Datasheet LT1121, LT1121-3.3, LT1121-5 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Micropower Low Dropout Regulators with Shutdown |
| Pages / Page | 16 / 9 — APPLICATIONS INFORMATION. Adjustable Operation. Thermal Considerations. … |
| File Format / Size | PDF / 275 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Adjustable Operation. Thermal Considerations. Figure 1. Adjustable Operation
Model Line for this Datasheet
- LT1121ACS8#PBF LT1121ACS8#PBF LT1121ACS8#TRPBF LT1121ACS8#TRPBF LT1121ACS8-3.3#PBF LT1121ACS8-3.3#PBF LT1121ACS8-3.3#TRPBF LT1121ACS8-3.3#TRPBF LT1121ACS8-5#PBF LT1121ACS8-5#PBF LT1121ACS8-5#TRPBF LT1121ACS8-5#TRPBF LT1121AHVCS8#PBF LT1121AHVCS8#PBF LT1121AHVCS8#TRPBF LT1121AHVCS8#TRPBF LT1121AHVIS8#PBF LT1121AHVIS8#PBF LT1121AHVIS8#TRPBF LT1121AHVIS8#TRPBF LT1121AIS8#PBF LT1121AIS8#PBF LT1121AIS8#TRPBF LT1121AIS8#TRPBF LT1121AIS8-3.3#PBF LT1121AIS8-3.3#PBF LT1121AIS8-3.3#TRPBF LT1121AIS8-3.3#TRPBF LT1121AIS8-5#PBF LT1121AIS8-5#PBF LT1121AIS8-5#TRPBF LT1121AIS8-5#TRPBF LT1121CN8#PBF LT1121CN8#PBF LT1121CN8-3.3#PBF LT1121CN8-3.3#PBF LT1121CN8-5#PBF LT1121CN8-5#PBF LT1121CS8#PBF LT1121CS8#PBF LT1121CS8#TRPBF LT1121CS8#TRPBF LT1121CS8-3.3#PBF LT1121CS8-3.3#PBF LT1121CS8-3.3#TRPBF LT1121CS8-3.3#TRPBF LT1121CS8-5#PBF LT1121CS8-5#PBF LT1121CS8-5#TRPBF LT1121CS8-5#TRPBF LT1121CST-3.3#PBF LT1121CST-3.3#PBF LT1121CST-3.3#TRPBF LT1121CST-3.3#TRPBF LT1121CST-5#PBF LT1121CST-5#PBF LT1121CST-5#TRPBF LT1121CST-5#TRPBF LT1121CZ-3.3#PBF LT1121CZ-3.3#PBF LT1121CZ-3.3#TRPBF LT1121CZ-3.3#TRPBF LT1121CZ-5#PBF LT1121CZ-5#PBF LT1121CZ-5#TRPBF LT1121CZ-5#TRPBF LT1121HVCS8#PBF LT1121HVCS8#PBF LT1121HVCS8#TRPBF LT1121HVCS8#TRPBF LT1121HVIS8#PBF LT1121HVIS8#PBF LT1121HVIS8#TRPBF LT1121HVIS8#TRPBF LT1121IN8#PBF LT1121IN8#PBF LT1121IN8-3.3#PBF LT1121IN8-3.3#PBF LT1121IN8-5#PBF LT1121IN8-5#PBF LT1121IS8#PBF LT1121IS8#PBF LT1121IS8#TRPBF LT1121IS8#TRPBF LT1121IS8-3.3#PBF LT1121IS8-3.3#PBF LT1121IS8-3.3#TRPBF LT1121IS8-3.3#TRPBF LT1121IS8-5#PBF LT1121IS8-5#PBF LT1121IS8-5#TRPBF LT1121IS8-5#TRPBF LT1121IST-3.3#PBF LT1121IST-3.3#PBF LT1121IST-3.3#TRPBF LT1121IST-3.3#TRPBF LT1121IST-5#PBF LT1121IST-5#PBF LT1121IST-5#TRPBF LT1121IST-5#TRPBF LT1121IZ-3.3#PBF LT1121IZ-3.3#PBF LT1121IZ-3.3#TRPBF LT1121IZ-3.3#TRPBF LT1121IZ-5#PBF LT1121IZ-5#PBF LT1121IZ-5#TRPBF LT1121IZ-5#TRPBF
Text Version of Document
LT1121/LT1121-3.3/LT1121-5
APPLICATIONS INFORMATION
The LT1121 is a micropower low dropout regulator with approximately 15ppm/°C. The adjust pin bias current has shutdown, capable of supplying up to 150mA of output a negative temperature coefficient. These effects are small current at a dropout voltage of 0.4V. The device operates and will tend to cancel each other. with very low quiescent current (30µA). In shutdown the The adjustable device is specified with the adjust pin tied quiescent current drops to only 16µA. In addition to the to the output pin. This sets the output voltage to 3.75V. low quiescent current the LT1121 incorporates several Specifications for output voltage greater than 3.75V will protection features which make it ideal for use in battery- be proportional to the ratio of the desired output voltage powered systems. The device is protected against both to 3.75V (V reverse input voltages and reverse output voltages. In OUT/3.75V). For example: load regulation for an output current change of 1mA to 150mA is –12mV typical battery backup applications where the output can be held at V up by a backup battery when the input is pulled to ground, OUT = 3.75V. At VOUT = 12V, load regulation would be: the LT1121 acts like it has a diode in series with its output ⎛ 12V ⎞ ( ) = (–38mV) and prevents reverse current flow. ⎝⎜ 3.75V ⎠⎟ • –12mV
Adjustable Operation Thermal Considerations
The adjustable version of the LT1121 has an output voltage Power handling capability will be limited by maximum range of 3.75V to 30V. The output voltage is set by the rated junction temperature (125°C). Power dissipated by ratio of two external resistors as shown in Figure 1. The the device will be made up of two components: device servos the output voltage to maintain the voltage at the adjust pin at 3.75V. The current in R1 is then equal 1. Output current multiplied by the input/output voltage to 3.75V/R1. The current in R2 is equal to the sum of the differential: IOUT • (VIN – VOUT), and current in R1 and the adjust pin bias current. The adjust 2. Ground pin current multiplied by the input voltage: pin bias current, 150nA at 25°C, flows through R2 into the IGND • VIN. adjust pin. The output voltage can be calculated according The ground pin current can be found by examining the to the formula in Figure 1. The value of R1 should be less Ground Pin Current curves in the Typical Performance than 400k to minimize errors in the output voltage caused Characteristics. Power dissipation will be equal to the by the adjust pin bias current. Note that in shutdown the sum of the two components listed above. output is turned off and the divider current will be zero. Curves of Adjust Pin Voltage vs Temperature and Adjust The LT1121 series regulators have internal thermal limiting Pin Bias Current vs Temperature appear in the Typical