Regulator with Independent Inputs FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Low Noise: 20µVRMS (10Hz to 100kHz) Low Quiescent Current: 25µA/Channel Independent Inputs Wide Input Voltage Range: 1.8V to 20V Output Current: 100mA/Channel Very Low Shutdown Current: 3300pF Figure 2. Stability 10 U dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high capacitances in a small package, but exhibit strong voltage and temperature coefficients as shown in Figures 3 and 4. When used with a 5V regulator, a 10µF Y5V capacitor can exhibit an effective value as low as 1µF to 2µF 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. 20 0 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 3027 F03 W UU Figure 3. Ceramic Capacitor DC Bias Characteristics 40 20 0 –20 –40 –60 –80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF 50 25 75 0 TEMPERATURE (°C) 100 125 Y5V X5R –100 –50 –25 3027 F04 Figure 4. Ceramic Capacitor Temperature Characteristics 3027f LT3027 APPLICATIO S I FOR ATIO 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. COUT = 10µF CBYP = 0.01µF ILOAD = 100mA VOUT 500µV/DIV 100ms/DIV 3027 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 (for each channel): 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). 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. Power dissipation from both channels must be considered during thermal analysis. The LT3027 regulator has internal thermal limiting designed to protect the device during overload conditions. U 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 tables list 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. MSE Package, 10-Lead MSOP COPPER AREA TOPSIDE* BACKSIDE 2500mm2 1000mm 225mm 100mm 2 2 2 W UU BOARD AREA 2500mm2 2500mm 2500mm 2500mm 2 2 2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 40°C/W 45°C/W 50°C/W 62°C/W 2500mm2 2500mm 2500mm 2500mm 2 2 2 *Device is mounted on topside. Table 2. DD Package, 10-Lead DFN COPPER AREA TOPSIDE* BACKSIDE 2500mm2 1000mm 225mm 2 2 BOARD AREA 2500mm2 2500mm 2500mm 2 2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 40°C/W 45°C/W 50°C/W 62°C/W 2500mm2 2500mm 2500mm 2 2 100mm2 2500mm2 2500mm2 *Device is mounted on topside. The thermal resistance juncton-to-case (θJC), measured at the Exposed Pad on the back of the die is 10°C/W. Calculating Junction Temperature Example: Given an output voltage on the first channel of 3.3V, an output voltage of 2.5V on the second channel, an input voltage range of 4V to 6V, output current ranges of 0mA to 100mA for the first channel and 0mA to 50mA for the second channel, with a maximum ambient temperature of 50°C, what will the maximum junction temperature be? 3027f 11 LT3027 APPLICATIONS INFORMATION The power dissipated by each channel of the device will be equal to: IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX)) where (for the first channel): IOUT(MAX) = 100mA VIN(MAX) = 6V IGND at (IOUT = 100mA, VIN = 6V) = 2mA so: P1 = 100mA(6V – 3.3V) + 2mA(6V) = 0.28W and (for the second channel): IOUT(MAX) = 50mA VIN(MAX) = 6V IGND at (IOUT = 50mA, VIN = 6V) = 1mA so: P2 = 50mA(6V – 2.5V) + 1mA(6V) = 0.18W The thermal resistance will be in the range of 40°C/W to 60°C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to: (0.28W + 018W)(60°C/W) = 27.8°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 + 27.8°C = 77.8°C Protection Features The LT3027 regulator incorporates several protection features which makes 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 devices are protected against reverse input 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 LT3027 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. 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 pins will turn off the device and stop the output from sourcing the short-circuit current. The ADJ pins 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 pins 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. In situations where the ADJ pins are connected to a resistor divider that would pull the pins above their 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. When the IN pins of the LT3027 are forced below the corresponding OUT pins or the OUT pins are pulled above the IN pins, 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 pins will have no effect on the reverse output current when the output is pulled above the input. 3027f 12 U W U U LT3027 TYPICAL APPLICATIO S Noise Bypassing Slows Startup, Allows Outputs to Track VIN1 3.7V TO 20V 1µF IN1 OUT1 0.01µF BYP1 ADJ1 10µF 422k VIN2 2.9V TO 20V 1µF IN2 LT3027 OUT2 0.01µF OFF ON SHDN1 SHDN2 GND BYP2 ADJ2 STARTUP TIME (ms) VIN 3.3V 154k 100k LTC2923 255k TRACK1 121k 115k TRACK2 GND 93.1k U VSHDN1/SHDN2 1V/DIV VOUT1 1V/DIV VOUT2 1V/DIV 3.3V AT 100mA 2ms/DIV 249k 3027 TA02b Startup Time 10µF 261k 10 2.5V AT 100mA 100 249k 3027 TA02a 1 0.1 10 100 CBYP (pF) 3027 TA02c 1000 10000 Power Supply Controller Provides Coincident Tracking Q1 3.3V 1µF 10nF VOL GATE ON RAMP FB1 243k RAMPBUF STATUS SDO LT3027 SHDN1 SHDN2 FB2 ADJ2 GND BYP2 OUT2 1.8V 255k IN1 ADJ1 IN2 BYP1 OUT1 10µF 2.5V 243k 115k 3027 TA04 10µF 3027f 13 LT3027 PACKAGE DESCRIPTIO 3.50 ± 0.05 1.65 ± 0.05 2.15 ± 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ± 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE 6) 14 U DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.675 ± 0.05 0.38 ± 0.10 10 3.00 ± 0.10 (4 SIDES) 1.65 ± 0.10 (2 SIDES) (DD10) DFN 1103 5 0.200 REF 0.75 ± 0.05 2.38 ± 0.10 (2 SIDES) 1 0.25 ± 0.05 0.50 BSC 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 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 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 3027f LT3027 PACKAGE DESCRIPTIO 2.794 ± 0.102 (.110 ± .004) 5.23 (.206) MIN 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) GAUGE PLANE 0.18 (.007) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 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. U MSE Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1663) BOTTOM VIEW OF EXPOSED PAD OPTION 0.889 ± 0.127 (.035 ± .005) 1 2.06 ± 0.102 (.081 ± .004) 1.83 ± 0.102 (.072 ± .004) 2.083 ± 0.102 3.20 – 3.45 (.082 ± .004) (.126 – .136) 10 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 10 9 8 7 6 0.497 ± 0.076 (.0196 ± .003) REF 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0° – 6° TYP 12345 0.53 ± 0.152 (.021 ± .006) DETAIL “A” SEATING PLANE 1.10 (.043) MAX 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 0.86 (.034) REF 0.17 – 0.27 (.007 – .011) TYP 0.50 (.0197) BSC 0.127 ± 0.076 (.005 ± .003) MSOP (MSE) 0603 3027f 15 LT3027 TYPICAL APPLICATIO S Startup Sequencing VIN1 3.7V TO 20V 1µF BYP1 VIN2 2.9V TO 20V 1µF ADJ1 IN2 LT3027 OUT2 OFF ON SHDN1 BYP2 SHDN2 GND 0.47µF ADJ2 249k 0.01µF 261k 10µF 249k 28k 2.5V AT 100mA IN1 OUT1 0.01µF 422k 10µF 35.7k 3.3V AT 100mA RELATED PARTS PART NUMBER LT1185 DESCRIPTION 3A, Negative LDO COMMENTS Accurate Programmable Current Limit, Remote Sense VIN: –35V to –4.2V, VOUT(MIN) = – 2.40V, Dropout Voltage = 0.8V, IQ = 2.5mA, ISD =