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LT3008 3A IQ, 20mA, 45V Low Dropout Linear Regulator FEATURES
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DESCRIPTION
The LT(R)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 3A. Ground pin current remains at less than 5% of output current as load increases. In shutdown, quiescent current is less than 1A. The LT3008 regulator optimizes stability and transient response with low ESR ceramic capacitors, requiring a minimum of only 2.2F 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. 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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Ultralow Quiescent Current: 3A 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 (2.2F minimum) Shutdown Current: <1A Current Limit Protection Reverse-Battery Protection Thermal Limit Protection TSOT-23 and 2mm x 2mm DFN Packages
APPLICATIONS
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Automotive Low Current Battery-Powered Systems Keep-Alive Power Supplies Remote Monitoring Utility Meters Low Power Industrial Applications
TYPICAL APPLICATION
3.3V, 20mA Supply with Shutdown
500 IN 1F LT3008 SHDN GND ADJ 619k 1%
3008 TA01a
Dropout Voltage/Quiescent Current
450 DROPOUT VOLTAGE (mV) 400 350 300 250 200 150 100 50 0 -50 -25 0 0 25 50 75 100 125 150 TEMPERATURE (C) 3008 TA01b
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ILOAD = 20mA
6 DROPOUT VOLTAGE 5 QUIESCENT CURRENT (A) 4 3 2 1
VIN 3.8V TO 45V
OUT 2.8M 1% 2.2F
VOUT 3.3V 20mA
IQ
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 .............................................-40C to 125C LT3008I ..............................................-40C to 125C Storage Temperature Range...................-65C to 150C Lead Temperature: Soldering, 10 sec TS8 Package Only ............................................. 300C
PIN CONFIGURATION
TOP VIEW TOP VIEW ADJ 1 OUT 2 OUT 3 7 6 GND 5 SHDN 4 IN SHDN GND GND GND 1 2 3 4 8 7 6 5 NC ADJ OUT IN
DC PACKAGE 6-LEAD (2mm 2mm) PLASTIC DFN TJMAX = 125C, JA = 65C/W TO 85C/W* EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 65C/W TO 85C/W*
* See Applications Information Section.
ORDER INFORMATION
LEAD FREE FINISH LT3008EDC#PBF LT3008IDC#PBF LT3008ETS8#PBF LT3008ITS8#PBF LEAD BASED FINISH LT3008EDC LT3008IDC LT3008ETS8 LT3008ITS8 TAPE AND REEL LT3008EDC#TRPBF LT3008IDC#TRPBF LT3008ETS8#TRPBF LT3008ITS8#TRPBF TAPE AND REEL LT3008EDC#TR LT3008IDC#TR LT3008ETS8#TR LT3008ITS8#TR PART MARKING* LDPS LDPS LTDSX LTDSX PART MARKING* LDPS LDPS LTDSX LTDSX PACKAGE DESCRIPTION 6-Lead (2mm x 2mm) Plastic DFN 6-Lead (2mm x 2mm) Plastic DFN 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 PACKAGE DESCRIPTION 6-Lead (2mm x 2mm) Plastic DFN 6-Lead (2mm x 2mm) Plastic DFN 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 TEMPERATURE RANGE -40C to 125C -40C to 125C -40C to 125C -40C to 125C TEMPERATURE RANGE -40C to 125C -40C to 125C -40C to 125C -40C to 125C
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/
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LT3008 ELECTRICAL CHARACTERISTICS