designed to protect the device during overload conditions. Performance Characteristics. The reference voltage at the For continuous normal load conditions the maximum junc- adjust pin has a slight positive temperature coefficient of tion 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 IN OUT VOUT heat sources mounted nearby must also be considered. LT1121 R2 + Heat sinking, for surface mount devices, is accomplished SHDN ADJ by using the heat spreading capabilities of the PC board GND R1 and its copper traces. Copper board stiffeners and plated 1121 • F01 through holes can also be used to spread the heat gener- ated by power devices. Tables 1 through 5 list thermal V R2 OUT = 3.75V 1 + + IADJ • R2 ( R1) ( ) resistances for each package. Measured values of thermal VADJ = 3.75V resistance for several different board sizes and copper IADJ = 150nA AT 25°C OUTPUT RANGE = 3.75V TO 30V areas are listed for each package. All measurements were taken in still air, on 3/32" FR-4 board with 1oz copper. All
Figure 1. Adjustable Operation
1121fg 9 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Applications Information Package Description Revision History Related Parts
APPLICATIONS INFORMATION
The LT1121 is a micropower low dropout regulator with approximately 15ppm/°C. The adjust pin bias current has shutdown, capable of supplying up to 150mA of output a negative temperature coefficient. These effects are small current at a dropout voltage of 0.4V. The device operates and will tend to cancel each other. with very low quiescent current (30µA). In shutdown the The adjustable device is specified with the adjust pin tied quiescent current drops to only 16µA. In addition to the to the output pin. This sets the output voltage to 3.75V. low quiescent current the LT1121 incorporates several Specifications for output voltage greater than 3.75V will protection features which make it ideal for use in battery- be proportional to the ratio of the desired output voltage powered systems. The device is protected against both to 3.75V (V reverse input voltages and reverse output voltages. In OUT/3.75V). For example: load regulation for an output current change of 1mA to 150mA is –12mV typical battery backup applications where the output can be held at V up by a backup battery when the input is pulled to ground, OUT = 3.75V. At VOUT = 12V, load regulation would be: the LT1121 acts like it has a diode in series with its output ⎛ 12V ⎞ ( ) = (–38mV) and prevents reverse current flow. ⎝⎜ 3.75V ⎠⎟ • –12mV
Adjustable Operation Thermal Considerations
The adjustable version of the LT1121 has an output voltage Power handling capability will be limited by maximum range of 3.75V to 30V. The output voltage is set by the rated junction temperature (125°C). Power dissipated by ratio of two external resistors as shown in Figure 1. The the device will be made up of two components: device servos the output voltage to maintain the voltage at the adjust pin at 3.75V. The current in R1 is then equal 1. Output current multiplied by the input/output voltage to 3.75V/R1. The current in R2 is equal to the sum of the differential: IOUT • (VIN – VOUT), and current in R1 and the adjust pin bias current. The adjust 2. Ground pin current multiplied by the input voltage: pin bias current, 150nA at 25°C, flows through R2 into the IGND • VIN. adjust pin. The output voltage can be calculated according The ground pin current can be found by examining the to the formula in Figure 1. The value of R1 should be less Ground Pin Current curves in the Typical Performance than 400k to minimize errors in the output voltage caused Characteristics. Power dissipation will be equal to the by the adjust pin bias current. Note that in shutdown the sum of the two components listed above. output is turned off and the divider current will be zero. Curves of Adjust Pin Voltage vs Temperature and Adjust The LT1121 series regulators have internal thermal limiting Pin Bias Current vs Temperature appear in the Typical designed to protect the device during overload conditions. Performance Characteristics. The reference voltage at the For continuous normal load conditions the maximum junc- adjust pin has a slight positive temperature coefficient of tion 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 IN OUT VOUT heat sources mounted nearby must also be considered. LT1121 R2 + Heat sinking, for surface mount devices, is accomplished SHDN ADJ by using the heat spreading capabilities of the PC board GND R1 and its copper traces. Copper board stiffeners and plated 1121 • F01 through holes can also be used to spread the heat gener- ated by power devices. Tables 1 through 5 list thermal V R2 OUT = 3.75V 1 + + IADJ • R2 ( R1) ( ) resistances for each package. Measured values of thermal VADJ = 3.75V resistance for several different board sizes and copper IADJ = 150nA AT 25°C OUTPUT RANGE = 3.75V TO 30V areas are listed for each package. All measurements were taken in still air, on 3/32" FR-4 board with 1oz copper. All
Figure 1. Adjustable Operation
1121fg 9 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Applications Information Package Description Revision History Related Parts
