AMS317-1.8 查看數據表（PDF） - Advanced Monolithic Systems Inc

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AMS317-1.8

1A LOW DROPOUT VOLTAGE REGULATOR

Advanced Monolithic Systems Inc 

AMS317

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. For guaranteed specifications and test conditions, see the

Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Parameters identified with boldface type apply over the full

operating temperature range.

Note 2: Line and Load regulation are guaranteed up to the maximum power dissipation of 1.2 W. Power dissipation is determined by the input/output differential

and the output current. Guaranteed maximum power dissipation will not be available over the full input/output range.

Note 3: See thermal regulation specifications for changes in output voltage due to heating effects. Line and load regulation are measured at a constant junction

temperature by low duty cycle pulse testing. Load regulation is measured at the output lead ~1/8” from the package.

Note 4: Minimum load current is defined as the minimum output current required to maintain regulation. When 3V ≤ (VIN - VOUT) ≤ 25V the device is guaranteed

to regulate if the output current is greater than 10mA.

APPLICATION HINTS

The AMS317 series of adjustable and fixed regulators are easy to

use and are protected against short circuit and thermal overloads.

Thermal protection circuitry will shut-down the regulator should

the junction temperature exceed 165°C at the sense point.

Pin compatible with older three terminal adjustable regulators,

these devices offer the advantage of a lower dropout voltage,

more precise reference tolerance and improved reference stability

with temperature.

Stability

The circuit design used in the AMS317 series requires the use of

an output capacitor as part of the device frequency compensation.

The addition of 150µF aluminum electrolytic or a 22µF solid

tantalum on the output will ensure stability for all operating

conditions.

When the adjustment terminal is bypassed with a capacitor to

improve the ripple rejection, the requirement for an output

capacitor increases. The value of 22µF tantalum or 150µF

aluminum covers all cases of bypassing the adjustment terminal.

Without bypassing the adjustment terminal smaller capacitors can

be used with equally good results.

To ensure good transient response with heavy load current

changes capacitor values on the order of 100µF are used in the

output of many regulators. To further improve stability and

transient response of these devices larger values of output

capacitor can be used.

Protection Diodes

Unlike older regulators, the AMS317 family does not need any

protection diodes between the adjustment pin and the output and

from the output to the input to prevent over-stressing the die.

Internal resistors are limiting the internal current paths on the

AMS317 adjustment pin, therefore even with capacitors on the

adjustment pin no protection diode is needed to ensure device

safety under short-circuit conditions.

Diodes between the input and output are not usually needed.

Microsecond surge currents of 50A to 100A can be handled by the

internal diode between the input and output pins of the device. In

normal operations it is difficult to get those values of surge

currents even with the use of large output capacitances. If high

value

output capacitors are used, such as 1000µF to 5000µF and the

input pin is instantaneously shorted to ground, damage can occur.

A diode from output to input is recommended, when a crowbar

circuit at the input of the AMS317 is used (Figure 1).

D1

AMS317

VIN

IN OUT

VOUT

ADJ

R1

+ COUT

150µF

CADJ

10µF

R2

Figure 1.

Output Voltage

The AMS317 series develops a 1.25V reference voltage between

the output and the adjust terminal. Placing a resistor between

these two terminals causes a constant current to flow through R1

and down through R2 to set the overall output voltage. This

current is normally the specified minimum load current of 10mA.

Because IADJ is very small and constant it represents a small

error and it can usually be ignored.

AMS317

VIN

IN OUT

VOUT

ADJ

VREF R1

IADJ

50µA

R2

VOUT = VREF (1+ R2/R1)+IADJR2

Figure 2. Basic Adjustable Regulator

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140

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