PARAMETER Operating Voltage ADJ Pin Voltage (Notes 3, 4) Line Regulation (Note 3) Load Regulation (Note 3) Dropout Voltage VIN = VOUT(NOMINAL) (Notes 5, 6) VIN = 2V, ILOAD = 100A 2V < VIN < 45V, 1A < ILOAD < 20mA VIN = 2V to 45V, ILOAD = 1mA VIN = 2V, ILOAD = 1A to 10mA VIN = 2V, ILOAD = 1A to 20mA ILOAD = 100A ILOAD = 100A ILOAD = 1mA ILOAD = 1mA ILOAD = 10mA ILOAD = 10mA ILOAD = 20mA ILOAD = 20mA Quiescent Current (Notes 6, 7) GND Pin Current VIN = VOUT(NOMINAL) + 0.5V (Notes 6, 7) ILOAD = 0A ILOAD = 0A ILOAD = 0A ILOAD = 100A ILOAD = 1mA ILOAD = 10mA ILOAD = 20mA COUT = 2.2F ILOAD = 20mA, BW = 10Hz to 100kHz ,
l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25C. (Note 2)
CONDITIONS
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MIN 2 594 588
TYP 600 600 0.6 0.4 0.5 115 170 270 300 3
MAX 45 606 612 3 2 5 180 250 250 350 340 470 365 500 6
UNITS V mV mV mV mV mV mV mV mV mV mV mV mV mV A A A A A A A VRMS nA V V A A A dB mA mA
3 6 21 160 350 92 -10 0.25 0.4 0.67 0.61 0.65 58 70 75 22 1 0.6
6 12 50 500 1200 10 1.5 1 2 <1
Output Voltage Noise (Note 9) ADJ Pin Bias Current Shutdown Threshold SHDN Pin Current Quiescent Current in Shutdown Ripple Rejection (Note 3) Current Limit Input Reverse Leakage Current Reverse Output Current
VOUT = Off to On VOUT = On to Off VSHDN = 0V, VIN = 45V VSHDN = 45V, VIN = 45V VIN = 6V, VSHDN = 0V VIN - VOUT = 1.5V, VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 20mA VIN = 45V, VOUT = 0 VIN = VOUT(NOMINAL) + 1V, VOUT = - 5% VIN = -45V, VOUT = 0 VOUT = 1.2V, VIN = 0
l l l l l
l l
30 10
A A
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=25C. Performance at - 40C and 125C is assured by design, characterization and correlation with statistical process controls. The LT3008I is guaranteed over the full - 40C to 125C 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.
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).
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LT3008 ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25C. (Note 2)
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.
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 9.69A 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.
TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Voltage
450 400 DROPOUT VOLTAGE (mV) 350 300 250 200 150 100 50 0 0 2 4 6 8 10 12 14 16 18 20 OUTPUT CURRENT (mA)
3008 G01
TJ = 25C, unless otherwise noted.
Dropout Voltage
450 2 1.8 MINIMUM INPUT VOLTAGE (V) 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 -50 -25 0 25 50 75 100 125 150
3008 G02
Minimum Input Voltage
ILOAD = 20mA
TJ = 125C DROPOUT VOLTAGE (mV) TJ = 25C
400 350 300 250 200 150 100 50 0 1mA 100A 20mA 10mA
0
-50 -25
0
25
50
75
100 125 150
3008 G03
TEMPERATURE (C)
TEMPERATURE (C)
ADJ Pin Voltage
0.612 0.610 0.608 ADJ PIN VOLTAGE (mV) 0.606 0.604 0.602 0.600 0.598 0.596 0.594 0.592 0.590 0.588 -50 -25 0 25 50 75 100 125 150
3008 G04
ADJ Pin Bias Current
10 6 5 QUIESCENT CURRENT (A) -50 -25 0 25 50 75 100 125 150
3008 G05
Quiescent Current
IL = 100A ADJ PIN BIAS CURRENT (nA)
8 6 4 2 0 -2 -4 -6 -8 -10 TEMPERATURE (C) 0 -50 -25 0 25 50 75 100 125 150
3008 G06
4 3 2 1
TEMPERATURE (C)
TEMPERATURE (C)
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LT3008 TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
30 27 QUIESCENT CURRENT (A) 24 21 18 15 12 9 6 3 0 0 2 4 6 8 10 12
3008 G07
TJ = 25C, unless otherwise noted.
