Datasheet LT3085 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Adjustable 500mA Single Resistor Low Dropout Regulator |
| Pages / Page | 28 / 9 — APPLICATIONS INFORMATION. Setting Output Voltage. Table 1. 1% Resistors … |
| File Format / Size | PDF / 304 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Setting Output Voltage. Table 1. 1% Resistors for Common Output Voltages. VOUT. RSET
Model Line for this Datasheet
- LT3085EDCB#PBF LT3085EDCB#TRMPBF LT3085EDCB#TRMPBF LT3085EDCB#TRPBF LT3085EDCB#TRPBF LT3085EMS8E#PBF LT3085EMS8E#PBF LT3085EMS8E#TRPBF LT3085EMS8E#TRPBF LT3085IDCB#PBF LT3085IDCB#TRMPBF LT3085IDCB#TRMPBF LT3085IDCB#TRPBF LT3085IDCB#TRPBF LT3085IMS8E#PBF LT3085IMS8E#PBF LT3085IMS8E#TRPBF LT3085IMS8E#TRPBF LT3085MPMS8E LT3085MPMS8E#PBF LT3085MPMS8E#PBF LT3085MPMS8E#TR LT3085MPMS8E#TRPBF LT3085MPMS8E#TRPBF
Text Version of Document
LT3085
APPLICATIONS INFORMATION
The LT3085 can be operated in two modes. Three terminal With the low level current used to generate the reference mode has the control pin connected to the power input pin voltage, leakage paths to or from the SET pin can create which gives a limitation of 1.35V dropout. Alternatively, the errors in the reference and output voltages. High quality “control” pin can be tied to a higher voltage and the power insulation should be used (e.g., Tefl on, Kel-F); cleaning IN pin to a lower voltage giving 275mV dropout on the of all insulating surfaces to remove fl uxes and other resi- IN pin and minimizing the power dissipation. This allows dues will probably be required. Surface coating may be for a 500mA supply regulating from 2.5VIN to 1.8VOUT or necessary to provide a moisture barrier in high humidity 1.8VIN to 1.2VOUT with low dissipation. environments.
Setting Output Voltage Table 1. 1% Resistors for Common Output Voltages
The LT3085 generates a 10μA reference current that fl ows
VOUT RSET
out of the SET pin. Connecting a resistor from SET to 1V 100k ground generates a voltage that becomes the reference 1.2V 121k point for the error amplifi er (see Figure 1). The reference 1.5V 150k voltage is a straight multiplication of the SET pin current 1.8V 182k and the value of the resistor. Any voltage can be generated 2.5V 249k and there is no minimum output voltage for the regulator. 3.3V 332k Table 1 lists many common output voltages and standard 5V 499k 1% resistor values used to generate that output voltage. A minimum load current of 1mA is required to maintain regulation regardless of output voltage. For true zero Board leakage can be minimized by encircling the SET voltage output operation, this 1mA load current must be pin and circuitry with a guardring operated at a potential returned to a negative supply voltage. close to itself; the guardring should be tied to the OUT pin. Guarding both sides of the circuit board is required. Bulk leakage reduction depends on the guard ring width. Ten IN LT3085 nanoamperes of leakage into or out of the SET pin and VCONTROL 10μA associated circuitry creates a 0.1% error in the reference voltage. Leakages of this magnitude, coupled with other + + + sources of leakage, can cause signifi cant offset voltage and V V IN CONTROL – OUT reference drift, especially over a wide temperature range. VOUT SET
If guardring techniques are used, this bootstraps any
COUT R C
stray capacitance at the SET pin. Since the SET pin is
SET SET
a high impedance node, unwanted signals may couple
3085 F01
into the SET pin and cause erratic behavior. This will
VOUT = RSET • 10μA
be most noticeable when operating with minimum output capacitors at full load current. The easiest way Figure 1. Basic Adjustable Regulator to remedy this is to bypass the SET pin with a small amount of capacitance from SET to ground, 10pF to 20pF is suffi cient.
3085fb 9 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS BLOCK DIAGRAM APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION REVISION HISTORY TYPICAL APPLICATION RELATED PARTS
APPLICATIONS INFORMATION
The LT3085 can be operated in two modes. Three terminal With the low level current used to generate the reference mode has the control pin connected to the power input pin voltage, leakage paths to or from the SET pin can create which gives a limitation of 1.35V dropout. Alternatively, the errors in the reference and output voltages. High quality “control” pin can be tied to a higher voltage and the power insulation should be used (e.g., Tefl on, Kel-F); cleaning IN pin to a lower voltage giving 275mV dropout on the of all insulating surfaces to remove fl uxes and other resi- IN pin and minimizing the power dissipation. This allows dues will probably be required. Surface coating may be for a 500mA supply regulating from 2.5VIN to 1.8VOUT or necessary to provide a moisture barrier in high humidity 1.8VIN to 1.2VOUT with low dissipation. environments.
Setting Output Voltage Table 1. 1% Resistors for Common Output Voltages
The LT3085 generates a 10μA reference current that fl ows
VOUT RSET
out of the SET pin. Connecting a resistor from SET to 1V 100k ground generates a voltage that becomes the reference 1.2V 121k point for the error amplifi er (see Figure 1). The reference 1.5V 150k voltage is a straight multiplication of the SET pin current 1.8V 182k and the value of the resistor. Any voltage can be generated 2.5V 249k and there is no minimum output voltage for the regulator. 3.3V 332k Table 1 lists many common output voltages and standard 5V 499k 1% resistor values used to generate that output voltage. A minimum load current of 1mA is required to maintain regulation regardless of output voltage. For true zero Board leakage can be minimized by encircling the SET voltage output operation, this 1mA load current must be pin and circuitry with a guardring operated at a potential returned to a negative supply voltage. close to itself; the guardring should be tied to the OUT pin. Guarding both sides of the circuit board is required. Bulk leakage reduction depends on the guard ring width. Ten IN LT3085 nanoamperes of leakage into or out of the SET pin and VCONTROL 10μA associated circuitry creates a 0.1% error in the reference voltage. Leakages of this magnitude, coupled with other + + + sources of leakage, can cause signifi cant offset voltage and V V IN CONTROL – OUT reference drift, especially over a wide temperature range. VOUT SET
If guardring techniques are used, this bootstraps any
COUT R C
stray capacitance at the SET pin. Since the SET pin is
SET SET
a high impedance node, unwanted signals may couple
3085 F01
into the SET pin and cause erratic behavior. This will
VOUT = RSET • 10μA
be most noticeable when operating with minimum output capacitors at full load current. The easiest way Figure 1. Basic Adjustable Regulator to remedy this is to bypass the SET pin with a small amount of capacitance from SET to ground, 10pF to 20pF is suffi cient.
3085fb 9 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS BLOCK DIAGRAM APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION REVISION HISTORY TYPICAL APPLICATION RELATED PARTS
