Advanced Monolithic Systems, Inc.

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AMS5105

APPLICATION NOTES

Definition of Terms

the circuit stops to regulate against further reduction in input

voltage. Measured when the output voltage has dropped 100mV

from the nominal voltage obtained at 1V input, dropout voltage is

dependent upon load current and junction temperature.

respect to ground.

unregulated input voltage and the regulated output voltage for

which the regulator will regulate.

the input voltage. The line regulation is measured under conditions

of low dissipation or by using low duty cycle pulse testing such

that the average chip temperature is not significantly affected.

load current at constant chip temperature.

life-test conditions after 1000 hours with maximum rated voltage

and junction temperature.

does not contribute to the positive load current. The regulator

ground lead current.

voltage for a thermal variation from room temperature to either

temperature extreme.

External capacitor

The AMS5105 series requires an output capacitor of 2.2

µF or

greater to ensure device stability, as shown in Figures 1 through 4.

Without the capacitor the device may oscillate. Most types of

tantalum or electrolytic capacitor can be used in the applications.

The value of this capacitor can be increased without limits. For

higher loads, the value of the capacitor should be increased,

especially when the output voltage is set for 2.5V or less. The

AMS5105 lowest fixed output voltage value is 1.5V.

Programming the Output Voltage

The AMS5105 may be programmed for any output voltage

between its 1.25V reference and its 6V maximum rating, allowing

for dropout and power dissipation. As shown in Figure 3, an

external pair of resistors is required.

The equation for the output voltage is:

Typical application circuit (adjustable output)

TYPICAL APPLICATION

GND

ENABLE

2

3

1

5

+

2.2 F

+

C

IN

+V

IN

V

OUT

AMS5105-X

2.2 F

C

OUT

+V

IN

V

OUT

Figure 2

GND

V

OUT

2

3

1

+V

IN

+V

IN

V

OUT

AMS5105-X

+

2.2 F

+

C

IN

2.2 F

C

OUT

Figure 1

R

1

GND

FB

V

OUT

V

REF

R

2

ENABLE

4

2

3

1

5

+V

IN

+

AMS5105

2.2 F

+

C

IN

2.2 F

C

OUT

+V

IN

V

OUT

1.25V

Figure 3