GND Pin Current
400 VOUT = 3.3V ILOAD = 1A GND PIN CURRENT (A) VOUT = 3.3V 350 300 GND CURRENT (A) 250 200 150 100 50 0 0 1 2 3 4 5 10mA (RLOAD = 330) 100 20mA (RLOAD = 165) 1000
GND Pin Current vs ILOAD
VIN = 3.8V VOUT = 3.3V
10
100A (RLOAD = 33k) 1mA (RLOAD = 3.3k) 6 7 8 9 10 1 0.001 0.01 0.1 1 10 100
3008 G09
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
3008 G08
LOAD (mA)
SHDN Pin Thresholds
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 2 1.8 SHDN PIN INPUT CURRENT (A)
SHDN Pin Input Current
2 1.8 SHDN PIN INPUT CURRENT (A) 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 5 10 15 20 25 30 35 SHDN PIN VOLTAGE (V) 40 45
3008 G11
SHDN Pin Input Current
SHDN PIN THRESHOLD (V)
1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0
OFF TO ON
VSHDN = 45V
ON TO OFF
0
25 50 75 100 125 150 TEMPERATURE (C)
3008 G10
0 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
3008 G12
Current Limit
100 90 80 CURRENT LIMIT (mA) 70 60 50 40 30 20 10 0 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
3008 G13
Reverse Output Current
50 45 VIN = 45V REVERSE OUTPUT CURRENT (A) 40 35 30 25 20 15 10 5 0 -50 -25 0 ADJ OUT 25 50 75 100 125 150 TEMPERATURE (C)
3008 G14
Input Ripple Rejection
90 80 INPUT RIPPLE REJECTION (dB) 70 60 50 40 30 20 10 0 10 100 1000 10000 100000 1000000
3008 G15
OUT = ADJ = 1.2V IN = SHDN = GND
VIN = 2.1V + 50mVRMS VOUT = 600mV ILOAD = 20mA
VIN = 2V
10F
2.2F
FREQUENCY (Hz)
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LT3008 TYPICAL PERFORMANCE CHARACTERISTICS
Input Ripple Rejection
80 70 INPUT RIPPLE REJECTION (dB) LOAD REGULATION (mV) 60 50 40 30 20 10 VIN = VOUT (NOMINAL) + 2V + 0.5VP-P RIPPLE AT f = 120Hz ILOAD = 20mA 0 25 50 75 100 125 150 TEMPERATURE (C)
3008 G16
TJ = 25C, unless otherwise noted.
Load Regulation
OUTPUT NOISE SPECTRAL DENSITY (V Hz) 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
3008 G17
Output Noise Spectral Density
100 COUT = 2.2F ILOAD = 20mA 5V 3.3V 2.5V 1.8V 1.5V 1V 0.6V
IL = 1A to 20mA VOUT = 600mV VIN = 2V
10
1
0 -50 -25
0.1
10
100
1k 10k FREQUENCY (Hz)
100k
3008 G18
RMS Output Noise vs Load Current
500 450 400 OUTPUT NOISE (VRMS) 350 300 250 200 150 100 50 0 0.001 0.01 0.1 1 2.5V 1.8V 1.5V 1.2V 0.6V 10 100
3008 G19
Transient Response
5V IOUT = 1mA TO 20mA VIN = 5.5V VOUT = 5V COUT = 2.2F VOUT 50mV/DIV
COUT = 10F
3.3V
IOUT 20mA/DIV 500s/DIV
3008 G21
ILOAD (mA)
Transient Response
IOUT = 1mA TO 20mA VIN = 5.5V VOUT = 5V COUT = 10F VOUT 50mV/DIV
Transient Response (Load Dump)
VOUT 50mV/DIV 45V
IOUT 20mA/DIV 500s/DIV
3008 G22
VIN 10V/DIV 1ms/DIV
VOUT = 5V IOUT = 20mA COUT = 4.7F
3008 G23
12V
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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 0.1F to 10F 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 2.2F 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.
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LT3008 APPLICATIONS INFORMATION
The LT3008 is a low dropout linear regulator with ultralow quiescent current and shutdown. Quiescent current is extremely low at 3A and drops well below 1A 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. 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 25C, 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 0.97A. 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 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 100A 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 1A.
Table 1. Output Voltage Resistor Divider Values
VOUT 1V 1.2V 1.5V 1.8V 2.5V 3V 3.3V 5V R1 604k 590k 590k 590k 590k 590k 619k 590k R2 402k 590k 887k 1.18M 1.87M 2.37M 2.8M 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.
VOUT = 600mV * (1 + R2/R1) - (IADJ * R2) VADJ = 600mV IADJ = 0.4nA at 25C OUTPUT RANGE = 0.6V to 44.5V
IN VIN LT3008 SHDN GND
OUT R2 ADJ R1
VOUT
3008 F01
Figure 1. Adjustable Operation
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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 2.2F with an ESR of 3 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 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 10F Y5V capacitor can exhibit an effective value as low as 1F to 2F 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.
20 0 CHANGE IN VALUE (%)
BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F CHANGE IN VALUE (%) X5R
40 20 0 -20 -40 -60 -80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F 50 25 75 0 TEMPERATURE (C) 100 125
3008 F03
X5R
-20 -40 -60 Y5V -80
Y5V
-100
0
2
4
8 6 10 12 DC BIAS VOLTAGE (V)
14
16
3008 F02
-100 -50 -25
Figure 2. Ceramic Capacitor DC Bias Characteristics
Figure 3. Ceramic Capacitor Temperature Characteristics
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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 = 22F ILOAD = 10A
Thermal Considerations The LT3008's maximum rated junction temperature of 125C 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 125C. 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.
VOUT 500V/DIV
100ms/DIV
3008 F04
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
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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 45C/W thermal resistance. Demo circuit DC 1388A's board layout achieves this 45C/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* 2500mm2 1000mm2 225mm2 100mm2 50mm2 BACKSIDE 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 BOARD AREA 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 65C/W 70C/W 75C/W 80C/W 85C/W
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 85C, 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 65C/W to 85C/W depending on the copper area. So the junction temperature rise above ambient approximately equals: 0.1898W(75C/W) = 14.2C The maximum junction temperature equals the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJ(MAX) = 85C + 14.2C = 99.2C
*Device is mounted on the topside.
Table 3: Measured Thermal Resistance for TSOT-23 Package
COPPER AREA TOPSIDE* 2500mm2 1000mm2 225mm2 100mm2 50mm2 BACKSIDE 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 BOARD AREA 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 65C/W 67C/W 70C/W 75C/W 85C/W
*Device is mounted on the topside.
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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 125C. The IN pin withstands reverse voltages of 50V. The device limits current flow to less than 20A (typically less than 1A) 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
100 90 REVERSE CURRENT (A) 80 70 60 50 40 30 20 10 0 0 1 23456789 OUTPUT AND ADJ VOLTAGE (V) 10 OUT CURRENT ADJ CURRENT
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 1A. 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.
3008 F05
Figure 5. Reverse Output Current
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12
LT3008 TYPICAL APPLICATIONS
Keep-Alive Power Supply
NO PROTECTION DIODES NEEDED! VIN 12V 1F IN LT3008 SHDN GND ADJ 619k 1% OUT 3.3V 2.8M 1% 2.2F LOAD: SYSTEM MONITOR, VOLATILE MEMORY, ETC.
3009 TA02
Last-Gasp Circuit
LINE POWER DCHARGE RLIMIT IN SUPERCAP 1F LT3008 SHDN GND ADJ 590k 1% OUT 5V 4.32M 1% 2.2F LINE INTERRUPT DETECT PWR FAULT GND
3008 TA03
VLINE 12V TO 15V
SENSE
TO MONITORING CENTER
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13
LT3008 PACKAGE DESCRIPTION
DC Package 6-Lead Plastic DFN (2mm x 2mm)
(Reference LTC DWG # 05-08-1703)
R = 0.115 TYP 0.56 0.05 (2 SIDES) 2.00 0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.25 0.50 BSC 1.42 0.05 (2 SIDES) 0.05 0.200 REF 0.75 0.05 1 0.25 0.50 BSC 1.37 0.05 (2 SIDES) 0.00 - 0.05 BOTTOM VIEW--EXPOSED PAD
(DC6) DFN 1103
0.38 4 6
0.05
0.675 2.50 0.05 1.15 0.61 0.05 0.05 (2 SIDES)
0.05
PIN 1 BAR PACKAGE TOP MARK OUTLINE (SEE NOTE 6)
0.05
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
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
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14
LT3008 PACKAGE DESCRIPTION
TS8 Package 8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1639 Rev O)
0.52 MAX 0.65 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 ID
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.65 BSC
0.22 - 0.36 8 PLCS (NOTE 3)
0.80 - 0.90 0.20 BSC 1.00 MAX DATUM `A' 0.01 - 0.10
0.30 - 0.50 REF
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
0.09 - 0.20 (NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
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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 Average Power Savings for Low Duty Cycle Applications 0mA to 10mA Pulsed Load, IN = 12V
100 90 2.8M 1% ADJ 619k 1%
3008 TA04a
VIN 12V 1F
IN LT3008 SHDN GND
OUT
3.3V 2.2F POWER SAVINGS (%) LOW DUTY CYCLE PULSED LOAD 0 TO 10mA
80 70 60 50 40 30 20 10 0 0.1 10A IQ 1 DUTY CYCLE (%)
3008 TA04b
100A IQ 30A IQ
10
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PART NUMBER LT1761 LT1762 LT1763 LT1764/LT1764A LT1962 LT1963/LT1963A DESCRIPTION 100mA, Low Noise Micropower LDO 150mA, Low Noise Micropower LDO 500mA, Low Noise Micropower LDO 3A, Low Noise, Fast Transient Response LDOs 300mA, Low Noise Micropower LDO 1.5A, Low Noise, Fast Transient Response LDOs 20mA, 3A IQ Micropower LDO 100mA, Low Voltage VLDO 500mA, Low Voltage VLDO 1.1A, Parallelable, Low Noise, Low Dropout Linear Regulator COMMENTS VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 20A, ISD < 1A, Low Noise < 20VRMS , Stable with 1F Ceramic Capacitors, ThinSOTTM Package VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 25A, ISD < 1A, Low Noise < 20VRMS , MS8 Package VIN : 1.8V to 20V, VOUT = 1.22V, VDO = 0.3V, IQ = 30A, ISD < 1A, Low Noise < 20VRMS , S8 Package VIN : 2.7V to 20V, VOUT = 1.21V, VDO = 0.34V, IQ = 1mA, ISD < 1A, Low Noise < 40VRMS , "A" Version Stable with Ceramic Capacitors, DD and TO220-5 Packages VIN : 1.8V to 20V, VOUT(MIN) = 1.22V, VDO = 0.27V, IQ = 30A, ISD < 1A, Low Noise: < 20VRMS , MS8 Package VIN : 2.1V to 20V, VOUT(MIN) = 1.21V, VDO = 0.34V, IQ = 1mA, ISD < 1A, Low Noise: < 40VRMS , "A" Version Stable with Ceramic Capacitors, DD, TO220-5, SOT223 and S8 Packages VIN : 1.6V to 20V, Low IQ: 3A, VDO = 0.28V, 2mm x 2mm DFN and SC-70-8 Packages VIN : 0.9V to 10V, VOUT(MIN) = 0.20V, VDO = 0.15V, IQ = 120A, ISD < 1A, 3mm x 3mm DFN and MS8 Packages VIN : 0.9V to 10V, VOUT(MIN) = 0.20V, VDO = 0.16V, IQ = 120A, ISD < 3A, 5mm x 5mm DFN and SO8 Packages 300mV Dropout Voltage (2-supply operation), Low Noise: 40VRMS, 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 x 3 DFN Packages; "-1" version has integrated internal ballast resistor 275mV Dropout Voltage (2-supply operation), Low Noise: 40VRMS, 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 x 3 DFN packages
LT3009 LT3020 LT3021 LT3080/ LT3080-1
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500mA, Parallelable, Low Noise, Low Dropout Linear Regulator
ThinSOT is a trademark of Linear Technology Corporation.
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 1108 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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